How do wild birds adjust to captivity? Impacts on stress physiology and behavior.
Abstract: When wild animals are brought into captivity, they experience many
stimuli that may be interpreted as potentially dangerous and activate the stress response,
a set of hormonal pathways that are activated to maintain homeostasis in the face of
harmful stimuli. If stressors are repeated or ongoing, the stress response may become
dysregulated and lead to the suite of symptoms known as ... read more"chronic stress." In this
dissertation, I reviewed the current literature to determine whether chronic stress
decreases with time after capture, indicating adjustment to captivity. While some chronic
stress symptoms frequently decrease over time (i.e. weight loss, leukocyte redistribution),
other symptoms can linger for months or years in some species (i.e. elevated
glucocorticoids, reproductive dysfunction). I conducted several experiments on the chronic
stress of captivity in newly-captured wild house sparrows (Passer domesticus). I monitored
glucocorticoid levels, adrenomedullary variables, and weight in house sparrows over the
first 6 weeks of captivity. The birds had decreased mass up to day 35, elevated baseline
glucocorticoids at day 7 that then declined, and elevated heart rate until day 20,
indicating that the animals suffered chronic stress that only decreased after several
weeks. To determine whether chronic captivity stress could be reduced pharmacologically, I
tested the effects of 4 drugs over the first 7 days of captivity. The anxiolytic diazepam
and the α-adrenergic receptor antagonist phentolamine had no effect on chronic stress. The
β-adrenergic receptor propranolol prevented the increase in baseline glucocorticoids.
Mitotane (which causes chemical adrenalectomy) resulted in decreased heart rate after 1
week, even when it did not cause the expected reduction of glucocorticoids. The hormones of
stress can influence behavior. Neophobia, or the fear of novel objects, is an ecologically
relevant, easily quantified behavior. While characterizing neophobia in captive wild birds,
I documented a seasonal effect on food motivation in house sparrows. Finally, I analyzed
the connection between the adrenomedullary response and neophobia in another passerine, the
European starling (Sturnus vulgaris). I found no relationship between heart rate and
behavior. Therefore, not every aspect of captivity (i.e. novelty) may contribute to the
overstimulation of the stress response leading to chronic stress symptoms.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Biology.
Advisor: L. Michael Romero.
Committee: J. Michael Reed, Philip Starks, and Brian Walker.
Keywords: Endocrinology, Physiology, and Biology.read less