Zonotrichia Albicollis Research Articles

British Ornithologists' Union Records Committee: 42nd Report (October 2013)

British Ornithologists' Union Records Committee: 42nd Report (October 2013)

Hormonal regulation of vasotocin receptor mRNA in a seasonally breeding songbird

Behaviors associated with breeding are seasonally modulated in a variety of species. These changes in behavior are mediated by sex steroids, levels of which likewise vary with season. The effects of androgens on behaviors associated with breeding may in turn be partly mediated by the nonapeptides vasopressin (VP) and oxytocin (OT) in mammals, and vasotocin (VT) in birds. The effects of testosterone (T) on production of these neuropeptides have been well-studied; however, the regulation of VT receptors by T is not well understood. In this study, we investigated steroid-dependent regulation of VT receptor (VTR) mRNA in a seasonally breeding songbird, the white-throated sparrow (Zonotrichia albicollis). We focused on VTR subtypes that have been most strongly implicated in social behavior: V1a and oxytocin-like receptor (OTR). Using in situ hybridization, we show that T-treatment of non-breeding males altered V1a and OTR mRNA expression in several regions associated with seasonal reproductive behaviors. For example, T-treatment increased V1a mRNA expression in the medial preoptic area, bed nucleus of the stria terminalis, and ventromedial hypothalamus. T-treatment also affected both V1a and OTR mRNA expression in nuclei of the song system; some of these effects depended on the presence or absence of a chromosomal rearrangement that affects singing behavior, plasma T, and VT immunolabeling in this species. Overall, our results strengthen evidence that VT helps mediate the behavioral effects of T in songbirds, and suggest that the chromosomal rearrangement in this species may affect the sensitivity of the VT system to seasonal changes in T.

White-throated sparrows adjust behaviour in response to manipulations of barometric pressure and temperature

Correlational evidence suggests that animals may use changes in barometric pressure to predict or respond to changes in weather. Birds adjust the timing of migratory flights and migratory restlessness in response to changing weather, and they make facultative movements in response to storms during winter and breeding. Using the pressure chamber of a hypobaric climatic wind tunnel we tested the responses of white-throated sparrows, Zonotrichia albicollis, to experimental changes in air pressure alone, or air pressure and temperature in combination. Sparrows in wintering (short-day) condition were exposed to gradual changes in pressure/temperature at dawn that simulated large but realistic high- and low-pressure weather systems. During a drop in pressure, birds approached their food cup more quickly and moved more often. There was no effect of increasing pressure and no additional effects of temperature change. Sparrows in spring migratory condition (photostimulated) were exposed to pressure/temperature changes in the evening. Decreases in temperature resulted in less migratory restlessness during the first hour of night, but there was no additional effect of pressure changes. These experimental results indicate that white-throated sparrows can facultatively adjust their behaviour in direct response to changing barometric pressure and temperature.

Differential Regulation of Adipokines May Influence Migratory Behavior in the White-Throated Sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

Spatial, temporal, molecular, and intraspecific differences of haemoparasite infection and relevant selected physiological parameters of wild birds in Georgia, USA

The prevalence of five avian haemoparasite groups was examined for effects on health and associations with extrinsic factors. Overall, 786 samples were examined from six sites in two Georgia (USA) watersheds, during breeding and non-breeding periods in 2010 and 2011. Among the four most commonly infected species, Haemoproteus prevalence was significantly higher in Northern Cardinals (Cardinalis cardinalis) compared to Indigo Buntings (Passerina cyanea) and Tufted Titmice (Baeolophus bicolor) while prevalence in White-throated Sparrows (Zonotrichia albicollis) was significantly higher than in Indigo Buntings. Higher prevalence of Plasmodium was noted in Tufted Titmice and Northern Cardinals. While Leucocytozoon prevalence was highest in White-throated Sparrows, Trypanosoma prevalence was highest in Tufted Titmice. Interesting differences in infection probabilities were noted between foraging guilds with Haemoproteus associated with low-middle level strata and birds in the middle-upper strata were more likely to be infected with Plasmodium and Trypanosoma. In contrast, ground-foraging birds were more likely to be infected with Leucocytozoon. Breeding season was correlated with higher polychromasia counts and higher prevalence of Haemoproteus, Plasmodium and Trypanosoma. In addition, prevalence of infection with certain haemoparasite genera and packed cell volume (PCV) were different among host species. Body mass index was inversely correlated with prevalence of microfilaria infection but positively related to Haemoproteus infection. However, we found no relationship between PCV or polychromasia levels with haemoparasite infection. Molecular characterization of 61 samples revealed 19 unique Haemoproteus (n=7) and Plasmodium (n=12) haplotypes with numerous new host records. No differences were noted in haplotype diversity among birds with different migratory behaviors or foraging heights, thus additional studies are needed that incorporate molecular analysis, host biology, and vector biology into comprehensive models on parasite ecology. Detailed morphological examination of these parasites is also necessary to determine if closely related haplotypes represent single species or morphologically distinct, but closely related, haplotypes.

A Physiological Assessment of Seasonal Differences in Spring and Autumn Migration Stopover at Braddock Bay, Lake Ontario

Abstract. This study investigated seasonal differences in fat deposition and nutritional status of migrating passerine birds at an important stopover site on the south shore of Lake Ontario. Birds were captured during spring and autumn stopovers, and their plasma metabolites were measured as indicators of refueling rates (plasma triglyceride) and nutritional state (plasma uric acid). Catharus thrushes had higher plasma triglyceride and lower plasma uric acid in autumn than in spring, whereas Red-eyed Vireos had higher plasma triglyceride in spring than in autumn, but no seasonal differences in plasma uric acid. There were no seasonal differences in plasma triglyceride concentrations in White-throated Sparrows (Zonotrichia albicollis) and Blackpoll Warblers (Setophaga striata), although White-throated Sparrows had plasma uric acid higher in spring than in autumn, suggesting they were consuming more protein than were those captured during autumn migration. These data suggest that songbirds use this site for...

Testosterone alters genomic responses to song and monoaminergic innervation of auditory areas in a seasonally breeding songbird

Behavioral responses to social stimuli often vary according to endocrine state. Our previous work has suggested that such changes in behavior may be due in part to hormone-dependent sensory processing. In the auditory forebrain of female white-throated sparrows, expression of the immediate early gene ZENK (egr-1) is higher in response to conspecific song than to a control sound only when plasma estradiol reaches breeding-typical levels. Estradiol also increases the number of detectable noradrenergic neurons in the locus coeruleus and the density of noradrenergic and serotonergic fibers innervating auditory areas. We hypothesize, therefore, that reproductive hormones alter auditory responses by acting on monoaminergic systems. This possibility has not been examined in males. Here, we treated non-breeding male white-throated sparrows with testosterone to mimic breeding-typical levels and then exposed them to conspecific male song or frequency-matched tones. We observed selective ZENK responses in the caudomedial nidopallium only in the testosterone-treated males. Responses in another auditory area, the caudomedial mesopallium, were selective regardless of hormone treatment. Testosterone treatment reduced serotonergic fiber density in the auditory forebrain, thalamus, and midbrain, and although it increased the number of noradrenergic neurons detected in the locus coeruleus, it reduced noradrenergic fiber density in the auditory midbrain. Thus, whereas we previously reported that estradiol enhances monoaminergic innervation of the auditory pathway in females, we show here that testosterone decreases it in males. Mechanisms underlying testosterone-dependent selectivity of the ZENK response may differ from estradiol-dependent ones

Seasonal differences in behavior patterns of the migratory white-throated sparrow

Avian migration and associated changes in behavior patterns occur on a seasonal basis and are regulated by both circadian and circannual clocks. It is well known that seasonally migrating birds must alter the temporal partitioning of behaviors in order to successfully complete nocturnal migration, although the precise changes in allocation have not previously been examined. Because of the difficulties related to the study of bird migration in the wild, many studies regarding the physiology of migration have been performed in captivity, where nocturnal migratory restlessness is readily observable at the appropriate times of the year. Even so, quantifying the amount and timing of daily behavioral rhythms in migrating and non-migrating individuals has not previously been performed. We used video recordings of a common nocturnal migrant, the white-throated sparrow (Zonotrichia albicollis), to generate a basic ethogram and to chart the timing and frequency of occurrence of each behavior in order to compare migrant individuals with non-migrating birds. Our study suggests that the specific allocation of behaviors are altered during migration and that these changes might contribute to the development of the “migratory syndrome”.

Oxidative stress, circulating antioxidants, and dietary preferences in songbirds

Oxidative stress is an unavoidable consequence of metabolism and increases during intensive exercise. This is especially problematic for migratory birds that metabolize fat to fuel long-distance flight. Birds can mitigate damage by increasing endogenous antioxidants (e.g. uric acid) or by consuming dietary antioxidants (e.g. tocopherol). During flight, birds may increase protein catabolism of lean tissue which may increase circulating uric acid and many birds also consume an antioxidant-rich frugivorous diet during autumn migration. We evaluated three related hypotheses in a migratory passerine: (1) protein consumption is positively related to circulating antioxidants, (2) a dietary oxidative stressor [i.e. polyunsaturated fatty acid (PUFA)] influences antioxidant capacity and oxidative damage, and (3) oxidative stress influences dietary antioxidant preferences. White-throated Sparrows (Zonotrichia albicollis) consuming a high protein diet increased circulating uric acid; however, uric acid, antioxidant capacity, and oxidative stress did not differ between birds consuming a high PUFA versus a low PUFA diet, despite increased oxidative damage in high PUFA birds. Birds did not prefer antioxidant-rich diets even when fed high PUFA, low protein. We conclude that White-throated Sparrows successfully mitigated oxidative damage associated with a high PUFA diet and mounted an endogenous antioxidant response independent of uric acid, other circulating antioxidants, and dietary antioxidants.

Behavioral Characterization of a White-Throated Sparrow Homozygous for the ZAL2m Chromosomal Rearrangement

The white-throated sparrow is rapidly becoming an important model in the genetics of social behavior because of a chromosomal rearrangement that segregates with a behavioral phenotype. Within a population, 50 % of individuals are heterozygous for a rearranged chromosome 2 (ZAL2(m)). These birds sing more and are more aggressive than the other 50 %, who lack the rearrangement. A disassortative mating system, in which heterozygotes almost never interbreed, ensures that ZAL2(m)/2(m) homozygotes are extremely rare. Here, we provide the first systematic characterization of such a homozygote, a hatch-year female. Her plumage was atypical of her age and sex, resembling that of an adult male. She was extremely vocal and aggressive, dominating her opponents in behavioral tests. Her phenotype was thus an exaggerated version of a typical ZAL2/2(m) heterozygote, supporting the hypothesis that alleles inside the ZAL2(m) rearrangement confer high aggression and further emphasizing this species' value as a model of social behavior.

Morph Matters: Aggression Bias in a Polymorphic Sparrow

In species with discrete morphs exhibiting alternative behavioral strategies, individuals may vary their aggressive behavior in competitive encounters according to the phenotype of their opponent. Such aggression bias has been documented in multiple polymorphic species evolving under negative frequency-dependent selection, but it has not been well-studied under other selection regimes. We investigated this phenomenon in white-throated sparrows (Zonotrichia albicollis), a passerine with plumage polychromatism maintained by disassortative mating. The two distinct color morphs differ with respect to reproductive strategy in that white-striped birds invest more in territorial aggression than tan-striped birds. Whether territorial aggression in this species is biased according to the morph of an intruder is less understood. We found that during peak territorial and mating activity, both color morphs and sexes can exhibit aggression bias, but whether they do so depends on the strategy (morph) of the intruder. During simulated territorial intrusions, resident white-striped males and tan-striped females, which represent the opposite ends of a continuum from high to low territorial aggression, altered their territorial responses according to intruder morph. Tan-striped males and white-striped females, which represent the middle of the continuum, did not show a bias. We propose that because of the disassortative mating system and morph differences in reproductive strategy, the fitness risks of intrusions vary according to the morphs of the resident and the intruder, and that aggression bias is an attuned response to varying threats to fitness.

Rapid Effects of Hearing Song on Catecholaminergic Activity in the Songbird Auditory Pathway

Catecholaminergic (CA) neurons innervate sensory areas and affect the processing of sensory signals. For example, in birds, CA fibers innervate the auditory pathway at each level, including the midbrain, thalamus, and forebrain. We have shown previously that in female European starlings, CA activity in the auditory forebrain can be enhanced by exposure to attractive male song for one week. It is not known, however, whether hearing song can initiate that activity more rapidly. Here, we exposed estrogen-primed, female white-throated sparrows to conspecific male song and looked for evidence of rapid synthesis of catecholamines in auditory areas. In one hemisphere of the brain, we used immunohistochemistry to detect the phosphorylation of tyrosine hydroxylase (TH), a rate-limiting enzyme in the CA synthetic pathway. We found that immunoreactivity for TH phosphorylated at serine 40 increased dramatically in the auditory forebrain, but not the auditory thalamus and midbrain, after 15 min of song exposure. In the other hemisphere, we used high pressure liquid chromatography to measure catecholamines and their metabolites. We found that two dopamine metabolites, dihydroxyphenylacetic acid and homovanillic acid, increased in the auditory forebrain but not the auditory midbrain after 30 min of exposure to conspecific song. Our results are consistent with the hypothesis that exposure to a behaviorally relevant auditory stimulus rapidly induces CA activity, which may play a role in auditory responses.

Habitat selection and fidelity by White-throated Sparrows (Zonotrichia albicollis): generalist species, specialist individuals?

Individuals from habitat generalist species are often thought to be habitat generalist themselves, but this assumption should be examined in light of mounting evidence for native and phenotypic habitat preference. We experimentally tested whether the White-throated Sparrow ( Zonotrichia albicollis (Gmelin, 1789)) exhibits habitat preferences at the individual level. The White-throated Sparrow was a habitat generalist species in our study area, with high occupancy of clearcuts as well as mature forests. However, males in mature forests whose territories were clear-cut in the winter following their breeding season (n = 14), dispersed twice as far as males from uncut mature forests (n = 21). New territories selected by males after clearcuts contained significantly more mature forest than what remained in the territory that they abandoned, but not as much mature forest as was found in their former territory. Gain in uncut habitat after dispersal was positively correlated with dispersal distance. Clear-cut locations left vacant by dispersing males were colonized by new conspecifics. Our results suggest that individual sparrows use only a subset of their species’ wide range of habitats. We question the assumption that individuals from a generalist species are versatile and unlikely to be affected by habitat disturbance.

Long‐term changes in spatial distribution of birds responding to a group‐selection timber harvest

AbstractWe investigated the spatial response of 20 bird species to a group‐selection timber harvest within a 40‐ha forest stand over a 20‐year period (5 yr preharvest and 15 yr postharvest). To characterize the spatial response of each species, we examined trends in 3 metrics: proportion of harvest‐created canopy‐gap area that occurred within the area used by a species in each year, average distance to the nearest gap of all observations of a species in a year, and distribution of distances between observations and gaps for each species in each year. Eight species (eastern wood‐pewee [Contopus virens], winter wren [Troglodytes troglodytes], hermit thrush [Catharus guttatus], Nashville warbler [Vermivora ruficapilla], black‐and‐white warbler [Mniotilta varia], pine warbler [Dendroica pinus], common yellowthroat [Geothlypis trichas], and white‐throated sparrow [Zonotrichia albicollis]) responded positively to the timber harvest (i.e., the proportion of gaps in their area of use increased, the distance from gaps decreased, and their use of gaps and edges [0–25 m from gaps] increased). In contrast, veeries (Catharus fuscescens), black‐throated green warblers (Dendroica virens), and ovenbirds (Seiurus aurocapillus) avoided gaps and edges. Changes in spatial distributions were generally short‐lived; by 15 years postharvest the use of the harvested areas by nearly all species had approached preharvest levels. The spatial response of birds to group‐selection timber harvesting indicates that there are unlikely to be serious long‐term effects of the harvest on forest bird populations. However, there may be more subtle, short‐term effects, such as crowding of mature‐forest bird species into surrounding forest, which merit further study. © 2012 The Wildlife Society.

Response of bird communities to single-tree selection system harvesting in northern hardwoods: 10–12 years post-harvest

We previously investigated the responses of forest birds to habitat changes 1–7years post-harvest in three northern Ontario tolerant hardwood forest stands cut under the selection system. The same three cut blocks and a control area were re-sampled in 2009, 10–12years post-harvest, to compare community composition, total and species abundances and species richness. We found that the breeding bird communities of the selection cut blocks had not fully recovered 10–12years post-harvest. Veery, Chestnut-sided Warbler, Magnolia Warbler, American Redstart and Mourning Warbler numbers were elevated in all three cut blocks, and White-throated Sparrow numbers were elevated in two of the three cut blocks, 10–12years post-harvest. In contrast, Ovenbird numbers remained depressed in two cut blocks 10–12years post-harvest. Overall, species richness remained high in all three cut blocks, even though total abundance declined. The data suggest that repeated applications of selection cutting could have long-term, cumulative effects on forest bird communities.

Estradiol-dependent modulation of serotonergic markers in auditory areas of a seasonally breeding songbird.

Because no organism lives in an unchanging environment, sensory processes must remain plastic so that in any context, they emphasize the most relevant signals. As the behavioral relevance of sociosexual signals changes along with reproductive state, the perception of those signals is altered by reproductive hormones such as estradiol (E2). We showed previously that in white-throated sparrows, immediate early gene responses in the auditory pathway of females are selective for conspecific male song only when plasma E2 is elevated to breeding-typical levels. In this study, we looked for evidence that E2-dependent modulation of auditory responses is mediated by serotonergic systems. In female nonbreeding white-throated sparrows treated with E2, the density of fibers immunoreactive for serotonin transporter innervating the auditory midbrain and rostral auditory forebrain increased compared with controls. E2 treatment also increased the concentration of the serotonin metabolite 5-HIAA in the caudomedial mesopallium of the auditory forebrain. In a second experiment, females exposed to 30 min of conspecific male song had higher levels of 5-HIAA in the caudomedial nidopallium of the auditory forebrain than birds not exposed to song. Overall, we show that in this seasonal breeder, (a) serotonergic fibers innervate auditory areas; (b) the density of those fibers is higher in females with breeding-typical levels of E2 than in nonbreeding, untreated females; and (c) serotonin is released in the auditory forebrain within minutes in response to conspecific vocalizations. Our results are consistent with the hypothesis that E2 acts via serotonin systems to alter auditory processing.

Birdsong: Is It Music to Their Ears?

Since the time of Darwin, biologists have wondered whether birdsong and music may serve similar purposes or have the same evolutionary precursors. Most attempts to compare song with music have focused on the qualities of the sounds themselves, such as melody and rhythm. Song is a signal, however, and as such its meaning is tied inextricably to the response of the receiver. Imaging studies in humans have revealed that hearing music induces neural responses in the mesolimbic reward pathway. In this study, we tested whether the homologous pathway responds in songbirds exposed to conspecific song. We played male song to laboratory-housed white-throated sparrows, and immunolabeled the immediate early gene product Egr-1 in each region of the reward pathway that has a clear or putative homologue in humans. We found that the responses, and how well they mirrored those of humans listening to music, depended on sex and endocrine state. In females with breeding-typical plasma levels of estradiol, all of the regions of the mesolimbic reward pathway that respond to music in humans responded to song. In males, we saw responses in the amygdala but not the nucleus accumbens – similar to the pattern reported in humans listening to unpleasant music. The shared responses in the evolutionarily ancient mesolimbic reward system suggest that birdsong and music engage the same neuroaffective mechanisms in the intended listeners.

Neural Distribution of Vasotocin Receptor mRNA in Two Species of Songbird

The neurohypophyseal hormones vasopressin and oxytocin are produced and released within the mammalian brain, where they act via multiple receptor subtypes. The neural distributions of these receptors, for example, V1a and oxytocin receptors, have been well described in many mammals. In birds, the distribution of binding sites for the homologous neuropeptides, vasotocin (VT) and mesotocin, has been studied in several species by using synthetic radioligands designed to bind to mammalian receptors. Such binding studies, however, may not reveal the specific distributions of each receptor subtype. To identify and map the receptors likely to bind VT and mesotocin, we generated partial cDNA sequences for four VT receptor subtypes, VT1, VT2 (V1b), VT3 (oxytocin-like), and VT4 (V1a), in white-throated sparrow (Zonotrichia albicollis) and zebra finch (Taeniopygia guttata). These genes shared high sequence identity with the homologous avian and mammalian neurohypophyseal peptide receptors, and we found evidence for VT1, VT3, and VT4 receptor mRNA expression throughout the brains of both species. As has been described in rodents, there was striking interspecific and intraspecific variation in the densities and distribution of these receptors. For example, whereas the VT1 receptor mRNA was more widespread in zebra finch brain, the VT3 (oxytocin-like) receptor mRNA was more prevalent in the sparrow brain. Although VT2 (V1b) receptor mRNA was abundant in the pituitary, it was not found in the brain. Because of their association with brain regions implicated in social behavior, the VT1, VT3, and VT4 receptors are all likely candidates for mediating the behavioral effects of VT.

Behavioral and physiological effects of photoperiod-induced migratory state and leptin on a migratory bird, Zonotrichia albicollis: I. Anorectic effects of leptin administration

The hormone leptin is involved in the regulation of energy balance in mammals, mainly by reducing food intake and body adiposity and increasing energy expenditure. During energetically demanding periods, leptin’s action is often altered to facilitate fat deposition and maintain high rates of food intake. Despite the present controversy over the existence of an avian leptin, there is evidence that a leptin receptor exists in birds and its activation influences energy intake and metabolism. However, it is unknown whether the effects of the activation of leptin receptor on energy balance are modulated during migration. We manipulated photoperiod to induce migratory behavior in captive white-throated sparrows ( Zonotrichia albicollis) and injected migratory and wintering sparrows with either murine leptin or PBS for 7 days. We measured food intake, changes in body composition and foraging behavior to test if leptin’s effects are altered during migratory state. Leptin decreased foraging behavior, food intake and fat mass in wintering sparrows, but had no effect on foraging behavior or food intake in migratory sparrows. Migratory sparrows injected with leptin maintained fat better than sparrows injected with PBS. Thus, sparrows’ responses to leptin changed with migratory state, possibly to aid in the increase and maintenance of rates of food intake and fat deposition. We also found that long-form leptin receptor and SOCS3 were expressed in tissues of sparrows, including the hypothalamus, but their expression did not change with migratory state. Further study of the leptin receptor system and other regulators of energy balance in migratory birds will increase our understanding of the physiological mechanisms that are responsible for their ability to complete energetically demanding journeys.

Behavioral and physiological effects of photoperiod-induced migratory state and leptin on Zonotrichia albicollis: II. Effects on fatty acid metabolism

The migratory flights of birds are fuelled largely by fatty acids. Fatty acid transporters, including FAT/CD36, FABPpm and H-FABP, and enzymes involved in fatty acid oxidation (CPT, CS, HOAD) are seasonally up-regulated in flight muscle to meet the demands of this intense aerobic exercise. The mechanisms that control these biochemical changes in response to migration are mostly unknown. We studied the effects of a photoperiod-induced migratory state and a 7 day treatment with murine leptin (1 μg/g body mass, twice per day) on fatty acid metabolism in captive white-throated sparrows. Sparrows that were exposed to a long-day migratory photoperiod increased flight muscle FAT/CD36 and H-FABP mRNA by 154% and 589%, respectively, and had 32% higher H-FABP protein than birds kept on a short-day photoperiod that mimicked wintering conditions. Migrants increased activities of flight muscle CPT, CS and HOAD by 57%, 23% and 74%, respectively, and decreased LDH activity by 31%, reflecting an increase in aerobic relative to anaerobic capacity. The expression of fatty acid transporters and the activities of metabolic enzymes in cardiac muscle were unaffected by migratory state. Leptin had no effect on transport proteins or enzymes in either skeletal or cardiac muscle suggesting that other signaling pathways control fatty acid metabolism during migration. These data indicate that photoperiod alone is sufficient to prime flight muscles for migratory flights by promoting enhanced protein-mediated fatty acid transport and oxidation. However, the endocrine controls and other factors underlying these changes remain to be thoroughly investigated.