Dispersion of displaying male sage grouse

Summary The degree to which male sage grouse select lek sites and females select nesting sites to maximize proximity to the other sex was examined by contrasting male dispersions with the dispersions and movements of females in the months preceeding incubation. Wintering females exhibit highly overlapping ranges due to shared use of central refuging areas. In late winter and early spring, females move an average 9 km from wintering areas to select nest sites and males begin occupying leks. Pooled evidence suggests that females select nest sites independently of male dispersion whereas males adjust lek occupation so as to maximize proximity to females. Relevant observations include females visiting nest sites before leks, moving further to select a nest site than to select a lek, and increasing their distance to leks as a result of selecting nest sites. In addition, males avoid leks until females have moved to within 5 km of the arenas, abandon early season leks as local female densities drop, and exhibit dispersions in which mean ratios of females/male are similar across leks. Contrasts between predicted and observed dispersions of males showed that hotspot settlement models are adequate to explain male dispersions on very coarse scales (2 km or greater); on finer scales, habitat preferences of males and tendencies for males to cluster tightly must be invoked in addition to hotspots to explain specific lek sitings.     

Home range shifts by breeding female Townsend's voles (Microtus townsendii ): a test of the territory bequeathal hypothesis

Numerous accounts of partial or complete breeding dispersal by adult females reported in the literature on microtines have been interpreted as maternal bequeathal. However, for most species, no causal relationship between a female's movements between successive litters and the settlement of her offspring in the natal range has been demonstrated. I tested predictions from the bequeathal hypothesis using data from an intensive study of Townsend's voles where genetical relationship had been determined by marking most pups in the maternal nest before weaning. After correcting statistically for temporal changes in the distance moved between successive litters I rejected the following predictions: (1) that females with one or several daughters of reproductive age should be more likely to disperse or disperse farther between successive births than females without such daughters; (2) that mothers should be more likely to bequeath their range to their daughters in spring when the latter would gain most from having ready access to a breeding range; (3) that daughters benefit from their mother abandoning the natal range through an increase in their probability of recruitment; and (4) that daughters actually use the home range vacated by their mother. I critically reassess the empirical studies quoted as evidence that breeding dispersal is a form of parental investment in microtines and other mammals. Most empirical studies cited in support of the bequeathal hypothesis often only contain anecdotal reports of movements by breeding females or do not mention it as one of its possible adaptive functions. Some studies contain evidence only consistent with the bequeathal hypothesis whereas others are incompatible with this explanation. Documented evidence of bequeathal comes exclusively from species which rely on a semi-permanent resource such as a midden, mound or burrow. I conclude that there is no indication from Townsend's voles or any other microtines that females abandon their breeding range to their female offspring as a form of parental investment. Received: 27 February 1996 / Accepted after revision: 1 March 1997     

Nest-Site Selection in Individual Loggerhead Turtles and Consequences for Doomed-Egg Relocation

Abstract:  Relocation of eggs is a common strategy for conservation of declining reptilian populations around the world. If individuals exhibit consistency in their nest-site selection and if nest-site selection is a heritable trait, relocating eggs deposited in vulnerable locations may impose artificial selection that would maintain traits favoring unsuccessful nest-site selection. Conversely, if most individuals scatter their nesting effort and individuals that consistently select unsuccessful nest sites are uncommon, then artificial selection would be less of a concern. During the 2005 nesting season of loggerhead turtles ( Caretta caretta ) at Mon Repos beach, Queensland, Australia, we measured the perpendicular distance from the original nest site to a stationary dune baseline for in situ (unrelocated) and relocated clutches of eggs. We observed the fate of in situ clutches and predicted what would have been the fate of relocated clutches if they had not been moved by mapping tidal inundation and storm erosion lines. In 2005 turtles deposited an average of 3.84 nests and did not consistently select nest sites at particular distances from the stationary dune baseline. Selection of unsuccessful nest sites was distributed across the nesting population; 80.3% of the turtles selected at least one unsuccessful nest site and when previous breeding seasons were included, 97% selected at least one unsuccessful nest site. Females with nesting experience selected more successful nest sites than females with little or no experience. Relocating eggs vulnerable to tidal inundation and erosion saves the progeny from a large percentage of the population and the progeny from individuals who may in subsequent years nest successfully. Our results suggest that doomed-egg relocation does not substantially distort the gene pool in the eastern Australian loggerhead stock and should not be abandoned as a strategy for the conservation of marine turtle populations.     

Social organization of woodchucks (Marmota monax)

Summary The social organization of woodchucks (Marmota monax) in southeast Ohio was studied at two sites, at one for two 2 years (1979–1980) and the other for 3 years (1981–1983). Spatial organization was determined by trapping and radio tracking. The home ranges of adult females did not overlap in the early spring but during late spring and summer there was some overlap (<10%) as females expanded their home ranges. Adult females tended to occupy the same home range in consecutive years. Some adult males occupied well-defined home ranges that did not overlap the home ranges of other males but did overlap extensively the home range of one to three adult females. These males tended to occupy the same home range in consecutive years. Infants used the same home range of their dam until about 2–3 months of age when most males and females apparently dispersed. About 35% of the juvenile females did not disperse until their second spring, just before their mother's new litter first emerged from their burrow. The average social group consisted of an adult male with two female kin groups comprising an adult female, an offspring (usually female) of the previous year, and the young of the year. Interactions within the kin group and with the adult male were relatively frequent and generally amicable. Interactions between kin groups both within and between different social groups were relatively rare and agonistic. The social organization of woodchucks in Ohio differs from that described in previous studies of woodchucks elsewhere and from that predicted by current models proposed by others on the evolution of social organization of marmots.     

Philopatry and nesting phenology of pine snakes Pituophis melanoleucus in the New Jersey Pine Barrens

Summary We studied nesting behavior of pine snakes Pituophis melanoleucus from 1977 to 1989. Female pine snakes in the New Jersey Pine Barrens excavate tunnels and a nest chamber for egg deposition. Over 70% of all nests had old, hatched shells remaining in the nests from previous years. The presence of hatched shells and the incidence of recaptured females in the same nest indicates nest site tenacity for some females. From 1977 to 1988 we branded 98 females and 45 were recaptured in the same general nesting area. All 45 recaptured females were recaptured one to four times at the same nest site; two of these snakes were captured in three years at the same site and in one year at a different site. We conclude that females show a high degree of nest site philopatry. We suggest that high nest site philopatry is selected for because it promotes location of sites that are safe from predators (buried, hatched shells) and contain suitable temperature conditions. Offprint requests to: J. Burger     

Nest-site selection of passerines: effects of geographic scale and public and personal information

Nest-site selection is an important determinant of individual fitness in birds. Understanding what information individuals use to choose nest sites is therefore important for understanding the evolution of nest-site selection, the dynamics of populations, and the conservation of species. We used five years of mark-recapture data for Mountain Bluebirds (Sialia currucoides) to examine how dispersal probability and nest-site selection vary with potential cues of nest-site quality. Dispersal distance between breeding seasons and nest-site selection were modeled as a function of personal reproductive success, conspecific density, conspecific reproductive success, and habitat type. Between years, the dispersal probability was related to personal reproductive success, not conspecific information, and individuals fledging fewer young dispersed longer distances. For dispersing individuals, the probability that a nest site was selected in year i was negatively related to distance from the nest site selected in year i - 1 for all age and sex classes, and positively related to conspecific density and reproductive success in year i - 1 for both second-year (SY) and after-hatch-year (AHY) females. However, nest-site selection in year i was more strongly related to conspecific density in year i- 1 for hatch-year (HY) females and was much more strongly related to the reproductive success of conspecifics in year i - 1 for AHY females. Nest-site selection of HY and AHY males was not consistently related to the metrics of conspecific information, but we suspect that relationships were obscured by competitive interactions. We found no evidence indicating that individuals respond differently to conspecific information at longer distances, suggesting that individuals limit dispersal to areas where they have prior knowledge. We predict that these patterns of nest-site selection will allow birds to loosely track nest-site quality and maintain an ideal free distribution, where average fitness is equal in all habitat types.     

Sex allocation in a monomorphic seabird with a single-egg clutch: test of the environment, mate quality, and female condition hypotheses

Sex allocation theory posits that mothers should preferentially invest in sons when environmental conditions are favorable for breeding, their mates are of high quality, or they are in good body condition. We tested these three hypotheses in rhinoceros auklets (Cerorhinca monocerata), monomorphic seabirds that lay a single-egg clutch, in 2 years that differed in environmental conditions for breeding. Results supported the environment and mate quality hypotheses, but these effects were interactive: offspring sex was independent of paternal traits in the poor year for breeding, while females mated to larger and more ornamented males reared more sons in the better year. Conversely, offspring sex was unrelated to female condition, as indexed by hatching date. We propose that good rearing conditions enable females to rear sons possessing the desirable phenotypic attributes of their mates. Results also supported two critical assumptions of sex allocation theory: (1) dimorphism in offspring condition at independence: daughters fledged with higher baseline levels of corticosterone than sons and (2) differential costs of rearing sons versus daughters: mothers rearing sons when environmental conditions were poor completed parental care in poorer condition than mothers rearing daughters in the same year and mothers rearing either sex when conditions were better. These novel results may help to explain the disparate results of previous studies of avian sex allocation.     

Philopatry,reproductive success of females,and maternal investment in the red-necked wallaby

Summary Female red-necked wallabies settle within their mothers' home ranges, apparently for life, while males disperse at about two years of age. However, sons spend much more time with their mothers before dispersing than do daughters of similar ages. Females who associate regularly with their subadult offspring are less likely to reproduce successfully at their next breeding attempt than are females who spend little time with their subadults, and sons therefore impose greater short-term reproductive costs on their mothers than do daughters. Females who are generally gregarious also suffer reduced reproductive success, even though reproductive success is independent of local density. It is suggested that the reproductive costs to females of associating with their subadult offspring, and other relatives, are incurred through tolerance of ecological competition from those kin, and therefore reflect a form of prolonged maternal investment, which is initially heaviest in sons but is sustained for longer periods in daughters. Females produce equal numbers of male and female offspring, and spend equal amounts of time suckling them in infancy.     

Testing the navigational abilities of ocean migrants: displacement experiments on green sea turtles (Chelonia mydas)

Like many animals migrating through the oceans, sea turtles face difficult navigational tasks when they have to reach distant, specific sites. The paradigmatic case of Brazilian green turtles (Chelonia mydas), which nest on the tiny Ascension Island in the middle of the Atlantic Ocean, has often been the subject of hypotheses concerning their navigational mechanisms. To investigate their nature, we displaced 18 females from Ascension and tracked them by satellite after release from eight different points in the ocean, 60-450 km away from the island. Four turtles moved to Brazil soon after the release, 4 moved in various directions before heading to Brazil, and 10 reached the island. All the successful trips, bar 1, were winding but ended with a final straight segment of variable length, as if the turtles were searching for a sensory contact with the island which they obtained at various distances. The approach to Ascension mostly occurred from the direction opposite to the trade wind, suggesting a navigational role of wind-borne information originating from the island.     

Female defence polygyny in the bumblebee wolf,Philanthus bicinctus (Hymenoptera: Sphecidae)

Summary In the digger wasp Philanthus bicinctus the first adult males emerge about a week before the first females. The sex ratio of emerging wasps is near unity. Females appear to mate once and do so when they first start to nest, not when they first emerge.Males defend mating territories in a large area of female ground nests. Territoriality begins when females first start to nest and throughout the season coincides with the digging activities of females initiating rests. During the day territoriality occurs only when females are engaged in digging activities.Males compete for certain territory sites within the resting area; the most frequently occupied male territories are in areas where the density of nests is highest. About half of the males are excluded from nesting area territories. Some of these males defend areas among the flowers of snakeweed where females occasionally forage; this appears to be a loser tactic of males unable to obtain nesting area territories.Although there was no significant difference in the sizes of males on nesting area and snakeweed territories, within the nesting area larger males usually occupy territories with the higher nest densities.     

Sex-specific differences in site fidelity and the cost of dispersal in yellow-headed blackbirds

Male migratory birds tend to be more faithful than females to previous breeding sites, suggesting sex differences in costs or benefits of dispersal. In Illinois, greater site fidelity by male yellow-headed blackbirds (Xanthocephalus xanthocephalus) was associated with reduced reproductive success the following year for dispersers relative to non-dispersers. Dispersing females suffered no reduction in reproductive success the following year. Males that attracted few social mates, and thus had low reproductive success, were more likely to disperse, whereas females dispersed in response to low-patch reproductive success, regardless of their individual performance. Males that dispersed appeared to be successful acquiring territories because none was observed as a floater. The rate of dispersal by males in this low-density population was greater than in more dense populations where dispersing males may be less successful at acquiring territories. Despite success at obtaining territories, males that dispersed acquired territories on the periphery of wetlands where fewer females nested, resulting in lower reproductive success. In the second year after dispersing, however, males moved onto more central territories where they acquired larger harems. Thus, dispersal by males may be a long-term strategy requiring at least 2 years for benefits to be realized. Long-term success was enhanced because dispersing males moved to wetlands on which reproductive success was higher than on the wetlands they left. In addition to demonstrating that both individual and patch reproductive success affect dispersal decisions, these data indicate that when evaluating costs and benefits of dispersal, researchers should use a time frame beyond 1 year.     

The influence of maternal rank and infant sex on maternal investment trends in rhesus macaques: birth sex ratios,inter-birth intervals and suckling patterns

Summary In the new colony of rhesus macaques at Madingley, no overall difference was found in the length of the inter-birth intervals following the birth of male and female infants. The lack of overall differences in the reproductive costs of raising sons and daughters, was associated with an absence of differences in suckling patterns between male and female infants. It is argued that similar pre-weaning investment in sons and daughters may be related to the presence of similar growth rates for male and female infants during the first year of life. Most high ranking mothers reproduced in consecutive years, while low ranking mothers were more likely to experience two year long inter-birth intervals. Further analyses revealed that this difference was mainly due to the fact that low ranking mothers always failed to reproduce the year after raising a daughter. Thus, no difference was found in the length of inter-birth intervals between high ranking mothers with infants of either sex and low ranking mothers with sons. The daughters of low ranking females suckled more frequently and making more nipple contacts per bout, and such high nipple stimulation was responsible for the reproductive inhibition experienced by their mothers. It is suggested that the high degrees of nipple stimulation may have been a consequence of the high levels of aggression that low ranking females with daughters have been shown to receive, since their mothers could have allowed frequent ventro-ventral contact in order to protect them. Given that low ranking mothers find daughters reproductively costly to raise, it is possible that such high reproductive costs have played a significant role in the evolution of sex ratio biases at birth. As in other primate populations, in this colony low ranking females produced a greater proportion of sons than daughters, and high ranking mothers showed the opposite trend.     

Movements of dispersing flying squirrels in relation to siblings and parents

Knowledge of kin interactions can be informative in explaining the processes underlying dispersal. By dispersing, relatives can avoid kin competition for resources or mates and prevent inbreeding. We investigated sibling movements in relation to each other and parents before and after dispersal in radio-collared juvenile flying squirrels (Pteromys volans L.). Before dispersal, most siblings moved in different areas and were not in contact while exploring the surroundings of natal area. After dispersal, all siblings settled far away from each other, as they dispersed different distances and to random directions compared to each other. No clear effect of litter size or presence of same-sex siblings was observed on dispersal. Time spent in the same nest with the mother did not differ between dispersing sons and daughters. Mother did not force dispersers to leave the natal nest; instead, the mother often moved away from the nest before offspring. Father and offspring were not observed to be in contact before dispersal. Dispersal direction was unaffected by the location of fathers’ home range. We conclude that after dispersal interaction between relatives is limited in flying squirrels, but we did not find any indication that interaction between relatives before dispersal is determining dispersal decision. Siblings’ settlement far away from each other was already indicated by the movement within the natal home range, but, interestingly, the latter could not be used to predict dispersal patterns of sexes.     

Relationship between body size, provisioning rate, longevity and reproductive success in females of the solitary bee Osmia cornuta

Body size has often been related to reproductive success in bees and wasps. The objective of this 3-year study was to analyze the relationship between nesting female body size, provisioning rate and longevity and their effect on several traits related to parental investment and reproductive success in the solitary bee Osmia cornuta. Body size was not correlated to longevity, and it was only correlated to provisioning rate in the third year (with poor weather conditions during nesting). Variation in fecundity, offspring size and offspring mortality was not well explained by nesting female body size in any of the 3 years. However, in the third year, small females biased their investment toward males, the sex requiring smaller pollen–nectar provisions. Large females were more successful usurpers of other females' nests, but fecundity of usurpers was no higher than fecundity of nonusurpers. Large females were more likely to establish at the release site, probably in relation to size-dependent vigor at emergence. A review of the literature on parental investment in solitary aculeate Hymenoptera showed a stronger relationship between body size and reproductive success in wasps than in bees. In O. cornuta, fecundity was strongly related to longevity and provisioning rate in all 3 years. Offspring size was associated with provisioning rate in 1 year, when females with higher provisioning rates tended to produce larger sons and daughters. Both longevity and provisioning rate appeared to be strongly conditioned by stochastic events.     

Communal nesting in an ‘asocial’ mammal: social thermoregulation among spatially dispersed kin

Communal nesting can help defray the high cost of endothermic heat production in cold environments, but such social behavior is generally thought to be incompatible with the persistent defense of exclusive territories in typically ‘asocial’ animals. We examined the propensity for communal nesting in female red squirrels (Tamiasciurus hudsonicus), which maintain individual year-round territories, through intensive monitoring of litters over 22 years and by radio-tracking females during 3 years in late winter/early spring. Communal nesting was exceptionally rare during lactation: of 1,381 litters tracked to emergence, we observed a single instance in which two closely related (r?=?0.5) females pooled their litters into a single nest. In contrast, nest sharing between 2–3 females was relatively common in the late winter/early spring, prior to mating; at least 12 of 63 females (19 %) engaged in communal nesting during a year of systematic tracking of radio-collared females from late February to April. Communal nesting occurred more frequently when temperatures were colder, suggesting that such aggregations might function to reduce thermoregulatory costs. These social associations were typically, though not exclusively, between closely related individuals (r?≥?0.25 for seven of eight cases; mother–daughter dyads: four of eight), suggesting this cooperative behavior might evolve through kin selection and/or may reflect extended parental care. Our results demonstrate that female red squirrels engage in communal nesting, typically with closely related kin, despite a dispersed population structure that stems from the persistent defense of individual territories.     

Parental investment and its ecological consequences in the solitary wasp Sceliphron assimile (Dahlbom) (Sphecidae)

Summary The sphecid wasp Sceliphron assimile Dahlbom builds mud cells whose volumes are positively correlated to maternal length, the relationship being highly significant for daughters (Fig. 1). However, small females build cells longer and wider in relation to their own body length than large females do (Fig. 3). Cell volume closely regulates the total weight of prey stocked per cell (Figs. 4, 10). Maternal length is directly related to prey size and inversely related to the number of prey stocked (Fig. 5). Female length, above a threshold of 19 mm, probably does not influence her chance of starting a nest (Fig. 6) but is strongly positively correlated to achieved fecundity. Large females have larger offspring and a higher proportion of daughters than small females do (Fig. 7), but this is largely controlled by maternal behaviour rather than by genetical mechanisms (Fig. 10). The results are in general agreement with those of Trivers and Hare (1976) for solitary wasps, but large progeny are cheaper to produce per unit weight than small ones, and for a given weight sons are cheaper to produce than daughters.     

Aggregation and dispersal based on social cues as a nest-site selection strategy in a resource-defence polygynandry mating system

Many animals must choose a nest site in order to reproduce. However, it is unclear how nest-site selection strategies vary across different mating systems. We must therefore explore nest-site selection strategies in a range of mating systems, including the interaction between resource-defence polygyny and polyandry (i.e. polygynandry). In this study, we imposed a re-settlement event in the terrestrial toadlet Pseudophryne bibronii and measured the influence of the spatial position of each male’s nest site with respect to rival males on the likelihood that it would be abandoned or receive eggs. We captured every calling male in a population, measured their breeding success and released them back into the breeding area. We then recorded the establishment and abandonment of nest sites by males over 26 consecutive nights. Spatial positioning did not have any significant effects on male-breeding success, supporting claims that females show less discrimination between nest sites when they are polyandrous and spread their eggs amongst multiple male nests. However, we found that males consistently selected nest sites according to a site’s spatial position, which suggests that fitness benefits unrelated to male breeding success (e.g. reduced mortality risk) might influence male nesting decisions. Overall, our study provides new evidence that the mating system adopted by a population can influence the cues that individuals respond to when selecting nest sites.     

Recruitment of mates and deceptive behavior by male Tengmalm's owls

Summary Tengmalm's owl Aegolius funereus is a hole-nesting polygynous species in which female nomadism is a reaction to cyclic lows of staple prey. For 2 years during a peak in vole abundance, I examined recruitment of mates and male singing behavior in a local population. Females and about half of the breeding males seemed to arrive successively throughout the breeding period of the first year. In contrast, a majority of the breeding males and likely also females were already on the breeding grounds at the beginning of the breeding season in the second year. Before breeding in the first peak year, males were singing at up to five different nest holes. All early breeding males (67% of total number) continued to sing at secondary nest holes after attracting and installing primary females. Secondary singing locations were never closer than 300 m from primary females' nest holes, although closer locations were used for singing before mating. All bigynous males with nests within the study area were also singing at tertiary nest holes, but none successfully attracted a third female. Polyterritoriality was confirmed by a late male settling between primary and secondary nest holes of a bigynous male. Polyterritorial behavior and reduced breeding success of secondary females are in line with the deception model. Females apparently could not discriminate between paired and unpaired singing males. Females made short visits to different males before mating. During courtship, the number and quality of nest holes defended by males may have been of particular importance to female choice.     

Helper contributions to reproductive success in the splendid fairy-wren (Malurus splendens)

Summary In Malurus splendens, helpers were present in 65% of 226 group-years with at least one helper female in 37% of group-years. Most females helped for only one year, while many males did so for at least two years. Most were offspring of one or both present breeders, and in 53% of helper-years, helped both parents. For 159 helpers of known age and parentage, the mean coefficient of relatedness to the offspring was 0.47. Novice females with or without helpers produced fewer fledglings per season than females with one year breeding experience and the same level of help. Helpers did not affect production of fledglings per year by females with one year of experience. Females with two or more years experience and at least two helpers produced more fledglings than equivalent birds with one or no helpers. Experience and helpers have little effect on production of fledglings per nest but they lead to more females renesting after a first brood has been raised. Fewer than 20% of novices renest after fledging one brood, while for females with at least two years experience, the percent renesting after success is 40% with no help, 56% with one helper and 69% with 2 or more helpers. Experienced females begin their first clutch earlier than novices, and helpers reduce the time to renest after success from 66 days for an experienced female with no helpers to 50 days for females with at least two years experience and two or more helpers. Breeding females with helpers survive better (76%) than those with no helpers (55%), and helpers thus gain future indirect fitness. Despite their close relatedness to breeders and offspring, in only 19% of group-years did helpers increase their indirect fitness from an increase in productivity.     

Parasitic common goldeneye (<Emphasis Type="Italic">Bucephala clangula</Emphasis>) females lay preferentially in safe neighbourhoods

Nest predation has been suggested as an explanation of the adaptive significance and evolution of conspecific brood parasitism, an alternative reproductive tactic pursued by females in several animal taxa. I used new nest boxes that contained only decoy eggs and were erected on lakes differing in real nest predation risk to test this hypothesis in the common goldeneye (Bucephala clangula), a hole-nesting duck. I used broken eggs to simulate predation risk of the boxes to determine if parasites having no previous experience with the boxes discriminate between seemingly safe and risky nest sites. Parasites laid eggs in the experimental boxes independently of the simulated predation risk, suggesting that they do not use broken eggs or nest disarray as indicators of predation intensity. Parasites preferred experimental boxes on lakes where real nest predation risk was low, supporting the nest predation risk hypothesis. Assuming that females in high risk areas have had experience of nest predation, they may take this into account in selecting host nests.