Efficacy of intervention to relieve nest box competition for Orange‐bellied Parrot Neophema chrysogaster

We use an experimental approach to evaluate the effectiveness of removing nests of a dominant competitor to create vacant nest boxes for a critically endangered parrot. We compared the number of times that Tree Martin (Petrochelidon nigricans – the dominant competitor at nest boxes) perched at or entered nest boxes intended for Orange‐bellied Parrot (Neophema chrysogaster – the subordinate nest competitor) over three time periods (before, immediately after and one week after experimental nest destruction). In the before period, rates of nest attendance by martins in treatment and control nests were not explained by treatment group. After experimental nest destruction, total attendance at boxes by martins rose to a mean of 6.1 visits over three five‐minute surveys in the treatment group, compared with 3.3 visits at control boxes. Within individual surveys, martins visited treatment boxes 4.4 times per survey one week after nest destruction, compared with only 1.6 visits in the control group. Martins in the treatment group rapidly rebuilt their nests and laid replacement clutches, and within a week, all boxes were reoccupied. Nest destruction did not increase nesting opportunities for the parrot, and increased vigilance of the dominant competitor may in fact reduce nesting opportunities in nearby boxes. Our study suggests that removing martin nests is an ineffective management action for alleviating nest competition for this parrot.     

Biparental incubation and allofeeding at nests of Sagebrush Brewer's Sparrows

Facultative male incubation and allofeeding are thought to be behavioral adaptations by which male songbirds maximize their fitness by reducing the energetic stress of their mates. However, few data are available for most species that exhibit these behaviors so the extent to which they might enhance male fitness remains unclear. Among North American sparrows, male incubation is known in four species, but the relative contributions of each sex have been estimated for only one species. We quantified biparental incubation and allofeeding in Sagebrush Brewer's Sparrows (Spizella breweri breweri) with 24‐h video surveillance of nests (N = 24) at two locations in northern Nevada. We detected biparental incubation at both sites (17 of 24 nests, 71%), and found that mean constancy (i.e., proportion of 24‐h period eggs were covered) was significantly higher at biparental nests than at uniparental nests, and mean recess duration (i.e., when eggs were uncovered) was significantly shorter. Incubation constancy at biparental nests in our study was the highest yet reported in the genus Spizella (range = 0.87–0.96), and constancy at uniparental nests (mean = 0.76, range = 0.71–0.81) was greater than that of congeners where female‐only incubation is thought to be the norm. Biparental incubation was more likely on colder days, but a comparison of models where incubation strategy and its interaction with ambient temperature were included as independent variables revealed that temperature was not the best predictor of constancy. Allofeeding occurred at very low frequency and only at biparental nests (11 of 20, 55%). Biparental nests with allofeeding had more incubation sessions per hour than biparental nests without allofeeding. The recipient usually left the nest immediately after being fed, and the feeding individual assumed the role of incubator. Our results suggest that some factor other than low ambient temperatures favors biparental incubation by Sagebrush Brewer's Sparrows. One possibility is that male incubation and the resulting increase in incubation constancy may better conceal nests and reduce the likelihood of nest predation. The low frequency of allofeeding at nests with biparental incubation in our study suggests that it serves some function other than improving female nutritional status or reducing activity levels at nests. Rather, allofeeding may serve as an intraspecific signal important for maintaining the social bond between mates.     

Costs and response to conspecific brood parasitism by colonial red-breasted mergansers

Costs of conspecific brood parasitism (CBP) are expected to be influenced by a species’ life history traits. Precocial birds lay large clutches, and clutches that have been enlarged by CBP can affect host fitness through a longer incubation period, displaced eggs, and lower hatching success. We examined costs and response to CBP by hosts in a population of colonial red-breasted mergansers (Mergus serrator; n?=?400 nests over 8 years) within which 29% of parasitized clutches were enlarged considerably (≥?15 eggs). Length of the incubation period did not increase with clutch size. The mean number of eggs displaced from a parasitized nest during incubation (2.8) was 2×?greater than at an unparasitized nest (1.4). Hatching success declined by 2% for each additional egg in the nest. Thus, for a nest with?≥?15 eggs, one or more fewer host eggs hatch relative to an unparasitized nest with the same number of host eggs, assuming equal probability of success for all eggs. Hosts were 40% more likely to desert nests receiving 2 or 6 experimental eggs relative to unparasitized control nests, although it is unknown whether hens deserting a nest renested elsewhere. Our study indicates that costs of CBP to hosts during nesting may be limited to those red-breasted mergansers incubating the largest clutches (≥?15 eggs), and it raises questions about the adaptive significance of deserting a parasitized clutch.     

Handicapped females receive more feedings during incubation from their mates: support for the female nutrition hypothesis

The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance. The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic requirements during incubation.     

Prolactin and parental behavior in Adélie penguins: effects of absence from nest, incubation length, and nest failure

Adélie penguin (Pygoscelis adeliae) males and females, nesting in Antarctica, alternate attendance at the nest with absences of many days to forage at sea. We investigated the importance of tactile input from egg and chicks on prolactin levels by observing nest attendance patterns and obtaining blood samples (1) during the first nest exchange of the incubation stage, (2) from birds whose incubation period was artificially increased or decreased by about 10 days, and (3) from birds whose nests had failed. Prolactin levels in females after 8 to 11 days of absence from the breeding colony did not differ from those in incubating males and did not change after females resumed incubation. Moving eggs between nests resulted in nests in which chicks hatched after about 26, 36 (normal), or 46 days. Duration of incubation did not affect prolactin levels in the parents measured during incubation, at the pip stage, hatch stage, or early brood stage. Adults first left their chicks unguarded on about the same calendar date, regardless of chick age. However, chicks from long incubation nests averaged 8 days younger when they were left unguarded than chicks from control or short-incubation nests. In females, there was no effect of nest failure on prolactin levels. In males, prolactin levels were slightly lower after nest failure than in males tending nests. Testosterone was significantly higher in males after nest failure than in males still tending nests. Prolactin is elevated in Adélie penguins as part of the program of cyclical hormonal changes that accompany the lengthy reproductive season and is relatively independent of tactile input. Sustained prolactin secretion is probably required for the maintenance of parental behavior in offshore feeding species that must be absent from the nest for many days at a time.     

Does Threat to the Nest Affect Incubation Rhythm in a Small Passerine?

Nest predation is a crucial factor influencing breeding success in birds. One possible way to protect nests is to modify parental activity in the vicinity of the nest. Here, we provide experimental evidence for an adjustment of incubation pattern during periods when there is an increased risk of nest predation in a small passerine. We compared the behaviour of incubating meadow pipit (Anthus pratensis) females during presentations of stuffed dummies of a nest predator (the magpie Pica pica) and a harmless intruder (the crossbill Loxia curvirostra) and during an undisturbed control incubation period. Females significantly decreased their activity in the presence of the nest predator. Specifically, after being flushed out, they returned to the nest later and moved to and from the nest less than when the harmless intruder was present. These results document the ability of birds to assess the nest predation risk and adjust their appropriate incubation strategy.     

Supplemental food alters nest defence and incubation behaviour of an open‐nesting wetland songbird

Climate‐driven increases in spring temperatures are expected to result in higher prey availability earlier in the breeding season for insectivorous birds breeding in wetland habitats. Predation during the incubation phase is a major cause of nesting failure in open‐nesting altricial birds such as the Eurasian reed warbler. The nest predation rate in this species has recently been shown to be substantially reduced under conditions of experimentally elevated invertebrate prey availability. Food availability near the nest may be an important determinant of adult incubation and nest defence behaviours during the incubation period. We used two experimental studies to compare incubation behaviour and nest defence in food‐supplemented and unsupplemented adult Eurasian reed warblers during the incubation phase. In the first study we measured nest defence behavioural responses to a taxidermic mount of a native predator (stoat Mustela erminea). In the second study we used temperature loggers installed in nests to measure breaks in incubation as a measure of nest vulnerability. Food‐supplemented birds responded aggressively to the presence of a predator more quickly than those in the unsupplemented group, suggesting they are closer to their nest and can more quickly detect a predator in the vicinity. Food‐supplemented birds also had shorter breaks in incubation (both in terms of maximum and mean off‐bout durations), presumably because they were foraging for shorter periods or over shorter distances from the nest. This study therefore identifies the behavioural mechanisms by which changes in food availability may lead to changes in nest survival and thus breeding productivity, in open‐nesting insectivorous birds.     

Effects of down collection on incubation temperature, nesting behaviour and hatching success of common eiders (Somateria mollissima) in west Iceland

Incubating common eiders (Somateria mollissima) insulate their nests with down to maintain desirable heat and humidity for their eggs. Eiderdown has been collected by Icelandic farmers for centuries, and down is replaced by hay during collection. This study determined whether down collecting affected the female eiders or their hatching success. We compared the following variables between down and hay nests: incubation temperature in the nest, incubation constancy, recess frequency, recess duration, egg rotation and hatching success of the clutch. Temperature data loggers recorded nest temperatures from 3 June to 9 July 2006 in nests insulated with down (n = 12) and hay (n = 12). The mean incubation temperatures, 31.5 and 30.7°C, in down and hay nests, or the maximum and minimum temperatures, did not differ between nest types where hatching succeeded. Cooling rates in down, on average 0.34°C/min and hay nests 0.44°C/min, were similar during incubation recesses. Females left their nests 0–4 times every 24 h regardless of nest type, for a mean duration of 45 and 47.5 min in down and hay nests, respectively. The mean frequency of egg rotation, 13.9 and 15.3 times every 24 h, was similar between down and hay nests, respectively. Hatching success adjusted for clutch size was similar, 0.60 and 0.67 in down and hay nests. These findings indicate that nest down is not a critical factor for the incubating eider. Because of high effect sizes for cooling rate and hatching success, we hesitate to conclude that absolutely no effects exist. However, we conclude that delaying down collection until just before eggs hatch will minimize any possible effect of down collection on females.     

How do goannas find sea turtle nests?

Squamate reptiles rely heavily on visual and chemical cues to detect their prey, so we expected yellow‐spotted goannas (Varanus panoptes) which are predators of sea turtle nests on mainland beaches in northern Australia would use these cues to find sea turtle nests. Ghost crabs (Ocypode ceratophthalmus and Ocypode cordimanus) are also common on Australian sea turtle nesting beaches and frequently burrow into sea turtle nests. However, the potential for ghost crab burrowing activity at sea turtle nests to signal the location of a nest to goannas has not been investigated. Here, we used camera traps and presence of tracks at nests to record goanna activity around selected nests during the incubation period and 10 days after hatchling turtles emerged from their nests. We also recorded the number of ghost crab burrows around nests to evaluate ghost crab activity. Our results indicated that nest discovery by goannas was independent of nest age, but that the nest visitation rate of goannas and crabs increased significantly after a nest had been opened by a goanna or after hatchlings had emerged from the nest. There was no apparent connection between ghost crab burrows into a nest and the likelihood of that nest being predated by goannas.     

Incubation failure and nest abandonment by Leach's Storm‐Petrels detected using PIT tags and temperature loggers

ABSTRACT The nocturnal activity of burrow‐nesting seabirds, such as storm‐petrels and shearwaters, makes it difficult to study their incubation behavior. In particular, little is known about possible differences in the incubation behavior of adults at successful and unsuccessful nests. We combined the use of passive integrated transponder (PIT) technology and nest‐temperature data loggers to monitor the incubation behavior of 10 pairs of Leach's Storm‐Petrels (Oceanodroma leucorhoa). The mean incubation bout length was 3.31 ± 0.59 (SD) days for individual adults at successful nests (N= 4) and 1.84 ± 1.16 d for individuals at unsuccessful nests (N= 6). Mean bout length for pairs in successful burrows (3.51 ± 0.56 d) did not differ significantly (P= 0.07) from that for pairs in unsuccessful burrows (1.80 ± 1.20 d), perhaps due to one failed nest with a high mean bout length (4.15 d). The total number of incubation bouts per parent (4.3 ± 1.9 bouts) did not differ with hatching success. Adults whose nests failed repeatedly exhibited truncated incubation bouts (< 12 h) prior to complete nest failure and were more likely than successful parents to make brief visits to nearby, occupied nesting burrows. Our results suggest that the decision by Leach's Storm‐Petrels to abandon a nest is not an abrupt one. Rather, failed nesting attempts may be characterized by truncated incubation bouts where individuals pay the energetic cost of travel to and from the burrow, but do not remain long enough to successfully incubate the egg.     

Function of egg punctures by Shiny Cowbirds in parasitized and nonparasitized Creamy‐bellied Thrush nests

ABSTRACT Avian brood parasites usually remove or puncture host eggs. Several hypotheses have been proposed to explain the function of these behaviors. Removing or puncturing host eggs may enhance the efficiency of incubation of cowbird eggs (incubation‐efficiency hypothesis) or reduce competition for food between cowbird and host chicks in parasitized nests (competition‐reduction hypothesis) and, in nonparasitized nests, may force hosts to renest and provide cowbirds with new opportunities for parasitism when nests are too advanced to be parasitized (nest‐predation hypothesis). Puncturing eggs may also allow cowbirds to assess the development of host eggs and use this information to decide whether to parasitize a nest (test‐incubation hypothesis). From 1999 to 2002, we tested these hypotheses using a population of Creamy‐bellied Thrushes (Turdus amaurochalinus) in Argentina that was heavily parasitized by Shiny Cowbirds (Molothrus bonariensis). We found that 56 of 94 Creamy‐bellied Thrush nests (60%) found during nest building or egg laying were parasitized by Shiny Cowbirds, and the mean number of cowbird eggs per parasitized nest was 1.6 ± 0.1 (N= 54 nests). At least one thrush egg was punctured in 71% (40/56) of parasitized nests, and 42% (16/38) of nonparasitized nests. We found that cowbird hatching success did not differ among nests where zero, one, or two thrush eggs were punctured and that the proportion of egg punctures associated with parasitism decreased as incubation progressed. Thus, our results do not support the incubation‐efficiency, nest‐predation, or test‐incubation hypotheses. However, the survival of cowbird chicks in our study was negatively associated with the number of thrush chicks. Thus, our results support the competition‐reduction hypothesis, with Shiny Cowbirds reducing competition between their young and host chicks by puncturing host eggs in parasitized nests.     

Why do Both Parents Incubate in the Kentish Plover?

Incubation by both parents is a common parental behaviour in many avian species. Biparental incubation is expected if the survival prospects of offspring are greatly raised by shared care, relative to the costs incurred by each parent. We investigated this proposition in the Kentish plover Charadrius alexandrinus, in which both parents incubate the clutch, but one parent (either the male or the female) usually deserts after hatching of the eggs. We carried out a mate‐removal and food supplementation experiment to reveal both the role of the sexes and food abundance in maintaining biparental incubation by removing either the male or the female from the nest for a short period of time. In some nests we provided supplementary food for the parent that remained at the nest to reduce the costs of incubation, whereas other nests were left unsupplemented. Although males spent more time on incubation after their mate had been removed, females’ incubation did not change. Notwithstanding the increased male incubation, total nest attentiveness was lower at uniparental nests than at biparental controls. However, incubation behaviour was not influenced by food supplementation. We conclude that offspring desertion during incubation is apparently costly in the Kentish plover, and this cost cannot be ameliorated with supplementary food.     

The effect of climate on nest orientation in the Rufous Hornero Furnarius rufus

ABSTRACT

Capsule: Within breeding season changes in nest orientation of the Rufous Hornero Furnarius rufus may reflect responses to the local climate.

Aims: To explore the effect of climate on the orientation of closed-cup nests of the Rufous Hornero at a subtropical urban site throughout its breeding period.

Methods: The breeding season was divided into two periods: a cold period with low rainfall and a warm, humid period. For each period, the mean nest entrance orientation and distribution were estimated and compared against a random orientation model.

Results: A total of 42 nests were found during the first period of reproduction and 32 during the second period. In both cases, the mean orientation was non-random and significantly different between the two periods: nests were more likely to be orientated towards the northwest in the first period and to the east in the second period.

Conclusions: Climate variation throughout the breeding season was reflected in differences in nest entrance orientation. This could be because this species takes advantage of solar radiation to increase the temperature within the nest during the first cold months of the breeding season and reduces the humidity of the nest, generated by intense rain, as the season progresses.     

Intraseasonal effects of clutch manipulation on parental provisioning and residual reproductive value of eastern phoebes (Sayornis phoebe)

Summary First clutches of double-brooded eastern phoebes Sayornis phoebe were manipulated (up two eggs, down 2 eggs or no change) to test for intraseasonal reproductive tradeoffs and to test whether size of first brood influenced food delivery rates to nestlings and nestling quality in second broods.Considering all nests from both broods, rate of feeding nestlings increased linearly with brood size but nestling mass per nest decreased with increasing brood size. High nestling weights in small broods may have resulted from parents delivering better quality food, but we did not test this.Among treatment groups in first broods, nestlings from decreased broods weighed more than those in control or increased broods. Treatment did not influence the likelihood that second nests would be attempted after successful first nests nor did it alter the interval between nests. Nestlings of parents that renested weighed more than those of parents that did not, regardless of treatment, suggesting that post-fledging care may preclude renesting. Mass of individual females did not change between broods, regardless of brood size. Clutch sizes of second attempts were not affected by manipulations of first broods but increasing first broods reduced the number of nestlings parents were able to raise to day 11 in their second broods. However, manipulation of first broods did not affect mean nestling mass per nest of nestlings that survived to day 11.In phoebes, parents of small first broods are able to raise nestlings in better condition. We predict that in harsh years, parents of small first broods would be more likely to renest. Parents of enlarged first broods sacrificed quality of offspring in second broods, which seems a reasonable strategy if nestlings from second broods have lower reproductive value.     

Influence of nests of leaf‐cutting ants on plant species diversity in road verges of northern Patagonia

Abstract. It has been suggested that ant nests are the most frequent small‐scale disturbance that affect vegetation patterns. However, their effects on plant diversity are little studied. We document effects of nests of the leaf‐cutting ant Acromyrmex lobicornis on physical‐chemical soil properties and their influence on plant diversity near road verges in a desert steppe in NW Patagonia, Argentina. We analysed nest soils and controls for nitrogen, phosphorus, organic matter, moisture retention capacity and texture. We also analysed the vegetation on 42 nests (30 active and 12 abandoned or without life) and 42 areas without nests. Soil around nests had a greater nutrient content and capacity to retain moisture than control soils, which is mainly due to the presence of organic waste that the ants deposit on the soil surface. We found no association between the occurrence of nests and specific groups of plants, but plant diversity was higher at nest‐sites than at nearby non‐nest sites. This increased diversity – which is also found on abandoned nests – is mainly due to the occurrence of a larger number of native and exotic plant species on nest‐sites that are uncommon elsewhere in the study area. The most abundant plant species showed similar cover values at nest and non‐nest sites. This suggests that changes in diversity are associated to edaphic changes caused by nests rather than by changes in competitive balance caused by dominant species exclusion. We propose that the nests of Acromyrmex lobicornis, through increasing the availability of resources, generate favourable microsites that can function both as ‘refuges’ for less frequent native species, and as‘stepping stones’ for less frequent exotic plant species.     

Unusual incubation rhythms the Spotted Barbtail, Premnoplex brunnescens

The Spotted Barbtail (Premnoplex brunnescens) inhabits the understory of humid montane forests in Central and South America. Apart from basic information on eggs and nest form, little has been published on its breeding ecology. Using temperature sensors in nest cups, I have collected data on the diurnal patterns of egg-coverage from three nests in eastern Ecuador and reveal a remarkable incubation rhythm. After providing near-constant coverage during the morning, adults leave the eggs unattended for most of the afternoon, returning to the nest only in the late afternoon. The mean duration (±standard deviation) of this period of absence, across the entire incubation period at three nests, was 6.4 ± 1.9 h. These results are discussed in relation to their physiological and ecological significance.     

Communal nesting under climate change: fitness consequences of higher incubation temperatures for a nocturnal lizard

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current ‘cold’ nests (mean = 23.2 °C, range 10–33 °C) and future ‘hot’ nests (27.0 °C, 14–37 °C). ‘Hot’ incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10 months. In 2014 and 2015, hot‐incubated hatchlings had higher annual mortality (99%, 97%) than cold‐incubated (11%, 58%) or wild‐born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78– 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52– 1.0) with mean times to extinction of 18–44 years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest‐site choices. Over the period 1992–2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest‐site selection. The impacts of climate change may therefore be especially severe on communal nesting species, particularly if such species occupy thermally challenging environments.     

Effects of parents and Brown‐headed Cowbirds (Molothrus ater) on nest predation risk for a songbird

Nest predation limits avian fitness, so ornithologists study nest predation, but they often only document patterns of predation rates without substantively investigating underlying mechanisms. Parental behavior and predator ecology are two fundamental drivers of predation rates and patterns, but the role of parents is less certain, particularly for songbirds. Previous work reproduced microhabitat‐predation patterns experienced by Yellow Warblers (Setophaga petechia) in the Mono Lake basin at experimental nests without parents, suggesting that these patterns were driven by predator ecology rather than predator interactions with parents. In this study, we further explored effects of post‐initiation parental behavior (nest defense and attendance) on predation risk by comparing natural versus experimental patterns related to territory density, seasonal timing of nest initiation, and nest age. Rates of parasitism by Brown‐headed Cowbirds (Molothrus ater) were high in this system (49% nests parasitized), so we also examined parasitism‐predation relationships. Natural nest predation rates (NPR) correlated negatively with breeding territory density and nonlinearly (U‐shaped relationship) with nest‐initiation timing, but experimental nests recorded no such patterns. After adjusting natural‐nest data to control for these differences from experimental nests other than the presence of parents (e.g., defining nest failure similarly and excluding nestling‐period data), we obtained similar results. Thus, parents were necessary to produce observed patterns. Lower natural NPR compared with experimental NPR suggested that parents reduced predation rates via nest defense, so this parental behavior or its consequences were likely correlated with density or seasonal timing. In contrast, daily predation rates decreased with nest age for both nest types, indicating this pattern did not involve parents. Parasitized nests suffered higher rates of partial predation but lower rates of complete predation, suggesting direct predation by cowbirds. Explicit behavioral research on parents, predators (including cowbirds), and their interactions would further illuminate mechanisms underlying the density, seasonal, and nest age patterns we observed.     

Influence of Nest Deprivation on Behaviour,Hormonal Concentrations and on the Ability to Resume Incubation in Domestic Hens (Gallus domesticus)

In this study, we investigated the influence of the length of nest deprivation period (3 vs. 6 d) on the ability to renest of incubating hens. We focused on the hens' behaviour, particularly on nesting and calls, on their prolactin, luteinizing hormone (LH) and oestradiol concentrations. Nest deprivation induced a drop of prolactin and an increase of LH plasmatic concentrations in hens. These changes in circulating pituitary hormones were followed by changes in ovarian function: the persistent rise of plasmatic oestradiol gave evidence of the resumption of ovarian activity. After nest deprivation, the number of clucks increased significantly and food calls appeared; these results demonstrate that ‘maternal’ calls can be emitted outside the maternal context. Our results suggest that the onset of typical maternal calling is strongly controlled by internal state such as plasmatic hormonal concentrations, independently of social stimulation. None of the 10 hens deprived for 6 d resumed incubation when given the opportunity, whereas, after a 3 d deprivation period, three out of 10 hens renested and two hens incubated sporadically and then gradually abandoned their nests. Long periods of nest deprivation appear to disrupt the habits of sitting and nesting. Before nest reopening, all the hens presented low levels of plasmatic prolactin. Plasma prolactin concentrations of the renesting hens increased after nest boxes were reopened and returned to levels found in incubating hens. We suggest that pituitary prolactin rather than plasmatic prolactin is responsible for the maintenance of incubating potential in hens deprived of their nests.     

Concentrations of plasma prolactin and luteinizing hormone following nest deprivation and renesting in ring doves (Streptopelia risoria)

Ring doves with increased plasma prolactin and low plasma LH (Group A) or with low plasma prolactin and low plasma LH (Group B) which had been incubating sterile eggs for 12 or 18 days, respectively, had their nests and eggs removed for 3 days. Upon nest return, observations were made on the birds' readiness to renest and on changes in plasma prolactin and LH. Birds from Group A demonstrated a far greater tendency to resume incubation than birds from Group B. Nest deprivation resulted in a sharp fall in the concentration of plasma prolactin in birds which were deprived of their nests after 12 days of incubation (Group A). Following resumption of incubation no subsequent increase in the prolactin levels was observed in Group A or B. The concentration of plasma LH rose sharply after nest deprivation in both sexes of both groups and declined after return of the nests. Birds in Groups A and B which returned to their nests laid a new clutch of eggs while continuing to incubate. The total length of uninterrupted sitting following nest return was 20.9 +/- 0.48 days (n = 8). These results suggest that (1) once the mechanism responsible for the increase in plasma prolactin during incubation is disrupted, it cannot be reactivated unless the whole reproductive cycle is repeated. (2) The inhibition of LH secretion during incubation involves neural mechanisms which do not necessarily involve the anti-gonadotrophic action of prolactin.