Behaviour and breeding biology of the cooperatively breeding Grey-backed Fiscal Shrike Lanius excubitorius in Kenya

Grey-backed Fiscal Shrikes Lanius excubitorius were studied over a 2j year period near Lake Naivasha, Kenya. Grey-backs are cooperative breeders, with group sizes ranging from two to II. Only one pair breeds per group, with all other group members aiding in the rearing of young. The study population ranged from 64 to 79 individuals that occurred in from 13 to 16 groups. Non-breeding helpers made up to 66% of the population, with male helpers being more numerous overall than females. The annual survival rate was 65%, with no differences detected between the survival of males and females, or of breeders and helpers. Only male helpers were observed to acquire breeding status within the natal territory. Some female helpers acquired breeding positions in territories adjacent to their natal territories. Group territorial displays occurred throughout the year but were most pronounced prior to breeding during rainy periods. Reproductive success was very low, with only 14.5% of the recorded breeding attempts leading to fledged young. Large groups (four or more birds) had greater reproductive success than small groups, but many factors other than, or in addition to, group size may have influenced this pattern. The breeding male contributed the most food to the incubating female and to the nestlings. Male helpers and the breeding female contributed more to nestlings than did female helpers. Observations on the post-fledging period indicate that socialization and establishment of dominance may be of importance in group-living species living in a restricted ecological and social setting.     

Sex-bias and timing of natal dispersal in cooperatively breeding Puff-throated Bulbuls Alophoixus pallidus

While natal dispersal can have a significant impact on population dynamics, it is typically difficult to quantify. We investigated timing of natal dispersal of the cooperatively breeding Puff-throated Bulbul Alophoixus pallidus in a tropical evergreen forest by modelling the probability of staying in or dispersing from their natal territory whilst taking into account the effects of sex, group size, and the presence of helper(s). Birds did not disperse until the beginning of and during the breeding season following the hatching year. Dispersal was strongly female-biased both in frequency and distance: most females (95%) dispersed away from their natal territories, and of those relocated, traversed 2–7 territories. In contrast, 50% of males remained in the natal territory as helpers in their second year, while relocated dispersing males crossed 1–2 territories. Natal dispersal was not influenced by either group size or the presence of helpers. Males that fledged earlier in the breeding season exhibited higher rates of philopatry than the males that fledged later, but no correlation between fledging date and philopatry was observed in females. The probability of staying in the natal territory during the second year was 0.58 ± 0.14 SE and 0.05 ± 0.04 for males and females, respectively. These findings may add to our understanding of how natal dispersal can reflect social patterns and kin structure in cooperative breeding species from a little-studied tropical forest region.     

Genetic and environmental influences on natal dispersal distance in a resident bird species

We analyzed more than 1,600 dispersal events from two populations of a North American cooperatively breeding woodpecker species to determine what factors influence natal dispersal distance and whether distance traveled affects reproduction later in life. We found significant heritability of natal dispersal distance, in both males and females, indicating substantial additive genetic variance for this behavioral trait. Natal dispersal distance additionally was affected by social and ecological factors: individuals dispersing in their first year of life moved longer distances than those staying on their natal site as helpers for a prolonged time prior to dispersal, and increasing territory isolation led to longer dispersal distances. Successful dispersers incurred fitness costs, with lifetime fledgling production (in both sexes) and lifetime production of recruits to the breeding population (in females only) decreasing with increasing natal dispersal distance. We conclude that natal dispersal distance has a genetic basis but is modulated by environmental and social factors and that natal dispersal distance in this species is (currently) under selection.     

Strategic reduction of help before dispersal in a cooperative breeder

In cooperative breeders, sexually mature subordinates can either queue for chances to inherit the breeding position in their natal group, or disperse to reproduce independently. The choice of one or the other option may be flexible, as when individuals respond to attractive dispersal options, or they may reflect fixed life-history trajectories. Here, we show in a permanently marked, natural population of the cooperatively breeding cichlid fish Neolamprologus pulcher that subordinate helpers reduce investment in territory defence shortly before dispersing. Such reduction of effort is not shown by subordinates who stay and inherit the breeding position. This difference suggests that subordinates ready to leave reduce their investment in the natal territory strategically in favour of future life-history perspectives. It seems to be part of a conditional choice of the dispersal tactic, as this reduction in effort appears only shortly before dispersal, whereas philopatric and dispersing helpers do not differ in defence effort earlier in life. Hence, cooperative territory defence is state-dependent and plastic rather than a consistent part of a fixed life-history trajectory.     

Reverse sex-biased philopatry in a cooperative bird: genetic consequences and a social cause

The genetic structure of a group or population of organisms can profoundly influence the potential for inbreeding and, through this, can affect both dispersal strategies and mating systems. We used estimates of genetic relatedness as well as likelihood-based methods to reconstruct social group composition and examine sex biases in dispersal in a Costa Rican population of white-throated magpie-jays ( Calocitta formosa , Swainson 1827), one of the few birds suggested to have female-biased natal philopatry. We found that females within groups were more closely related than males, which is consistent with observational data indicating that males disperse upon maturity, whereas females tend to remain in their natal territories and act as helpers. In addition, males were generally unrelated to one another within groups, suggesting that males do not disperse with or towards relatives. Finally, within social groups, female helpers were less related to male than female breeders, suggesting greater male turnover within groups. This last result indicates that within the natal group, female offspring have more opportunities than males to mate with nonrelatives, which might help to explain the unusual pattern of female-biased philopatry and male-biased dispersal in this system. We suggest that the novel approach adopted here is likely to be particularly useful for short-term studies or those conducted on rare or difficult-to-observe species, as it allows one to establish general patterns of philopatry and genetic structure without the need for long-term monitoring of identifiable individuals.     

Philopatry and natal dispersal in a sedentary population of western marsh harrier

Dispersal is a key life-history trait because it influences population dynamics and population genetic structure. From a behavioural perspective, the study of natal dispersal requires some understanding of the mechanisms that affect individual movements, because movements of an animal form a path that is continuous throughout its life. Our aim was to investigate juvenile dispersal strategies in the western marsh harrier Circus aeruginosus , between fledging and first breeding attempt (from 1 to 4 years later, depending on the sex and individual). Using radio tracking, we monitored dispersing juvenile harriers and their home-range size variations within a sedentary population in central western France from 2001 to 2007. Juvenile dispersal strategy was mainly characterized by a very high natal philopatry (i.e. birds that remained within the study area) and short-distance dispersal. All but one bird (out of 39) remained within the study area between their first winter and their first spring, and 96.0% during their first spring. The distance moved at 2 years of age was significantly larger for males than for females (3800± sd 3593 m and 935± sd 481 m for seven males and six females, respectively), in contrast to most bird species studied so far. Home-range size was not sex biased and significantly decreased with age. In addition, non-breeding birds had larger home ranges (1603± sd 2128 ha) than breeders (349± sd 185 ha). Using data obtained from other populations, juvenile marsh harrier dispersal strategies appeared to be determined by migratory status (migratory birds dispersing farther) and demographic parameters (juvenile survival or fecundity).     

Social organization,demography and genetic mating system of a Tibetan cooperative breeder

Knowledge of cooperative breeding in birds from longitudinal studies is available only for a small proportion of species. This paper reports data from a 12‐year study on the Tibetan Ground Tit Pseudopodoces humilis. On average, 27.2% (range: 13.0–36.1%) of monogamous pairs in each year contained one (85.4%) or more (14.6%) male helpers, 83.7% of which were yearlings staying on natal territories. Most helpers (89.6%) helped once and then bred independently. Adults had male‐biased sex ratios, low annual survival rates (averaging 0.50) and shorter longevities (averaging 1.8 years) compared with low‐altitude avian cooperative breeders, suggesting that mate shortage promotes helping behaviour in this species. Incest occurred rarely (2.1% of pairs), probably because kin recognition occurs through year‐around living in family groups. There was a low level (3.1% of broods) of extra‐pair parentage, which could facilitate the maintenance of cooperative breeding.     

Turnover and dispersal in a Peregrine Falco peregrinus population

In south Scotland, most Peregrines returned to the same territories to breed in successive years, though a few females changed territory from one year to the next.
Annual mortality among breeding birds was at most 9% among females (or 11% in both sexes combined). There may have been considerable annual variation, however, and excluding one exceptional year out of five reduced the estimate for females to 7%. These estimates are maxima, but are still considerably lower than those obtained from ring recoveries of dead birds reported by members of the public.
Among trapped birds, four males first bred at age two years, one at three and another at four or five; two females first bred at one year, 13 at two years old and one at three. Five other females which were seen to be in first-year plumage but were not trapped, also laid eggs, and 12 other such paired females held territory but did not lay. Only one paired male held territory in first-year plumage.
In their movements between natal and breeding territories, some females moved further than males, with median distances of 83 and 58 km respectively. In addition, of birds trapped breeding in the study area, a greater proportion of the males than of the females had been born locally, despite an equal sex ratio among fledglings; this was also consistent with a greater dispersal of females. In general, Peregrines made much longer movements in their first year of life than subsequently. Movements were in any direction.     

Dispersal, interpatch movements, and survival in a shrubland breeding bird community

ABSTRACT Dispersal events can affect the distribution, abundance, population structure, and gene flow of animal populations, but little is known about long‐distance movements due to the difficulty of tracking individuals across space. We documented the natal and breeding dispersal of shrubland birds among 13 study sites in a 1000 km² area in southeastern Ohio. In addition, we radio‐marked and tracked 37 adult males of one shrubland specialist, the Yellow‐breasted Chat (Icteria virens). We banded 1925 juveniles and 2112 adults of nine shrubland species from 2002 to 2005. Of these, 33 (1.7%) juveniles were encountered in subsequent years (2003–2006) as adults (natal dispersal) and 442 (20.9%) birds initially banded as breeding adults were re‐encountered in subsequent years (breeding dispersal). Apparent survival of juvenile shrubland birds on their natal patches was 0.024 (95% CI 0.016–0.036). After accounting for the probability of detection, we found that 21% of birds banded as juveniles and recaptured as adults returned to their natal patches, whereas 78% of adult birds showed fidelity to the patch where they were originally captured. Moreover, natal dispersers tended to move farther than breeding dispersers (corrected natal median = 1.7 km ± 0.37; corrected breeding median = 0.23 km ± 0.10). We used our estimates of natal dispersal and annual apparent survival to estimate true survival at 0.11 (95% CI 0.07–0.18) for juveniles in their first year. However, this estimate was only applicable for birds dispersing within 7 km of their natal patches. Interpatch movements of radio‐marked Yellow‐breasted Chats were not uncommon, with 13 of 37 males located in more than one habitat patch. Overall, we observed low natal philopatry, but high adult site fidelity for shrubland birds in our study area. Considering the frequency of short‐distance movements observed (median = 531 m, range = 88–1045 m), clustering of patches within 1 km might facilitate use of shrubland habitat.     

Social composition of destination territories and matrix habitat affect red-cockaded woodpecker dispersal

We studied the influence of matrix habitats and destination territory social composition on dispersal choices made by red-cockaded woodpeckers (Picoides borealis). We compared matrix habitats and social conditions for 165 dispersals documented between 1995 and 2005 with similarly distanced destinations that went unselected. We modeled data with discrete choice analysis methods, and ranked models using a model selection approach. Model-averaged parameters indicated that juvenile female, and juvenile and helper male red-cockaded woodpeckers dispersed across matrix forests with characteristics similar to those used for breeding. Models differed for sex and social classes, but results generally indicated that birds chose not to transit forests with greater densities of hardwood trees and young pines, and that dispersal was more likely to occur across forests with more large diameter pine trees. Dispersers of both sexes also chose destinations without non-breeding helpers that might present aggressive social challenges to dispersers, particularly males. Juvenile females and helper males also preferred to disperse to territories that were currently occupied by breeding woodpeckers. Previous studies documented the influence on dispersal of travel distance, natal area social interactions and resources, and resources at dispersal destinations. Our results extend factors that affect dispersal movement to include matrix habitats traversed by dispersers and the social composition of destination territories. As such, results have key implications for promoting population connectivity and conservation management of endangered red-cockaded woodpeckers, as well as other resident territorial birds. © 2011 The Wildlife Society.     

Paying to stay or paying to breed? Field evidence for direct benefits of helping behavior in a cooperatively breeding fish

Several hypotheses aim to explain the evolution of helping behavior,but conclusive experimental support for evaluating the relativeimportance of individual hypotheses is still lacking. We reporton two field experiments conducted to test the "territory inheritance"and "pay-to-stay" hypotheses in the cooperatively breeding cichlidfish Neolamprologus pulcher The territory inheritance hypothesiswas tested by removing one parent, which created breeding vacancies.In 39% of cases, same-sex helpers took over the breeding spot;in 44% of cases helpers continued helping new breeders, and17% were evicted by new breeders. Helpers that were closelysize matched to the removed breeder had a better chance of gainingthe breeding spot Male helpers tended to continue helping aftera takeover more often than females.The pay-to-stay hypothesiswas tested-by temporarily removing helpers. Whereas breedersdid not respond aggressively to removals, other group membersattacked the removed helpers on their return, and 29% were eventuallyevicted. The returning helpers assisted more by increasing theirrate of territory maintenance and defense and visiting the broodchamber more frequently Size and sex of removed helpers didnot explain the observed aggressive reactions of other groupmembers. Thus, our results support both hypotheses: N. pulcherneeds to pay with help to be allowed to remain protected inthe family group, and there they may inherit the natal territory.N. pulcher helpers gain direct benefits from helping behavior.     

Life histories and the evolution of cooperative breeding in mammals

While the evolution of cooperative breeding systems (where non-breeding helpers participate in rearing young produced by dominant females) has been restricted to lineages with socially monogamous mating systems where coefficients of relatedness between group members are usually high, not all monogamous lineages have produced species with cooperative breeding systems, suggesting that other factors constrain the evolution of cooperative breeding. Previous studies have suggested that life-history parameters, including longevity, may constrain the evolution of cooperative breeding. Here, we show that transitions to cooperative breeding across the mammalian phylogeny have been restricted to lineages where females produce multiple offspring per birth. We find no support for effects of longevity or of other life-history parameters. We suggest that the evolution of cooperative breeding has been restricted to monogamous lineages where helpers have the potential to increase the reproductive output of breeders.     

Group structure,within-group conflict and reproductive tactics in cooperatively breeding Galápagos mockingbirds,Nesomimus parvulus

Reproductive conflict within groups can be an important feature of cooperative breeding systems, especially when more than one individual of a sex breeds within a social group. Relationships between group structure, dominance, within-group conflict and reproductive tactics of cooperatively breeding Galápagos mockingbirds were examined on Isla Genovesa. Territorial groups of 2–24 adults included up to three breeding females, with 42% of the groups containing more than one (plural groups); females in most plural groups nested separately. Territory size increased with group size, but the area available per pair in plural groups was smaller than in singular groups (groups with only one breeding pair). Most pairings were monogamous, and males usually outnumbered females; high-ranking males obtained mates more frequently than subordinate males. In 3 relatively dry years, but not in a wet El Niño year, subordinate pairs in plural groups fledged fewer young than dominant pairs or pairs breeding in singular groups. Interference by dominant breeders, often leading to abandonment of nests by subordinate pairs, appears to account for these differences: through nest disruption in drier years, dominant individuals may reduce the cost of sharing their territories and increase the chances of recruiting helpers. Dominant males in plural groups may also father young through extra-pair copulations with subordinate females. Despite costs imposed by within-group conflict, subordinate breeders have higher long-term reproductive success than birds that defer breeding. Plural group structure is maintained because unpredictable climatic variation favours opportunistic breeding by subordinates.     

Reproductive biology of captive male cottontop tamarin monkeys as a function of social environment

The cottontop tamarin, Saguinus oedipus oedipus, is a cooperatively breeding monkey in which mature male and female offspring serve as helpers to assist in rearing younger siblings. Generally, only one female per social group reproduces; breeding restriction is mediated in postpubertal female offspring through low and acyclic levels of reproductive hormones. We investigated (1) reproductive activity of postpubertal male offspring, and (2) whether aggression towards male offspring and a cortisol-mediated stress response might restrict breeding of male offspring in the natal group. We examined sexual behaviour, olfactory communication and urinary hormone levels (testosterone, dihydrotestosterone, luteinizing hormone, cortisol) of the subject males while we manipulated their social environment from housing in natal groups to pairing with a novel female, and after the production of their own offspring. Mounting and erection rates of the male subjects were as high in the natal group as when paired with a novel female. However, most mounts in the natal group were directed towards other males, and complete copulation sequences did not occur with natal-group females. Social environment had no significant effect on olfactory investigation of breeding females. Although hormone levels increased significantly after the subjects were removed from the natal group, the elevation was transient; the hormone levels of subjects in their natal groups did not differ from the levels shown by the same males when successfully producing their own offspring. Male offspring received more contact aggression in the natal group than when paired with the novel female. However, most of the aggression was received from siblings rather than the breeding pair, and levels of cortisol did not correspond with levels of aggression. Thus, at both a behavioural and endocrine level, mature male offspring in captive natal groups were potentially fertile, but sexual activity with natal-group females appeared to be behaviourally restricted and directed instead towards group males. In wild cottontop tamarin groups, this reproductive potential may allow male helpers flexibility to respond to breeding opportunities. Copyright 2001 The Association for the Study of Animal Behaviour.     

The Social System of a Communal Breeder,the Bay-winged Cowbird Molothrus badius

Molothrus badius (bay-winged cowbird), an icterine blackbird with cooperative breeding, shares behavioural and ecological characteristics with other communal nesters: it is sedentary, has a high annual survival rate (76.2%) and a strong nest-site tenacity (mean breeding dispersal of 41.9 and 89.4 m for males and females). Behavioural data, including collective agonistic displays, suggest group territoriality. Before egg hatching most breeders occurred as single pairs showing territorial behaviour (82% of nests), and nesting was usually solitary (distances to nearest nests of 25–103 m). Most breeders were apparently monogamous, with a 2.5% incidence of extrapair copulations in the territory during clutch formation. During the nestling stage one to four helpers occurred at 95% of M. badius nests. Most helpers were 1–2 years old, but older breeding adults (mostly males) that failed to rear their own offspring helped at the end of the season. The number of helpers increased (up to 4) with nestling age. Helpers were also recruited during the postfledging period, and group size reached up to 10 adults at this stage. Helpers mobbed predators and brood parasites, and provided 35% of the nestling food. Provisioning rate was positively and significantly correlated with number of helpers, although age of nestlings was the best predictor of overall food delivery rate. The helping system was almost obligate and productivity comparisons between nests with/without helpers are not possible. Data suggest that helpers increased the breeding success per nest. The correlation between the provisioning rates of parents and helpers was negative but non-significant. In 18% of nests 3 to 4 individuals were present before the nestling period, including cases of apparently polyandrous trios and one case of joint nesting by two pairs. Within Brown 's (1987) categories of social organization M. badius is mainly group territorial with plural nesting. Habitat requirements of M. badius are wide and nest sites do not appear to limit breeding. Kinship plays a role in the social system, as 9 of 12 helpers marked as nestlings helped their parents.     

Testis size depends on social status and the presence of male helpers in the cooperatively breeding cichlid Julidochromis ornatus

Cooperatively breeding animals, in which helpers may participatein reproduction with dominant breeders, are ideal species forexamining intraspecific variation in testis size because theyoften exhibit both monogamous breeding (low risk of sperm competition)and polyandrous breeding (high risk) within a population. However,little is known about testis investment as a result of spermcompetition in these animals. The substrate-brooding cichlidfish Julidochromis ornatus has a cooperatively breeding system,in which some males mate monogamously and other males reproduceas dominant breeders or helpers within cooperatively breedinggroups, in which male helpers frequently sire young. We examinedthe relationship between testis investment and male social statusin relation to the risk of sperm competition. As predicted fromsperm competition models, in groups with male helpers, boththe male breeders and the male helpers invested more in testesmass, compared to breeding males without male helpers. We alsofound a positive relationship between the testes mass of malebreeders and their male helpers, suggesting that males increasetheir investment in reproductive capability under the risk ofsperm competition. Sperm competition models also predict thatlarger testes are associated with increased siring success.Our paternity analysis supported this prediction; we found apositive relationship between testis investment by male helpersand the number of offspring they sired.     

Philopatry and colony fidelity of Shags Phalacrocorax aristotelis on the east coast of Britain

Shag Phalacrocorax aristotelis colonies from the Firth of Forth south to the Fame Islands (SE Scotland and NE England) were surveyed in 1982 and 1983 for nesting Shags ringed as chicks or adults in the previous 20 years. On average, 5% of 863 Shags ringed as chicks were breeding away from their natal colony, and only 1% of 401 marked adults had left their breeding colony. The proportion p of chicks that settled at or beyond distance D from the natal colony followed the relationship p = 0.263D-^0.771, implying that more Shags moved 10 km or beyond to breed than expected from diffusion models or a constant-rate dispersal model; adjusted for birds that settled outside the study area, the relationship was p = 0.314D^-0771. There was no effect of colony size on emigration rate, but females showed a greater tendency to settle away from the natal colony than did males. At the natal colony, more males (69%) than females (47%) nested within 300 m of their birthplace. Two mechanisms appear to determine where a Shag settles to breed: a navigational one governing the return to the natal colony, plus the competitive process of nest-site establishment.     

Natal dispersal patterns are not associated with inbreeding avoidance in the Seychelles warbler

In this study, we test whether patterns of territory inheritance, social mate choice and female-biased natal dispersal act as inbreeding avoidance mechanisms in the cooperatively breeding Seychelles warbler. Our results show that Seychelles warblers do not reduce the likelihood of inbreeding by avoiding related individuals as mates. The occurrence of natural and experimentally induced territory inheritance did not depend on whether the remaining breeder was a parent of the potential inheritor or an unrelated breeder. Furthermore, dispersing individuals were no less related to their eventual mates than expected given the pool of candidates they could mate with. The female bias in natal dispersal distance observed in the Seychelles warbler does not facilitate inbreeding avoidance because, contrary to our prediction, there was no sex difference in the clustering of related opposite sex breeders around the natal territories of dispersers. As a result, the chance of females mating with relatives was not reduced by their greater dispersal distance compared with that of males.     

Female extrapair mate choice in a cooperative breeder: trading sex for help and increasing offspring heterozygosity

Sexual conflict between males and females over mating is common. Females that copulate with extrapair mates outside the pair-bond may gain (i) direct benefits such as resources or increased paternal care, (ii) indirect genetic benefits for their offspring, or (iii) insurance against infertility in their own social mate. Few studies have been able to demonstrate the different contexts in which females receive varying types of benefits from extrapair mates. Here, I examined sexual conflict, female extrapair mate choice, and patterns of extrapair paternity in the cooperatively breeding superb starling Lamprotornis superbus using microsatellite markers. Although extrapair paternity was lower than many other avian cooperative breeders (14% of offspring and 25% of nests), females exhibited two distinct mating patterns: half of the extrapair fertilizations were with males from inside the group, whereas half were with males from outside the group. Females with few potential helpers copulated with extrapair mates from within their group and thereby gained direct benefits in the form of additional helpers at the nest, whereas females paired to mates that were relatively less heterozygous than themselves copulated with extrapair mates from outside the group and thereby gained indirect genetic benefits in the form of increased offspring heterozygosity. Females did not appear to gain fertility insurance from copulating with extrapair mates. This is the first study to show that individuals from the same population mate with extrapair males and gain both direct and indirect benefits, but that they do so in different contexts.