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PubMed1988

Control of aggression and dominance in white-throated sparrows by testosterone and its metabolites.

In three experiments, we investigated whether testosterone itself or its metabolites activate aggression and dominance in white-throated sparrows Zonotrichia albicollis. Groups of five to six sparrows, each treated with a different steroid implanted subcutaneously, were observed in outdoor aviaries during late winter to determine the birds' rates of aggression (supplantations and attacks scaled to the number of available subordinates) and dominance rankings with opponents not previously encountered. In Experiment 1, testosterone (T) had a greater effect on aggression and dominance than did androstenedione, 5 alpha-dihydrotestosterone (D), androsterone, or estradiol (E). In Experiment 2, birds with T or D + E had higher aggression scores and dominance ranks than birds with either D or E alone. Birds with T and D + E did not differ. The testosterone metabolites, D and E, thus acted synergistically to determine rates of aggression and dominance ranks. To corroborate these results, in Experiment 3 we treated T-implanted birds with the following blocking agents: ATD, expected to reduce conversion of T to E (AT birds); progesterone, expected to reduce conversion of T to D (PT birds); or both (APT birds). The APT birds had lower aggression scores and dominance ranks than did AT or PT birds, despite having higher mean levels of circulating T than AT or PT birds or birds implanted with T alone. Cyproterone acetate also reduced aggression scores and dominance in T-implanted birds. We conclude that the hormonal control of aggression and dominance in these birds requires conversion of testosterone to both androgenic and estrogenic metabolites.

Aggression↗

PubMed1989

Testosterone induction of song in photosensitive and photorefractory male sparrows.

Song in male songbirds is activated by the sex steroid testosterone (T). Using male song sparrows (Melospiza melodia), we compared effects of T in the normal spring state of photosensitivity (i.e., when the pituitary-gonadal axis is sensitive to stimulation by increasing daylength) and in the late summer-early fall state of photorefractoriness (i.e., when they are insensitive to increasing daylength). Photosensitive males experienced short days for 8 weeks and then long days for another 22 weeks to induce photorefractoriness. T implants were given to the birds twice, first when on short days and photosensitive, and second when on long days and photorefractory. Song rates were compared among 5 conditions: (1) photosensitive, short days, low T titers; (2) photosensitive, short days, high T titers; (3) photosensitive, long days, high T titers; (4) photorefractory, long days, low T titers; and (5) photorefractory, long days, high T titers. Plasma levels of T were monitored throughout the experiment by radioimmunoassay. T was equally effective in inducing song in both the photosensitive and photorefractory conditions. Thus, no seasonal change was found in the sensitivity to hormone action of the neural target sites mediating this behavior in song sparrows. Photosensitive birds sang at a higher rate when on long days than when on short days, however, even though there was no concomitant increase in plasma levels of T. This finding suggests that environmental factors can alter the expression of song activated by similar levels of T.

Animals↗

PubMed1990

Plasma levels of prolactin and gonadal steroids in relation to multiple-brooding and renesting in free-living populations of the song sparrow, Melospiza melodia.

Plasma levels of testosterone (T), estradiol (E2), and prolactin were measured in samples collected from free-living song sparrows, Melospiza melodia. In males, plasma levels of T were elevated early in the season when territories were established and when females laid the first clutch of eggs. Thereafter, T levels declined and remained low throughout the remainder of the breeding cycle. However, if the first brood was lost to a predator, or by experimental removal of the nest, plasma levels of T increased as renesting, to replace the clutch, occurred. Circulating levels of prolactin in males began to rise during the egg-laying stage of the first brood, reached a maximum toward the end of the incubation stage, remained elevated until breeding was terminated, and then declined throughout the moulting stage to basal values in October. Prolactin levels remained high throughout the breeding season irrespective of whether a brood was raised successfully or whether the nest was lost and renesting occurred. In females, plasma levels of E2 were elevated prior to the egg-laying stage for each brood as is typical of multiple-brooded species. However, prolactin titers rose dramatically during egg-laying for the first clutch (slightly higher than in males) and were maximal by onset of incubation. Only females of this species incubate, although males do feed young. As in males, plasma prolactin in females remained high between broods and during experimentally induced renesting, and then declined to basal by the end of the moult stage in October. These data suggest that there are no differences in the temporal patterns of prolactin concentrations in blood between multiple-brooding and renesting. In a separate experiment, captive male song sparrows were transferred from a short day to artificial long days (18L 6D) and a control group was maintained on 9L 15D. In the long-day group, prolactin levels rose abruptly over the first 20 days, as the testes developed, and remained high well into postnuptial moult after the gonads had regressed. Prolactin remained basal in the control group. These data suggest that the temporal pattern of circulating prolactin levels throughout the breeding season is regulated at least partly by changing photoperiod. However, nonphotoperiodic factors are also important since photoperiodically induced increases in prolactin are significantly less than those seen in free-living individuals. These differences may be related to parental behavior.

Animals↗

PubMed1992

Hormonal responses to removal of a breeding male in the cooperatively breeding white-browed sparrow weaver, Plocepasser mahali.

The white-browed sparrow weaver (Plocepasser mahali) is a cooperatively breeding Ploceid finch that lives in groups of up to 11 individuals. Each group consists of a dominant breeding male and female and a varying number of nonreproductive birds that help feed young and defend the group territory. Experimental removal of the dominant male resulted in attempts by other males to take over the group. Removal of a subordinate, nonbreeding male, as a control, resulted in no change of status among group members. During takeover, there was a transitory increase in plasma levels of luteinizing hormone in the new dominant male, but no change in testosterone levels. As reported in previous investigations, dominant males tended to have higher levels of testosterone than females or subordinate males, but this was not related to the heightened aggression of the takeover. Plasma levels of luteinizing hormone, testosterone, and corticosterone did not differ between the other status groups. The possibility that luteinizing hormone, or a hitherto unidentified androgen, may regulate aggression in the white-browed sparrow weaver is discussed.

Aggression↗

PubMed1981

Quantitative analysis of the respiratory system of the house sparrow, budgerigar and violet-eared hummingbird.

In the house sparrow, the budgerigar and the violet-eared hummingbird the volumes of the lungs and air sacs are estimated from silicone casts. The quantitative composition of the lungs and of their compartments are measured on lung slices, the relative volumes of the parabronchi on histological sections, and the volume composition of the blood-air capillary network of the parabronchi on electron micrographs. On electron micrographs the exchange surface and the thickness of the air-blood diffusion barrier are also measured. From these data the morphological membrane diffusion capacity is calculated and related to several organ weights. The volume of the lungs and air sacs makes up 14-22% of the total body volume, the lungs only 2.3-2.9%. The exchange surface varies from 61 cm2/g (budgerigar) over 70 cm2/g (house sparrow) to 99 cm2/g (violet-eared hummingbird). The very thin barrier in these small birds results in a membrane diffusion capacity of 0.122 in budgerigars up to 0.271 ml O2/mm Hg . min . g in violet-eared hummingbirds. The various parameters are compared with those of corresponding mammals, and the quantitative advantages of the avian respiratory system are discussed.

Animals↗

PubMed2004

The effects of combined aromatase inhibitor and anti-androgen on male territorial aggression in a tropical population of rufous-collared sparrows, Zonotrichia capensis.

Territorial aggression, exhibited by male vertebrates in a reproductive context, is generally thought to be mediated by elevated levels of the gonadal steroid hormone testosterone. Rufous-collared sparrows from Papallacta, Ecuador are only aggressive during the breeding season when plasma testosterone concentrations are elevated. However, previous experiments have determined that during the breeding season testosterone does not increase in response to territorial challenges and testosterone implants do not make males more aggressive. This relationship between testosterone and aggression is different from closely related northern latitude species. We conducted another experiment investigating the role of testosterone in mediating territorial aggression, during the breeding season, in male rufous-collared sparrows. We predicted that blocking the actions of the testosterone would suppress aggression in response to territorial challenges. During the early breeding season males were captured using a simulated territorial intrusion and there was no relationship between time to capture and plasma testosterone, dihydrotestosterone, and corticosterone concentrations. Individual males were then implanted with both the aromatase inhibitor ATD and the anti-androgen Flutamide or empty implants as a control. After one week, birds were challenged with a simulated territorial intrusion and the aggressive responses measured. There were no differences in individual behavioral responses (number of songs, flights, closest approach, or time within 5 m) or overall aggression between the two groups. Androgen levels were elevated, post-implant, in the experimental group suggesting that the treatment was successful by blocking the negative feedback system. We conclude that pharmacologically inhibiting testosterone during the breeding season does not affect territorial aggression in these birds.

Aggression↗

PubMed2005

Seasonal gonadal recrudescence in song sparrows: response to temperature cues.

Day length predicts changing of seasons at mid-latitudes, but additional environmental cues (e.g., temperature, rainfall) give more precise information about timing of food peaks critical for offspring survival. We tested the effects of temperature on seasonal reproductive development of male song sparrows (Melospiza melodia morphna) from two populations: the Western Washington coast (3 m) and Cascade Mountains (500-1220 m). Previous work has shown that the timing of gonadal recrudescence can differ between the two sites in the field by as much as two months. However, in the laboratory under identical controlled conditions, testes grow at the same rate. To test whether temperature alone could account for a portion of the variation we measured in the field, we captured birds from each site and held them in temperature controlled environmental chambers that mimicked temperatures experienced either in the mountains or on the coast. We increased day length on a natural schedule, and measured testis volume, levels of circulating androgens and prolactin, and song rates. Increasing day length stimulated gonadal growth in all groups. We found only modest effects of temperature on reproductive development. In the mountain birds colder, montane temperatures slowed rates of growth, delaying the onset of growth by one month. Since temperature changes more markedly during the early winter months in the mountains than on the coast, increasing temperature may be a more relevant cue in timing of reproduction in the mountain population. These data suggest that while temperature helps to explain some of the variation in reproductive timing of free living sparrows, another as yet untested cue in the field may play a more important role. Furthermore, our data suggest that individuals within the same species may rely on different proximate cues for reproductive timing depending on the specific habitat in which they live.

Analysis of Variance↗

PubMed1997

Testis-dependent and -independent effects of photoperiod on volumes of song control nuclei in American tree sparrows (Spizella arborea).

Songbirds exhibit seasonal changes in the volumes of song control nuclei. Birds on long, spring-like days have larger nuclei than do birds on short, winter-like days. The mechanisms mediating volumetric changes have not been determined unequivocally, but testosterone (T) is probably involved. This study examined whether testicular factors are uniquely responsible for seasonal changes in the song system, or whether photoperiod has testis-independent effects. Male American tree sparrows were exposed to one of three photoperiodic conditions: (1) Photosensitive birds were retained on short days (8L:16D). Plasma T is rarely detected in such birds. (2) Photosensitive birds were moved from short days to long days (20L:4D) and photostimulated for three weeks. Photostimulation elevates circulating T in photosensitive birds. (3) Photorefractory birds were held at least four months on 20L:4D. Such birds seldom have detectable levels of T, even though they are on long days. In each condition, there were both intact and castrated birds. Castration typically removes circulating T in tree sparrows. The volumes of the high vocal center (HVC), nucleus robustus archistriatalis (RA), and area X were measured. Song nuclei were largest in intact photostimulated birds. Other long-day birds (i.e. castrated photostimulated, and intact and castrated photorefractory groups) had larger song nuclei than did short-day intact or castrated photosensitive birds and did not differ from each other. These data indicate that photoperiod has both testis-dependent and -independent effects on the volumes of song control nuclei.

Animals↗

PubMed2003

Integrating stress physiology, environmental change, and behavior in free-living sparrows.

As weather deteriorates, breeding animals have a diverse array of options to ensure survival. Because of their mobility, birds can easily abandon territories to seek out benign conditions away from the breeding site. The timing of abandonment, however, may have repercussions for territory size, mate quality, reproductive success, and survival. There is a large body of evidence indicating that the adrenocortical response to stress plays a role in mediating the onset and maintenance of this behavioral switch. Here we develop a model describing the interactions of weather, food availability, body condition, and stress physiology in initiating departure from the breeding site. We tested the model using a population of white-crowned sparrows breeding at high elevation in the Sierra Nevada, where severe weather at the beginning of the breeding season often induces temporary abandonment of breeding territories and facultative altitudinal migration to lower elevation refugia. The data show that (1). during inclement weather, exogenous corticosterone delays return to the breeding site after territory abandonment; (2). during good weather, exogenous corticosterone alone does not induce territory abandonment, but does increase activity range around the breeding site; and (3). the magnitude of the corticosteroid response to stress is inversely related to body condition of the sparrow.

Adipose Tissue↗

PubMed1998

Anterior forebrain pathway is needed for stable song expression in adult male white-crowned sparrows (Zonotrichia leucophrys).

The anterior forebrain pathway of the avian song system is involved in juvenile song learning, but its function in adult song behavior is not known. This report uses lesions to study the role of a particular forebrain nucleus, IMAN, in the seasonal regeneration of song in adult white-crowned sparrows (Zonotrichia leucophrys oriantha). White-crowned sparrows, even when acoustically isolated as juveniles, crystallize a single song which they maintain throughout adulthood. The lateral portion of the magnocellular nucleus of the anterior neostriatum (1MAN) was lesioned bilaterally in adult males maintained on short days (8 h of light). Daylength was increased to 16 h following the surgeries, and all birds were recorded in the post-lesion singing season. Lesioned birds showed a large decrease in song note frequency following the lesions, significantly larger than did intact, age-matched controls. Further changes were seen in the post-lesion songs of seven of 11 successfully lesioned males. These changes included variability in song pattern, loss of frequency control and addition of new notes, some of which had been practiced during juvenile song development. These changes seemed especially large in birds that had either been acoustically isolated or had not fully copied a tape-tutor song during juvenile song development. These results are the first to indicate that the motor memories for song elements that had been practiced and discarded early in life are retained, and they suggest that 1MAN affects seasonal song expression by selectively reinforcing a particular song pattern.

Animals↗

PubMed1999

Alterations in hypothalamic-pituitary-adrenal function associated with captivity in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii).

Gambel's white-crowned sparrows were captured and brought into captivity in order to study seasonal changes in the function of the hypothalamic-pituitary-adrenal (HPA) axis in captive birds. 30 min of restraint elicited a rise in corticosterone titers that varied depending upon the season and physiological state of the birds. Restraint elevated corticosterone titers significantly more during the fall (within 2 weeks of capture from the wild) than during either the winter or during a prealternate or prebasic molt. We also examined what changes in the HPA axis could account for altered corticosterone levels. Exogenous ACTH significantly elevated corticosterone levels beyond the response to restraint during the fall, indicating a dramatic enhancement of the adrenal's ability to secrete corticosterone. Exogenous ACTH was ineffective at other times, suggesting that the adrenal's ability to release corticosterone often limits circulating levels. We further inferred the pituitary's ACTH secretory ability by injecting exogenous corticotrophin-releasing factor, arginine vasotocin, and mesotocin and measuring corticosterone release. Pituitaries failed to respond to any exogenous releasing factor during the fall, suggesting that the pituitary may be the site in the HPA axis regulating corticosterone release at this time. When compared to wild-caught birds, these results suggest that captivity alters both adrenal and pituitary function during restraint in white-crowned sparrows, and that this change depends upon the season and/or physiological state of the animal. Captivity thus appears to have a profound affect on the function of the HPA axis, and these results reiterate the caution that must be used to extrapolate laboratory data to field conditions.

Adrenocorticotropic Hormone↗

PubMed2002

Preference for mirror images and video image in Java sparrows (Padda oryzivora).

Java sparrows were exposed to a mirror and a frosted mirror, a mirror and a live bird, a mirror and a live bird with frosted screen, a closed circuit TV monitor and a TV program or the closed circuit monitor and an upside down monitor. The birds showed strong preference for the self-image on the mirror, the live bird and the self-image on the monitor. They preferred almost equally to the mirror and the frosted live bird. These results suggest that the Java sparrows saw the self-image on the mirror as conspecific image.

Journal Article↗

PubMed1998

Seasonal changes in adrenal sensitivity alter corticosterone levels in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii).

Recent work indicates that Gambel's white-crowned sparrows modulate corticosterone release seasonally in response to capture and restraint. Free-living white-crowned sparrows dramatically elevate both baseline and stress-induced corticosterone levels during the breeding season compared with either wintering or migrating birds. Although corticosteroid binding globulin capacity also rises during breeding, it does not fully compensate for elevated glucocorticoid levels. Consequently, we examined what hypothalamic-pituitary-adrenal axis changes could account for seasonal changes in glucocorticoid levels. During winter and fall migration, exogenous ACTH failed to elevate corticosterone levels beyond the response to capture and handling, suggesting that the adrenal's ability to release corticosterone limits circulating levels during these seasons. In contrast, not only were corticosterone levels higher during breeding, but adrenals further responded to an exogenous ACTH signal, indicating a dramatic enhancement of the adrenal's ability to secrete corticosterone. Furthermore, we inferred the pituitary's ACTH secretory ability by injecting exogenous corticotrophin-releasing factor (CRF), arginine vasotocin (AVT) and mesotocin and measured corticosterone release. Pituitaries in breeding birds appear to respond to exogenous CRF and AVT, suggesting hypothalamic control of corticosterone release during this season. Taken together, these results suggest that seasonal modulation of corticosterone release in this species is controlled primarily at the adrenal.

Adrenal Glands↗

PubMed2000

Dietary modulation of intestinal enzymes of the house sparrow (Passer domesticus): testing an adaptive hypothesis.

Insectivorous/frugivorous passerine species studied so far lack the ability to modulate intestinal maltase activity, in contrast to galliformes. We tested for dietary modulation of small intestine (SI) enzymes including maltase in house sparrows to understand whether the difference between the galliformes on the one hand, and the passerines on the other, reflects a phylogenetic pattern (maltase modulated in galliformes but not passerines), a dietary pattern (maltase modulated in granivores but not insectivore/frugivores), some other pattern, or chance. We also tested the prediction that intestinal peptidase activity would be increased on a high protein (HP) diet. Birds were fed three diets high in starch, protein, or lipid for 10 days. For birds on the HP diet (60.3% protein) we observed the predicted upward modulation of aminopeptidase-N activity, as compared with the lower-protein, high starch (HS) (12.8% protein) diet. In contrast, birds eating the HS diet had similar maltase and sucrase activities, and only slightly higher isomaltase activity, compared with birds eating the high protein (HP), starch-free diet. Birds eating high lipid (HL) diet had low activities of both carbohydrases and peptidase. Considering that the statistical power of our tests was adequate, we conclude that house sparrows show little or no increase in carbohydrases in response to elevated dietary carbohydrate. We cannot reject the hypothesis that maltase lability among avian species has a phylogenetic component, or that high dietary fat has a depressing effect on both carbohydrase and peptidase activities.

Adaptation, Physiological↗

PubMed2001

Seasonal variations of in vivo and in vitro melatonin production in a passeriform bird, the house sparrow (Passer domesticus).

Melatonin, released from the pineal gland, is an important signal within the circadian pacemaking system of passeriform birds. Until now, seasonal variations in melatonin production have only been examined in a few avian species and the role of melatonin in the regulation of annual rhythms in birds is unclear. We investigated plasma melatonin in a group of house sparrows kept in an outside aviary in spring (March/April), summer (May/June), autumn (September/October), and winter (December/January). The durations of elevated melatonin values mirrored the seasonal changes in night length to a certain degree, the melatonin signal being longest in winter and shortest in summer. Additionally, plasma melatonin peak amplitudes differed significantly among seasons, with highest values in spring and summer and lowest values in winter. Cultured explanted pineal glands obtained from animals in winter and summer showed patterns of in vitro melatonin release comparable to in vivo circulating melatonin with different durations of elevated melatonin and peak amplitude values. These data indicate that the circadian pacemaking system of the house sparrow changes properties seasonally, either as a result of endogenous mechanisms or in response to environmental conditions. These properties are maintained in the pineal gland even after isolation from the animal.

Animals↗

PubMed2001

Vocal syntax development in the white-crowned sparrow (Zonotrichia leucophrys).

Birdsong development exemplifies the interplay between experience and predisposition that occurs during behavioral ontogeny. Songbirds must hear song models to develop normal song, yet they preferentially learn conspecific song when given a choice in the laboratory. To the extent that features guiding this selective learning are pre-encoded in the brain, such features should also develop in the song of young birds not exposed to them in tutor models. To investigate whether song syntax-phrase number and order--is such a feature in the white-crowned sparrow (Zonotrichia leucophrys), the authors tutored males of this species with separate phrase models. Birds learned and assembled these into songs of species-typical sequence, suggesting that syntax is to some degree pre-encoded in white-crowned sparrows. Birds also learned heterospecific phrases, confirming previous evidence that note phonology is not the primary cue for selective song learning in this species.

Animals↗

PubMedDate not supplied

Demographic study of a wild house sparrow population by DNA fingerprinting.

Over the past twenty years, several techniques from biochemical and molecular genetics, such as enzyme electrophoresis and isoelectric focusing, have been widely and successfully applied to the study of population differentiation and evolution. However, they have been less applicable to demographic problems such as assigning parentage to individuals within a population. This stems from a general weakness of data derived from enzyme loci: allele frequencies at polymorphic loci are sufficiently skewed that the majority of individuals are of one or two genotypes. Many enzyme systems can only be examined post mortem, so that the loci are of little use if the animals are to be studied in the wild. The search for new and more sensitive techniques for detecting genetic variation has continued, and recently a major discovery has come from molecular biology. Jeffreys et al. have reported the detection of a type of hypervariable 'minisatellite' DNA that is extraordinarily polymorphic in human populations. We have applied their technique to several bird species and particularly to a population of house sparrows (Passer domesticus) near Nottingham. We report here that one of the human minisatellite clones is a suitable probe for sparrow DNA and that it reveals variation as extensive as that found in man. These results suggest that analysis of minisatellite DNA will be a powerful tool in the study of demographic population genetics.

Animals↗

PubMed2002

Widespread local house-sparrow extinctions.

House-sparrow populations have declined sharply in Western Europe in recent decades, but the reasons for this decline have yet to be identified, despite intense public interest in the matter. Here we use a combination of field experimentation, genetic analysis and demographic data to show that a reduction in winter food supply caused by agricultural intensification is probably the principal explanation for the widespread local extinctions of rural house-sparrow populations in southern England. We show that farmland populations exhibit fine-level genetic structuring and that some populations are unable to sustain themselves (sinks), whereas others act as sources.

Agriculture↗