Endocrine and body weight changes of nesting and non-nesting Canada geese

Ambient temperature and air pressure modulate hormones and behaviour in Greylag geese (Anser anser) and Northern bald ibis (Geronticus eremita)

Ambient temperature and air pressure are relevant stimuli that can elicit hormonal responses in alignment with adjusting individuals' physiology and behaviour. This study investigated possible changes in corticosterone (C) and testosterone (T) and contingencies with behaviour in response to ambient temperature and air pressure, and it evaluated the temporal response dynamics of these hormones in 12 individual Greylag geese (Anser anser) over 26 and 12 individual Northern bald ibis (Geronticus eremita) over 27 days, during late winter. Immunoreactive metabolites of C and T were analysed non-invasively from 626 fecal samples by means of group-specific antibodies and correlated to behaviour and weather factors. In both species, high C levels correlated with low temperatures 24h before sampling, but low C levels correlated with high air pressure 6-12h before sampling. In both species, C levels and behavioural activity were negatively correlated. In addition, temperature had a positive influence on T levels in both species 12-24h before sampling. The fact that weather conditions influenced changes in levels of C, while social interactions did not, is indicative of a general mechanism of graduated physiological adjustment to environmental variations affecting metabolism, stress responses and behaviour.

Longitudinal monitoring of sex steroid hormones in excrement of spectacled eiders (Somateria fischeri)

From the 1970s to the 1990s, the breeding population of spectacled eiders (Somateria fischeri) in western Alaska declined by 96%, which led to the listing of this species as threatened under the Endangered Species Act in 1993. Since then, the population has stabilized, but has not recovered to pre-decline numbers. While little is known about reproductive endocrinology in spectacled eiders, in other avian species, estrogen and testosterone are known to initiate and modulate various reproductive processes including yolk protein synthesis, reproductive behaviors and secondary sex characteristics. Measurement of the metabolites of estrogen and testosterone (EM and TM, respectively) in excrement reflect circulating hormone concentrations and provide a non-invasive method to monitor reproductive physiology. We measured concentrations of excreted EM in captive females and TM in males to (1) determine the efficacy of commercially available radioimmunoassay kits to detect EM and TM, (2) describe annual profiles of EM and TM concentrations, and (3) define the reproductive season of captive spectacled eiders using endocrine status. Excrement samples were collected from captive female and male spectacled eiders three times per week throughout 1 year. Female EM and male TM levels were quantified using radioimmunoassay. Mean female EM profile exhibited values exceeding the threshold for "peak" values (EM>193.3 ng/g) from mid-February to early July, and again in September. Additionally, the highest average concentrations of EM were seen in March, May and September. Elevated TM concentrations occurred in mid March, mid May and late June. These data suggest that levels of excreted sex steroids reflect patterns predicted by breeding landmarks in the annual cycle and will assist in field monitoring and captive breeding programs for spectacled eiders.

Proximate and ultimate factors explaining floating behavior in long-lived birds

Avian populations are composed of reproductive individuals coexisting in space and time with young, non-breeding conspecifics or "floaters". Despite the fact that first breeding can be delayed for years and can exert profound effects on fitness, many aspects of the behavior, ecology and physiology of young floaters remain poorly understood. By means of combining endocrine, behavioral and life history information from a population of black kites (Milvus migrans) monitored long-term, we tested several hypotheses suggesting endocrine function as a determinant of floating status. Sexual function in non-breeding males, estimated through determination of systemic testosterone and progesterone levels, was similar to that in reproductively active conspecifics. Floating females, on the contrary, displayed an endocrine pattern of circulating estrogens and progesterone that was parallel in timing but reduced in magnitude as compared to breeders. Our results suggest that floaters are not physiologically constrained to reproduce, but the cost-benefit balance of attaining complete gonadal function is sexually dependent. While young, unmated males could increase their breeding prospects by attaining sexual maturity regardless of their social environment, natural selection would favor females relying on social cues to mature. Consistent with the sexual roles of socially monogamous species, gonadal recrudescence and testosterone production would allow unmated males to access breeding resources (e.g. through male-male competition and extra-pair fertilizations). Unmated females, on the contrary, would reduce physiological costs by means of delaying ovarian maturation until establishing pair bonds with a male providing access to breeding resources.

Comparative analysis of male androgen responsiveness to social environment in birds: the effects of mating system and paternal incubation

Male androgen responses to social challenges have been predicted to vary with mating system, male-male aggressiveness, and the degree of paternal investment in birds ("challenge hypothesis," Am. Nat. 136 (1990), 829). This study focused on the interspecific predictions of the challenge hypothesis. Comparative methods were used to control for effects of the phylogenetic relatedness among the sampled species. Male androgen data of 84 bird species were collected from literature records on seasonal androgen patterns. From these, the androgen responsiveness (AR) was calculated as described in the original challenge hypothesis (i.e., maximum physiological level/breeding baseline). Scatterplots of AR versus mating strategy, male-male aggressiveness, and the degree of paternal care confirmed the expected interspecific patterns. When phylogenetic analyses were performed among all of the sampled species, the effects of paternal investment disappeared while the AR remained covarying to a high degree with mating system and male-male aggressiveness. Although these mechanisms may be different at the intraspecific level, this suggests that interspecific differences of AR in male birds may have evolved in response to changes of mating strategies, rather than in response to altered paternal duties. However, control for phylogeny among the subsample of 32 passerine species revealed that if any paternal investment contributed to the observed variance in AR, then the change from "no male incubation" to "male shares incubation duties" represented the most effective, whereas the male's contribution to feeding offspring did not explain the observed variation of AR.

Sex-related differences in the effects of late winter pairing activity and seasonal influences on neuroendocrinology and gonadal development of mallards

The importance of late winter pairing activity on the neuroendocrinology of wild waterfowl is unknown. In this study, we examined the sex-related differences in the roles of late winter pairing activity and seasonal influences on neuroendocrine and reproductive physiology in both male and female mallards. Our main goals were to determine (1) which physiological responses were influenced by pairing status or by seasonal changes and (2) whether responses differed between the sexes. Thus, physiological responses of mallards in different pairing status categories were assessed at two times: January 28 to February 5 and February 24 to March 3. Ducks were assigned to one of the following pairing status categories: strong pairs, temporary pairs, unpaired or lone birds within the flock, or birds isolated in same-sex groups. Seasonal changes correlated with increases in both gonadal mass and hypothalamic content of vasoactive intestinal peptide in both sexes, whereas only pairing status correlated with changes in body mass in both sexes. The main sex-related differences were the following: (1) Seasonal decreases in hypothalamic gonadotrophin releasing hormone II content occurred only in females. (2) Seasonal increases in serum prolactin occurred only in males, whereas levels in females were low throughout the study. (3) Both male and female gonadal masses increased seasonally, but male gonadal mass was initially twice that of females. (4) Body mass of both sexes was influenced by pairing status correlations (i.e., all paired or lone birds were heavier than isolated birds), but body mass in males decreased seasonally. No sex-related differences occurred in hypothalamic gonadotrophin releasing hormone I content or circulating serum luteinizing hormone. Taken together, these results indicate that seasonal reproduction in mallards is regulated not only by seasonal but also by social cues, and differences occur between the sexes, months in advance of actual breeding.

Seasonal patterns of sex steroids determined from feces in different social categories of Greylag geese (Anser anser)

Seasonal patterns of fecal 17beta-OH-androgen, estrogen, and progesterone equivalents of male and female greylag geese (Anser anser) were analyzed in a flock of free-living geese. These were compared among social categories determined by pairbond status and breeding success. The annual cycle was divided into 13 phases. Phasewise intra-sexual comparisons were made between social categories. The seasonal variation obtained from feces was in general agreement with the literature on plasma patterns in geese and other temperate-zone birds. However, there were distinct differences in seasonal hormone patterns among the social categories. In unpaired males, androgen was elevated for a longer period of time during sexually active phases compared with paired males. In male geese, high levels of androgen did not interfere with parenting but were related to pairbond status, whereas in females, androgen and progesterone were positively related to parental behavior. In the Fall, androgen, progesterone, and estrogen peaked only in unpaired males. In unsuccessful females, estrogen started to increase earlier in the Winter and was higher in amplitude and duration than that in females guarding offspring. In general, fecal steroids showed a clear-cut difference only between sexually active and parental phases of the year in the successfully breeding pairs, whereas unpaired males retained a hormonal state closer to sexually active phases throughout the year.

Heat-stress response of broiler cockerels to manipulation of the gonadal steroids, testosterone and estradiol

1. Estradiol supplementation resulted in heat-stress mortality in both intact and caponized cockerels accompanied by depressed plasma corticosterone. 2. Phenotype-selection for large comb and high plasma testosterone increased heat tolerance which was attributed to an increased plasma corticosterone. 3. The results suggested that the presence of testosterone had a positive influence on the heat tolerance of broiler cockerels.

Thyroid and adrenal function in the ring dove (Streptopelia risoria) during food deprivation and a breeding cycle

The concentration of plasma triiodothyronine (T3), thyroxine (T4), corticosterone, and glucose as well as body weight and food intake were measured in pairs of ring doves throughout a breeding cycle and during food deprivation. During courtship and incubation the levels of plasma T4 were significantly higher in males than in females. A transitory decrease in food intake in both sexes was measured at the onset of incubation but was not associated with a change in body weight or in levels of plasma thyroid hormones. After the eggs had hatched, food intake increased but was associated with a reduction in body weight and concentrations of plasma T3 and T4, although plasma corticosterone and glucose both increased. Food deprivation for 48 hr resulted in a significant fall in the concentration of plasma T3 and an increase in plasma corticosterone. These changes suggest that all the food was not being digested by the adult birds during brooding but was almost exclusively regurgitated to feed the squabs.

Hormonal patterns in breeding and nonbreeding kestrels, Falco tinnunculus: field and laboratory studies

Plasma levels of luteinizing hormone (LH), androgens, and corticosterone (B) were measured in breeding and nonbreeding kestrels, both in the field and in captivity under different food conditions. LH levels in breeding males were elevated from courtship through incubation and androgen concentration peaked during courtship and laying. Seasonal changes in LH and androgens were similar in breeding and nonbreeding males, although androgens declined sharply after laying in breeding males. Egg laying was characterized by marked increases in both female body mass and plasma concentrations of LH and B. In both breeding and nonbreeding females LH and B increased during pair formation and courtship (March-April), although maximum levels were lower in nonbreeders. Two marked differences were found between free-living and captive (paired) birds. First, during winter plasma levels of LH were basal in free-living birds, while significantly elevated in both captive males and females. Second, during courtship androgen levels in breeding males were three-fold higher in the field than in captivity, probably as a result of intermale aggression under natural conditions. Females breeding early, late, or not at all had similar LH concentrations on arrival and during early courtship. Before breeding there were also no differences in LH (males and females) or in androgen levels (males) between pairs fed ad libitum and pairs temporary food rationed. However, captive females with experimentally reduced food intake showed low levels of B until their rations were increased. Nonbreeders showed hormonal changes similar to breeders, except for those changes in females that were associated with laying. These results suggest that at the start of the breeding season both nonbreeding and breeding kestrels have functional reproductive systems. That some breed early, late, or not at all is primarily an effect of food availability and is not due to hormonal modulation of the reproductive cycle.

Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. I. Males

Behavioral and endocrine changes associated with reproductive events were studied in free-living male house sparrows (Passer domesticus). Circulating levels of luteinizing hormone (LH), testosterone (T), and dihydrotestosterone (DHT) were maximal during egg-laying and declined during incubation and the first 2/3 of the nestling stage. As the young approached fledging, levels of LH and T rose to levels similar to those of the first egg-laying stage. This pattern was repeated three to five times during the prolonged breeding season of this species. Multivariate statistical analysis demonstrated that elevated levels of LH and androgens during egg-laying stages were associated with high rates of intrusion at nests by conspecifics, especially other adult males, and elevated levels of agonistic activity, nest defense, and mate-guarding behavior by breeding males. Feeding rates of males declined significantly as plasma levels of T began to rise. Concentrations of corticosterone (B) were high during each egg-laying and nestling stage and were correlated with high or rising levels of reproductive hormones. This suggests that reproductive activity, while energetically demanding, was not overly stressful to these birds. Body mass and fat depots were lowest during the final brood of the season. We suggest that the temporal pattern of circulating levels of T in male house sparrows is an adaptation which compromises between two conflicting selective pressures: a high level of male-male competition for limiting nesting sites in a semicolonial setting, and a strong demand for parental care associated with large broods of altricial young.

Primary feather molt and serum luteinizing hormone concentration in chukar partridge (Alectoris chukar) during a photoperiodically induced molt with or without fasting

In two experiments, 135 adult chukar partridge of two genetic lines, one selected for high egg production and a random-bred control line, were induced to molt by reducing photoperiod from 16 hr light/day to 8 hr light/day on Day 0. In Experiment 1, feed was removed from approximately half the birds on Day 0 and returned on Day 7. Birds in Experiment 2 were not fasted. Photoperiod was increased to 16 hr light/day on Day 56. Primary feather molt scores, body weights, and, in Experiment 2, serum luteinizing hormone (LH) levels were monitored weekly through Day 85. Prior to the short day period, birds selected for high egg production and females had lower molt scores than controls or males, respectively. Fasting had no effect on molt scores, egg production, or body weights (except during the fasting period). Selected-line birds returned to lay approximately 3 days earlier and laid approximately 16 more eggs during the second production period than controls. Six days before photoperiod was reduced, immunoreactive serum LH levels were 5 to 8 ng/ml; they declined during short days to about 4 ng/ml. Within 8 days after relighting, LH levels increased to approximately 33 ng/ml in males and 18 ng/ml in females. Luteinizing hormone levels remained elevated in males throughout the subsequent 4 weeks but declined in females as egg production resumed.

Corticosterone secretion through long incubation shifts in Diomedea albatrosses

Blood samples were collected from free-living incubating Diomedea albatross during single incubation shifts, both daily (wandering albatross D. exulans and every 2 days (grey-headed albatross D. chrysostoma and black-browed albatross D. melanophris), and the concentration of corticosterone was determined. Within 48 hr a significant increase in the corticosterone concentration was observed in each species. The magnitude of the increase was greater in the grey-headed and black-browed albatrosses than in the wandering albatross. Corticosterone concentrations rose steadily through the incubation shift in grey-headed and black-browed albatrosses, but fluctuated erratically in wandering albatrosses. All three species of albatross fast during incubation and the increase in adrenocortical activity is probably related to the voluntary deprivation of food and water.

The influence of prolactin on food intake of turkey hens

The effect of intracerebroventricular (ICV) injections of turkey prolactin on food intake of turkey hens was studied. Adult, nonlaying medium-weight turkey hens, exposed to 6 hr of light per day, were used in Experiment 1. In Experiments 2 and 3, medium-weight and large-weight turkey hens, respectively, exposed to a long photoperiod and in production, were used. Prolactin was injected into free-feeding hens at doses ranging from 800 to 3200 ng. The ICV injection of prolactin had no significant effect on food intake of hens maintained under 6 hr light per day and not in egg production. In hens exposed to long photoperiods and in egg production, the ICV injection of prolactin caused a significant decrease in food intake. These results suggest that prolactin, acting at the level of the central nervous system, decreases food intake in photostimulated turkey hens.

Variations in plasma corticosterone, estrone, estradiol-17 beta, and progesterone concentrations with forced renesting, molt, and body weight of captive female American kestrels

Corticosterone, progesterone, estradiol-17 beta, and estrone were quantified in plasma collected weekly (April-September) from renesting and nonlaying female American kestrels (Falco sparverius) paired with males in captivity. Hormone levels and body weights for laying females were maximal during courtship and egg-laying periods, while those for non-layers showed no such distinct peaks. This demonstrated that these profiles were not controlled solely by photoperiod. Plasma corticosterone levels were elevated in all females during August and September when kestrels are preparing for migration. For laying females, body weight was positively correlated with plasma estrogen levels. A low spring body weight gain, and not stress, may have prevented the females from breeding in captivity. The photoperiodic control of molt did not appear to be mediated directly by the hormones studied, since there were no changes in hormone levels associated with the onset of molt.

The relationship between plasma concentrations of prolactin and consumption of feed and water during the reproductive cycle of the domestic turkey

The plasma concentrations of prolactin (PRL) were measured throughout the reproductive cycle of turkey hens. Plasma PRL levels increased during egg laying from 20.1 +/- 3.9 ng/ml (means +/- SEM) at the first oviposition to 55.6 +/- 5.1 ng/ml at the last oviposition. Levels of PRL increased during incubation and were maintained between 70 and 90 ng/ml. After the poults were hatched, the concentration of PRL decreased rapidly and by 7 days after hatch, PRL levels were not significantly different from those observed before egg laying. The consumption of feed and water decreased significantly (P less than .05) during incubation to less than 10% of that observed during egg laying. The intake of feed and water increased rapidly after the poults were hatched. Hens lost 17% of their body weight during the incubation period. The concentration of D-(-)-3-hydroxybutyrate (DBHB) increased 16-fold during the incubation period and decreased rapidly after the poults were hatched. Body temperature and the concentration of glucose were significantly (P less than .05) depressed during incubation. Hematocrit increased significantly (P less than .05) during the transition from egg laying to incubation. These data suggest that the changes in the concentration of PRL may be related to the large changes in intermediary and water metabolism that occur during broodiness.

Simultaneous quantification of progesterone, estrone, estradiol-17 beta and corticosterone in female American kestrel plasma

Progesterone, estrone, estradiol-17 beta and corticosterone were quantified simultaneously for the first time in female American kestrel (Falco sparverius) plasma. A mean level for each hormone was determined for the laying and non-laying periods of the summer (April-September), and for February. Means were comparable to those of other wild avian species and were significantly higher for the laying period than for the other 2 periods. The mean corticosterone level for February was higher than that for the non-laying summer period. Plasma from laying kestrels, unlike that from other avian species, required lipid removal before column chromatography. Of 2 lipid removal techniques compared, i.e. the cold methanol and hexane:methanol techniques, the latter proved superior.

Serum levels of luteinizing hormone (LH), prolactin, estradiol, and progesterone in laying and nonlaying canvasback ducks (Aythya valisineria)

Temporal changes in the levels of serum luteinizing hormone (LH), prolactin, estradiol, and progesterone associated with the reproductive patterns of 53 wild captive canvasback ducks were measured. The reproductive endocrinology of both laying and nonlaying females was compared in this 3-year study. Females that remained sexually inactive had ovaries with small, undeveloped follicles. Nonlaying ducks also had lower serum levels of LH (P less than 0.01), prolactin (P less than 0.05), estradiol, and progesterone than those of laying ducks in mid-April (during prelay), mid-May (on the fourth day of egg production), and mid-June (during postlay and incubation). Prolactin levels of both layers and nonlayers increased over this time interval (P less than 0.01) but levels of nonlayers were significantly lower than those of layers for the three blood-sampling dates. The low prolactin levels demonstrate that reproductive failure was not a result of inhibition by high serum prolactin levels. Intravenous injections of luteinizing hormone-releasing hormone (LHRH) in female canvasbacks resulted in significantly elevated (P less than 0.01) serum LH on the prelay blood sampling date. Lack of reproduction in nonbreeding canvasbacks was thus associated with low circulating serum LH levels but with LHRH-sensitive pituitary pools. These data suggest that lack of reproduction was a result of the failure of the hypothalamus to release releasing factors. The serum hormones of laying canvasbacks varied temporally with stages of the nesting cycle. LH levels increased prior to egg laying and fluctuated during the laying period. LH levels decreased at the onset of incubation but increased after loss of clutch, with renesting activity. Serum prolactin levels of layers were low prior to egg laying and increased gradually through laying of the first clutch, the renesting period, and laying of the second clutch. The highest prolactin levels occurred in ducks incubating their eggs. Prolactin levels decreased in ducks that failed to incubate their eggs. Serum estradiol levels increased sharply between 2 and 5 weeks prior to egg laying and remained high until the second day of egg production. Estradiol levels decreased when the fourth egg was produced, and remained low through the laying of the first clutch, the renesting period, and laying of the second clutch. Progesterone fluctuated widely through the nesting cycle, showing several major peaks before laying and another during incubation.

Plasma corticosterone in wild starlings (Sturnus vulgaris) immediately following capture and in relation to body weight during the annual cycle

Free-living starlings (Sturnus vulgaris) were caught by mist netting. Blood samples were taken from them between 20 sec and 4 min after capture and assayed for corticosterone. Before 1 min corticosterone levels were constant (10.3 nmol litre-1) but after 1 min they increased rapidly (27.0 +/- 3.6 nmol litre-1 min-1). Male and female free-living starlings were caught throughout the year with mist nets, and traps placed in nest boxes. Blood samples were taken within 1 min of capture and body weights recorded. Plasma corticosterone varied between 3 and 13 nmol litre-1. In both sexes the level was high during winter and through the breeding season. It fell to low levels during late summer and increased again during autumn. Body weight in both sexes was highest in midwinter and lowest in midsummer but there was no correlation between body weight and plasma corticosterone concentration.