Tom Hahn
102 Zoology Field Laboratory
530.752.8531
tphahn (at) ucdavis (dot) edu
(Note: aka Tom Coombs-Hahn)
UC Davis Graduate Group affiliations:
Animal Behavior Graduate Group
Molecular, Cellular and Integrative Physiology Graduate Group
Avian Sciences Graduate Group
B.S., Biological Sciences,
M.S., Biological Sciences,
Ph.D., Zoology,
Animal Behavior (NPB 102), Behavioral Endocrinology (NPB 152/PSC 123)
Effects of the environment on animal physiology and behavior. Focus on mechanisms of regulation of avian cycles of reproduction, plumage molt and migration by environmental factors such as day length, food, and social factors, and on behavioral and physiological responses to unpredictable environmental events.
| Professional Affiliations: Society for Integrative and Comparative Biology (SICB), Division of Animal Behavior (secretary), and Division of Comparative Endocrinology Society for Neuroscience (SFN) Society for Behavioral Neuroendocrinology (SBN) |
| Selected Publications: Hahn, T. P. and S. A. MacDougall-Shackleton. 2008. Adaptive specialization, conditional plasticity, and phylogenetic history in the reproductive cue response systems of birds. Philosophical Transactions of the Royal Society B 363: 267-286. MacDougall-Shackleton, S. A. and T. P. Hahn. 2007. Adaptation and evolution of photoperiod response systems in birds. Journal of Ornithology 148 (Supplement 2): 219-224. DOI: 10.1007/s10336-007-0172-y. Schoech, S. J. and T. P. Hahn. 2007. Food supplementation and timing of reproduction: Does the responsiveness to supplementary information vary with latitude? Journal of Ornithology 248 (Supplement 2): 625-632. DOI: 10.1007/s10336-007-0177-6. Wada, H., T. P. Hahn and C. W. Breuner. 2007. Development of stress reactivity in white-crowned sparrow nestlings: Total corticosterone response increases with age, while free corticosterone response remains low. General and Comparative Endocrinology 150: 405-413. Pravosudov, V. V., K. Sanford and T. P. Hahn. 2007. On the evolution of brain size in relation to migratory behaviour in birds. Animal Behaviour 73: 535-539. MacDougall-Shackleton, S. A., M. Katti, and T. P. Hahn. 2006. Tests of absolute refractoriness in four species of cardueline finch that differ in reproductive schedule. Journal of Experimental Biology 209: 3786-3794. Goodson, J. L., C. J. Saldanha, T. P. Hahn, and K. K. Soma. 2005. Recent advances in behavioral neuroendocrinology: Insights from studies on birds. Hormones and Behavior 48: 461-473. Pereyra, M. E., S. M. Sharbaugh, and T. P. Hahn. 2005. Interspecific variation in photo-induced GnRH plasticity among nomadic cardueline finches. Brain Behavior and Evolution 66: 35-49. MacDougall-Shackleton, E. A., E. P. Derryberry, J. Foufopoulos, A. P. Dobson, and T. P. Hahn. 2005. Parasite-mediated heterozygote advantage in an outbred songbird population. Biology Letters 1: 105-107. Hahn, T. P., M. E. Pereyra, M. Katti, G. M. Ward, and S. A. MacDougall-Shackleton. 2005. Effects of food availability on the reproductive system. Pp. 167-180 in Functional Avian Endocrinology, A. Dawson and P. J. Sharp, eds. Narosa Publishing House, New Delhi, India. MacDougall-Shackleton, S. A., M. E. Pereyra, and T. P. Hahn. 2005. GnRH, photorefractoriness, and breeding schedules of cardueline finches. Pp. 97-110 in Functional Avian Endocrinology, A. Dawson and P. J. Sharp, eds. Narosa Publishing House, New Delhi, India. Sockman, K. W., K. B. Sewall, G. F. Ball, and T. P. Hahn. 2005. Modulation of male song effort in response to female reproductive competence: The economy of a courtship decision in the Cassin’s finch. Biology Letters 1: 34-37. MacDougall-Shackleton, S. A., G. F. Ball, E. Edmonds, R. Sul, and T. P. Hahn. 2005. Age and sex related variation in song-control regions in Cassin’s finches, Carpodacus cassinii. Brain, Behavior and Evolution 65: 262-267. Hahn, T. P., K. W. Sockman, C. W. Breuner and M. L. Morton. 2004. Facultative altitudinal movements by mountain white-crowned sparrows, Zonotrichia leucophrys oriantha, in the Sierra Nevada. Auk 121: 1269-1281. Hahn, T. P., M. E. Pereyra, S. M. Sharbaugh and G. E. Bentley. 2004. Physiological responses to photoperiod in three cardueline finch species. General and Comparative Endocrinology 137: 99-108. Morton, M. L., M. E. Pereyra, J. D. Crandall, E. A. MacDougall-Shackleton, and T. P. Hahn. 2004. Reproductive effort and survival in the mountain white-crowned sparrow. Condor 106: 131-138. Sewall, K. B, T. R. Kelsey, and T. P. Hahn. 2004. Discrete variants of evening grosbeak flight calls. Condor 106: 161-165. Maney, D. L., E. A. MacDougall-Shackleton, S. A. MacDougall-Shackleton, G. F. Ball, and T. P. Hahn. 2003. Immediate early gene responses to hearing song correlate with receptive behavior and depend on dialect in a female songbird. Journal of Comparative Physiology A 189: 667-674. Breuner, C. W., M. Orchinik, T. P. Hahn, S. L. Meddle, I. T. Moore, N. T. Owen-Ashley, T. S. Sperry, and J. C. Wingfield. 2003. Differential mechanisms for plasticity of the stress response across latitudinal gradients. American Journal of Physiology: Regulatory, Integrative, and Comparative Physiology 285: R594-R600. Bentley, G. E., N. C. Audage, E. K. Hanspal, G. F. Ball, and T. P. Hahn. 2003. Photoperiodic response of the hypothalamo-pituitary-gonad axis in male and female canaries, Serinus canaria. Journal of Experimental Zoology 296A: 143-151. Breuner, C. W. and T. P. Hahn. 2003. Integrating stress physiology, environmental change, and behavior in free-living sparrows. Hormones and Behavior 43: 115-123. Marsh, R. H., S. A. MacDougall-Shackleton, and T. P. Hahn. 2002. Photorefractoriness and neural response to day length in American Goldfinches, Carduelis tristis. Canadian Journal of Zoology 80: 2100-2107. MacDougall-Shackleton, E. A., E. P. Derryberry, and T. P. Hahn. 2002. Non-local male mountain white-crowned sparrows have lower paternity and higher parasite loads than males singing local dialect. Behavioral Ecology 13: 682-689. MacDougall-Shackleton, S. A, P. J. Deviche, R. D. Crain, G. F. Ball, and T. P. Hahn. 2001. Seasonal changes in brain GnRH immunoreactivity and song-control nuclei volumes in an opportunistically breeding songbird. Brain, Behavior and Evolution 58: 38-48. MacDougall-Shackleton, S. A., E. A. MacDougall-Shackleton, and T. P. Hahn. 2001. Physiological and behavioural responses of female mountain white-crowned sparrows to natal- and foreign-dialect songs. Canadian Journal of Zoology 79: 325-333. MacDougall-Shackleton, S. A., R. E. Johnson, and T. P. Hahn. 2000. Gray-crowned Rosy-finch (Leucosticte tephrocotis). In The Birds of North America, No. 559 (A. Poole and F. Gill, Eds.). Philadelphia: The Birds of North America Inc. Bentley, G. E., B. D. Spar, S. A. MacDougall-Shackleton, T. P. Hahn, and G. F. Ball. 2000. Photoperiodic regulation of the reproductive axis in male zebra finches, Taeniopygia guttata. General and Comparative Endocrinology 117: 449-455. Harbison, H. E., D. A. Nelson, and T. P. Hahn. 1999. Long-term persistence of song dialects in the mountain white-crowned sparrow. Condor 101: 133-148. Hahn,T.P. 1998. Reproductive seasonality in an opportunistic breeder, the Red Crossbill, Loxia curvirostra. Ecology 79: 2365-2375. Cho, R. N., T. P. Hahn, S. A. MacDougall-Shackleton, and G. F. Ball. 1998. Seasonal variation in brain GnRH in free-living breeding and photorefractory house finches, Carpodacus mexicanus. General and Comparative Endocrinology 109: 244-250. Hahn, T. P., T. Boswell, J. C. Wingfield, and G. F. Ball. 1997. Temporal flexibility in avian reproduction: Patterns and mechanisms. Current Ornithology 14: 39-80. V. Nolan, Jr., E. D. Ketterson, and C. F. Thompson (eds.), Plenum, New York and London. Hahn, T. P. 1996. Cassin's Finch. (Carpodacus cassinii). In The Birds of North America, No. 240 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia; The American Ornithologists' Union, Washington, D. C. Hahn, T. P., J. C. Wingfield, R. Mullen, and P. J. Deviche. 1995. Endocrine bases of spatial and temporal opportunism in arctic-breeding birds. American Zoologist 35: 259-273. Hahn, T. P. and G. F. Ball. 1995. Changes in brain GnRH associated with photorefractoriness in house sparrows (Passer domesticus). General and Comparative Endocrinology 99: 349-363. Hahn, T. P. 1995. Integration of photoperiodic and food cues to time changes in reproductive physiology by an opportunistic breeder, the red crossbill, Loxia curvirostra (Aves: Carduelinae). Journal of Experimental Zoology 272: 213-226. Wingfield, J. C., and T. P. Hahn. 1994. Testosterone and territorial behavior in sedentary and migratory sparrows. Animal Behavior 47: 77-89. |
| Research Summary: My research integrates behavior, physiology, ecology, and evolution, and centers on how birds deal with changes in their environment. I am interested specifically in (1) how birds make behavioral and physiological adjustments to conditions that fluctuate in space and time, and (2) how their particular physiological and behavioral tactics reflect the predictability or unpredictability of fluctuations in the environment. I concentrate on the neuroendocrine/endocrine system because it forms a key interface between the organism and the environment, providing mechanisms by which animals can respond to environmental changes with appropriate adjustments in behavior and physiology. I am committed to using field studies (both descriptive and experimental) to establish the nature of these adjustments to a changing environment, complemented with laboratory experiments to identify the environmental cues and physiological mechanisms that regulate timing of these adjustments. I am likewise committed to taking a collaborative approach, as this allows greater diversity of expertise to be brought to bear on complex problems in integrative biology. It is also much more fun than working in isolation, and provides opportunities for my graduate students and undergraduates to forge lasting contacts outside UC Davis. My current research has two main specific emphases. The first relates to behavioral and physiological adjustments that occur in the long-term (i.e., reproductive cycles). The primary focus of this work is a comparative project on the reproductive neuroendocrine physiology and environmental cue responsiveness of cardueline finches, a diverse group that includes goldfinches, canaries, rosefinches, several types of grosbeaks, and crossbills. The diversity of reproductive schedules in this group, from highly seasonal rosefinches and grosbeaks to extremely flexible or opportunistic crossbills, provides an excellent basis for studying how specific features of the neuroendocrine system relate to degree of reproductive plasticity. I’m particularly interested in how temporal plasticity of the hypothalamic gonadotropin releasing hormone (GnRH) system relates to changes in responsiveness to environmental cues (e.g., cycles of photosensitivity and photorefractoriness), as well as to degree of reproductive flexibility. Taking an explicitly comparative approach promises to permit evaluation of the idea that different degrees of temporal reproductive plasticity depend on specific features of the neuroendocrine system, such as dramatic up- and down-regulation of the GnRH neuronal system on a seasonal basis. The second main research area relates to adjustments that occur in the short-term (i.e., responses to environmental stressors). This work involves a long-term field project in the Sierra Nevada of California, in collaboration with Creagh Breuner (University of Montana; http://dbs.umt.edu/research_labs/breunerlab/). Our work on mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) at Tioga Pass extends a long-term field study begun in the 1960s by Martin L. Morton of Occidental College. Despite Morton’s comprehensive ecophysiological and behavioral studies, there still remain many unexplored features of mountain white-crowned sparrow biology. Creagh and I have been investigating how the white-crowns, just back from their wintering grounds in Mexico, cope with the May snowstorms that frequently occur along the Sierra crest. These storms can be life threatening, increasing the costs of thermoregulation while concealing sources of food for ground feeding birds like white-crowns. However, the steepness of the eastern Sierra escarpment permits sparrows to escape bad weather in the high country via short flights downslope. Using radio telemetry, we have confirmed that the Tioga Pass white-crowns regularly and repeatedly move down to low elevation refuges in Lee Vining Canyon and the Mono Basin during poor weather. Individual sparrows vary dramatically in their propensity to engage in this facultative altitudinal migration behavior, with some departing for lower elevation at the first whiff of bad weather, and others successfully riding out the high country storms. We are particularly interested in the roles that body condition (especially fat stores that can temporarily sustain birds when food is inaccessible) and hormonal physiology (which orchestrates appropriate behavioral and physiological responses to environmental stressors) play in regulating the sparrows’ facultative altitudinal migration behavior. My involvement in this project is actually currently winding down, but Creagh will be continuing with it. I’m also interested in how animals’ early experience affects their behavior and physiology later in life, particularly with respect to birds’ learned vocalizations and habitat preferences. |
| Current Laboratory Members: Current Postdoctoral Fellows: Heather Watts: PhD Michigan State University. Ecology and evolution of social behavior in spotted hyenas. Environmental regulation of behavior and physiology. Current Doctoral Students: Current Masters Students: Former Laboratory Members: Former Doctoral Students: Former Masters Students: |