In a new study, researchers from the University of Exeter and the University of Plymouth monitored thermographic changes in captive flocks of juvenile pheasants (Phasianus colchicus) while they engaged in spontaneous aggressive interactions during a brief period of confinement; they found that head temperature dropped sharply in the few seconds prior to an attack, followed by an increase and then a more gradual decline back down towards baseline levels; aggressors were on average slightly hotter than recipients, but the changes in temperature were similar for both roles.
Infrared thermographic image taken from FLIR Tools, showing an aggressive encounter between two juvenile pheasants (middle right of the image). The scale at the top indicates the color coding of temperatures, while the red, upwards-pointing triangles automatically pinpoint the maximum temperature within a selection box drawn manually around each pheasant’s head. Here, the aggressor on the left (Bx1), with a maximum head temperature of 37.5 degrees Celsius, has just delivered an aggressive peck to the recipient on the right (Bx2), who has a maximum head temperature of 35.7 degrees Celsius. The background reference temperature is 26.5 degrees Celsius, taken from a white plastic drinker filled with water (Sp1), suspended above the pen floor (top left of image). Image credit: Sophia et al., doi: 10.1098/rstb.2020.0442.
University of Exeter’s Dr. Tim Fawcett and his colleagues used thermal cameras to watch juvenile pheasants and to see how their temperature changed during aggressive interactions that establish the pecking order.
The study involved 126 juvenile pheasants (aged 6-7 weeks at the time of the study) that were being reared at the Rothamsted Research farm at North Wyke, Devon, UK.
The birds were a mix of full-sibs, half-sibs and unrelated individuals that had hatched in artificial incubators from eggs collected from pens of freely mating polygynandrous adults.
“We recorded acts of aggressive dominance behavior occurring naturally in groups of captive-reared juvenile pheasants, alongside detailed infrared thermographic measurements of their head temperature,” the scientists explained.
“Like other galliforms, juvenile pheasants have areas of naturally bare skin around the eye and ear with a high density of blood vessels, making them highly suitable for infrared thermography studies.”
“Pheasants are precocial, so in captivity a large number of chicks can be hatched on the same day and reared under standardized conditions without their parents, thereby eliminating differences in age and parental care.”
“In the wild, pheasants exhibit harem defense polygyny, with dominant males maintaining control of territories (and access to females) over a prolonged period. An individual adult male’s social rank strongly influences his mating success.”
“In captivity, pheasant chicks are aggressive towards one another and sexual segregation emerges within the first few weeks of life, perhaps driven by female avoidance of aggressive males.”
The authors found that pheasants — both the instigator and the recipient of the aggression — grew more cool-headed before a fight, due to a stress response in which blood rushes to the body’s core.
Their heads became hotter again after the confrontation, as normal blood flow was restored.
“We were surprised that both individuals in these aggressive encounters followed a similar pattern of cooling and heating,” Dr. Fawcett said.
“We expected that a fight would be more stressful for the pheasant on the receiving end of the aggression, and therefore that we’d see a stronger response in them.”
“We can’t say for certain what causes this pattern, but it could be that maintaining a place at the top of the pecking order is just as stressful as being at the bottom.”
While male and female pheasants followed a similar pattern of cooling and heating before and after a fight, females were cooler on average.
“Thermal cameras provide a unique opportunity to non-invasively measure dynamic changes in physiological state over a short period of time,” said Dr. Mark Whiteside, a researcher at the University of Plymouth.
“Using this technique we were able to measure responses to aggressive interactions, in semi-natural environments, in real time.”
The team’s results were published in the journal Philosophical Transactions of the Royal Society B.
_____
Knoch Sophia et al. 2022. Hot-headed peckers: thermographic changes during aggression among juvenile pheasants (Phasianus colchicus). Phil. Trans. R. Soc. B 377 (1845): 20200442; doi: 10.1098/rstb.2020.0442
Source link: https://www.sci.news/biology/aggressive-pheasants-10444.html
