The functional significance of multiple nest-building in the Australian Reed Warbler Acrocephalus australis

The vast majority of bird species build a nest in which to breed. Some species build more than one nest, but the function of most multiple nest-building remains unclear. Here we describe the unusual nest-building behaviour of the Australian Reed Warbler Acrocephalus australis , and test experimentally the hypotheses that multiple nest-building is related to individual condition or territory quality, and plays a role in mate assessment. Australian Reed Warblers built two types of nest structures: 'type I' nests, which were used for eggs and nestlings, and 'type II' nests, which were structurally distinct from type I nests, did not support eggs, nestlings or adults and were not essential for successful breeding. The number of type II nests built in each territory varied. Type II nests were only built before breeding had commenced in a territory and females were not observed participating in their construction, supporting a role in female mate choice. Birds provided with supplementary food built significantly more type II nests than control birds. However, supplementary-fed birds did not have greater pairing success, and the addition of further type II nests to territories did not increase the pairing rate or type II nest construction in those territories. There was no relationship between the presence of type II nests and either reproductive success or likelihood of nest predation. We discuss the implications of these results in light of previous suggestions regarding the function of multiple nest-building in birds.     

Serum prolactin concentrations and the initiation of maternal behavior in the rat

Maternal behavior and serum prolactin were measured in pregnant and virgin female rats. Pregnant rats were either ovariectomized or shamovariectomized on Day 17 of pregnancy, while virgin females were ovariectomized at the same age. Two days after surgery nests were rated and the three treatment groups were tested for responsiveness to rat pups. Both pregnant treatment groups built superior nests compared to the virgin group and also responded more frequently to rat pups within a 1 hr test period than the virgin controls. In addition, significantly more ovariectomized pregnant subjects responded to pups than did intact pregnant females. Serum prolactin levels did not differ among the three treatments nor did exposure to pups affect serum prolactin levels. In each treatment group serum prolactin was less than 15 ng/ml, well below the 139.7 ng/ml mean found on Day 23 of pregnancy. These data suggest that high levels of serum prolactin during late pregnancy are not essential for the initiation of maternal behavior in the rat.     

Induction of maternal nest building in virgin female mice by the presentation of young

Ovariectomized and intact adult virgin female mice presented with two 1-day-old mouse pups built larger nests and more nests rated “maternal” than did intact animals not proffered young. Virgin females presented with live 1-day olds behind a wire partition in their homecages also constructed larger nests and more nests rated “maternal” as compared to animals presented with freshly killed 1-day olds, 19-day olds, or with no pups behind the partition.     

Free female mate choice in house mice affects reproductive success and offspring viability and performance

We tested a critical assumption of sexual dialectics theory (Gowaty 1997, Feminism and Evolutionary Biology, Chapman & Hall) using house mice, Mus musculus. We asked if female house mice accrue viability benefits for their offspring when they mate with males they prefer versus with males they do not prefer. Our experiment was designed to eliminate or control other mechanisms of reproductive competition besides female mate choice. After allowing females to discriminate behaviourally between two males, which were at random with respect to phenotypic variation discriminating females were paired with preferred (P) or nonpreferred (NP) males. We then tested whether females mating with males they preferred had offspring of higher viability than females mating with nonpreferred males. In pairwise comparisons, we tested for differences in offspring performance in dominance contests and in nest-building skill. At weaning, we exposed half of the pups to cold stress. We tested progeny performance and viability in the laboratory or in outdoor field enclosures. In comparison to P females, NP females produced significantly fewer litters. Sons from P matings were socially dominant to sons from NP matings. Adult offspring from P matings built better nests than those from NP matings. In field enclosures significantly fewer NP than P offspring survived to 60 days after introduction. Male and female progeny from P matings established larger home ranges and constructed better nests than progeny from NP matings. This is the first demonstration of progeny viability differences for females allowed to express mate preferences between males presented to them at random. Copyright 2000 The Association for the Study of Animal Behaviour.     

Effects of cold on nest-building by wild and domestic mice, Mus musculus L.

Nest-building by male and virgin female wild and laboratory mice kept at a temperature of 2^o C was compared with that of controls kept at 23^o C. The amount of cotton wool pulled into the cage was recorded over 24 hours. Nest quality was also assessed. The tests of nest-building were conducted in both cold and warm environments. Cotton pulling was usually at a lower rate in the cold environment, but there was no corresponding decrement in final nest quality. Previous experience in the cold, compared with absence of such experience, resulted in higher scores by wild mice tested in either environment, and by laboratory mice tested in the cold environment. Wild mice that built high quality nests used less cotton wool in the cold than in the warm environment. The tendency for wild mice to pull more cotton wool and build better nests than laboratory mice was more pronounced among cold-treated animals. Differences in body weight did not account for the differences between wild and laboratory mice.
In further experiments nest-building was observed over 16 days. In the cold environment there was an initial depression of nest-building by both wild and laboratory mice, followed by a steady improvement over 6 days.
Both males and virgin females sometimes made well constructed nests even in the warm environment. In the cold environment the effect of previous cold-exposure on wild mice was the rapid construction of a good nest.     

Effects of behavioural time budgets and nest-building efficiency on male reproductive performance in red bishops ( Euplectes orix )

In this study we have investigated the effect of nest-building behaviour, courtship behaviour, and male–male interactions on male reproductive performance of the red bishop (Euplectes orix), a highly polygynous, colonially breeding weaverbird species. Previous studies on red bishops have revealed that male reproductive success is mainly determined by the number of nests built in a territory, and that reproductive success and the number of nests both vary substantially among males. Here we test whether the high variation observed in reproductive performance is related to male behavioural patterns (as assessed by time-budget analysis) and/or nest-building efficiency (as assessed by the number of fibres incorporated in the nest in unit time). We collected data on male time budgets and analysed behavioural patterns for three breeding seasons. A greater number of nests built was positively related to both the amount of time allocated to nest-building behaviour and the efficiency of nest building. Neither the amount of time spent in courtship behaviour nor the amount of time spent in male–male interactions was related to reproductive success. Male reproductive success, irrespective of the number of nests built, was partly determined by the number of fibres incorporated, suggesting some importance of nest quality in terms of nest chamber density to male reproductive success. There were no trade-offs with regard to time allocated to different behaviour. Instead, males differed with regard to their territory attendance and activity levels, which might be because of differences in energy resources and may thus reflect inherent differences in male body condition and, ultimately, male genetic quality.     

Male Song Stimulation of Female Reproduction in Canaries: Features Relevant to Sexual Displays are not Relevant to Nest-building or Egg-laying

Recent studies conducted in our laboratory have demonstrated that a special type of song phrase (‘sexy’ phrases) containing bipartite syllables composed of abrupt frequency falls and short silences stimulate female canaries to solicit for copulation. The study was undertaken to determine whether sexy phrases also facilitated other aspects of the reproductive activity of the female canary, namely, nest-building and egg-laying. During the first experiment, we studied the effect of sexy and non-sexy songs on copulation solicitation displays in 1-year-old females without reproductive experience and in mature females with previous reproductive experience. We confirmed that sexy songs elicited more sexual responses than did non-sexy songs in yearlings and in mature females. During the second experiment, we studied the effect of male songs on nest-building activities and egg-laying in 1-year-old inexperienced females, and in mature, experienced females. The songs of conspecific males significantly triggered and increased nest-building behaviour in female canaries whatever their age or reproductive experience. In contrast, song effects on egg-laying were only found in young females. One-year-old inexperienced females exposed to sexy or non-sexy songs laid more eggs and laid earlier than did 1-year-old inexperienced controls; no such differences were observed in mature, experienced females. The efficiency of songs in promoting nest-building or egg-laying appeared to be unrelated to their efficiency in eliciting sexual responses. No difference was found between females exposed to sexy songs and females exposed to non-sexy songs; differences were only found between control and the two groups of song-exposed females. This result demands further experiments in order to determine whether other song phrase types may account for the stimulating effects of male song on female nest-building and egg-laying.     

Elaborate Nests in a Weaverbird: A Role for Female Choice?

Studies on sexual selection have focused on behaviour and morphology, but several groups of animals build elaborate structures associated with acquiring a mate. I investigated female choice for nests built by male baya weavers (Ploceus philippinus). Nest choice by females should be strong, as nests are obvious direct benefits provided by males. I used a field experiment supplemented with correlational information to ask whether females appear to base mate choice decisions on male behaviour, nest architecture, and nest location. When the nests of highly visited males were exchanged with those of poorly visited males, female visits remained highest at the original male and location. I found no relationship between female choice and male display or other behaviour. Correlational analyses show that nest location was a better predictor of female choice than was nest architecture. These data suggest that current female choice is driven more by access to safe nesting sites rather than to well‐built nests, possibly because all males are able to build nests of adequate quality. However, nest architecture is unlikely to be irrelevant to females, and its role deserves further investigation.     

Maternal Aggression and Litter Size in the Female House Mouse

It has been commonly argued that, in house mice, female post-partum fighting against a male intruder functions to protect the offspring from infanticide. The aim of this study was to test the hypothesis that maternal aggression is actually related to pup defence and, specifically, according to parental investment theory, that its intensity should increase with litter size. 60 nulliparous albino female mice were mated and randomly assigned to four experimental groups in which litters were culled at birth to 0, 4, 8, or 12 pups, respectively. On day 8 after delivery all females were tested for maternal aggression against a stranger adult male conspecific (5-min exposure). No aggression occurred in the group in which all pups had been removed. In the other groups, the proportion of females displaying overt aggression increased with litter size. Several scores of female agonistic behaviour (proportion of females displaying overt aggression, total attacking time, frequency of tail rattling) were significantly higher for the females rearing 8 and 12 pups than for the females rearing 4 pups. Aggressive behaviour of females rearing 12 pups was not significantly higher than that of females rearing 8 pups. No male committed infanticide. These results support the hypothesis that rodent maternal aggression is strictly related to offspring defence and are consistent with the theoretical prediction that, the costs of the defence being equal and the gain in fitness increasing with litter size, the intensity of maternal defence of the young should increase with their number.     

Limitation of reproductive success by food availability and litter size in the bank vole,Clethrionomys glareolus

Food limitation has been suggested as one of the most important factors affecting life history evolution in terrestrial vertebrates. However, this inference is based mainly on evidence from birds, and reproductive trade-offs may differ among groups with different forms of parental care. To study whether the costs of enlarged litters (decreased mass of offspring) would appear when food is not limiting, we performed outdoor enclosure experiments in which we manipulated simultaneously the litter size (control versus litter plus two pups) and food availability (control versus food-supplemented) of female bank voles, Clethrionomys glareolus. The weaning success of females increased significantly in response to supplementary food. When females were provided with extra food, no differences were observed in body masses of weanlings of control and enlarged litters. Further, food-supplemented females grew to larger sizes during nursing than unsupplemented females. Our experiment suggests that energetic requirements during nursing constrain the number of offspring that can be raised successfully in a particular breeding attempt. The results also indicate that unlimited food resources may increase future reproductive potential of females because they can use more energy for somatic growth.     

Do Laboratory Mouse Females that Lose Their Litters Behave Differently around Parturition?

Efficiency in laboratory mouse breeding is hampered by poor reproductive performance, including the loss of entire litters shortly after birth. However, the underlying mechanisms are not yet fully understood and establishing the cause of death in laboratory mouse pups can be complicated. Newborn mouse pups are generally hidden in nests, dead pups are often eaten by the female, and the widespread practice of leaving periparturient females undisturbed complicates inspection, which may delay the discovery of pup loss. In order to efficiently prevent problems with litter loss, it is important to find key factors for survival. We investigated differences in periparturient behavior between female laboratory mice whose pups survived until weaning and females whose entire litters were lost. Video recordings of 82 primiparous females of the C57BL/6 strain or knockouts with C57BL/6 background were used. The mice were observed from 24 h before until 24 h after parturition and female behaviors coded using a pre-established ethogram. The relationship between behavior and survival was analyzed using logistic models, where litter survival was regressed on the proportion of 30-s observations with at least one occurrence of the behavior. We found that females with surviving litters performed more nest building behavior during the last 24 h before parturition (p = 0.004) and spent less time outside the nest during the entire observation period (p = 0.001). Increased litter survival was also associated with more passive maternal behaviors and the female ignoring still pups less. Females that lost their litters performed more parturition-related behaviors, suggesting prolonged labor. The results indicate that maternal behavior plays a significant role in laboratory mouse pup survival. Complications at parturition also contribute to litter mortality.     

Effects of stimuli emanating from the nest on the reproductive cycle in the ring dove. II: building during the pre-laying period.

The nest is a major focal point of the reproductive cycle in the ring dove (Streptopelia risoria). This study shows that the state of the nest is an important determinant of the type of nest-building exhibited. For example, birds faced with an empty nest bowl every day removed more material from dispensers and built more actively than did those allowed to construct nests normally. Conversely, those given completed nests were not very active, but were more efficient in using the little they removed from the dispensers and showed a reversal of sex roles in building. The relations between nest-building and egg-laying, and between male and the female are discussed.     

Studies of pericopulatory pregnancy blockage and the gestation period in deer mice (Peromyscus maniculatus)

It has previously been shown that female deer mice in cycling estrus that copulate with or are exposed to more than one male at the time of mating have a lower probability of delivering a litter than when mating with and being exposed to just one male. In the present research the effect of post-mating exposure to the bedding of a strange versus a familiar male was studied in females in postpartum estrus. In four experiments females in postpartum estrus were protected from pericopulatory pregnancy blockage, presumably by suckling-induced elevated prolactin levels. Varying female experience, number of ejaculations, and the presence of suckling pups had no effect on this protection. Thus, both the pericopulatory block and the Bruce effect (a more delayed type of pregnancy blockage) occur in cycling, but not suckling, females. This suggests that the two may have a common mechanism and leads to a new perspective in the search for adaptive significance. In addition, the subsequent gestation periods were prolonged in females nursing young; the length was affected by the number of pups weaned from the previous litter and the number of pups being carried.     

NEST PARASITISM AND DISPLAY OF CHESTNUT SPARROWS IN A COLONY OF GREY-CAPPED SOCIAL WEAVERS

Chestnut Sparrows Passer eminibey near Magadi, Kenya, built no nests of their own but usurped nests newly built by Grey-capped Social Weavers Pseudonigrita arnaudi. The sparrows laid eggs and raised their own young in the appropriated nests. The sparrows were synchronized in their breeding with the social weavers but appeared to have a slightly later peak of breeding. Breeding of the sparrows may be stimulated by the sight of breeding activity of the social weavers. Breeding occurred in May and June at the end of a rainy season.
Male Chestnut Sparrows display at the nests with the wings raised. The display is given for several hours each day. Examination of nests built by the social weavers is an element of courtship display by the male sparrow.
In the subfamily Passerinae there is a greater difference in the form of the courtship display between the Chestnut Sparrow and other species of Passer than between nest-building species of Passer and other genera. The display of Chestnut Sparrows is derived from the nest-advertisement display of nest-building Passer. Its exaggerated form may be an adaptation related to pair formation and intrapair sexual stimulation in the absence of male nest-building behaviour.     

The biology of the eumenid mud-wasp Pachodynerus msidens in trapnests

Abstract. 1. The biology of the eumenid mud-wasp Pachodynems nasidens (Latr.) was studied in trapnests.
2. Females nested in traps placed in the shade and some nested in the same traps from which they had emerged.
3. The nesting behaviour and nest structure were generally similar to those of other eumenids that nest in borings, but a temporary crescent-shaped plug at the nest entrance and the use of both dry soil and mud for nest-building seems unique to P.nasidens .
4. Like most other eumenids, P.nasidens collected caterpillars, mainly Pyral-idae, Olethreutidae, Alucitidae and Thyrididae.
5. In linear nests, the innermost cells contained females and the outermost cells males, resulting in proterandry. One female can make several nests, each showing proterandry.
6. Female immatures were larger and took more time to develop than males. Also, their cells were larger and stocked with more food than male cells, hence needing more time to be provisioned.
7. The greater 'cost' to produce a female and a sex ratio biased toward females in short traps and about unity in longer traps, leads to a comment on parental investment.     

Building multiple nests is associated with reduced breeding performance in a south temperate population of Grass Wrens Cistothorus platensis platensis

Grass Wrens Cistothorus platensis build two types of non-breeding nest structures: platforms and dummy nests. Platforms are rudimentary accumulations of grasses concealed between vegetation. Dummy and breeding nests are dome-shaped with a similar structural layer. We used a nest-removal experiment and observational data to evaluate several hypotheses regarding the adaptive significance of building multiple nests in a south temperate population of Grass Wrens. Building non-breeding nests was not a strategy of males to attract additional females, as most of these nests were built after pair formation and both sexes collaborated during building. Building non-breeding nests was not a post-pairing display as the presence of multiple nests did not increase female investment in the breeding attempt: clutch size and female provisioning to nestlings did not differ between experimental and control territories where no non-breeding nests were removed. Similarly, in non-manipulated territories, clutch size and female provisioning were not correlated with the number of non-breeding nests or with males’ nest-building effort. Contrary to this hypothesis, the number of non-breeding nests was associated with delayed clutch initiation and reduced hatching success. The presence of non-breeding nests did not reduce nest predation and brood parasitism, which did not differ between experimental and control territories. We did not detect differences in concealment between non-breeding and breeding nests, suggesting that non-breeding nests were not the result of abandonment before egg-laying to reduce subsequent nest predation. Dummy nests did not provide shelter; they were not used frequently for roosting over the breeding season and were not maintained during the non-breeding season. We suggest that building non-breeding nests may be an attempt by males to manipulate the decision of females to breed with a mate they might otherwise reject or to start reproduction earlier than optimal for the females.     

The influence of the sex of litter-mates on subsequent maternal behaviour in Rattus norvegicus.

Female rats reared in unisexual (U) or bisexual (B) cross-fostered litters were mated at 75 days of age and their maternal behaviour compared by periodic observation over 20 days following birth of their litters. In two separate experiments, U-females showed a lower incidence of pregnancy and, at birth, of litters with ten or more pups than B-females (P less than 0-05). Litters culled to ten animals on the day after birth were significantly heavier in B- than in U-females, although this difference was not evident at weaning as litters reared by U-females showed a relatively greater (P less than 0-01) increase in weight during the investigation than the corresponding litters reared by B-females. Using a scoring method, no difference was evident in the opportunities that U- and B-females offered for their pups to suck, and, when not nursing pups in the nest, both groups of females engaged equally in activities such as grooming, sleeping, eating, and rearing on their hind legs. Throughout the 20-day observation period, B-females maintained significantly more elaborate nests (as scored on an arbitrary scale) than U-females. This difference was evident in females rearing litters of both five and ten animals, and was observed in two separate experiments. In addition, whereas only 15 per cent of U-females were observed nest-building, over 60 per cent of B-females were noted to be engaged in this activity on one or more occasions (P less than 0-001). It is suggested that, in the light of previous findings, these results may reflect differences in oestrogen and/or progesterone metabolism in unisexually-reared and bisexually-reared female rats.     

Breeding system can affect the offspring sex ratio in Syrian hamsters

Nulliparous female Syrian hamsters were used to investigate the effect of two different breeding systems on the fertility of the female Syrian hamster. We hypothesized that females submitted to a harem system (HS) would deliver smaller and more female-biased litters than in a monogamic system. Ten female and 10 adult male hamsters housed individually (G1) were kept in a monogamic temporary breeding system, while 10 females and five males (G2) were submitted to HS with two females and a male permanently housed together since female weaning. Females from G1 and G2 delivered, respectively, 47 and 50 litters, and produced 364 (G1) and 383 (G2) weaned pups without any difference in litter size, mean weight of weaned pups and body condition of dams. Interparturition intervals were shorter and the percentage of male pups per litter was higher in the HS possibly as a result of different endocrine conditions provided by different breeding systems. Besides providing evidence that housing conditions can influence the sex of hamster offspring, our findings suggest a mechanism for the non-random distribution of male and female pups in hamster litters.     

Modulation of gonadotrophin and prolacrin secretion by daylength and breeding behaviour in free-living starlings, Sturnus vulgaris

Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured by radioimmunoassay in plasma samples collected from free-living starlings, Sturnus vulgaris , trapped in nest-boxes. By leaving some nest-boxes undisturbed, and repeatedly destroying nests in others, birds from a single-brooded population were trapped whilst nest-building, incubating or feeding nestlings, at different times throughout the normal breeding season. In both males and females trapped whilst nest-building, plasma LH and prolactin levels increased progressively from mid March until late May. In females sampled during incubation, LH and FSH levels were high throughout May but decreased in early June. Prolactin levels were highest in late May. In both males and females trapped during mid May, LH levels were highest in these birds which were nest-building at this time and lowest in those feeding nestlings, FSH did not change significantly, and prolactin was low in those birds which were nest-building and high in those incubating or feeding nestlings. In female starlings from a double-brooded population, levels of LH and FSH were much lower whilst feeding the second brood than when feeding the first brood, whereas prolactin levels were similar. The results suggest that incubation and feeding behaviour inhibit the increase in LH secretion caused by increasing daylength, but stimulate prolactin secretion in excess of that caused by increasing daylength.     

Infanticide in great reed warblers: secondary females destroy eggs of primary females

In 1994–1995 artificial nests with attached model eggs were put into territories that were known to have been occupied by male great reed warblers,Acrocephalus arundinaceusin previous years. Because the eggs were made of soft plasticine, predators left peckmarks in them and this enabled us to identify predators by comparing peckmarks with reference marks made by various species. Previous field data had suggested that infanticidal behaviour existed in our study population, as nests of primary females suffered a three times higher rate of nest loss during the egg-laying period than nests of secondary and monogamous females. The presence of infanticide was supported by the experiment. Small peckmarks resembling those of a great reed warbler occurred almost exclusively in territories occupied by great reed warblers, in particular when a new female settled in the territory. The newly settled females built nests closer to depredated than non-depredated nests. That small peckmarks occurred when new females settled strongly suggests that it is secondary female great reed warblers that commit infanticide on eggs of primary females. Females of low harem rank are expected to gain from infanticidal behaviour because a low ranked female gets a higher proportion of male parental investment when the nest of the primary female fails.