Adult Site Fidelity Research Articles

Movement of juvenile migratory birds from settlement to adulthood across the non-breeding range.

Among migratory vertebrates, high levels of fidelity to non-breeding sites during adulthood are common. If occupied sites vary in quality, strong site fidelity can have profound consequences for individual fitness and population demography. Given the prevalence of adult site fidelity, the regions of the non-breeding range to which juveniles first migrate, and the scale of any subsequent movements, are likely to be pivotal in shaping distributions and demographic processes across population ranges. However, inherent difficulties in tracking migratory individuals through early life mean that opportunities to quantify juvenile settlement and movements across non-breeding ranges, and the mechanisms involved, are extremely rare. Through long-term, range-wide resightings of hundreds of colour-marked individuals from their first migration to adulthood and the application of state-space models, we quantify levels of juvenile and adult regional-scale movements and distances at different life stages across the whole non-breeding distribution range in a migratory shorebird, the Black-tailed Godwit (Limosa limosa islandica). We show that the probability of individuals changing non-breeding regions (seven historical wintering regions spanning the Western Europe range) at all ages is very low (mean movement probability = 10.9% from first to subsequent winter, and 8.3% from first adult winter to later winters). Movement between regions was also low between autumn and winter of the same year for both juveniles (mean movement probability = 17.0%) and adults (10.4%). The great majority of non-breeding movements from the first autumn to adulthood were within regions and less than 100 km. The scarcity of regional-scale non-breeding movements from the first autumn to adulthood means that the factors influencing where juveniles settle will be key determinants of non-breeding distributions and of the rate and direction of changes in distributions.

Dispersal of juvenile Barrow’s goldeneyes (Bucephala islandica) mirrors that of breeding adults

Barrow’s goldeneyes across western North America have been shown to have a high degree of subpopulation independence using several data types. However, evidence for structured populations based on mitochondrial DNA, band recoveries, and tracking of adults is discordant with evidence from autosomal DNA. We used satellite tracking data from both juveniles and adults marked on natal and breeding grounds, respectively, in British Columbia, Canada to evaluate the hypothesis that male-biased juvenile dispersal maintains genetic panmixia of Pacific Barrow’s goldeneyes otherwise structured by migratory movements and high winter and breeding site fidelity of adults. We found that juvenile males traveled to overwintering sites located within the range of the overwintering sites of juvenile females, adult males, and adult females. Juvenile males migrated at the same time, travelled the same distance when moving between natal and overwintering sites, and had the same winter dispersion as juvenile females. Although juveniles did not travel with attendant females, all juveniles overwintered within the wintering range of adults. We tracked some juveniles into the following spring/summer and even second winter. Prospecting juveniles of both sexes travelled from their wintering grounds to potential breeding sites in the proximity of Riske Creek and within the bounds of the breeding locations used by adults. Juveniles tracked for more than a year also showed relatively high winter site fidelity. Because Barrow’s goldeneyes pair on wintering grounds, our tracking data are not consistent with the hypothesis that male-biased juvenile dispersal explains the genetic structure in the mitochondrial DNA and panmixia in the autosomal DNA of Barrow’s goldeneye. We suggest that uncommon or episodic dispersal of males might be enough to homogenize autosomal DNA but is unlikely to influence demographic population structure relevant to contemporary population management.

What can exploratory modelling tell us about the ecobiology of European sea bass (Dicentrarchus labrax): a comprehensive overview

European sea bass, Dicentrarchus labrax , is a highly valuable species in Europe, both for aquaculture in the Mediterranean Sea and for commercial and recreational fisheries in the North East Atlantic Ocean. Subjected to increasing fishing pressure, the wild population has recently experienced significant recruitment fluctuation as well as a northward extension of its distribution area in the North Sea. While the nature of the ecological and/or physiological processes involved remains unresolved, ontogenetic habitat shifts and adult site fidelity could increase the species’ vulnerability to climate change and overfishing. As managers look for expert information to propose management scenarios leading to sustainable exploitation, exploratory modelling appears to be a cost-efficient approach to enhance the understanding of recruitment dynamics and the spatio-temporal scales over which fish populations function. A conceptual modelling framework and its specific data requirements are discussed to tackle some sound ecological questions regarding this species. We consequently provide an updated review of current knowledge on bass population structure, biology and ecology. This paper will hence be particularly valuable to develop spatially-explicit models of European sea bass dynamics under environmental and anthropogenic forcing. Knowledge gaps requiring further research efforts are also reported.

How do African Black Oystercatchers Haematopus moquini recruit into high-density populations?

Theoretical and empirical studies of oystercatchers both suggest that levels of adult site fidelity, natal philopatry and age-at-first-breeding are interrelated consequences of life-history decisions made by potential breeders. All are fundamental to explaining population dynamics and have important conservation implications. The African Black Oystercatcher Haematopus moquini is classified as Near Threatened and virtually nothing is known of the biology of sexually mature birds that have yet to become established as breeders (i.e. ‘floaters’). Using an extensive ringing/ recapture/resighting data set from islands off the west coast of South Africa where densities of territorial oystercatchers are very high, this study aimed to explore (1) the degree to which African Black Oystercatchers exhibit natal philopatry, (2) the age at which they enter the breeding population, and (3) the factors that might determine age-at-first-breeding. Both natal site philopatry and adult breeding site fidelity for island-reared birds were high with almost 100% returning to their natal sites. There is a clear, age-based recruitment pattern of oystercatchers into the island breeding populations, but time spent at a site, rather than age per se, may determine a bird's success in establishing a territory.

Migratory connectivity of Palaearctic–African migratory birds and their responses to environmental change: the serial residency hypothesis

In most long‐distance migratory birds, juveniles migrate without their parents and so are likely to lack detailed knowledge of where to go. This suggests the potential for stochasticity to affect their choice of wintering area at a large scale (> 1000 km). Adults, in contrast, may re‐use non‐breeding sites that promote their survival, so removing uncertainty from their subsequent migrations. I review the evidence for large‐scale stochastic juvenile site selection followed by adult site fidelity, and then develop a ‘serial‐residency’ hypothesis based on these two traits as a framework to explain both the migratory connectivity and the population dynamics of migrant birds and how these are affected by environmental change. Juvenile stochasticity is apparent in the age‐dependent effects of weather or experimental displacement on the outcome of migration and in the very wide variation in the destinations of individuals originating from the same area. Adults have been shown to be very faithful to their wintering grounds and even to staging sites. The serial residency hypothesis predicts that migrants that show these two traits will rely on an individually unique but fixed series of temporally and spatially linked sites to complete their annual cycle. As a consequence, migratory connectivity will be apparent at a very small scale for individuals, but only at a large scale for a population, and juveniles are predicted to occur more often at less suitable sites than adults, so that survival will be lower for juveniles. Migratory connectivity will arise only through spatial and temporal autocorrelation with local environmental constraints, particularly on passage, and the distribution and age structure of the population may reflect past environmental constraints. At least some juveniles will discover suitable habitat that they may re‐use as adults, thus promoting overall population‐level resilience to environmental change, and suggesting value in site‐based conservation. However, because migratory connectivity only acts on a large scale, any population of migrants will contain individuals that encounter a change in suitability somewhere in their non‐breeding range, so affecting average survival. Differences in population trends will therefore reflect variation in local breeding output added to average survival from wintering and staging areas. The latter is likely to be declining given increasing levels of environmental degradation throughout Africa. Large‐scale migratory connectivity also has implications for the evolutionary ecology of migrants, generally because this is likely to lead to selection for generalist traits.

Movements of brown bullheads in Presque Isle Bay, Lake Erie, Pennsylvania

Presque Isle Bay, Lake Erie, was listed as an Area of Concern (AOC) by the International Joint Commission in part because of the high incidence of external tumor in brown bullheads. Verifying the source of the possible contaminant exposure is critical to addressing the AOC designation. We used telemetry tracking ( n = 49 fish) to test the hypothesis that adult bullheads captured within the bay during spawning season do not exit the bay during the post-spawning summer and fall months. We analyzed genetic variation at 15 microsatellite loci for 112 adult fish from 5 locations, 4 inside the bay and 1 outside, in order to test for possible differences. Data from fixed-station receivers suggested fish did not leave Presque Isle Bay during the study period. Predicted locations outside Presque Isle Bay were only 0.1% of all predicted locations and were below the 0.2% error rate based on known manual relocations. However, there was evidence for movement within Presque Isle Bay. Most movement was between Misery Bay or Lagoons and the open bay area. Whereas telemetry results showed tendency for adult site fidelity, genetic results showed no differences among locations, indicating that there is a single panmictic population. Our telemetry data suggest that brown bullheads are likely a useful indicator species for environmental conditions in Presque Isle Bay, since adults likely are retained in the system.

Factors Responsible for the Long-Term Dynamics of the Pied FlycatcherFicedula hypoleucaPopulations in the Taiga of Karelia, Russia

Abstract. A Pied Flycatcher population breeding in nest-boxes in a Karelia forest was studied from 1981 to 2007. Breeding density varied between 47.3 and 94.6 pairs/km2. The density of the breeding population was influenced by three demographic factors: maximum summer population density in the previous season, male return rate and immigration rate. Three relatively independent processes play a significant part in the population dynamics of the study area: 1) initial abundance and reproductive intensity, 2) survival rate between breeding seasons, and 3) redistribution of birds across their range. The weather in spring, when the birds arrive and settle, was found to be equally important. The population density, nest site fidelity of adults and yearlings, and immigration rate were related to temperature patterns in May. It may be assumed that the spring weather influences the birds' survival and their distribution across the northern part of their range, as well as the participation of one-year old birds in ...

Factors Influencing Fidelity Of House Finches To A Feeding Station

House Finches (Carpodacus mexicanus) in North America are a commonly-studied species, but basic aspects of their life history remain poorly understood. I banded and observed marked House Finches at a backyard feeding site in a suburban neighborhood in Atlanta, Georgia from August 2002 through July 2004 to address how age, gender, mycoplasmal conjunctivitis, and time of year affected fidelity of individual House Finches to this site. Of 386 House Finches banded, I recaptured 77 and recorded 1,210 reobservations. More than half (55%) of all birds banded were not seen again and, of those that were, almost half (44%) were seen for less than 2 months. A House Finch's age, gender, and month of capture significantly affected how many times it was subsequently encountered (recaptured or reobserved), but not the duration of time it spent at the site of banding. Young birds (HYs) were encountered more often than adults (AHYs), and females more than males. Young birds with mycoplasmal conjunctivitis were encountered less often than those without, but this was not true for adults. These data indicate high site fidelity of adults during the breeding season and low site fidelity of juveniles early in the summer that becomes higher in late summer. Most birds captured in fall were encountered for up to 3 months. These results are discussed in relation to previous studies and their implications for transmission of Mycoplasma gallisepticum among House Finches.

Fine‐scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations

We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km(2). Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations < or = 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation.

Natal dispersal, adult home ranges and site fidelity of mountain hares Lepus timidus in the boreal forest of Sweden

Using radio-telemetry we investigated natal dispersal, adult home ranges and site fidelity of mountain hares Lepus timidus in northern Sweden. We captured 48 leverets from 20 litters while these were still suckling and radio-tracked them for up to 37 months. Leverets showed limited dispersal; < ⅓moved far enough to leave the home range of an average adult female. We radio-collared and tracked 73 adult hares to determine annual and seasonal home ranges along with site fidelity. Males had significantly larger annual and winter-spring home ranges than did females. Both sexes, and especially males, had significantly larger home ranges during winter-spring than during summer-autumn. Adults showed strong site fidelity. None of the adults dispersed from an established home range even though some long-distance excursions were recorded, especially for the males during the breeding season in spring. Limited natal dispersal and a high degree of adult site fidelity suggest that dispersal of mountain hares, as juveniles or as adults, occurs at a low rate in the boreal forest during prevailing conditions, i.e. during low densities and in a continuous population. We conclude that the mountain hare seems to be a philopatric species compared with other small game species in the same ecosystem.

Population genetics of the diamondback terrapin (Malaclemys terrapin)

We examined the population genetic structure of the diamondback terrapins (Malaclemys terrapin), within and among estuaries. Based on mark-recapture studies, these estuarine turtles have high site fidelity that is likely to make them vulnerable to local extinctions. We tested if observed site fidelity of adults would be reflected in intraestuarine population genetic structure of six highly polymorphic microsatellite loci (five tetranucleotide and one dinucleotide). No evidence was found for population structuring within the Charleston estuary nor among three different estuaries in South Carolina. We then examined four other terrapin populations from North Carolina to New York, as well as from the Florida Keys and from Texas. With increasing geographical distance, genetic differentiation increased from South Carolina through New York, but overall values were low. The dinucleotide locus contributed significantly more to the genetic differentiation of some population comparisons than any of the other loci. Interestingly, terrapins from South Carolina to New York were much more genetically similar to those from Texas (rho = 0.154) than to those from Florida (rho = 0.357). We attribute this pattern to extensive translocations of terrapins during the early 20th century to replenish diminished populations and to provide turtle farms with stocks. Terrapins collected in Texas were especially sought for shipment to the northeastern US because of their larger size. Our study indicates no population structure within or among adjacent estuaries. Thus, the mark-recapture information from adult and subadult feeding locations is a poor predictor of population genetic structure. Additionally, it appears that past human activities may have drastically altered the genetics of current populations. Finally, our data suggest that translocation of eggs or head starting of terrapins within estuaries or among adjacent estuaries is acceptable from a genetic standpoint.

Winter spacing and non‐breeding social system of the Coal Tit Parus ater in a subalpine forest

In the genus Parus, non‐breeding social territoriality has often been attributed to the presence of food hoarding which, by increasing the value of an area, is thought to favour the existence of exclusive territories. To test this, it is necessary to analyse the social structure of hoarding populations inhabiting different environments. I studied Coal Tit spacing patterns and winter social systems in a colour‐ringed hoarding population inhabiting a mountain coniferous forest in the Pyrenees. Using data on home range, range overlap and social coherence, the social system was found to be based on adult birds that had previously bred together and which occupied relatively small home ranges. Large home ranges of resident juveniles overlapped extensively with each other and with those of adults. However, resident juveniles were resighted much closer to their ringing place than was expected at random, suggesting restricted floater ranges. Associations, composed mainly of juveniles, seemed to be rather large and loose, with little coherence. No territorial defence by any group of birds was detected during the study. Therefore, the social organization described for the present Coal Tit population is similar to the loose, non‐territorial basic flock system of non‐hoarding species. Resident social patterns seemed to be linked primarily to the availability of breeding resources, probably leading to the high site fidelity of adults and the floater life of resident juveniles. On the other hand, short‐term survival chances may attract transients to a rich food supply and thus affect flocking strategies of birds. High availability of resources allowing a high population density seems to be the main proximate factor influencing the spacing patterns described.

Do gravid black flies (Diptera: Simuliidae) oviposit at their natal site?

We present information on an aniline dye marking method for black flies. In the laboratory, adults were sprayed with 2% aqueous solutions of four colors of aniline dyes; brilliant blue and methyl orange gave the best results in longevity trials. In field trials we were able to recapture 1.3% of newly emerged marked and released flies at oviposition sites. Mark–release–recapture experiments were designed to distinguish among three competing models concerning oviposition site selection by gravid female black flies: (1) larval site fidelity (“Do flies return to the site that they experienced as larvae?”), (2) adult site fidelity (“Do flies return to the site that they experienced as adults?”), and (3) no site fidelity (“Do flies oviposit at random, i.e., without regard to adult or larval experience?”). Models 1 and 2 were rejected. There is, however, no reason to reject Model 3, the no site fidelity model. Thus, we conclude that for members of the S. venustum/verecundum complex (i.e., S. rostratum, S. venustum, and S. truncatum) females find an “apparently suitable” waterway in which to oviposit; this may or may not be their natal site.

Ecological Significance of Brood-Site Fidelity in Black Brant: Spatial, Annual, and Age-Related Variation

-We examined use of brood-rearing sites by female Black Brant (Branta bernicla nigricans) that nested at Tutakoke River, Alaska, 1987 to 1993. Adult females exhibited fidelity to brood-rearing sites; however, we observed site-specific and annual variation in movements among sites. Site fidelity of adults was not related to their hatching date, and hatching dates of females did not vary among brood-rearing sites, suggesting that site selection was unaffected by competition. Movement among sites was affected by distance between sites, but this relationship varied annually and among sites. Variation in forage characteristics may affect movements among sites. Natal-site fidelity was equal to fidelity probability of adults, indicating social inheritance of sites and perhaps facilitation through nepotism. We observed heterogeneity in survival probabilities of goslings and adults among sites. For goslings, heterogeneity in survival was probably related to variation in growth. We observed no relationship between hatching date and use of brood-rearing sites. Previously documented seasonal declines in growth of goslings are more likely affected by declines in forage quality and abundance than by site-specific variation in forage characteristics because use of brood-rearing sites was not related to hatching dates. Received 23 April 1997, accepted 11 November 1997. ENVIRONMENTAL CONDITIONS that precocial young experience before fledging may affect their growth, survival, and future fecundity (Sedinger et al. 1995). The relationship between environment and fitness is particularly evident in northern latitudes where growing seasons are short. Fitness of geese nesting in arctic and subarctic regions is affected by seasonal (Sedinger and Raveling 1986) and spatial variation (Cooch et al. 1993) in forage quality and abundance. Goslings hatching late grow slower (Cooch et al. 1991, Sedinger and Flint 1991, Lindholm et al. 1994) and have lower survival and fecundity than goslings hatching early (Sedinger et al. 1995). Growth of young Lesser Snow Geese (Chen c. caerulescens) and Barnacle Geese (Branta leucopsis) varies among brood-rearing sites (Larsson and Forslund 1991, Cooch et al. 1993). Spatial variation in habitat quality may lead to heterogeneity in survival and subsequent reproductive performance (Cooch et al. 1993, Rockwell et. al. 1993). In addition, fidelity to natal sites may cause genetic-environmental covariance and inflated estimates of heritability I Present address: Institute for Wetland and Waterfowl Research, Ducks Unlimited, Inc., One Waterfowl Way, Memphis, Tennessee 38120, USA. E-mail: mlindberg@ducks.org for growth metrics (Larsson and Forslund 1992). Although the distribution of goslings among brood-rearing sites affects the fitness of these birds, the use of brood-rearing habitats and factors affecting the distribution of birds during brood rearing are poorly described. The distribution of birds among habitats may be influenced by fitness costs and benefits associated with those habitats (Nichols et al. 1983). Birds should occupy the highest quality habitats, but by using these habitats, they may decrease habitat quality. As habitat quality declines, birds should select unoccupied habitats of similar quality as the habitat currently occupied (Fretwell 1972). If all birds occupy habitats of similar suitability, then their distribution may be described as ideal free (Fretwell and Lucas 1970). In an ideal free distribution, all individuals would have similar fitness. The pattern of habitat selection in geese may be particularly complex because geese may initially improve the quality of the habitat through fecal nitrogen deposition, which increases aboveground primary productivity (Hik and Jefferies 1990). Furthermore, movements among habitats may be opposed by competition with conspecifics. Alternatively, advantages of site familiarity may favor fidelity. Ecological advantages of site fidelity and resulting site familiar-

A field study of spatial ecology and movements of a threatened snake species, Hoplocephalus bungaroides

Information on movement patterns, home range sizes and site fidelity of endangered fauna may provide a basis for conservation planning (size and location of reserves; vulnerability to habitat fragmentation; feasibility of natural recolonisation of ‘restored’ habitats, etc.). To obtain such information, we surgically implanted miniature radio transmitters in 25 individual broad-headed snakes Hoplocephalus bungaroides, a small (mean snout-vent length = 57 cm, mean mass = 51 g) viviparous elapid snake reliant upon sandstone outcrops in southeastern Australia. We also carried out a mark-recapture study of this threatened species. Our telemetered snakes spent long periods of time sequestered inside retreat-sites (rocks, crevices, tree hollows) and thus were active on only 21% of days. Gravid females had small home ranges (mean size = 0·05 ha, convex polygon method) and remained near cliffs during summer, whereas most males and non-gravid females moved long distances (up to 780 m) away from cliff tops during summer and had larger home ranges (mean size = 3·3 ha). Movements by the snakes were more frequent and extensive when they were in the woodland (mean interval between successive moves = 2·9 days; mean displacement per move = 159 m) than when they were in the rock outcrops (means = 6·3 days, 37 m). Home ranges were larger in summer than in spring, and were larger in 1994–95 than in other years. Home ranges of males showed little spatial or temporal overlap in spring, but females were found within the areas used by males. During summer there was little temporal or spatial overlap of home ranges of adults, which suggests that snakes may actively avoid conspecifics of either sex while foraging in the forest. Many adult snakes showed strong site fidelity, frequently returning to the same rocks where they were initially captured. Dispersal of juvenile snakes from their birth sites was relatively limited (maximum recorded distance = 375 m after 6 months). Our results have significant implications for conservation of this threatened taxon. The fixed home ranges and high site fidelity of adults coupled with the low dispersal rates of juvenile broad-headed snakes mitigate against successful natural recolonisation of rehabilitated habitats. Thus, habitat restoration may need to be combined with release of captive-bred progeny, or field-caught neonates. The exclusive home ranges of adult snakes suggest that social interactions (avoidance of conspecifics) may limit population densities, and hence that (i) removal of some neonates may not reduce future densities of adults, and (ii) habitat destruction is likely to be a more serious long-term threat than removal or killing of individual snakes. The large home ranges, and frequent and extensive movements, of snakes in woodland indicate that conservation reserves must incorporate large forest areas adjacent to sandstone outcrops.

Demography and Lifetime Reproductive Success in the Polygynous Great Reed Warbler

I analysed demographic parameters and lifetime reproductive success in a Swedish population of Great Reed Warblers. The population was followed on a daily basis in 1985-1993 when all breeding Great Reed Warblers were individually marked and >95% of the young fledged in the study area were ringed. Between-year breeding site fidelity of adults was relatively high both for males (55%) and females (51%), and it seemed not to be affected by previous breeding results. Natal site fidelity was also relatively high as 14% of the fledglings hatched in the study area returned to breed in subsequent years. Each year, however, about 50% of the breeders were hatched outside the study area (i. e. immigrants). The production of lifetime recruits was biased so that 17% of the males and 13% of the females produced more than 50% of the recruits in the population. There was no difference in lifetime reproductive success between native birds and immigrants, suggesting that immigrants contributed substantially to the local gene pool. Despite this, effects of non-incestuous inbreeding, measured as lowered hatchability of eggs among broods of genetically more similar pair members, were found in the study population. This may be a result of the dispersal pattern between local Great Reed Warbler populations in Sweden and also a consequence of the short history of these small populations.

Site infidelity in song sparrows

In each of 4 years of study of a breeding population of song sparrows ( Melospiza melodia) approximately two-thirds of the males holding territories at the beginning of the breeding season had abandoned those territories before the end of the breeding season and overall 83% of those males were never seen again. Males were more likely to abandon a territory following a nest failure but some individuals left after a success and some remained after a failure. Indirect evidence suggested that territory quality also influenced a male's decision to stay or go. Data on nesting success suggested that both birds that stay or those that move benefit from their actions. Between years, males showed the same lack of site fidelity, but were more likely to return to a territory on which they had been successful. Females also showed little site fidelity within breeding seasons, and although they abandoned territories for the same reasons as males, they appeared to move independently of their mate. Only one of 146 birds banded as a nestling was ever resighted as an adult. Together, the low adult site fidelity and low natal philopatry indicate a much higher level of outbreeding than has been estimated previously for this species. We discuss the implications of these results and propose that, rather than being an evolved attribute to maintain an optimal level of inbreeding, site fidelity is a conditional strategy related to intraspecific competition for territories.