Marilyn Ramenofsky

Season and Migration Alters the Corticosterone Response to Capture and Handling in an Arctic Migrant, the White-Crowned Sparrow (Zonotrichia leucophrys gambelii)

The Gambels race of white-crowned sparrow (Zonotrichia leucophrys gambelii) migrates each year from their wintering grounds in the Southwestern United States to the Arctic to breed. Associated with this migration is a change in both the nonstressed and the stress-induced levels of circulating plasma corticosterone. Birds were captured at two sites on their wintering grounds (New Mexico and Arizona). Although stress-induced corticosterone levels were elevated at each site compared to nonstressed levels, there were no differences between wintering sites. These were also similar to levels in birds caught in Washington state during fall migration. In contrast, nonstressed corticosterone values were greatly elevated in birds on their breeding grounds in Alaska and similar to stress-induced levels in wintering birds. Corticosterone levels rose even further in response to the stress of capture and handling in breeding birds. These augmented corticosterone levels during breeding were not associated with weather. Both nonstressed and stress-induced corticosterone levels were similar in birds caught on their breeding grounds on two different years, one with temperatures during mid-May of approximately 0 degree C during a snow storm and the other with temperatures in the mid-20s. These results suggest that seasonal physiological changes, and not local conditions, underlie seasonal changes in corticosterone levels. Furthermore, birds caught in Washington state during spring migration had intermediate levels of both nonstressed and stress-induced corticosterone. Corticosterone release may function differently during spring and fall migrations.

Corticosterone, foraging behavior, and metabolism in dark-eyed juncos, Junco hyemalis

Male, dark-eyed juncos, Junco hyemalis, were held in captivity under conditions simulating winter temperature and photoperiod. Birds were administered corticosterone (B), metapyrone (MET), or control (empty) implants in silastic tubing. B implants resulted in higher plasma levels of B, especially on the first day following implantation. After 4 days, B-implanted birds had significant atrophy of the flight muscles and increased storage of fat in the furcular and abdominal adipose depots. Despite the increased fat deposition, no differences in adipose tissue lipoprotein lipase (LPL) activity or plasma levels of glycerol or free fatty acid were observed after 4 days of treatment. There were no differences in muscle LPL activity when enzyme activity was expressed per tissue. However, when enzyme activity was expressed per gram of tissue, muscle LPL was significantly greater in the B-treated birds. Therefore, despite the atrophy of muscle tissue, the LPL enzyme had been preserved. No differences were observed in either foraging behavior or food consumption, even in light of the dramatic changes in fat and muscle masses in B-treated birds. These data are discussed in light of the chronic effects of B which may be applicable to the advanced stage of stress in birds.

Evidence for a navigational map stretching across the continental U.S. in a migratory songbird

Billions of songbirds migrate several thousand kilometers from breeding to wintering grounds and are challenged with crossing ecological barriers and facing displacement by winds along the route. A satisfactory explanation of long-distance animal navigation is still lacking, partly because of limitations on field-based study. The navigational tasks faced by adults and juveniles differ fundamentally, because only adults migrate toward wintering grounds known from the previous year. Here, we show by radio tracking from small aircraft that only adult, and not juvenile, long-distance migrating white-crowned sparrows rapidly recognize and correct for a continent-wide displacement of 3,700 km from the west coast of North America to previously unvisited areas on the east coast. These results show that the learned navigational map used by adult long-distance migratory songbirds extends at least on a continental scale. The juveniles with less experience rely on their innate program to find their distant wintering areas and continue to migrate in the innate direction without correcting for displacement.

Agonistic behaviour and endogenous plasma hormones in male Japanese quail

Agonistic relationships established among male Japanese quail (Coturnix coturnix) in shortterm dyadic encounters of a round-robin tournament were stable and appeared to be maintained by a form of recognition. The aggressive or submissive behaviour displayed by competitors throughout the tournament did not relate to their circulating levels of luteinizing hormone, androstenedione, 5 α-dihydrotestosterone or corticosterone. However, plasma levels of testosterone were correlated with fighting success in the early phases of the tournament, before agonistic associations were defined. Once relationships stabilized, levels of plasma testosterone in winners declined to values comparable with those of the losers and the qualitatively distinct displays observed in winners or losers were no longer correlated with plasma levels of testosterone. In light of other work, these data suggest that androgens, primarily testosterone, influence the aggressiveness of an individual in initial encounters, helping in turn to determine dominance relationships between opponents. Thereafter, other factors such as learned response biases take precedence. The maintenance of stable social relationships appears to be independent of circulating levels of testosterone in adult male Japanese quail.

Regulation of Migration

ABSTRACT Migration is a widespread and ancient phenomenon commonly involving a seasonal response to predictable changes in the environment. Such changes include the four seasons at the higher latitudes and wet–dry seasons in the tropics. In general, migrations are movements to breeding grounds followed by a postbreeding return to areas for nonreproductive activities. We focus on these seasonal migrations and summarize processes by which diverse organisms prepare and adjust to different phases of the migration life history stage, such as preparation, onset (actual traveling), and termination. This framework enables investigations of physiological and behavioral mechanisms involved in each phase, as well as studies of how environmental signals control this diverse and successful process across the taxa.

Grand Challenges in Migration Biology

Abstract Billions of animals migrate each year. To successfully reach their destination, migrants must have evolved an appropriate genetic program and suitable developmental, morphological, physiological, biomechanical, behavioral, and life-history traits. Moreover, they must interact successfully with biotic and abiotic factors in their environment. Migration therefore provides an excellent model system in which to address several of the “grand challenges” in organismal biology. Previous research on migration, however, has often focused on a single aspect of the phenomenon, largely due to methodological, geographical, or financial constraints. Integrative migration biology asks ‘big questions’ such as how, when, where, and why animals migrate, which can be answered by examining the process from multiple ecological and evolutionary perspectives, incorporating multifaceted knowledge from various other scientific disciplines, and using new technologies and modeling approaches, all within the context of an annual cycle. Adopting an integrative research strategy will provide a better understanding of the interactions between biological levels of organization, of what role migrants play in disease transmission, and of how to conserve migrants and the habitats upon which they depend.

Baseline and Stress‐Induced Plasma Corticosterone during Long‐Distance Migration in the Bar‐Tailed Godwit, Limosa lapponica

The specific roles of corticosterone in promotion of avian migration remain unclear even though this glucocorticosteroid is elevated in many migrating bird species. In general, glucocorticosteroids promote metabolic homeostasis and may elicit effects on feeding and locomotion. Because the migratory stages of refueling and flight are characterized by distinct behaviors and physiology, the determination of corticosterone levels during each stage should help identify potential processes in which corticosterone is involved. We measured baseline levels of corticosterone in bar‐tailed godwits (Limosa lapponica) during two distinct stages of migration: (1) immediately after arrival at a false stopover site just short of the Wadden Sea and (2) throughout the subsequent 4‐wk refueling period on the Wadden Sea. Plasma corticosterone was higher in arriving than in refueling birds. In addition, corticosterone increased with size‐corrected body mass during the refueling phase, suggesting that corticosterone rises as birds prepare to reinitiate flight. Therefore, elevated corticosterone appears associated with migratory flight and may participate in processes characterizing this stage. We also performed a capture stress protocol in all birds and found that corticosterone increased in both arriving and refueling godwits. Therefore, the normal course of migration may be typified by corticosterone concentrations that are lower than those associated with stressful and life‐threatening episodes.

The low-affinity glucocorticoid receptor regulates feeding and lipid breakdown in the migratory Gambel's white-crowned sparrow Zonotrichia leucophrys gambelii.

SUMMARY Plasma corticosterone increases during spring migration in a variety of bird species, including the Gambels white-crowned sparrow Zonotrichia leucophrys gambelii. Corticosterone is elevated specifically in association with migratory flight, suggesting that corticosterone may promote processes such as energy mobilization and/or migratory activity. General effects of glucocorticoids support such a prediction. Because glucocorticoids exert permissive effects on food intake, corticosterone may also participate in the regulation of migratory hyperphagia. To examine the role of corticosterone during migration, we induced Gambels white-crowned sparrows to enter the migratory condition and compared food intake and locomotor activity between controls and birds injected with RU486 - an antagonist to the low-affinity glucocorticoid receptor (GR). In addition, we investigated effects of RU486 in birds that were subjected to a short-term fast. Results indicate that RU486 did not affect locomotor activity. However, consistent with its effects in mammals, RU486 suppressed food intake. Thus, hyperphagia and migratory restlessness, the two behaviors that characterize migration, may be regulated by different mechanisms. Lastly, RU486 antagonized fasting-induced lipid mobilization, as evidenced by decreased plasma free fatty acids. Thus, data on spring migrants suggest that endogenous corticosterone levels act through the GR to support hyperphagia and that the GR promotes availability of lipid fuel substrates in association with periods of energetic demand, e.g. during migratory flight.

Testosterone and Aggressive Behaviour during the Reproductive Cycle of Male Birds

Over the last two decades, great advances have been made in our understanding of the endocrine control of aggression in both reproductive and non-reproductive contexts. These new insights stem primarily from work which has focused on endocrine, neuroendocrine and enzymatic activity in the brain-gonad axis during the dramatic developmental periods of either puberty or seasonal breeding. Despite these sophisticated advances, simple correlations of circulating levels of hormones with either aggressive behaviour or social dominance have proved to be equivocal. Recent work on rodents (Schuurman 1980; Keveme et al. 1978; Brain 1983) and primates including man (e.g. Dixson 1980; Bernstein et al. 1983; Mazur 1983) suggest that such correlations depend to a great extent on taxonomie class, age, experience, social context, and other environmental influences. In primates, for example, simple correlations of plasma androgen and aggressive behaviour have been difficult to establish (Eaton and Resko 1974; Phoenix 1980). It is possible that the complex and diverse social systems, as typified by primates, may serve to obscure detection of any relationship (Dixson 1980; Bernstein et al. 1983). This, in addition, makes design of the critical experiment difficult, if not artificial. In rodents, with social systems that are generally less complex than primates, the evidence for correlations of circulating levels of hormones such as testosterone (T) with aggressive behaviour are more convincing, although not exclusively so. Once again, evidence suggests that these correlations are dependent upon age and social context, as well as environmental influences such as day length, presence of a mate, diet, and weather variables.

Copulation activates Fos-like immunoreactivity in the male quail forebrain

It has been demonstrated using Fos immunocytochemistry that copulation activates specific cell populations in the mammalian brain. Prior to this study, no similar work has been carried out in birds. In mammals, Fos has identified brain circuits activated by genital (penile)/somatosensory and by olfactory/vomeronasal stimuli. Such inputs, of course, should play little or no role in birds (no penis, little or no role for olfaction) and a differential responsiveness could therefore be expected. Male Japanese quail (Coturnix japonica) were allowed to interact freely with adult females and the presence of active sexual behavior, including cloacal contact movements, was confirmed in each case. Control subjects were exposed to a domestic chick (same size as an adult quail) and no sexual behavior was observed. Copulation induced the appearance of Fos-like immunoreactive (FLI) cells in the preoptic area, the hyperstriatum ventrale, parts of the archistriatum, and the nucleus intercollicularis. Induction of FLI cells was observed throughout the rostral to caudal extent of the preoptic region of males from the level of the tractus septomesencephalicus to the level of the anterior commissure, and in the rostral part of the hypothalamus to the level of the supraoptic decussation. The FLI cells did not lie directly adjacent to the third ventricle, but were located 500-1000 microns from the ventricle wall at the level of the lateral edge of the medial preoptic nucleus or, in more caudal sections, in a position ventrolateral to the bed nucleus striae terminalis. It is unlikely that the Fos induction in males resulted from copulation-induced endocrine changes because copulation did not affect plasma levels of luteinizing hormone or testosterone. It is concluded that the responses were due to copulation-associated somatosensory inputs and/or to stimuli originating from the female.