High Natal Philopatry Research Articles

Limited evidence of biased offspring sex allocation in a cavity-nesting conspecific brood parasite.

Sex allocation theory predicts that mothers should bias investment in offspring toward the sex that yields higher fitness returns; one such bias may be a skewed offspring sex ratio. Sex allocation is well-studied in birds with cooperative breeding systems, with theory on local resource enhancement and production of helpers at the nest, but little theoretical or empirical work has focused on birds with brood parasitic breeding systems. Wood ducks (Aix sponsa) are a conspecific brood parasite, and rates of parasitism appear to increase with density. Because female wood ducks show high natal philopatry and nest sites are often limiting, local resource competition (LRC) theory predicts that females should overproduce male offspring-the dispersing sex-when competition (density) is high. However, the unique features of conspecific brood parasitism generate alternative predictions from other sex allocation theory, which we develop and test here. We experimentally manipulated nesting density of female wood ducks in 4 populations from 2013 to 2016, and analyzed the resulting sex allocation of >2000 ducklings. In contrast to predictions we did not find overproduction of male offspring by females in high-density populations, females in better condition, or parasitic females; modest support for LRC was found in overproduction of only female parasitic offspring with higher nest box availability. The lack of evidence for sex ratio biases, as expected for LRC and some aspects of brood parasitism, could reflect conflicting selection pressures from nest competition and brood parasitism, or that mechanisms of adaptive sex ratio bias are not possible.

Philopatry in a reintroduced population of Bearded Vultures Gypaetus barbatus in the Alps

Following its eradication in the Alps in the early 1900s, the Bearded Vulture Gypaetus barbatus has been reintroduced in four Alpine regions since 1986. The first successful breeding since this reintroduction into the wild occurred in 1997 in the western Alps, and in 1998 in the Central Alps, thereby establishing two subpopulations. Here, we focus on the growth and the settlement patterns of one of the major subpopulations of reintroduced Bearded Vulture, that of the Central Alps. By 2015 there were 15 breeding pairs in the Central Alps, and the density within the core area was strikingly higher (18.8 pairs/1000 km2) than that outside it (overall density 3.4 pairs/1000 km2). New pairs showed high natal philopatry when settling, with maximum distances of 49.2 km from the nearest release sites. Among identified birds, born or released within the Central Alps, 85% (n = 26) paired and settled within this subpopulation and only four birds emigrated to the west. Three birds immigrated from the east or the west. Both the number of pairs and of offspring increased exponentially between 1998 and 2015. The growth of the Central Alpine subpopulation was characterized by concentric and continuous growth around the release sites. Moreover, there was an increase in the density of pairs within the core area. Possible explanations for the high natal philopatry observed include adaptive genetic components, abundant food resources and conspecific attraction. As a consequence of the substantial population increase, releases in the Central Alpine subpopulation were stopped after 2008. The population has grown almost exclusively on the basis of wild-born birds since then, and has become a major subpopulation of the Bearded Vulture in the Alps.

Intrinsic factors drive spatial genetic variation in a highly vagile species, the wedge‐tailed eagle Aquila audax, in Tasmania

Knowledge of dispersal in a species, both its quantity and the factors influencing it, are crucial for our understanding of ecology and evolution, and for species conservation. Here we quantified and formally assessed the potential contribution of extrinsic factors on individual dispersal in the threatened Tasmanian population of wedge‐tailed eagle Aquila audax. As successful breeding by these individuals appears strongly related to habitat, we tested the effect of landscape around sampling sites on genetic diversity and spatial genetic variation, as these are influenced by patterns of dispersal. Similarly, we also tested whether habitat intervening sampling sites could explain spatial genetic variation. Twenty microsatellites were scored, but only a small proportion of spatial genetic variation (4.6%) could be explained by extrinsic factors, namely habitat suitability and elevation between sites. However, significant clinal genetic variation was evident across Tasmania, which we explain by intrinsic factors, likely high natal philopatry and occasional long‐distance dispersal. This study demonstrates that spatial genetic variation can be detected in highly vagile species at spatial scales that are small relative to putative dispersal ability, although here there was no substantial relationship with landscape factors tested.

Biogeographical barriers to dispersal and rare gene flow shape population genetic structure in red‐footed boobies ( Sula sula )

Aim The ecological and biogeographical factors that influence population differentiation in seabirds are likely to be too complex and nuanced to be captured by many commonly held models of population differentiation. Pelagic seabirds exhibit high natal philopatry but can disperse long distances, potentially leading to long periods of genetic isolation with rare gene flow between isolated populations. Here, we assess levels of population genetic structure and gene flow in red-footed boobies (Sula sula) to test two hypotheses: (1) terrestrial and marine barriers to gene flow have caused population genetic differentiation among red-footed booby populations, and (2) despite high genetic differentiation among populations, rare gene flow still occurs among populations. Location Tropical oceans. Methods We genotyped 282 red-footed boobies at microsatellite, nuclear intron and mitochondrial markers. We applied basic tests of population differentiation, such as analysis of molecular variance, and applied modern statistical phylogeographical methods (e.g., structure, BayesAss) to investigate the history of gene flow. Results Red-footed boobies form four major genetic populations that correspond to oceanographic regions (Atlantic, Indian, Western+Central Pacific and eastern Pacific Oceans). However, gene flow has occurred recently among these populations. Further differentiation was found within ocean basins. Although the levels of gene flow within ocean basins are more difficult to assess, gene flow appears to have occurred between genetically differentiated Indian Ocean colonies. Main conclusions The population genetic structure of red-footed boobies has been driven primarily by major continental and marine barriers to gene flow that also drive differentiation in other pelagic seabirds (e.g., the Isthmus of Panama and eastern Pacific basin). However, dispersal across marine barriers (but not major continental barriers) appears to have been relatively common. We suggest that such patterns of long-term isolation and rare gene flow may be common to pelagic seabirds.

Seabirds mated for life migrate separately to the same places: behavioural coordination or shared proximate causes?

Long-term pair bonds occur in diverse animal taxa, but they are most common in birds, and can last from a few years to a lifetime. In many of these species, after the reproductive season, birds migrate to distant nonbreeding grounds where they remain for several months, and until recently, little was known about whether partners maintain contact during migration. This gap in knowledge was primarily due to past methodological difficulties in tracking long-term, large-scale movements of individuals. However, the development of new animal-borne geolocation devices has enabled researchers to track movements of individuals for a year or more. We tracked the annual migrations of both members of breeding pairs of Scopoli's shearwaters, Calonectris diomedea, breeding on Linosa Island (Italy) and found that although they did not migrate together, they did spend a similar number of days travelling to and from similar terminal nonbreeding areas. Although migration destinations were alike, they were not identical. That partners did not appear to travel or spend time together in the nonbreeding season suggests that similarities were not due to behavioural coordination. We performed additional analyses to uncover alternative, potential proximate mechanisms. First, we found that body mass of breeding adults during the chick-rearing period correlated positively with the decision to migrate further south, so conceivably pair members may migrate to similar areas because of shared reproductive costs; however, partners were not of similar body mass. Distances between nonbreeding areas for individuals that nested closer together were smaller than for individuals that nested far apart. As neighbours tend to be more closely related due to high natal philopatry, this suggests that similarities within pairs in migration behaviour may reflect the influence of shared genes on migration strategy.

Heritability of immunological characteristics in Florida Scrub-Jays (Aphelocoma coerulescens)

The degree to which immunological phenotype is under genetic control as opposed to plasticity in response to variable environmental conditions remains largely unknown in natural populations. We assessed different aspects of immune function in father–son pairs in Florida Scrub-Jays (Aphelocoma coerulescens (Bosc, 1795)), a species with high natal philopatry, to determine if the responses were heritable. Specifically, we examined heritability of the (i) heterophil to lymphocyte ratio, (ii) ability to kill the Gram-negative bacteria Escherichia coli in an in vitro challenge, and (iii) ability to kill the Gram-positive bacteria Staphylococcus aureus in an in vitro challenge. The heritability (h2) of each of the three measures described above was estimated as twice the slope of the regression (2β) from the mean value for each measure for sons on the mean value of the same measure for the father. Heritability estimates were high for all measures: heterophil to lymphocyte ratios (h2 = 1.54 ± 0.31) and E. coli (h2 = 1.84 ± 0.12) and S. aureus (h2 = 1.13 ± 0.16) killing abilities. Our results show a strong correlation between father and son immune function, as well as the influential nature of genetic inheritance and potential environmental effects associated with high natal philopatry on physiology.

Early age at first breeding and high natal philopatry in the Red‐necked Nightjar Caprimulgus ruficollis

Recruitment rates, natal philopatry and the onset of breeding activity are documented for the first time for the order Caprimulgiformes. Of 171 Red‐necked Nightjars Caprimulgus ruficollis ringed as fledglings in southwestern Spain between 2008 and 2011, 31 (18%) were later recovered. Females tended to disperse slightly further (680 m) than males (570 m), and no individual from the study site or nearby locations was ever recovered outside the area where it hatched, suggesting high natal philopatry. Most males (94%) and females (73%) recruited into the breeding population in their first year of life, and only a few individuals were not recovered until their second (10%) or third (7%) year of life. In contrast to most long‐lived birds, nearly all (95.5%) Red‐necked Nightjars started to reproduce in their first potential breeding season.

Philopatry, morphological divergence, and kin groups: structuring in thick-billed murres Uria lomvia within a colony in Arctic Canada

Many seabirds exhibit high natal philopatry despite their extreme dispersal ability and delayed reproduction, and some exhibit phenotypic clustering in colonies and fostering or adoption of neighbouring chicks. Previous investigations of kinship in a small thick-billed murre colony Uria lomvia (Alcidae) in Norway revealed high relatedness among breeders on cliff ledges. To investigate the presence of kin groups and within-colony genetic sub-structuring elsewhere, we investigated kinship within a larger murre colony on Coats Island, Nunavut, Canada. Morphological (five characters) and genetic data (five microsatellite loci and a fragment of the mitochondrial cytochrome b gene) were analysed. Strong morphological differentiation was found among ledges. Genetic structuring was overall weak but significant at the coarse scale for males among ledges and on the east vs. the west side of the colony. Global spatial autocorrelation analyses did not detect consistent, widespread spatial patterns, although local 2D analyses provided some evidence of a tendency for larger neighbourhood sizes for females and a broad range of small to large neighbourhoods for males. Average within-ledge relatedness was low overall, but ranged widely from slightly unrelated to greater than the level of cousins in both sexes. Kin-level relationships occurred on ledges more frequently for same-sex groups than expected by chance, suggesting that recruiting breeders (especially females) avoid or are unable to settle directly adjacent to relatives particularly of the opposite sex. Behavioural studies of natal dispersal of murres at Coats I. indicating that both sexes are highly philopatric, but that up to one-fifth of females may disperse, are concordant with this study. Overall, structuring was weaker than in Norway, and may be explained in part by genetic marker and sampling artifacts, and by the lack of genetic equilibrium suspected in the much larger Canadian Arctic colony. Natal philopatry may be an important factor driving the diversification of seabirds and kin groups in other colonies and species and may be more widespread than is currently acknowledged.

Piecing together the global population puzzle of wandering albatrosses: genetic analysis of the Amsterdam albatross Diomedea amsterdamensis

Wandering albatrosses have been subjected to numerous taxonomic revisions due to discoveries of new species, analyses of morphological data and, more recently, the inclusion of genetic data. The small population of albatrosses (170 individuals including 26 pairs breeding annually) on Amsterdam Island in the Indian Ocean, Diomedea amsterdamensis, has been given species status based on plumage and morphometrics, but genetic data published to date provide weak support and its specific status remains controversial for some authors. We used mitochondrial control region sequence data to elucidate the relationship of the Amsterdam albatross within the wandering albatross complex (Diomedea amsterdamensis, D. antipodensis, D. dabbenena and D. exulans). Three novel haplotypes were present in 35 individuals from Amsterdam Island, and were highly divergent (3.6–7.3%) from haplotypes found in the other three members of the wandering albatross complex. Low levels of genetic variation in Amsterdam albatross likely resulted, at least in part, from a population bottleneck. Geographic isolation in the wandering albatross complex is maintained by high natal philopatry. As Amsterdam Island is the only breeding ground for this critically endangered species, we strongly urge conservation efforts in the area, especially in relation to long line fisheries and other threats such as disease and introduced predators, and it be listed as a distinct species.

Extraordinary high natal philopatry in a migratory passerine

Natal dispersal is a key component of population dynamics in birds. It guarantees the genetic exchange of populations, favours range expansions and reduces intraspecific competition. In general, natal philopatry of migratory passerines is quite low (0–13.5%). In this study, we give evidence that, under specific conditions, migratory populations of passerine birds may show a considerably elevated natal philopatry. In a Linnet Carduelis cannabina population on the remote island of Helgoland in the North Sea, we found an extraordinary high return rate of yearlings (38%), which corresponds exactly to the annual survival rate of the species. Despite being completely migratory, the Linnets of Helgoland apparently return to a large extent to their native area and consequently might support the population maintenance on the island. Further studies are needed to reveal if this high natal philopatry is only an unusual 1-year event or a general characteristic of this partially isolated island population.

Integrating individual behaviour and landscape genetics: the population structure of timber rattlesnake hibernacula

Individuals of many species show high levels of fidelity to natal populations, often due to reliance on patchily distributed habitat features. In many of these species, the negative impacts of inbreeding are mitigated through specialized behaviours such as seasonal mating dispersal. Quantifying population structure for species with these characteristics can potentially elucidate social and environmental factors that interact to affect mating behaviour and population connectivity. In the northern part of their range, timber rattlesnakes are communal hibernators with high natal philopatry. Individuals generally recruit to the same hibernaculum as their mother and remain faithful to that hibernaculum throughout their lives. We examined the genetic structure of Crotalus horridus hibernacula in the northeastern USA using microsatellite loci. Sampled hibernacula exhibited only modest levels of differentiation, indicating a significant level of gene flow among them. We found no significant correlation between genetic differentiation and geographical distance, but did find significant positive correlation between genetic differentiation and a cost-based distance metric adjusted to include the amount of potential basking habitat between hibernacula. Therefore, thermoregulation sites may increase gene flow by increasing the potential for contact among individuals from different populations. Parentage analyses confirmed high levels of philopatry of both sexes to their maternal hibernaculum; however, approximately one-third of paternity assignments involved individuals between hibernacula, confirming that gene flow among hibernacula occurs largely through seasonal male mating dispersal. Our results underscore the importance of integrating individual-level behaviours and landscape features with studies of fine-scale population genetics in species with high fidelity to patchily distributed habitats.

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

AbstractDispersal 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).

Natal philopatry does not lead to population genetic differentiation in Buller's albatross (Thalassarche bulleri bulleri)

Genetic variability in the only two existing populations of Buller's albatross (Thalassarche bulleri bulleri) was assessed using six polymorphic microsatellite loci. Large biological samples were obtained from both the Snares (n = 99) and the Solander Islands (n = 27). Several measures of genetic differentiation including F(ST) and R(ST) and a principal coordinates analysis (PCO) suggest a complete absence of genetic structure between three breeding colonies on the Snares Islands, and between them and one breeding colony on the Solander Islands. Mark/recapture studies of recently banded albatross chicks on the Snares found high natal philopatry in T. b. bulleri, but the microsatellite DNA data suggest that sufficient gene flow still occurs between all four breeding colonies to maintain a genetically homogeneous population overall.

Clustering of related individuals in a population of the Australian lizard,Egernia frerei

Stable social aggregations are rarely recorded in lizards, but have now been reported from several species in the Australian scincid genus Egernia. Most of those examples come from species using rock crevice refuges that are relatively easy to observe. But for many other Egernia species that occupy different habitats and are more secretive, it is hard to gather the observational data needed to deduce their social structure. Therefore, we used genotypes at six polymorphic microsatellite DNA loci of 229 individuals of Egernia frerei, trapped in 22 sampling sites over 3500 ha of eucalypt forest on Fraser Island, Australia. Each sampling site contained 15 trap locations in a 100 x 50 m grid. We estimated relatedness among pairs of individuals and found that relatedness was higher within than between sites. Relatedness of females within sites was higher than relatedness of males, and was higher than relatedness between males and females. Within sites we found that juvenile lizards were highly related to other juveniles and to adults trapped at the same location, or at adjacent locations, but relatedness decreased with increasing trap separation. We interpreted the results as suggesting high natal philopatry among juvenile lizards and adult females. This result is consistent with stable family group structure previously reported in rock dwelling Egernia species, and suggests that social behaviour in this genus is not habitat driven.

Natal Philopatry and Close Inbreeding in Cory's Shearwater (Calonectris diomedea)

Close inbreeding is known in several bird species, although it is seldom observed (Greenwood et al. 1978, Craig and Jamieson 1988, Gibbs and Grant 1989, Bensch et al. 1994). Inbreeding can have important evolutionary consequences because it may carry both costs and benefits to fitness (Mayr 1963, Shields 1983, Greenwood 1989). However, the seemingly low rate of inbreeding in nature may result from the fact that documenting inbreeding requires long-term monitoring of marked individuals. Colonial waterbirds are good candidates for studies of inbreeding because they often exhibit high natal philopatry (Greenwood and Harvey 1982). Moreover, long-term studies allowing individual identification and monitoring are relatively easy and widespread in this group (Wooller et al. 1992). Curiously, however, only two cases of inbreeding have been reported for colonial waterbirds: Yellow-eyed Penguin (Megadyptes antipodes; Richdale 1957), and Mute Swan (Cygnus olor; Coleman et al. 1994). Here, we report two cases of close inbreeding in Cory's Shearwater (Calonectris diomedea) documented during an 18-year study. We also consider philopatric behavior in this species and its possible relationships with inbreeding. Cory's Shearwaters are highly philopatric (Ristow et al. 1990, Thibault 1993, Borg and Cachia-Zammit 1997), breeding only on islands in the Mediterranean Sea (C. d. diomedea), and along the west coast of Africa from the Cape Verde islands (C. d. edwardsii) to the Macaronesian and Berlenga islands (C. d. borealis). The biology of this species has been well documented, and geographic variation in biometric (Massa and Lo Valvo 1986), vocal (Bretagnolle and Lequette 1990), and genetic (Randi et al. 1989, Wink et al. 1993) traits tend to confirm this extreme philopatric behavior. Methods.-Our study was conducted on the Lavezzi Islands, south Corsica (300 to 400 breeding pairs). All adults and fledglings were banded and recaptured annually between 1978 and 1996 in five subcolonies totaling 104 to 133 nests (Thibault 1993); 1,045 chicks were banded during this period. Prospecting birds also have been recaptured, albeit irregularly (but more thoroughly since 1992; see Thibault 1993). Recaptured birds were sexed using bill dimensions that have about 95% predictive power (Ristow and Wink 1980, Granadeiro 1993, Thibault 1993).

Natal philopatry in passerine birds: genetic or ecological influences?

The degree of natal philopatry (the likelihood that individuals breed at or near their place of origin) can influence the extent of inbreeding in animal populations. Passerine birds have been cited as typically showing high natal philopatry, and natal philopatry has been proposed as an adaptation to promote optimal inbreeding. A review of published and unpublished studies of passerines showed that natal philopatry was typically low, so maintaining a high level of inbreeding appears relatively unimportant for such birds. Rather, natal philopatry appeared to be more strongly influenced by ecological factors. Migratory passerine exhibited low natal philopatry compared to resident passerines, as predicted if dispersal costs for young birds are an important determinant of natal philopatry. The erroneous view that natal philopatry for passerines is generally high has resulted from a reporting bias toward resident species that have sufficient natal philopatry to study. Natal philopatry was found to be evolutionarily labile; populations of the same species and pairs of closely related species that differed in their degree of isolation differed considerably in their degree of philopatry. Future studies of natal philopatry should consider both the ecological factors that could affect dispersal costs and the reporting biases that influence which data on philopatry tend to be reported.