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The effects of microwave radar on the behavior of Europeanstarlings (Sturnus vulgaris)

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Esteban Fernandez-Juricic
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CHAPTER 1: INTRODUCTION ........................................................................................1
CHAPTER 2: METHODS ...................................................................................................6
Bird Housing ............................................................................................................6
Experimental Setup ..................................................................................................6
Experiment ...............................................................................................................8
Behavioral Analysis .................................................................................................9
Surface Body Temperature Analysis .....................................................................10
Statistical Analysis .................................................................................................12
CHAPTER 3: RESULTS ...................................................................................................13
Reaction Time Results ...........................................................................................13
Behavioral Response Results .................................................................................13
Surface Body Temperature Results .......................................................................14
CHAPTER 4: DISSCUSSION ..........................................................................................15
LITERATURE CITED ......................................................................................................22
TABLES ............................................................................................................................28
FIGURES ...........................................................................................................................34
Losier, Juanita, E. M.S, Purdue University, December 2012. The Effects of Microwave
Radar on the Behavior of European Starlings (Sturnus vulgaris). Major Professor:
Esteban Fernandez-Juricic.
Bird strikes account for an annual loss of $650,000,000 in the United States due to
aircraft loss, damage, and delays; worldwide, there have been nearly 219 deaths since
1988. Investigations into novel methods of deterring birds from striking planes could
ultimately lead to a decrease in loss of life and damage caused to aircraft. Previous
observations suggest three things: 1) birds respond to aircraft as they would a predator, 2)
birds can detect different levels of microwave frequencies and 3) birds might respond to
microwaves produced by weather radar. The goal of this study was to determine whether
birds react to microwaves produced by radar in the same way as they do to predators. I
used wild caught European Starlings (Sturnus vulgaris), which were exposed to two
treatments (radar or a stuffed ground predator) in an enclosure under semi-natural
conditions. I found that the behavioral responses to the radar differed from those to the
predator. When starlings were exposed to the predator, they moved and flew around the
enclosure more frequently, moved their heads faster and hung from the walls of the
enclosure longer, likely to track the predator visually. However, when starlings were
exposed to the radar, they moved less and reduced their head movements. I did not find
significant differences in the time to detect the radar compared to the predator. When
starlings were exposed to the radar some body parts (back, cheek, chest, chest, and neck)
had higher temperatures than when exposed to the predator; but I found the opposite
temperature effect in their eyes and mouth. These results suggest that Starlings respond to
radar by reducing their locomotive and visual exploration behaviors and increasing the
temperature of some body parts, which may be associated with the hyperthermic effects
that microwaves can cause in animals. Future work should focus on how these responses
! D:!
may vary at different distances from the radar, which could have implications for the
potential use of these devices to minimize bird strikes.
A bird strike is the collision between a bird and an aircraft; and, currently, in 2012, there
is no type of aircraft or airport that is immune to the hazardous threat of bird strikes. The
Wright brothers recorded the first bird strike in 1905 when Orville Wright encountered a
flock of birds in-flight (Cleary et al., 2005). Since this incident, bird strikes have been a
problem. Overall strikes account for an annual loss of 650 million dollars in the United
States alone (due to aircraft loss, damage, and delays; Dolbeer 2011; Dale 2009; Dolbeer
2009;); worldwide, there have been nearly 219 deaths since 1988 (Dolbeer 2011; FAA
2011). As human growth increases exponentially, the number of airports increases as
well as the number of airplanes in the sky, both of which contribute to the threat of bird
Various factors contribute to the possibility of bird strikes. Many airports are built
with little regard to the bordering environment and organisms that inhabit them. For
example, the natural habitat surrounding modern airports may provide shelter, food, and
safety for a wide range of birdlife (Dolbeer 2011; Washburn et al. 2011; Blackwell et al.,
2009a; Dolbeer 2009; Blackwell & Wright 2006; Dolbeer 2005). Airplanes are being
built to produce less noise and fly faster, as jet travel replaces the piston-powered engine
(FAA 2011; Dolbeer 2011). This has resulted in providing animals with less warning
when planes are approaching, and less time to maneuver out of the way when alerted to
the presence of an airplane (Dolbeer 2009; Beason 2004). The location of airports, the
construction of airplanes as well as the abundance of birds in the area all have the
potential to cause a disaster (DeVault et al., 2009). For example, while a larger bird can
cause serious damage to a plane, so can flocks of smaller birds (DeVault et al., 2012;
Dolbeer 2011; Bernhardt et al., 2010; Thorpe et al., 2010; Klope et al., 2009; Martin et
al., 2011; Blackwell & Wright 2006; Bradwell et al., 2006).
Nowadays, there are multiple methods employed to lower the risk of bird strikes at
airports. Most attempts have been concentrated in the vicinity of the airport, on the
ground, such as trapping birds at airports, using trained falcons, loud noises (i.e. guns,
recorded bangs), painted birds on runways to discourage live birds (ACRP 2011;
Brenhardt et al., 2009; Barras et al., 2001), etc. However, there is no specific method that
has been developed to minimize the chances of bird-strikes when aircraft are beyond the
airport property (i.e., above 500 ft.). Some recent studies show that birds react to aircraft
as they would an approaching predator. By looking at the remains of birds that have been
struck by airplanes researchers can determine how birds react to approaching airplanes
(Dove et al., 2009; Bernhardt et al., 2010). Bernhardt et al., (2010) preformed necropsies
on birds that had been involved in bird strikes. Their observations indicated that birds that
had been hit by airplanes had injuries indicating birds had been in the midst of an antipredator maneuver.
There is anecdotal evidence suggesting that onboard weather radar could be used
for deterring birds: some pilots have noticed the rapid dispersal of approaching flocks
once they turn on their radar (T. DeVault, personal communication). However, there have
been no empirical studies, under controlled conditions, assessing how birds respond to
weather radar as a first step to determine its effectiveness as a potential bird deterrence
technique outside of the airport property.
Radars are used to detect information about distant objects (i.e. velocity of
objects, types of approaching object, or changes in incoming weather patterns). To do
this, radars transmit a signal, which bounce off an object and then travel to a receiver
(similar to how sound echoes). The signals that radars transmit are either radio waves or
microwaves (types of electromagnetic waves). Radio waves have wavelengths from
10cm or greater while microwaves range from 10 cm to 1/10 mm (Stimson et al., 1998).
There are a wide range of radars, all of which are classified based on their application
(tracking, navigation, use, range, etc.). MERLIN is a radar system used by the Air Force,
and some airports, to detect incoming or departing flocks of birds in the vicinity of an
airport. Information that is collected is then passed on to pilots who correct their path
(ACRP 2011; Coates et al., 2011; Nohara & Beason 2011, Bruderer 1997). Alternatively,
there is airborne weather, which transmits microwave frequencies to acquire advanced
warning of incoming weather conditions (Stimson 1998; Skolnik 1981). There are several
different types of weather radars (i.e. S-band, C-band, X-band, Ka-band). X-band radar is
used for the short distance detection of minute changes in the weather; it has a
wavelength of 2.5-4cm and transmits frequencies that are between 7-11GHz (Skolnik
1981). X-band is often used in modern weather radars such as the more common low
powered (100-watt) solid-state vacuum tube systems or high-powered (10-kilowatt)
magnetron systems (Honeywell 2007; Skolnik 1981). Magnetron systems are being
replaced by solid-state systems because they provide the same coverage and resolution
with less energy. Solid state (non-magnetron) radars provide additional wind shear
prediction systems, which is why they are built into the nose of the airplane (Honeywell
2007; Scholnik 1981).
Microwaves, which are emitted by solid-state radar, are a form of non-ionizing
radiation; the microwave phonons lack the energy required to ionize atoms or induce ion
formation (Stimson 1998); which means that microwaves do not contain sufficient energy
to chemically change substances through ionization. When living tissue is exposed to
microwaves, molecules vibrate at a faster rate, which causes friction inducing a
hyperthermic effect (Byman et al. 1986; Adair & Adams 1983; Schwab & Schafer 1972).
Previous experiments suggest that birds and mammals can detect low levels of
microwaves (Kumar et al., 2011; Bruderer et al., 1999, Byman et al., 1986). Aversion,
panic, anxiety, disorientation as well as overheating and specific aversion behavior were
demonstrated in mice (Kessari et al., 2011) and monkeys (Adair & Adams 1983); birds
also showed behaviors indicating thermal overload (Ahlbom et al., 2004; Wasserman et
al.1986; Chou & Guy1985; Byman et al., 1984; Wasserman et al., 1984a; Wasserman et
al., 1984b; Adair & Adams 19831983; Schwab & Schafer 1972; Richards 1968).
Wasserman (1984a) found that when birds were exposed to 2.45GHz, they responded as
soon as 30 seconds after the onset of radar exposure with behaviors of gasping, panting,
wing spreading, crouching and loss of muscular coordination. Birds that were trained to
fly in wind tunnels, and then made to fly while exposed to microwaves (2.45GHz) would
try repeatedly to land or expose their legs during flight to cool down, while control
groups (not exposed to microwaves) displayed no such behaviors (Byman et al., 1984).
Chou & Guy (1985) conducted tests using parakeets, quail, pigeons, chickens, and
turkeys and exposed them to three set frequencies (775, 915, and 2450 MHz) with varied
intensities, and measured the onset of behavioral responses. Overall, there was a
significant decreased in latency to aversion, overheating and stress responses as the
intensity was increased.
Despite the above studies it is not well understood how birds react to microwaves,
as the evidence has produced conflicting results. Wasserman et al., (1984b) placed Blue
Jays into an experimental enclosure with four compartments, two shielded from
microwaves and two unshielded. He found that when in the unshielded compartments,
birds performed non-random movements within the chamber that correlated with the
availability of microwaves and the intensity. The fact that these birds also selected a
shielded room over an unshielded one indicates that birds can detect microwaves and are
inclined to move to avoid its effects. Conversely, Bruderer et al., (1999) monitored flocks
of birds migrating at night and, from the ground, exposed them to a steady beam of light
and compared their behavioral responses to those that were exposed to X-band radar.
Overall, they found that birds reacted more intensely to the search light than to the Xband radar. Although in many cases there was flock disorientation immediately following
radar exposure.
From the perspective of using weather radars in the future to deter birds from
aircraft, the first question that needs to be addressed is whether birds respond to radar in
the same way as they do to predators (i.e., avoidance responses). The goal of this study
was to assess how European Starlings (Sturnus vulgaris) responded behaviorally and
thermally to a 9.33 GHz solid-state weather radar compared to predator exposure.
European Starling are a good study species because they are highly abundant in North
America (McGraw & Middleton 2009; Schwab & Marsh 1967), move in large flocks
during the winter (Goodwin 2001), and are commonly involved in bird strikes. From
1990 to 2001 European Starlings were responsible for 852 of the strikes reported to the
FAA and recorded on their National Wildlife Strike Database (Barras et al., 2001).
I conducted a semi-natural experiment, where I exposed an individual starling to
either solid-state weather radar, placed 5 meters away, or a predator model. I used two
parameters to measure their behavioral responses to these stimuli: first, reaction time
(time to respond to the predator or radar following onset of exposure) and second, several
behavioral responses (proportion of time scanning head up and rate of hanging on
enclosure walls, flying, scanning head up, crouching, walking around, and foraging).
Many of the selected behaviors have been associated with predator detection and in radar
response literature (Fernandez-Juricic & Rodriguez-Prieto 2010; Devereux et al., 2005;
Tisdale & Fernandez-Juricic 2009; Chou & Guy 1985; Byman et al., 1984; Wasserman et
al.1986; Wasserman et al., 1984a; Wasserman et al., 1984b).
Bird Housing
Between 2010 and 2011, European starlings were either caught from different areas in
Tippecanoe County, Indiana using an Australian Trap (1.5mx1.5mx1.5m) and a Decoy
Trap (1.2mx2.4x2.1m), and or (all juveniles used in experiment 2) obtained from a
USDA facility in Ohio. Following capture they were transported to and held at Purdue
University’s on-campus Small Animal Housing facility. There, the birds were kept in an
indoor aviary (1.9mx1.5mx1.8m) under a 12hr light cycle and given food and water ad
lib. Approximately 48 hours before being tested, birds were transported to the Purdue
owned Ross Reserve. At the Ross Reserve, Starlings were kept in outside aviaries
(3x2x2m), under natural light. On average, there were 25 birds per aviary; birds were
given food (mixture of bird chow/wild bird chow and cat food) and water ad lib (Asher &
Bateson 2007). All animal procedures were approved by the Purdue Animal Care and
Use Committee (PACCU) Protocol # 10-120.
Experimental setup
A track (3m long x 0.32m wide) was stretched along the 3-meter front end of the
experimental arena (refer to Figure 1). A stuffed cat on a skateboard was used as a
predator during certain trials. A clear fishing line, attached to the skateboard, stretched
across the track allowing the researcher to pull the cat across the track. The track was
perpendicular to the bird’s enclosure and the cat faced outwards towards the bird (refer to
Figure 2). The track was padded with soft rubber foam to reduce the amount of noise the
predator produced during a trial. To ensure that the bird could not view the cat or
skateboard, blinders (0.76mx0.3m) were attached to either end of the track. The
enclosure, where the bird remained during the course of a trial, had a cylindrical metal
top (0.61m-diameter, 0.48m-high, 2.5cm openings) on a wooden base (0.65m-diameter).
The enclosure sat opposite the track, one meter from the end of the arena. For each trial,
the wooden base of the enclosure was lined with seven cups of Metro-Mix potting soil
that had been mixed with 10 mealworms the night before. The experimental arena was
enclosed using shepherd hooks and tarp. The shepherd hooks were arranged in a
rectangle (6mx3m) and tarp was strung between the shepherd hooks using zip-ties. Tarps
were weighed down with cement blocks to minimize any noise or movement during a
trial. The tarp prevented the birds from viewing anything outside the experimental
enclosure, including the radar.
An individual bird was used for each trial; the behavior of that bird was recorded
using three cameras observing from different angles, and a fourth, JVC Enverio, camera
observed the actions of the stuffed cat (camera 4a; refer to Figure 1). Camera 4b, a FLIR
EX320 Infrared thermography camera (hereafter referred to as an IRT camera), recorded
the relative temperature of the bird during the course of a trial. The IRT used a 25° lens
(dimensions 320 x 240 pixels) and had a set emissivity value of 0.95 (as recommended by
Speakman & Ward 1998). Camera 4c, a JVC Enverio, was directed towards the bird and
was used to determine the behavioral response of the birds to its assigned treatment.
Camera 4d, a security camera, was attached to 2.5cm PVC pipes (painted black), directed
downwards for an overhead view of the bird (0.5m high). All cameras were kept in a
similar position throughout all the trials. Coaxial cables ran from all four cameras and
connected to a quad splitter Ganz DVR recording unit, which allowed all four cameras to
be recorded on a single screen simultaneously. The DVR was set outside on the porch of
a cabin approximately five meters from the experimental arena.
The radar used for this experiment was a Honeywell Solid State Weather Radar
model number RDR-4000. The radar was pre-set to have a peak transmission power of
35-63W and a transmission frequency of 9336-9376MHz. The antenna had a diameter of
30” and had a gain of 35 decibels (dBi). RDR-4000 airborne radars has a beam that is
three degrees wide that scans 180 degrees from 0-18,288 m to 320nm. For this
experiment, the radar was screwed to a base that held it in a horizontal position four feet
off the ground. The radar was connected to an Agilent DC System Power Supply Model
Number N5751A and used 180-200 VAC and 0.5 Amps. For each trial the power unit
was set to provide the radar with 185.3 volts and 0.5 amps. For safety reasons, the
observer wore a UniTech RF garment (jumpsuit, helmet, socks and gloves) during the
course of a trial. The presence of the metal cylindrical top (which sat on the base of the
experimental enclosure) did not affect the intensity of the radar microwaves. We
measured microwave intensity with a field meter (Holaday Hi E100 ETS Lindgren),
which was placed 5 m away from the radar under two conditions: with and without the
metal enclosure. We obtained 52 measurements over a period of 4 minutes in each
condition. We did not find significant differences in microwave intensity with and
without the metal enclosure (F 1,102 = 0.472; P =0.494).
From October to December 2011, I ran an average of 7 trials each morning, from 0730-
1200. All trials were conducted at the Purdue owned Ross Reserve. Following their initial
capture, each bird was banded using a unique 1-3 color band combination on their left
and or right leg. The 35 birds, 39 males and 12 females, were assigned a predator state
(yes/no) and a radar state (yes/no), and the distance was set at 5 meters.
Twelve to eighteen hours the night before their trial, birds were removed from the
main aviary and placed in a “food deprivation cage” (0.61mx0.61mx0.76m) where their
food was removed. The morning of a trial, the appropriate bird was removed from the
food deprivation cage and transported in a cotton “bird bag” to a cabin, where its weight,
sex, and band color were recorded. The experimenter used a Mastech light meter
(LX1330B) to measure light intensity (lux) and a Kestral 3500 portable weather station to
measure temperature (C°), humidity (%), and wind speed measurements (km/hr) of the
experimental arena (Figure 1). Once the information was recorded each of the cameras
was turned on and allowed to warm up for 1-2 minutes. The DVR was then turned on and
a white board, listing the bird’s unique band color combination, treatment, and radar
distance, was displayed to the camera along with a Fisher Scientific stopwatch. At this
point, the bird was released into the experimental enclosure, and the experimenter would
leave the arena. A trial officially commenced once the bird took its first peck at the
ground, therefore, in some cases, the experimenter was still within the experimental
arena. At the conclusion of a trial the experimenter would re-enter the arena and
recapture the bird and return it to the main aviary.
I compared the behavior and surface temperature of an individual birds under two
treatments: (1) radar on and no predator (hereafter, radar treatment) and (2) radar off and
predator (hereafter, predator treatment). I used 51 individuals of mixed sex and age (5
adult females, 9 adult males, 2 juvenile females, and 19 juvenile males).
The first treatment, predator treatment, placed birds individually into the
experimental enclosure and allowed them to forage for three minutes. At this point the
observer pulled the predator model across the track. After seven minutes the trial
concluded. Nineteen birds were used in this treatment (3 adult females, 5 adult males, and
11 juvenile males).
In the radar treatment, the focal individual was allowed to forage for two minutes.
After that, the radar was turned on for eight minutes. After 8 minutes of exposure, the
trial concluded and the radar was turned off. Under the radar treatment, the weather radar
was always at the same distance (5 m) from the enclosure with the bird. Sixteen
individuals were used in this treatment (2 adult females, 4 adult males, 2 juvenile
females, and 8 juvenile males).
The time from the first peck that the bird took and the time it took the bird to be
exposed to the radar or predator was different (2 minutes and 3 minutes respectively).
The difference in exposure time is a result of constraints placed on the experimental
design by a previous experiment.
Behavioral analysis
Virtual dub (Version 1.10.2, free online software at was used
to determine the reaction times to either the radar or predator through frame-by-frame
analysis of the videos obtained. Jwatcher (Blumstein & Daniel, 2007) was used to
quantify the different behaviors of the birds after the radar was turned on or the predator
was exposed to the birds.
To measure reaction times, I identified behaviors that could be associated with
responses to predators and anti-predator behavior (Blackwell et al., 2009; Tisdale &
Fernandez-Juricic 2009; Devereux et al., 2005; Table 1 lists and defines these behaviors).
I then recorded the frame and behaviors that occurred immediately following the onset of
a treatment to calculate reaction times from the treatment.
In order to measure the different behavioral responses of the bird to the main
treatment, I used Jwatcher, behavioral transcription software. Melissa Hoover coded the
following behaviors: proportion of time scanning head up, rate of hanging on cage, rate
of flying, rate of scanning head up, rate of crouching, rate of movement, rate of wing flip,
and rate of pecking (Table 2 lists and defines all behaviors). I divided the radar treatment
into two intervals: before and after radar exposure. Before the radar exposure, coding
began one minute after the bird’s initial peck, and continued for 1 minute until the radar
was turned on. After the radar exposure, coding was done over 8 minutes.
The predator treatment was divided into two intervals: before and after the
exposure to the predator. Before predator exposure, coding began one minute after the
first peck, and continued for 2 minutes, until the predator was released. After the predator
exposure, coding was conducted for 7 minutes.
Surface Body Temperature Analysis
I used an Infrared Thermography Camera (hereafter referred to as an IRT camera), FLIR
EX320, with a 27 mm lens (1/250 spot ratio and dimensions 320 x 240 pixels), and an
emissivity value of 0.95 (as recommended by Speakman & Ward 1998) to record the
relative temperature of a starling when it was exposed to a predator or radar. All images
were recorded in grey (white hot, black cold) color pallet. The IRT camera was
connected to the DVR video equipment, which meant I could examine the variation in
temperature of the bird over the course of the trial.
I took into account the fact that Steen & Steen (1965) proposed that the legs of
birds provide the best location for heat dissipation, while non-vascularized areas, such as
feathers, are used to primarily to keep heat in in cold environments and allow cool air in
in hot environment, but due to a low sample size, I was unable to include the temperature
of the leg in the analysis. Speakman et al. (1986) recorded the change in body
temperatures of European Starlings in flight as they were exposed to a wide range of
ambient temperatures. He found that as birds flew in environments with high ambient
temperatures, they used their head, ventral brachial areas (the wings), and feet to dissipate
heat. For this experiment I used an IRT camera to monitor how the surface body
temperature of different areas of the starling may have changed in response to exposure
to microwaves.
I selected the spot meter setting, which would independently select the maximum
temperature within view of the camera. Throughout an individual trial the spot meter
would scan an object (in this case the Starling) and select the maximum temperature
(between back, chest, cheek, eye, head, mouth, and neck). In the cases where the Starling
was outside of the brackets the IRT camera could not track a change in temperature. To
increase accuracy of the IRT camera’s thermal reading I developed a set of guidelines,
following preliminary tests, which allowed me to acquire more accurate surface body
temperatures during analysis. These guidelines accounted for the sporadic movements of
the bird and any adjustments made by the IRT camera to ensure that the temperature
measurements were accurate. Throughout analysis there were three cases where the bird
was within brackets, outside brackets, or outside view of the camera. If the bird was
within the brackets and moving (Figure 3a), the cursor had a 3-frame delay in tracking
the movement of the bird and providing accurate temperatures. In these cases I would
wait for the cursor to land on the immobile bird and count five additional frames before
recording a temperature. If the bird was outside the brackets but still on screen (Figure
3b) the IRT camera detected the temperature of the bird but did not display it since it was
outside the brackets. In these circumstances once the bird entered the brackets I waited
an additional thirteen frames before recording the temperature. The last guideline was for
circumstances where the bird was completely off screen (Figure 3c). I would wait until
the bird moved within the brackets and then count eighteen frames, which allowed the
IRT camera time to adjust to the bird’s temperature and indicate it with the cursor.
In order to determine whether exposure to the radar had an affect on the surface
body temperature of the bird I divided each of my trials into intervals based on whether it
was before or after its treatment. I divided each of those intervals into 20-second bouts.
During these 20-second bouts I recorded three temperatures for each area of the body
(back, cheek, chest, eyes, head, mouth, and neck) when they were indicated by the IRT
camera’s cursor (Figure 4). For the birds involved in either treatment I calculated an
average temperature for those seven areas of the body.
Statistical Analysis
I used a General Linear Mixed Models (GLM) in SAS 9-3 statistical software to
determine changes in reaction times, behavioral responses, and surface body temperature
between the radar and predator treatments.
Reaction Time Results
There were no significant differences between the time it took the European Starlings to
detect the radar (2.09±0.29) as compared to the predator (1.98±0.25; F1, 31=0.07,
P=0.794). Additionally, ambient temperature (F1, 31=0.04, P=0.832) and body mass (F1,
=1.13, P=0.328) did not have a significant effect on the reaction time of the starlings to
the treatments (radar or predator).
Behavioral Response Results
The analysis indicated an effect of treatment (predator or radar) and before and
after exposure (before or after treatment) on the behavioral responses (flying, hanging on
cage, scanning head up, crouching, pecking, movement, and wing flipping) of starlings
(refer to Table 3).
Starlings that were exposed to the predator flew more after being exposed to the
predator, as compared with birds that flew more before being exposed to the radar
(Figure 5a). Starlings that were exposed to the predator hung on the cage more after being
exposed to the predator, as compared with birds who hung more before being exposed to
the radar (Figure 5b). Body mass had a positive effect on the hanging rate of the bird.
Starlings spent a large proportion of time scanning with their head up after being exposed
to the predator, as well as before they were exposed to the radar (Figure 5c). Starlings had
a higher rate of scanning with their head up after they were exposed to the predator and
before they were exposed to the radar, as compared to birds that were exposed to the
radar (Figure 5d). Body mass had a positive effect on the head up rate of the bird.
Starlings crouched more after being exposed to the predator, and before being exposed to
the radar, as compared to birds that were exposed to the radar (Figure 5e). The pecking
rate of the starlings was not significantly influenced by exposure to the radar or predator
(Figure 5f). The ambient temperature positively influenced the pecking rate of starlings.
Starlings moved around their enclosure more after they were exposed to the predator as
well as before they were exposed to the radar (Figure 5g). Starlings that were exposed to
the radar rearranged their wings more after being exposed to the radar, but before being
exposed to the radar they had low rates of wing reshuffle, as well as after being exposed
to the predator (Figure 5h). Additionally, ambient temperature and body mass had a
negative effect on the rate of wing flip. None of the other studied factors (sex, food
deprivation time) significantly influenced the behavioral responses of the starlings.
Surface Body Temperature Results
Treatment (predator or radar) had a significant effect on the surface body temperatures
(of the back, cheek, chest, eyes, head, mouth and neck) of starlings.
After birds were exposed to the radar their back, cheek, chest, head and neck, had
higher temperatures than birds that had been exposed to the predator. However, after
starlings were exposed to the radar they had lower temperatures in their eyes and mouth,
compared to birds that had been exposed to the predator (Figure 6 and Table 4).
Overall, I found that starlings did not respond to radar as they would a predator
behaviorally as well as in terms of surface body temperature. I discuss these results in
light of the literature.
Birds have a multitude of behavioral responses that help them avoid heat stress;
observed behaviors have been panting, wing spreading, sleeking plumage, altering of
body orientation in relation to sun, seeking shade, covering feet with body, urohydrosis,
bathing, rearranging feathers, reducing body movements, if bird is flying- increasing
altitude, or exposing legs to airstream; (Ruben & Jones 2000; Bennett & Ruben 1999;
Ward et al., 1999; Speakman 1998 Swaddle & Witter 1997; St-Laurent & Larochlle
1994, Wasserman et al., 1984a; Wasserman et al., 1984b; Bryant 1983, Steen & Steen
1965). According to previous studies, a bird’s response to increased ambient
temperatures depends on the size, activity, and species of the bird (reviewed in Speakman
1998). Multiple experiments have examined the behavioral responses of birds exposed to
an increase in temperature while participating in strenuous activity (i.e. flying). Bryant
(1983) made field observations of the behavior of tropical birds at different times of the
day. He noted a drastic decrease in active birds at midday once temperatures had peaked.
Birds that continued being active at midday were observed panting, continually altering
their body orientation in relation to sun, and flying with legs hanging. Some birds would
continue activity in short bursts—seeking shade in between; while other birds would
cease the majority of their activity when the sun was at its highest. Overall, Bryant
(1983) found that birds in the field alter their activity when they have the greatest
potential for over-heating. Torre-Bueno et al., (1976) trained wild-caught starlings to fly
in a wind tunnel and then manipulated the ambient temperatures. In temperatures above
28°C, starlings were observed panting (open bill, that widened as temperature and flying
time increased), attempting to land repeatedly, and extending legs (to expose to cool
airstream). The above studies indicate that birds will alter their activities when exposed
to increased ambient temperatures. Moreover, other studies have shown that birds
exposed to microwaves (2.45GHz or more) will behave as though they had been exposed
to an increase in ambient temperature, with the same or increased thermoregulatory
behaviors. Similar behaviors were seen in budgerigars (Byman et al., 1986) trained to fly
in a wind tunnel and exposed to microwaves (2.45GHz). As the intensity of the
microwaves and flying time increased, the birds attempted to land more often and would
expose their legs to the airstream. In the above experiments, the birds partook in
strenuous exercise in environments that had either steadily increasing ambient
temperatures or caused an increase in surface body temperature. At moderate ambient
temperatures, in the wild, birds rarely drag legs or pant during flight (Ward et al 1999).
While flying is a very strenuous activity, and, depending on the length of time a bird flies
or the time of day, can lead to hyperthermia (Byman et al., 1986; Bryant 1983; TorreBueno et al., 1976; Heinrich et al., 1971). Activities, such as flying, can cause a 10 to
23-fold increase in the normal basal metabolic rate of a bird (Mcfarland & Budgell 1970).
In my experiment, starlings responded to an increase in temperature (exposure to
microwaves) by reducing a majority of their behavioral responses: flying and moving
around the cage less, moving their heads slower and hanging from the cage of the
enclosure for shorter periods of time. Overall, starlings reduced their locomotive and
visual explorative behaviors once they were exposed to the radar.
Conversely, I found that once starlings were exposed to the radar they had an
increase in their rate of wing flips, which was higher then those that had been exposed to
the predator. Starlings that were exposed to the radar displayed a significant increase in
wing rearrangement behavior (Figure 5g), in order to increase the circulation of air
beneath their feathers. Birds can alter the position of their feathers (i.e. raise or flatten
against their body), which modifies the insulation properties of their feathers, with this
they can to insulate their body (when cold) or dissipate heat (when hot; McFarland &
Budgell 1970). McFarland & Budgell (1970) investigated the position of body feathers
in response to a step change in ambient temperature (20°C to 40°C within 30 sec and
maintained at 40°C for 10 min). They found that birds altered the physical property of
their feathers (from normal to sleeked) as they increased the ambient temperature.
Additional rearrangement of the feathers or feather maintenance circulates air along skin
(reducing thermal load), which is a thermoregulatory behavior in response to increased
temperature (Ruben & Jones 2000; Swaddle & Waddle 1997; St-Laurent & Larochlle
1994). I propose that the drastic reduction in pecking, movement, flying, scanning,
crouching and an increase in wing rearrangement following exposure to the radar, is the
result of the birds seeking to avoid thermal overload in their back, cheek, chest, neck and
head, areas of their body that had a higher temperature.
Microwaves cause molecules to vibrate at a faster rate, causing friction and an
increase in heat in living tissue (Stimson 1998; Scholnik, et al., 1962). In my analysis I
compared the surface body temperature of birds that had been exposed to the radar to the
surface body temperatures of birds that were exposed to the predator. My results indicate
that birds that were exposed to the radar had higher temperatures on their back, cheek,
chest, head, and neck, while birds that had been exposed to the predator had higher
temperatures in their eyes and mouths. In this experiment, it is unclear whether the
mouth and eyes increased in temperature as a direct result of the starlings being exposed
to the predator; or whether the birds experienced an increase in temperature in their back,
chest cheek, head, and neck as a direct result of being exposed to the radar, I will discuss
this in light of the literature.
In suddenly stressful situations (such as the appearance of a predator) organisms
immediately react with a “fight or flight” response, a series of physiological reactions in
response to acute stress (McEwen 2005). During this period the body will direct blood to
areas that can aid in either escape, such as limbs (to escape) or lungs (to increase
respiratory rate) etc. Birds that are exposed to a predator should direct blood flow to
certain areas that would aid in their “flight” (i.e. legs, wings, brain, eyes, lungs, etc.;
Siegel 1980). To explain the higher temperatures of the eye and mouth, we consider that
birds exposed to the predator, experienced an acute stress response; therefore there were
lower temperatures in areas where blood was diverted away (body core, in this case, the
back, cheek, chest, head, and neck), to extremities that would aid in escape in the flight
response, and, higher temperatures in areas that would need increased blood flow
(McEwen 2005; Siegel 1980): the eyes, for sharper vision-to detect potential predators
and an escape route, and the mouth as respiration increases. Comparably, the starlings
that had been exposed to the radar had higher temperatures in their back, cheek, chest,
head, and neck, and, lower temperatures in their eyes and mouth, but, only when
contrasted with the temperatures of birds that had been exposed to the predator. While it
is possible that the higher temperature of the eyes and mouth and the lower temperature
of the back, cheek, chest, head and neck were a direct response to being exposed to the
predator, if we take into consideration both the behavioral and physiological response of
the starling to the radar and compare it to the responses to the predator, an acute stress
response seems less likely.
Alternatively, I postulate that the insulation properties of feathers, may have
affected the physiological and behavioral responses of starlings exposed to the radar.
Feathers provide a layer of protection that allows birds to contain metabolically produced
heat in cold environments and reduce heat absorption in hot environments (Ruben &
Jones 2000; Wolf & Walsberg 2000; Swaddle 1997). To explain the high temperatures of
the back, cheek, chest, head and neck of the birds exposed to the radar, I consider the
responses of the chickens involved in an experiment conducted by Horowitz et al (1978).
In this experiment they trained two groups of chickens to perform an instrumental task in
response to a decrease in ambient temperature so that when the temperature was lowered
birds learned to peck at areas of their enclosure to increase ambient temperatures. One set
of chickens was featherless (plucked) and the other had their feathers (normal); both
groups of chickens were subjected to a steady decrease in ambient temperatures. At
ambient temperatures of 5°C and 0°C, plucked chickens were unable to reduce their heat
loss and responded with their learned instrumental task. Plucked chickens kept pecking
until the ambient temperature was high enough that they were able to maintain a body
temperature not significantly different from the body temperatures of normally feathered
chickens, without the aid of feathers. Normally feathered chickens, in reduced
temperatures never preformed the trained instrumental task; instead they fluffed feathers
or squatted to enclose unfeathered areas (feet and legs) in the feathers. This study
demonstrates the important role that feathers play in a birds thermoregulation: without
feathers the plucked chickens had a reduced ability to naturally regulate their internal
body temperature, and an increased motivation to increase the ambient temperature;
feathered chickens self-maintained their internal body temperature and performed
species-specific behaviors to keep extremities warm, in response to reduced temperatures.
In my experiment, the IRT camera detected higher surface temperatures in birds exposed
to the radar in areas that were covered by feathers (back, cheek, chest, head and neck)
and a decrease in surface temperature around areas that were uncovered. I propose that
areas covered by feathers (back, cheek, chest, head, and neck) reduced the starling’s
ability to regulate temperatures in that area, while areas uncovered by feathers (eyes and
mouth) were unencumbered by an insulating layer.
Future experiments would help us determine whether the temperature increase (of
the chest, cheek, chest and neck) or temperature decrease (of eyes and mouth) was a
result of the fight or flight response or feather insulation. Taking into account the
properties of feathers and my results it is clear that the areas that were exposed to the air
(eye and mouth) could readily dissipate heat. While areas that were concealed by
feathers: back, cheek, chest, neck, and head had a lower temperature than exposed areas:
eyes and mouth.
Microwave radiation has a penetrating depth of 10mm and has been shown to
have biological effects on living tissue (heating surface, causing changes in nerve and
muscle response, etc.). The resulting effects of exposure depend on the characteristic of
the source, target, distance between source and target, and environmental conditions
(Honeywell 2007; Stimson 1998; Wasserman et al. 1984, Scholnik, et al., 1962). In this
case, the results indicate that the microwaves may have had a thermal effect on the
feathered areas of the birds exposed to the radar. I postulate that microwaves had a
thermal effect on the bird’s skin; which means that areas that were not covered by
feathers (eyes and mouth) were able to dissipate heat normally, but areas insulated by
feathers (back, cheek, chest, head and neck) trapped the heat between the feathers and the
Whatever the reason for the thermal disparity between the various parts of the
body, the results do indicate that being exposed to the microwaves has a cost. The
starlings exposed to the microwaves drastically reduced their activities; I propose that this
occurred in order to decrease the physiological strain of reducing elevated body
temperatures. Other organisms may rely on their hearing or sense of smell to detect
predators while birds will rely heavily on their visual systems (Blackwell et al 2009;
Tisdale & Fernandez-Juricic 2009; Lima & Bednekoff 1998). With this in mind, once
starlings were exposed to the radar they reduced the proportion of time being vigilant and
rate of scanning. Conversely, if we take into account Lima & Bednekoff (1999), the birds
may still be able to detect an approaching predator, so the reduction in vigilance behavior
may not have as large a cost as I am proposing.
My results indicate that weather radars do have an effect on the behavioral and
thermal responses of starlings. Starlings that were exposed to the radar appeared to
reduce their activity in order to avoid radar-induced heat-stress. At this point, there is
little generalization I can make based on my results as the experiment was conducted
under some restricted conditions: animals were at a fixed distance from the radar (5
meters). However, I can speculate about some potential bird-aircraft encounter scenarios
assuming that the effects I found hold at farther distances. First, under a bird-aircraft
encounter with the radar activated, I hypothesize that birds would reduce their behavioral
responses due to thermal stress, lose altitude, and thus reduce the chances of a bird strike.
Second, a bird-aircraft encounter with the radar activated, I hypothesize that birds would
reduce their attention towards the aircraft given the distracting effects of the radar, and
actually increase the chances of a bird strike by failing to avoid the aircraft on time.
These scenarios are speculative and should be subject to empirical testing in the future.
Future experiments in a more natural setting should investigate whether weather
radar reduces bird activity (as found in this study) or birds do try to leave and avoid the
heating effects. Additional experiments should determine the maximum distance at which
the bird is behaviorally influenced by the radar. Realistically, in order for the weather
radars to be used as a bird strike deterrent several things must be taken into account,
including: the speed of the aircraft and the speed of the bird, the distance between the
bird and a plane, the avoidance behaviors of birds etc. Future experiments should explore
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Table 1. Descriptions of behaviors used to assess reaction times to radar and predator
Step forwards
Step back
Foot Lift
Side Step
Bird takes 1-3 steps forwards and then stops
Bird puts one leg back and moves backwards motion
Bird lifts foot then places in same place
Bird steps to side
Pivot, bird lifts one leg and places it at an angle of
about 90° to the first foot and brings body and leg
Bird uses beak to probe at ground
Bird purges food
Bird extends wings and flaps them to leave ground
Bird pushes off with feet from ground, and returns
Hanging on enclosure
Bird one or both feet and hangs on side of enclosure
Backwards flip
Bird flips backwards
Bird settles on the ground
Lift head while head up
Bird lifts head while in head up position.
Lower head while head up
Bird lowers head while in head up position
Horizontal movement of
Bird shifts head in a horizontal movement while in a
head while head up
head up position
Lift head while head down
Bird lowers head while head in head down position
Lower head while head down Bird lowers head while the head in head down position
Horizontal movement of
Bird shifts head in a horizontal movement while in a
head while head down
head down position
Decrease in head movement
Frame where the head movement rate decreases
Bird bends legs, body get closer to the ground
Neck Extension
Bird extends neck
Body Upright
Bird changes from a crouched to an upright position
Bird runs beak through feathers or feet
Feather Rustle
Full body shake where bird sways
Bird extends feathers out so it appears enlarged
Wing Flip
Bird rearranges its wings
Bird ceases movement for 3 or more frames
Table 2: Descriptions of behaviors used to quantify the behavioral responses to radar.
Bird uses hind feet to propel itself into motion
(forwards or backwards, at a walk, hop or run)
Bird flaps wings and leaves the ground or side
of enclosure
Bird bends legs and lowers chest to the ground.
Bird is touching the side or top of enclosure
Hang on Enclosure
Scan Head up
Movement of the head above the plane of the
Bird examines the ground with its beak;
Wing Flip
Bird rearranges wings along back
Table 3. Effect of treatment, before and after exposure (to radar or predator), treatment x
before and after exposure, controlling for ambient temperature and body mass, on the
reaction time of European starlings under two experimental treatments: With Predator
and With Radar. Results from generalized linear model. An asterix indicates behavioral
responses that were log transformed. Significant values are in bold face.
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
1, 31
Fly rate
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
Hang on Enclosure Rate
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
Proportion of time head up
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
Head up rate
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
Crouching rate**
Before and after
Treatment x before and
after exposure
Ambient temperature
Body mass
Pecking rate**
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
1, 31
1, 31
1, 31
1, 31
Before and after exposure
Treatment x before and
after exposure
Ambient temperature
Body mass
1, 31
1, 31
1, 31
1, 31
1, 31
Before and after
Treatment x before and
after exposure
Ambient temperature
Body mass
1, 31
1, 31
1, 31
1, 31
1, 31
Movement rate
Wing Flip rate**
Table 4. Effect of treatment, body part, treatment x body part, ambient temperature and
body mass, on the temperature of a bird’s body part under two experimental treatments:
With Predator and With Radar. Results form generalized linear mixed model. Significant
values are bolded.
Body Part
Treatment x Body Part
Body Mass
Fig. 1. (1) Tarp surrounded the entire arena (6m x3m) and was strung up on (2) shepherd
hooks with zip ties. (3) The experimental enclosure was 1 m from the back of the arena.
(4) Four cameras recorded the behavioral responses of the bird, temperature changes of
the bird, and the movement of the predator model. (4a) Predator Camera-observed the
position and movement of the predator model in all trials. (4b) Bird Camera-recorded the
movements and behaviors of the bird in all trials. (4c) IRT Thermal camera (EX320)supplied surface thermography information of the bird for each trial. (4d) Overhead
Camera- provided top view of the bird’s movements and behaviors. (5) The track was 5m
away, at the front of the enclosure.
Fig. 2. (A) Predator model and the enclosure. (B) Close up of predator model, note the
blinders on either side of the track.
Fig. 3. I used three guidelines in order to ensure that the temperature measurements were
accurate: (A) within brackets and moving, (B) outside brackets, (C) outside the view of
the IRT camera,
Fig. 4. (A) Original Photo taken with Flir EX320 Infrared Camera (B) Figure depicts the
parts of the body that were selected to draw temperatures from for the thermal analysis.
The cursor would detect the hottest area of the body and settle; once it settled (according
to detailed thermal guidelines) I recorded the temperature. The areas of the body
measured for the detailed thermal analysis are indicated within the figure: back, neck,
head, eye, mouth cheek, and chest (shown: Experiment #2/Radar Treatment; Trial # 86 at
distance 5; III). Upper left hand corner are the readings from the body positions on the
bird. The scale on the right hand side indicates the temperature scale for both photos.
Fig. 5. Fixed effects of behavioral responses and interaction between treatment and
before and after exposure (to radar or predator). a) Rate at which the bird flew before and
after being exposed to the radar or predator. b) Rate at which bird hung on enclosure
before and after being exposed to the radar or predator. c) Relative Proportion of time the
bird spent in a head up position before and after being exposed to the radar. d) Rate at
which bird was in a head up position while being exposed to the radar and predator. e)
Log of the crouch rate of the bird before and after being exposed to the radar or predator.
f) Log of the peck rate of the bird before and after being exposed to the radar or predator.
g) Log of the wing flip rate before and after being exposed to the predator. h) Rate of
movement of bird before and after being exposed to the predator and radar.
Fig.6. Figure displays the statistical results from the detailed thermal analysis: the fixed
effect of treatment (Radar treatment or Predator treatment) on the temperature of the
various body parts of the bird (head, chest, cheek, neck, back, mouth and eye).
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