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1.
Behavioral Ecology and Sociobiology - In the animal kingdom, conspicuous colors are often used for inter- and intra-sexual communication. Even though primates are the most colorful mammalian taxon,...  相似文献   

2.
In cooperatively breeding species, helpers may contribute to the success of the brood by increasing the number of independent offspring, but also, they may affect offspring condition and, hence, their survival and recruitment into the breeding population. This second type of benefits is rarely included in theoretical models or assessed in field studies. Immune response is a good proxy of individual quality and fitness, and there is good evidence that the performance of the immune system of chicks during the nestling phase is related to their chances of survival and future reproduction. However, no study has so far explored whether helpers at the nest might contribute to enhance immune functioning of nestlings in species with a cooperative breeding system. Here we investigate this issue in the azure-winged magpie (Cyanopica cyanus) and found for the first time a positive correlation between the number of helpers at nest and the cell-mediated immune response of nestlings. This effect was not explained by a general improvement of body condition of chicks because it was independent of individual variation in body mass or tarsus length. Our results suggest that helping can have subtle effects on the quality of offspring that may influence their survival and future reproduction.  相似文献   

3.
Kin selection has played an important role in the evolution and maintenance of cooperative breeding behaviour in many bird species. However, although relatedness has been shown to affect the investment decisions of helpers in such systems, less is known about the role that kin discrimination plays in other contexts, such as communal roosting. Individuals that roost communally benefit from reduced overnight heat loss, but the exact benefit derived depends on an individual's position in the roost which in turn is likely to be influenced by its position in its flock's dominance hierarchy. We studied the effects of kinship and other factors (sex, age, body size and flock sex ratio) on an individual's roosting position and dominance status in captive flocks of cooperatively breeding long-tailed tits Aegithalos caudatus. We found that overall, kinship had little influence on either variable tested; kinship had no effect on a bird's position in its flock's dominance hierarchy and the effect of kinship on roosting position was dependent on the bird's size. Males were generally dominant over females and birds were more likely to occupy preferred roosting positions if they were male, old and of high status. In this context, the effect of kinship on social interactions appears to be less important than the effects of other factors, possibly due to the complex kin structure of winter flocks compared to breeding groups.  相似文献   

4.
In cooperatively breeding acorn woodpeckers (Melanerpes formicivorus), helper males have a large positive effect on fledging success in good acorn crop years but only a small positive effect in poor acorn crop years, while helper females exhibit the opposite pattern. Based on these findings, we tested the “concealed helper effects” hypothesis, which proposes that laying females reduce investment in eggs (with respect to their size, number, or quality) in a way that confounds helper effects and results in an absence of a relationship between helpers and breeding success. Results generally failed to support the hypothesis. Mean egg size was positively related to temperatures during the 10 days prior to egg-laying and negatively related to the food supply as indexed by the prior fall’s acorn crop, but there were no significant differences vis-à-vis helpers except for interactions with the acorn crop that only partly corresponded to those predicted. With respect to clutch size, females laid larger clutches when assisted by female helpers, opposite the pattern predicted. Although our results suggest that egg size is adjusted to particular ecological circumstances, we conclude that neither egg nor clutch size is adjusted in a way that confounds the apparent effects of helpers, as proposed by the concealed helper effects hypothesis.  相似文献   

5.
Summary During a two year study of the moorhen, Gallinula chloropus, a quarter of the nests found had two or more females laying in them. This was the result of two features of the moorhens' breeding biology: (1) Cooperative nesting; two (or more) females were paired to the same male. Both laid in the same nest, the second laid a large clutch synchronously to the first, and both cooperated in parental care. (2) Intraspecific brood parasitism; some females (parasites or dumpers) laid a small number of eggs at random in the nests' of neighbours. Cooperatively nesting females were mother and daughter, while parasite and host were not. Parasitic females laid in their own nest as well, and generally did so after completing a dumping sequence. Parasitic eggs were laid at random during the host's laying and incubation period, and were about a quarter as likely to produce an independent chick as were non-parasitic eggs. Parasitic females would probably have reared more chicks by laying in their own nests straight away, instead of dumping any eggs at all, because there was a strong decline in reproductive success with season. Possible reasons why they did not do so are discussed. Parasitised pairs tended to rear fewer own chicks than non-parasitised pairs. There was no evidence that hosts selectively destroyed parasitic eggs. Four hypotheses that explain why hosts accepted dumped eggs are considered. (1) The host pair were unaware of the dump, (2) the host male had copulated with the dumping female, (3) the dumper was related to one of the host pair, and (4) there was a benefit to the host pair because they gained extra helpers. These hypotheses were not supported by the data, but further tests are needed. As the cost of desertion was greater than the cost of acceptance of parasitic eggs, hosts may have been forced to accept.  相似文献   

6.
‘False feeding,’ where helpers arrive at nests with food but fail to provision the young, has been reported in several cooperative species. This and other potentially ‘deceptive’ behavior has been interpreted as indicating that helping may operate as a signal within such social groups. We critically examine these phenomena in the provisioning behavior of the bell miner Manorina melanophrys. Excessively close observation distances can artificially elevate the rate of false feeding in this (and other) species, but once this had been accounted for, there was little evidence for any ‘deceptive’ behavior by helpers or breeders. Natural and experimentally induced variation in the presence of a potential conspecific audience at the nest did not have any consistent influence upon the rate of false feeds, which was low at 7.94% of 6,880 nest visits. Instead, encountering unexpectedly low levels of brood demand provided a more parsimonious explanation for those visits where helpers failed to feed nestlings or ate the food themselves. Failure to completely transfer a load to nestlings was more likely when the load contained a high proportion of sticky lerp, indicating a simple prey-transfer problem. Finally, individuals that arrived at nests without prey were often members of neighboring breeding pairs, suggesting that these few non-feeding visits may instead involve an information-gathering function. We, therefore, suggest that future studies explicitly exclude the possibility of observer disturbance and all aspects of normal provisioning behavior before applying the terms ‘false feeding’ or ‘deceptive’ and inferring anything more than straightforward helping at the nest.  相似文献   

7.
Although it is known that parents can differ in their optimal resource allocation to offspring in size-structured broods, the mechanisms determining differences in allocation rules of carers are not yet clarified. In cooperatively breeding species, breeders and non-reproductive helpers often differ in their fitness payoffs of providing care and in their breeding experience. Cooperative breeders thus provide an appropriate system to examine two hypotheses originally proposed to explain differences in food allocation among parents: (i) food allocation between carers differs because of the distinct cost-benefit ratio of selective feeding (i.e. breeders and helpers are expected to differ in food allocation) and (ii) carers differ in their ability to feed selectively (i.e. differences in food allocation are expected between experienced adults and inexperienced yearlings). We compared feeding rates with which breeders, old helpers and yearling helpers provisioned nestlings of different hatching rank. The influence of experience upon food allocation was further assessed by comparing food allocation of yearlings early and late during nesting. We show that allocation rules differ between age classes because breeders and old helpers fed the youngest chicks most, whereas yearlings showed the opposite pattern. The role of experience was supported by the fact that yearlings adjusted food allocation to that observed in experienced adults during the breeding season. We thus suggest that food allocation in El Oro parakeets depends either on differential skills of adults to transfer food to the youngest chick or on their ability to recognize nestling needs.  相似文献   

8.
Recent models of the evolution and dynamics of family structure in cooperatively breeding vertebrates predict that the opening of breeding vacancies in cooperatively breeding groups will result in (1) dispersal movements to fill the reproductive position, and (2) within-group conflict over access to reproduction. We describe the behavioral and demographic changes that followed the creation of breeding vacancies in three wild groups of cooperatively breeding common marmosets (Callithrix jacchus). Replacement of the breeding female was rapid when no adult females remained in the group, but did not occur for several months when other adult females were present. Aggression of adult animals towards same-sex potential immigrants was associated with a period of reduced affiliation, increased intragroup agonism, no intragroup sexual behavior, and frequent extragroup copulations. This ended with the fissioning of groups along sexual lines. After replacement, multiple males copulated with multiple females and vice versa, with no increases in sexually related aggression. Female-female conflict was resolved through infanticide. The lack of direct conflict between males is consistent with cooperative polyandry. After a breeding vacancy appeared, marmoset groups showed conflict of interests among group members similar to those shown by cooperatively breeding birds, but they used different behavioral mechanisms to resolve those conflicts. Our data provide important evidence from a cooperatively breeding mammal to support Emlen’s model for the evolution of vertebrate families, but they suggest that species-specific inter- and intrasexual competitive strategies should be considered before the model can be applied to other cooperatively breeding vertebrates. Received: 23 November 1999 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000  相似文献   

9.
The effects of landscape fragmentation on nest predation and brood parasitism, the two primary causes of avian reproductive failure, have been difficult to generalize across landscapes, yet few studies have clearly considered the context and spatial scale of fragmentation. Working in two river systems fragmented by agricultural and rural-housing development, we tracked nesting success and brood parasitism in > 2500 bird nests in 38 patches of deciduous riparian woodland. Patches on both river systems were embedded in one of two local contexts (buffered from agriculture by coniferous forest, or adjacent to agriculture), but the abundance of agriculture and human habitation within 1 km of each patch was highly variable. We examined evidence for three models of landscape effects on nest predation based on (1) the relative importance of generalist agricultural nest predators, (2) predators associated with the natural habitats typically removed by agricultural development, or (3) an additive combination of these two predator communities. We found strong support for an additive predation model in which landscape features affect nest predation differently at different spatial scales. Riparian habitat with forest buffers had higher nest predation rates than sites adjacent to agriculture, but nest predation also increased with increasing agriculture in the larger landscape surrounding each site. These results suggest that predators living in remnant woodland buffers, as well as generalist nest predators associated with agriculture, affect nest predation rates, but they appear to respond at different spatial scales. Brood parasitism, in contrast, was unrelated to agricultural abundance on the landscape, but showed a strong nonlinear relationship with farm and house density, indicating a critical point at which increased human habitat causes increased brood parasitism. Accurate predictions regarding landscape effects on nest predation and brood parasitism will require an increased appreciation of the multiple scales at which landscape components influence predator and parasite behavior.  相似文献   

10.
White-winged choughs (Corcorax melanorhamphos) are obligate cooperative breeders, living in groups which may contain up to 20 birds. Although breeding is dominated by a single pair, all birds contribute to rearing young, including the provisioning of nestlings. However, some birds which have carried food to the nest, even to the point of placing the food in the gaping mouth of a nestling, consume the food themselves rather than provision the nestlings. Birds which fail to feed nestlings are typically young, and are only likely to fail to deliver food when they cannot be observed by other group members. Birds which have just failed to deliver food are more likely to engage in alternative helping behaviours such as allopreening the nestlings than are helpers which have just delivered food in the conventional manner. Failure to deliver food is almost eliminated when foraging constraints are experimentally reduced by supplemental feeding of the group. Collectively these observations suggest that young white-winged choughs act deceptively by simulating helping behaviours without sacrificing food supplies. Received: 24 January 1997 / Accepted after revision: 6 June 1997  相似文献   

11.
Summary Breeding males or females were removed from groups of the cooperatively breeding acorn woodpecker to study (1) competition among individuals from different groups to fill the breeding vancancies, (2) conflict between parents and offspring within groups over replacement of the removed bird, and (3) conflict between parents and offspring for breeding status. Intense fights (power struggles) among nonbreeders from other groups to fill the breeding vacancies developed after the removals. In groups containing only helpers of the opposite sex as the removed bird, replacement was rapid, but in groups containing helpers of the same sex as the removed bird replacement was delayed substantially. In these latter groups parent-offspring conflict developed: helpers could not breed because their parent of the opposite sex was present, and they attacked potential replacements, while their remaining parent advertised for a new mate by calling. Once replacement had occurred, dominance interactions between parents and offspring and among siblings appeared to prevent some individuals from breeding. We conclude that the potential for competition among close kin is high in cooperative species because breeding opportunities are limited.  相似文献   

12.
Neolamprologus pulcher, a cooperatively breeding cichlid fish from Lake Tanganyika, lives in permanent social groups comprising one breeding pair and helpers of both sexes. Variation in group size (1-14 helpers) provides an opportunity to investigate factors that affect how many helpers remain in a group and in turn how group size affects reproductive success. This field study showed that larger groups live in larger territories with more shelter. Group size was more strongly correlated with territory quality than with breeder size. Experimental enhancement of territory quality did not affect group size but group size decreased when territory quality was reduced. Breeders living in a large group benefit because such individuals feed more often and have lower workloads and greater reproductive success. Helpers in larger groups also fed more frequently but did not have lower workloads. This is one of the first experimental studies to examine the factors influencing group size in cooperative breeders.  相似文献   

13.
The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.  相似文献   

14.
In semi-colonial species, some individuals choose to breed in isolation while others aggregate in breeding colonies. The origin and the maintenance of this pattern have been questioned, and inherited phenotype dependency of group breeding benefits has been invoked as one of the possible mechanisms for the evolution of semi-coloniality. Using field observations and behavioural tests in the semi-colonial barn swallow (Hirundo rustica), we tested the hypothesis that breeding group size is related to personality. We measured neophobia (the fear and avoidance of new things) and social tolerance of adults and showed that these two independent traits of personality are strongly related to breeding group size. The biggest colonies hosted birds with higher neophobia, and larger groups also hosted females with higher social tolerance. This parallel between group size and group composition in terms of individual personality offers a better understanding of the observed diversity in breeding group size in this species. Further studies are, however, needed to better understand the origin of the link between individual personality and group breeding strategies.  相似文献   

15.
Summary Measures of relative gamete contribution were related to degree of parental investment for both males and females from six groups of communally breeding pukeko (Porphyrio porphyrio). If there is a fitness cost to participation in parental duties, then for males parental investment should relate to degree of confidence of paternity while for females investment should relate to the number of eggs laid. Data were analysed in two ways: (1) by looking at individuals of the same sex within the same group to see if males that had a greater probability of paternity and females that had greater number of eggs in a nest subsequently invested relatively more in parental duties and (2) by pooling the data from the six groups and determining if there was a positive correlation between measures of presumed gamete contribution and amount of parental investment. The results from both types of analyses are variable and give no clear support for a positive relationship between presumed gamete contribution and parental investment even though a possible fitness cost is suggested. Factors which might influence investment are discussed.  相似文献   

16.
We assessed whether colonial breeding allows individuals to decrease their investment in predator defence, by presenting decoys of owls, foxes and crows to Montagu's harrier, Circus pygargus. Decoy detection increased with colony size, as did the number of individuals mobbing the decoy. The number of mobbers was greater for predators potentially risky for the adults (owl or fox) than for non-dangerous predators (crow). Recruits (breeding neighbours, fledglings and non-breeders) were present a lower percentage of the time, and attacked and alarm called less frequently than tested individuals. Nevertheless, the overall attack rate on the predator increased with the number of mobbers. When the size of the mobbing group increased, individuals were more likely to attack predators that represented a risk for adults, but did so less intensively and with a lower frequency of close dives. Thus, coloniality decreased the individual costs of defence in terms of risk taken, whilst enhancing defence efficacy. Birds alarm called more intensively when presented with dangerous predators than with the crow. The number of recruits significantly increased with increasing alarm rate of the tested individuals, even when taking colony size into account. Furthermore, the alarm rate of the tested birds also had a significant effect on the proportion of recruits that engaged in attacks against dangerous predators but not against the crow. The higher recruitment and attack rates for dangerous predators were thus apparently modulated through alarm calling. We discuss whether tested birds may manipulate recruits' behaviour to lessen their own risk.  相似文献   

17.
In many cooperatively breeding species, dominant females suppress reproduction in subordinates. Although it is commonly assumed that aggression from dominant females plays a role in reproductive suppression, little is known about the distribution of aggressive interactions. Here, we investigate the distribution of aggressive and submissive interactions among female meerkats (Suricata suricatta). In this species, dominant females produce more than 80% of the litters, but older subordinates occasionally breed. Dominant females commonly kill the pups of subordinates and usually evict older female subordinates from the group 1–3 weeks before the birth of the dominant female's litter. The aggression frequency of the dominant female toward subordinates and the submission frequency that each subordinate female showed to the dominant female increased as the age of the subordinate female increased and as the birth of the dominant female's pups approached. Moreover, as birth approached, both of these behaviors intensified more quickly between the dominant female and older subordinates than between the dominant female and younger subordinates. The aggression frequency of the dominant female toward each subordinate female predicted whether that subordinate female was evicted from the group; the submission frequency by each subordinate female predicted the timing of their eviction during the pregnancy period of the dominant female. These results support the idea that conflict between dominant and subordinate females increases with the age of subordinates and, since older subordinate females are most likely to reproduce, suggest that dominant females may less easily control reproductive attempts by older subordinate females.  相似文献   

18.
The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus, females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring sex ratio in primary compared with secondary nests. Received: 1 June 1999 / Received in revised form: 10 January 2000 / Accepted: 12 February 2000  相似文献   

19.
Indirect fitness benefits are believed to be an important force behind the evolution of cooperative breeding. However, helpers may associate with their relatives as a result of delayed dispersal, hence, kin associations might be a consequence of demographic viscosity rather than active choice. In addition, recent studies showed that helpers may have access to reproduction therefore direct benefits might also play an important role. Here, we investigate the possible roles of direct genetic benefits and kin associations on helping behavior in the sociable weaver Philetairus socius, a colonial and cooperatively breeding passerine. We used a microsatellite-based genotyping method to describe the genetic structure within nests and colonies. Within a colony, we found considerable genetic structure between males but not females. Sociable weaver colonies have several nests that are simultaneously active, giving individuals a choice of associating with a range of first-order kin to unrelated individuals. Helpers were significantly more related to the young in the helped nests than in other nests of the colony, suggesting an active choice for associating with kin. The helpers were generally offspring or first-order relatives of one (50%) or both (43%) breeders, although more infrequently, seemingly unrelated individuals also helped (7%). We found no supporting evidence of extrapair parentage and hence no direct genetic gains from helping in our population. This strong reproductive skew is contrary to theoretical models predicting conflicts over reproduction in stepfamilies. We discuss whether female decisions and/or other direct benefits of remaining in kin associations or helping might explain the high skew observed.  相似文献   

20.
Parental care may be costly to parents because it decreases resources allocated to self-maintenance and may thus reduce survival and future reproductive success. An inter-sexual conflict may exist in animals with obligatory bi-parental care, such as birds of prey, in which females incubate and brood, whereas males provision food for their families. We analysed 29 years of data (1981–2009) from a study population of Tengmalm’s owls Aegolius funereus in western Finland to examine the occurrence and timing of brood desertion and sequential polyandry, and recorded a total of 1,123 monogamous and 12 polyandrous females. These data were supplemented with the 29-year nationwide Finnish ringing data, which included 11,590 monogamous and 20 polyandrous females. The 12 polyandrous females started egg-laying in their two nests at intervals of 54–68 days (mean 60 days), thus deserting their first broods when the age of oldest young averaged 21 days. Thirty-two polyandrous females re-mated and raised a second brood at a median distance of 4.5 km (range 1–196 km). These females produced 79% more eggs, 93% more hatchlings and 73% more fledglings than did females that laid simultaneously but remained monogamous. Our results show that not only males, but also females of altricial species with bi-parental care can increase their fitness by deserting their first brood when it will be cared for by the males. Earlier studies have shown that male owls can increase their lifetime reproductive success by simultaneous polygyny, and we suggest that an inter-sexual “tug-of-war” over bi-parental care exists in Tengmalm’s owls.  相似文献   

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