The avian “hibernation” enigma: thermoregulatory patterns and roost choice of the common poorwill
Compared to mammals, there are relatively few studies examining heterothermy in birds. In 13 bird families known to contain heterothermic species, the common poorwill (Phalaenoptilus nuttallii) is the only species that ostensibly hibernates. We used temperature-sensitive radio-transmitters to collect roost and skin temperature (Tskin) data, and winter roost preferences for free-ranging poorwills in southern Arizona. Further, to determine the effect of passive rewarming on torpor bout duration and active rewarming (i.e., the use of metabolic heat to increase Tskin), we experimentally shaded seven birds during winter to prevent them from passively rewarming via solar radiation. Poorwills selected winter roosts that were open to the south or southwest, facilitating passive solar warming in the late afternoon. Shaded birds actively rewarmed following at least 3 days of continuous torpor. Average torpor bout duration by shaded birds was 122 h and ranged from 91 to 164 h. Active rewarming by shaded birds occurred on significantly warmer days than those when poorwills remained torpid. One shaded bird remained inactive for 45 days, during which it spontaneously rewarmed actively on eight occasions. Our findings show that during winter poorwills exhibit physiological patterns and active rewarming similar to hibernating mammals.
KeywordsHibernation Torpor Phalaenoptilus nuttallii Active rewarming Passive rewarming Roost choice
We gratefully acknowledge the field assistance of P. Bradshaw, G. Draheim, E. Geiger, J. and E. Penn, B. Sechler, and B. Woods. We thank B. Branan for his input and logistic support. We thank A. McKechnie, S. Parsons, B. Smit, B. Wolf, and two anonymous reviewers for comments on an earlier version of this manuscript that greatly improved its quality. We are grateful to the late D.W. Thomas for his input to C.P. Woods’ thesis and our thinking about these birds.
Author contribution statement
CPW and RMB conceived the ideas and designed methodology. CPW and RMB collected the data. CPW and RMB analysed the data. ZJC led the writing of the manuscript. All authors critically evaluated drafts and gave final approval for publication.
Funding for this research was provided in part by Faculty of Graduate Studies and Research at the University of Regina, the Peregrine Fund, Inc., and an NSERC Discovery grant to R.M.B.
Compliance with ethical standards
Conflict of interest
The authors declare no competing or financial interests.
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