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1. It has been shown that if oestrogen and progesterone are given to ovariectomised hens nesting behaviour will occur. Thus if these hormones are given to normal hens the excessive pacing found in some hens before laying might be reduced. 2. Experiments showed that oestrogen produced no noticeable effects and progesterone caused a high incidence of delayed oviposition and abnormal behaviour.
The administration of bromocriptine (CB154) to broody hens (Gallus domesticus) impaired resumption of lay. Resumption of lay was stimulated in broody birds treated with clomiphene citrate (an anti-oestrogen) alone or following CB154 administration. The increased oviposition rate following a single intramuscular injection (21 mg) of clomiphene was long lasting, persisting for at least 16 weeks after treatment. Treatment of broody hens with clomiphene consistently improved (by 4%) the hatchability of the fertile eggs subsequently laid.
Nesting behaviour of LSL hens from a deep litter house and from a battery system was compared. Every hen was tested in one of two trial chambers containing a wire mesh floor and a nest unit with 5 nesting materials: wire mesh, perforated plastic, synthetic grass, wheat straw and oat husk. Wheat straw and oat husk were preferred as nesting materials to perforated plastic, synthetic grass and wire mesh. The results from these trials were confirmed in a deep litter house. After the nesting material, oat husk, was changed in two of 10 communal nests the hens did not accept those two nests for the trial period of two weeks and laid elsewhere. Hens of the same breed and age reared together on deep litter showed no differences in nest site selection and nesting behaviour regardless of whether they had previously been housed in a deep litter house or in cages.
1. An experiment was done under commercial conditions to investigate the physiological effects of isolating broody turkey hens, for 72 h, in sand and wire floored pens on the third, 10th and 16th weeks of production. 2. Hens identified as broody and removed from the flock had higher plasma prolactin concentrations than the laying hens at each of the three experimental stages. 3. Confinement in sand and wire floored pens, induced a decline in plasma prolactin concentrations. This decline probably impeded immediate development of broody behaviour. Alternately, levels of prolactin higher than those of laying hens were again measured 7 and 14 days after treatment during third week but not after the 10th and 16th week of production. 4. Confinement did not induce consistent changes in luteinising hormone (LH) and progesterone concentrations from one period to an other. 5. An increase in the plasma concentration of D-(beta)-hydroxybutyrate was observed in the hens which had an egg present in the oviduct on day 2, 3 and/or 4 of the treatment. Subsequently, a decrease in ovulation rate was observed in the hens with higher concentrations of D-(beta)-hydroxybutyrate while under treatment, during the 10th week of production. 6. These data confirm that the effectiveness of the traditional methods for broodiness prevention under commercial conditions is related to the induction of a decrease of prolactin.
1. Twenty two hens (Gallus gallus domesticus) were given a free choice, for egg laying, between 4 nest boxes containing different quantities of wood shavings (litter): 3180 cm3 (large), 1060 cm3 (medium), 350 cm3 (small) and none (zero). 2. There was considerable individual variation in the quantity of litter selected for egg laying, but 17 hens laid 50% or more of their eggs in a single litter quantity. Hens selected the large quantity in preference to the small and zero. More searching, nest selection and nesting behaviours tended to be directed to the boxes with the largest quantities and also to the quantities that the hens finally selected for egg laying. 3. In a second experiment, the hens from experiment 1 which showed a preference for litter, and a further 22 naïve hens were given a choice of three nest boxes containing no litter and one containing one of 6 quantities. Over 30 trials there were 5 replicates using each of the three quantities used in experiment 1 plus 115 cm3, 40 cm3 and 10 cm3. 4. There was a wide range in the proportion of trials in which hens selected litter; for experienced hens the range was 0.43 to 0.97, but only two naïve hens were within this range, all others being between 0 and 0.43. 5. The pattern of choosing litter quantities was comparable but at different levels of preference in experienced and naïve hens and a contour map was derived enabling predictions to be made of the probability of a particular quantity being chosen. 6. The variability of individual responses suggest that no single type of nest box system can cater for the requirements of all hens.
Cave swallows (Petrochelidon fulva) and cliff swallows (P. pyrrhonota) nest in numerous colonies throughout the Texas portion of the Rio Grande along the U.S. border with Mexico. We collected swallows during 1999 and 2000 from eight locations along the Rio Grande to determine if delta15N and delta13C values could be used to predict 1,1-di-(p-chlorophenyl-)2,2-dichloroethene (DDE) and selenium (Se) contaminant burdens in insectivorous birds nesting across a geographic gradient in the Texas-Mexico border and to discern if stable isotopes could help discriminate between local versus nonlocal acquisition of contaminants. We analysed delta15N and delta13C in liver and muscle and DDE and Se in swallow carcasses. Within individuals, delta15N was higher in liver than in muscle of both species by an average of 1.34%, whereas delta13C was 0.145% higher in muscle than in liver. Significant differences occurred among locations in delta15N and delta13C values in liver and muscle of both species. Cave swallows from three locations in the Lower Rio Grande Valley were more enriched in delta15N than swallows from other sites. In general, swallows nesting in more northern latitudes along the Rio Grande had lower delta15N and delta13C values than those nesting farther south. Concentrations of DDE were significantly greater in swallows from El Paso, Llano Grande, and Pharr than in those from Brownsville, Falcon Lake, Laredo, Del Rio, and a reference site outside the Rio Grande. All swallows (n = 21) from El Paso, Llano Grande, and Pharr had DDE concentrations > or = 3 microg g(-1) wet weight (ww), a value three times greater than the estimated threshold in avian prey that could cause potential reproductive failures in raptors. Concentrations of Se also were significantly greater in El Paso and Del Rio than at other locations. Most Se concentrations were not of concern for direct effects on birds or their predators. Principal component analysis indicated some positive correlations between delta15N and delta13C values in tissues and contaminant concentrations in carcass; however, analysis of covariance suggested a stronger effect of location on concentrations of DDE and Se. At the local level (Llano Grande and Pharr) there was a significant positive correlation between delta15N in liver and DDE concentrations in swallow carcasses; however, Se concentrations were not significantly correlated with isotopes even at the local level. Our results provide a good database of delta15N and delta13C values for insectivorous birds nesting along the Rio Grande. Similar ecologies for cave and cliff swallows and their abundance and wide distribution along the Rio Grande make them ideal indicators of environmental pollution of this portion of the Texas-Mexico border.
The African brood parasitic finches (Vidua spp.) are host specialists that mimic the songs and nestling mouth markings of their finch hosts (family Estrildidae). Although recent molecular analyses suggest rapid speciation associated with host switches in some members of this group, the association of different Vidua lineages with particular host genera suggests the possibility of cospeciation at higher levels in the host and parasite phylogenies. We compared a phylogeny of all Vidua species with a phylogeny of their estrildid finch hosts and compared divergence time estimates for the two groups. Basal divergences among extant members of the Vidulidae and among Vidua species are more recent than those among host genera and species, respectively, allowing a model of cospeciation to be rejected at most or all levels of the Vidua phylogeny. Nonetheless, some tests for cospeciation indicated significant congruence between host and parasite tree topologies. This result may be an artifact of clade-limited colonization. Host switches in parasitic finches have most often involved new hosts in the same or a closely related genus, an effect that increases the apparent congruence of host and parasites trees.
The jelly around amphibian eggs presents a formidable barrier to oxygen diffusion. Therefore, egg capsules must be thin enough, and the dimensions of globular egg masses small enough, to avoid oxygen limitation leading to developmental retardation or death. The eggs of the Australian moss frog, Bryobatrachus nimbus, have the thickest jelly capsule known for any anuran amphibian. Laboratory measurements of respirometric variables predict that single prehatching embryos should be normoxic between 5 degrees and 20 degrees C, with Po(2 in) maintained above critical levels (10.2-17.0 kPa). However, numerical models of embryos amid larger egg masses (13-20 eggs) predict hypoxia at temperatures above 5 degrees C. Contrary to model predictions, however, B. nimbus embryos rarely experience hypoxia in natural nests, because embryos occur in one or two layers and the moss substrate permits aeration of the lower surface while photosynthesis probably supplies oxygen directly. After hatching, larvae move to oxygen-rich regions of the jelly mass and disperse more widely within the mass as temperatures increase. Although nest characteristics relieve diffusive constraints, small clutch sizes, low rates of embryonic and larval respiration, and the cool climate occupied by B. nimbus are the main characteristics that prevent hypoxia.
Species differ enormously in their territorial systems. Some species defend only small areas surrounded by undefended space, while others defend large contiguous territories. Using an optimization approach, we show that this variation can be explained from the density of two types of resources: divisible and nondivisible. We assume that benefits of territories are monotonously related to the defended amount of divisible resources (hereafter called food). In contrast, no benefits are obtained without a nondivisible resource (hereafter called nest site) in the territory, while more than one nest site does not further increase the benefits. The optimal territory size depends on the relative abundance of these resources. With a low density of nest sites, the optimal territory size is small and includes only the nest site. If the density of nest sites is relatively large, the optimal territory size is high, and territories are contiguous. Competition for these different resources yields contrasting patterns of how populations are regulated. If there is mainly competition for nest sites, we expect density-dependent exclusion through territoriality and no density-dependent reproduction. When competition is mainly for food, we expect density-dependent reproduction because optimal territory size will be compressed at higher densities, resulting in lower reproductive success. These predicted patterns indeed are observed in some well-studied passerine species for which both the territorial system and the occurrence of density dependence is known.
Do aggressive dominance and subordination in vertebrate broods and litters affect development? We examined 1,167 fledglings from two-chick broods of the blue-footed booby (Sula nebouxii), a species in which the first-hatched chick dominates with violent attacks throughout the nestling period and subordinates suffer lower fledging success, but if both broodmates survive, they grow to the same size. There was little evidence that dominant fledglings were more likely to recruit into the breeding population than were subordinate fledglings, and there was no evidence that dominant and subordinate recruits differed in their age, date, brood size, or nest success at first reproduction or in their summed brood sizes or total nest success over the first 5 yr or first 10 yr of life. Compared with dominants, subordinate fledglings were less prejudiced by late hatching and established clutches earlier over the first 10 yr, and subordinate recruits had 33% larger broods over the first 5 yr. However, in broods where both chicks fledged, accumulated reproductive success for chicks up to age 5 yr was similar for dominants and subordinates. Exercising dominance throughout infancy apparently does not fortify a chick for the future and may incur a long-term cost, and suffering violent subordination throughout infancy has little or no prejudicial effect and may even steel a chick for adult life.
Incubation in most avian species involves transferring heat from parent to egg through a highly vascularized brood patch. Some birds, however, do not develop a brood patch. Unusual among birds, these species hold their eggs under the webs of their feet, but the role of the feet in heat transfer is uncertain. Often the webs are positioned between the feathered abdomen and the egg during incubation, suggesting that either the abdomen, the feet, or both could transfer heat to the egg. We studied heat transfer from foot webs to eggs during incubation in Nazca boobies by spatially separating the feet from the abdomen using an oversized egg. We found that feet transfer heat to eggs independently of any heat that may be transferred from the abdomen. In addition, we found that incubating boobies had significantly greater vascularization in their foot webs, measured as a percentage of web area covered by vessels, than nonincubating boobies. We also found that males, whether incubating or nonincubating, had significantly less web vascularization than females. We concluded that vascularized Nazca booby feet function in the same way during incubation that vascularized brood patches do, acting as surrogate brood patches.
Little is known about the use of heterothermy by wild bats during summer, especially for tree-roosting species. Because thermal conditions within tree roosts can fluctuate widely with ambient temperature, which affects thermoregulatory energy expenditure during diurnal roosting, we measured skin temperatures of free-ranging male Nyctophilus geoffroyi (8 g) to quantify the relation between summer torpor use and roost thermal conditions. Bats roosted under bark on the northern (sunny) side of trees and entered torpor every day, usually near sunrise. Bats exhibited two bouts of torpor on most days: the first occurred in the morning, was terminated by partially passive rewarming, and was followed by a period of normothermy during the warmest part of the day; a second torpor bout occurred in the late afternoon, with arousal near sunset. On the warmest days, bats had only a single, short morning bout. On the coolest days, bats remained torpid throughout the day, and one 2-d bout was observed. Thus, presumably owing to their poorly insulated roosts and the high energetic cost of normothermy at temperatures below 30 degrees C, the extent and timing of heterothermy was closely related to the cycle of diurnal temperatures. Our study indicates that torpor use is important for energy maintenance during summer diurnal roosting of N. geoffroyi and likely of other small, tree-roosting bats.
We report the results of the first field study examining seasonal changes in corticosterone responses of typically long-lived birds of the order Procellariiformes. In particular, we examined whether grey-faced petrels Pterodroma macroptera gouldi showed changes in circulating baseline corticosterone concentrations and corticosterone responses to a standardized handling protocol across the breeding season. Such changes have been associated with changes in body condition and variations in energy demands on adult birds through the breeding season. During early incubation, males were in significantly better condition than females that had just completed laying, whereas during late incubation, males were in significantly poorer condition than females. In spite of these differences, there was no significant difference in baseline corticosterone concentrations between sexes or among birds at different reproductive stages. However, we detected significant differences in corticosterone responses associated with a standardized handling protocol at different stages through the breeding season. Responses were significantly greater during incubation compared with the prelay period and late chick rearing. Body condition was weakly and negatively correlated with maximum and total integrated corticosterone level, indicating that some of the individual variability in stress corticosterone responses could be explained by variation in body condition. However, the largest stress response occurred during late incubation and was independent of sex, although males were in relatively poor condition and females in relatively good condition. This period coincided with the breeding stage in which energy constraints on individual adults were higher than at other periods of the reproductive cycle and birds may be physiologically primed for extended fasts.
Trivers proposed that, if parental care by both sexes is advantageous, males should practice a "mixed" strategy of seeking extrapair copulations, while restricting their parental investment to offspring of social mates. We explore circumstances under which males should limit their parental care in the predicted manner. We find that Trivers's "mixed" strategy will generally be evolutionarily stable so long as either socially monogamous or polygynous males usually sire more offspring per brood from a social mate than they typically sire in broods of extrapair mates. Polygynous males should spread investment across their home nests unless the expected number of chicks sired in them differs widely. Whether polygynous males should restrict paternal care to social mates' offspring hinges additionally on resident male investment in broods containing extrapair young: if resident males contribute minimally, some investment by a polygynous extrapair male becomes more advantageous. Recently reviewed data on extrapair fertilization distributions within monogamous and polygynous passerines suggest that extrapair offspring often predominate numerically within their broods, consistent with sperm expenditure theory. Nevertheless, most species conform to the model's criterion regarding relative parentage levels in broods of social versus extrapair mates. Patterns of extrapair parentage thus appear sufficient to stabilize biparental care systems.
According to the original "sexy son" hypothesis, a female may benefit from pairing with an already-mated male despite a reduction in fecundity because her sons inherit their father's attractiveness. We used data from a long-term study of collared flycatchers (Ficedula albicollis) collected during 24 years to test this prediction. Our results show that the sons of polygynously mated females fledged in poor condition and therefore did not inherit their father's large forehead patch (a condition-dependent display trait) or mating status. From the female's perspective, polygynous pairing resulted in fewer recruited grandchildren than did a monogamous pairing. The reproductive value of sons did not outweigh the fecundity costs of polygyny because the low paternal care reduced the attractiveness of sons. When there are long-lasting parental effects on offspring attractiveness, costs of polygyny may include the production of nonsexy sons.
There are two major competing hypotheses for variation in clutch size among cavity-nesting species. The nest site limitation hypothesis postulates that nesting opportunities are more limited for weak excavators, which consequently invest more in each breeding attempt by laying larger clutches. Alternatively, clutch size may be determined by diet; the clutch sizes of strong excavators may be smaller because they are able to specialize on a more seasonally stable prey. We built a conceptual model that integrated hypotheses for interspecific variation in clutch size and tested it with comparative data on life-history traits of woodpeckers (Picidae) and nuthatches (Sittidae). In most analyses, diet explained more variation in clutch size among species than did propensity to excavate. Migratory status was positively associated with clutch size but was difficult to distinguish from diet since resident species consumed more bark beetles (a prey available in winter) and had smaller clutches than migratory species. The literature suggests that cavities are not limited in natural, old-growth forests. Although our data do not rule out nest site limitation, we conclude that annual stability of food resources has a larger impact on the evolution of clutch sizes in excavators than does limitation of nest sites.
A costs-benefits approach has frequently been used to understand the evolutionary origin and maintenance of promiscuity in animal populations. Recent meta-analyses suggest that direct costs to unfaithful females outweigh indirect benefits from infidelity in socially monogamous songbirds, suggesting that in this taxa, extrapair fertilization (EPF) evolved primarily as a self-interest male tactic. Here we present results of comparative analysis to show that standardized selection gradients acting against female infidelity (direct costs of promiscuity) explain variation in EPF rates at an interspecific level in passerines. This result confirms that costs to females resulting from reduced parental care from cheated males constrain promiscuity in this group. Our data indicate that females exert resistance over EPFs when the costs of infidelity are high and, conversely, that the rate of EPFs increases when selection on females to defend themselves against EPF attempts by males is weak and costs of infidelity are low.
In birds, it has been shown that reproductive effort may impair parental condition, while the relation of different condition indices to subsequent survival is still poorly understood. In this study, we measured body mass and various hematological condition indices in breeding great tits in relation to local survival. Number and quality of nestlings and the occurrence of second broods, potentially reflecting parents' breeding effort, were also considered in analyses. The great tits, both male and female, that returned the following year had had a higher albumin/globulin ratio, lower plasma globulin concentration, and a lower heterophile/lymphocyte ratio during breeding in the preceding year, compared to those who did not return. Surviving males (but not females) also had had a higher level of circulating lymphocytes, compared to nonsurvivors. There was no correlation between breeding effort and survival. We conclude that better immunological state and lower stress in great tits during breeding were positively related to their survival probability.