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Flushing Effects and Seasonal Changes on Corticosterone Levels in Adult Long-Eared Owls Asio otus

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Abstract

Long-eared Owls Asio otus were flushed and captured from communal winter roosts and nesting seasons to assess both initial and stress-induced corticosterone concentrations. We examined blood samples from 16 males and 8 females in the winter, and 16 males and 11 females in the breeding season. Corticosterone concentrations after flushing owls in either season were not correlated with the elapsed time from initial flush to capture, suggesting that these birds did not interpret flushing as stressful. In contrast, 30 min of handling and restraint during both seasons elicited robust increases in plasma cortlcosterone concentrations that did not differ by sex. Although stress-induced corticosterone levels did not differ seasonally, baseline levels were 50% lower during the winter compared to breeding, suggesting the breeding season is a more stressful time. These results indicate that capture techniques used in this study with Long-eared Owls were only stressful when successful, and that initial corticosterone concentrations vary seasonally.

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... This method is widely used and has garnered data concerning patterns of GC secretion and their various roles in wild animals (Deviche et al., 2010;French et al., 2008;Holding et al., 2014;Pereyra and Wingfield, 2003;Pravosudov et al., 2002;Refsnider et al., 2015). Many avian studies of seasonal patterns report higher CORT levels at the onset of breeding where it may serve to mobilize energy stores, and then levels declining post breeding when it may interfere with anabolic processes, such as feather molt (Foltz et al., 2015;Holding et al., 2014;Cornelius et al., 2011; DesRochers et al., 2009;Romero et al., 2009Romero et al., , 2005Pereyra and Wingfield, 2003;Raja-aho et al., 2013). In some species, plasma CORT levels are reduced during breeding when stress might interfere with limited opportunities for reproduction (e.g., a short breeding season), and thus, yearly CORT patterns often align closely with specific life-history patterns and environmental conditions (Holberton and Wingfield, 2003;Romero et al., 1997). ...
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Captive starlings were used to examine daily and seasonal changes in basal and stress-induced corticosterone levels. Birds were bled at 4 times during the daily cycle and during three different simulated seasons: under a short-day photoperiod (mimicking winter), under a long-day photoperiod (mimicking summer), and while undergoing a prebasic molt. Basal corticosterone samples were assayed from blood collected within 3 min of disturbance and corticosterone increases in response to handling and restraint were monitored in blood taken at 15, 30, and 45 min postdisturbance. Handling and restraint elicited robust increases in corticosterone at all times of the day and during all three seasons. Both basal and stress-induced levels varied with the time of day (with the exception of basal samples during molt). Levels were higher at night, during the bird's inactive period, and decreased during the day. These data indicate that starlings have daily rhythms in both basal corticosterone levels and in their response to stress, with more corticosterone released during the night in response to identical stimuli. Starlings also show pronounced seasonal variation in both basal and stress-induced corticosterone levels. Although birds held on short and long days had equivalent corticosterone levels, both basal and stress-induced levels were lower during molt. This parallels data from free-living birds and provides a laboratory model for studying seasonal corticosterone regulation.
Article
Corticosterone concentrations were measured in captive house sparrows (Passer domesticus) and found to vary both daily and with different photoperiods. Basal corticosterone was highest during the dark hours of the daily cycle and lowest during the light hours. This trend remained constant when the birds were held on short-day and long-day light cycles, and while the birds were undergoing a prebasic molt. At all times, corticosterone concentrations significantly increased in response to the stress of handling and restraint. Stress-induced corticosterone concentrations, however, only reflected a daily rhythm when the birds were held on short-days. Furthermore, even though mean basal corticosterone concentrations were equivalent over the short-day, long-day, and molt, total corticosterone output in response to stress was lower in molting birds, especially at night. Therefore, these data indicate that captive house sparrows modulate corticosterone in daily cycles that change in response to photoperiod.
Article
The vertebrate stress response helps animals respond to environmental dangers such as predators or storms. An important component of the stress response is glucocorticoid (GC) release, resulting from activation of the hypothalamic-pituitary-adrenal axis. After release, GCs induce a variety of behavioral and physiological changes that presumably help the animal respond appropriately to the situation. Consequently, GC secretion is often considered an obligatory response to stressful situations. Evidence now indicates, however, that free-living species from many taxa can seasonally modulate GC release. In other words, the magnitudes of both unstressed and stressed GC concentrations change depending upon the time of year. This review examines the growing evidence that GC concentrations in free-living reptiles, amphibians, and birds, but not mammals, are commonly elevated during the breeding season. This evidence is then used to test three hypotheses with different focuses on GC's energetic or behavioral effects, as well as on GC's role in preparing the animal for subsequent stressors. These hypotheses attempt to place annual GC rhythms into a physiological or behavioral context. Integrating seasonal differences in GC concentrations with either different physiological states or different life history stages provides clues to a new understanding of how GCs actually help in survival during stress. Consequently, understanding seasonal modulation of GC release has far-reaching importance for both the physiology of the stress response and the short-term survival of individual animals.
Long-eared Owl (Asio otus) The Birds of North America, no. 133. Academy of Natural Sciences Philadelphia, Immunocytochemical and histological differences in the interrenal axis of feral brown trout, Salmo trutta, in metal-contaminated waters
  • J S Marks
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Marks J.S., Evans D.L. & Holt D.W. 1994. Long-eared Owl (Asio otus). In: Poole A. & Gill F. (eds) The Birds of North America, no. 133. Academy of Natural Sciences Philadelphia, and AOU, Washington, D.C. Norris D.O., Felt S.B., Woodling J.D. & Dores R.M. 1997. Immunocytochemical and histological differences in the interrenal axis of feral brown trout, Salmo trutta, in metal-contaminated waters. Gen. Comp. Endocrinol. 108: 343–351.
Strigidae species accounts
  • D W Holt
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  • C Deppe
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Holt D.W., Berkley R., Deppe C., Enriguez-Rocha P.L., Olsen P.D., Petersen J.L., Rangel-Salazar J.L., Segars K.P. & Wood K.L. 1999. Strigidae species accounts. In: del Hoyo J., Elliot A. & Sargatal J. (eds) Handbook of birds of the world, Vol. 5. Lynx Ediciones, Barcelona, pp. 153-242.
Adrenocortical responses to stress and their modulation in free-living vertebrates Handbook of physiol-ogy; Section 7: The endocrine system; Volume IV: Coping with the Environment: Neural and Endocrine Mechanisms
  • J C Wingfield
  • L M Romero
Wingfield J.C. & Romero L.M. 2001. Adrenocortical responses to stress and their modulation in free-living vertebrates. In: McEwen B.S. & Goodman H.M. (eds) Handbook of physiol-ogy; Section 7: The endocrine system; Volume IV: Coping with the Environment: Neural and Endocrine Mechanisms. Oxford University Press, New York, pp. 211–234.