Competition For Nest Sites Research Articles

Angry caciques: intrasexual aggression in a Neotropical colonial blackbird

Intraspecific aggressive behavior usually mediates competition for breeding and non-breeding resources among females and for mating opportunities among males. Variation in intrasexual aggressive levels across social and breeding contexts might then differ between sexes or converge due to different reasons. We studied three colonies of the polygynous Red-rumped cacique (Cacicus haemorrhous) during one breeding season. We evaluated whether the frequency of female-female and male-male aggressive interactions (number of interactions corrected by total number of individuals of the focal sex) varied with social context (total number of individuals of each sex in the colony) and breeding stage (number of nests under construction and nests with offspring) at each colony. We also tested for the occurrence (linearity and steepness) of a dominance hierarchy among banded males in one colony. We predicted positive correlations between female-female aggression and nests under construction (i.e. competition for nest sites) and between male-male aggression and nests under construction (a proxy for fertile females) and also male-male aggression and number of males (i.e. disputes for dominance rank) in the colony. We observed 533 female-female and 608 male-male aggressive interactions. Female-female aggressive interactions increased with the number of nests under construction in the colony, and decreased during incubation and nestling stages. Male-male aggressive interactions increased with the number of nests under construction, but not with the number of males in the colony. However, we found a steep and linear dominance hierarchy among males shaped by aggressive interactions. Our results suggest that (i) females behave aggressively when competing during the nest-building stage, probably for nest sites and materials; and (ii) male aggression determines the dominance hierarchy and is related to mating opportunities.HIGHLIGHTS● We observed intrasexual aggressive interactions across breeding stages in a blackbird with female-only parental care.● Female-female and male-male aggressive interactions increased when nests were under construction in the colony.● Dominance hierarchy was evaluated for males and it was linear and steep.● Results suggest females compete for nest sites and male aggression shapes dominance and is associated with mating opportunities.

Long-Term Monitoring of Scripps's Murrelet and Guadalupe Murrelet at San Clemente Island, California: Evaluation of Baseline Data in 2012–2016

San Clemente Island (SCI) supports one of the smallest Scripps's Murrelet (Synthliboramphus scrippsi; SCMU) colonies in the world, and perhaps the only colony of Guadalupe Murrelets (S. hypoleucus; GUMU) in California. In 2012–2016, the U.S. Navy sponsored development of a long-term murrelet monitoring program at SCI that utilized nocturnal spotlight surveys, night-lighting at-sea captures, and nest monitoring. Standardized spotlight survey transects were established in nearshore waters off breeding areas at Seal Cove and southeast SCI (SESCI). Baseline mean spotlight counts were 29 ± 15 murrelets (n = 31) at Seal Cove in 2013–2016 and 21 ± 10 murrelets (n = 15) at SESCI in 2014–2016. We banded 201 SCMU captured in congregations at Seal Cove (n = 158) and SESCI (n = 43); 12% of the SCMU from Seal Cove and 7% from SESCI were recaptured ≥1 year after banding. We also banded 21 GUMU at Seal Cove, but none were recaptured. Murrelet nests or eggs were found in 6 shoreline breeding “refuges” at Seal Cove and SESCI that were seldom if ever visited by island foxes (Urocyon littoralis clementae) and feral cats (Felis catus). Incubating SCMU were observed in 4 nest sites, but in 8 other sites only eggs or eggshells were found. Overall hatching success was very low (12%; n = 17 clutches) in 2012–2016, apparently due to intraspecific competition for limited nest crevices at Seal Cove and predation (or possibly abandonment and subsequent egg scavenging) by foxes or black rats (Rattus rattus) at SESCI. Using spotlight survey data, we estimated 115 murrelet pairs (range 79–208) at SCI, including 110 pairs (range 76–199) of SCMU and 5 pairs (range 3–9) of GUMU, although a GUMU nest has not yet been found. Power analyses of Seal Cove spotlight data indicated that surveys conducted over 9 nights per year for 20 years could reliably (power ≥ 0.90) detect minimum population changes of ±1.7% per annum. Additional efforts are needed to (1) confirm the breeding status of GUMU; (2) investigate alternative methods of rat control to increase hatching success in murrelet breeding refuges; and (3) enhance breeding habitats to reduce intraspecific competition for nest sites and increase the number of monitored nests.

Nesting behaviour and breeding success of Willow Tits Poecile montanus in north-west England

ABSTRACTThe British Willow Tit Poecile montanus has undergone a substantial decline in abundance and a severe contraction in range since the 1970s, for reasons that are poorly understood. Breeding failure, due to nest-site competition and predation, has been suggested as a potential factor in the decline, but limited data exist for the nesting ecology and breeding productivity of the species in Britain. We studied a sample of 128 Willow Tit nests in a habitat mosaic of early successional woodland, scrub and wetland in a post-industrial landscape in north-west England, which is increasingly becoming a key refuge for the species in Britain. Results showed that nesting began in April, with standing deadwood of silver birch Betula pendula, common elder Sambucus nigra and black alder Alnus glutinosa being the most frequent nest sites, and the characteristics of nest sites are described. Daily survival rates and overall probability of nest survival are calculated, and details are given for the timing of breeding, clutch size, nestling survival and number of fledglings produced. Overall, 55% of nesting attempts were successful, although many first breeding attempts failed due to Willow Tits being evicted from their nest cavity by Blue Tits Cyanistes caeruleus, or nests being predated by Great Spotted Woodpeckers Dendrocopos major and, potentially, grey squirrels Sciurus carolinensis. Repeat breeding attempts were relatively more successful, but produced fewer fledglings on average. The results are discussed in the context of other studies of Willow Tits and some related species, and also the implications for the conservation of Willow Tits in Britain.

Sora (<i>Porzana carolina</i>) Parasitism of Red-winged Blackbird (<i>Agelaius phoeniceus</i>) Nests

Sora (Porzana carolina) is a conspecific brood parasite that also occasionally parasitizes nests of other species. Sora parasitism in nests of passerines is rare. Of 129 Red-winged Blackbird (Agelaius phoeniceus) nests found in North Dakota in 2009 and 2010, two (1.6%) were parasitized by Soras. The conditions favouring this rare parasitic behaviour may include competition for nest sites and high Sora density.

Nest-site competition and killing by invasive parakeets cause the decline of a threatened bat population.

The identification of effects of invasive species is challenging owing to their multifaceted impacts on native biota. Negative impacts are most often reflected in individual fitness rather than in population dynamics of native species and are less expected in low-biodiversity habitats, such as urban environments. We report the long-term effects of invasive rose-ringed parakeets on the largest known population of a threatened bat species, the greater noctule, located in an urban park. Both species share preferences for the same tree cavities for breeding. While the number of parakeet nests increased by a factor of 20 in 14 years, the number of trees occupied by noctules declined by 81%. Parakeets occupied most cavities previously used by noctules, and spatial analyses showed that noctules tried to avoid cavities close to parakeets. Parakeets were highly aggressive towards noctules, trying to occupy their cavities, often resulting in noctule death. This led to a dramatic population decline, but also an unusual aggregation of the occupied trees, probably disrupting the complex social behaviour of this bat species. These results indicate a strong impact through site displacement and killing of competitors, and highlight the need for long-term research to identify unexpected impacts that would otherwise be overlooked.

Receivers matter: the meaning of alarm calls and competition for nest sites in a bird community.

Animal communities may constitute information networks where individuals gain information on predation risk by eavesdropping on alarm calls of other species. However, communities include species in different trophic levels, and it is not yet known how the trophic level of the receiver influences the informative value of a call. Furthermore, no empirical study has yet tested how increased competition may influence the value of alarm calls for distinct receivers. Here, we identify the importance of alarm calls emitted by a small owl, the little owl (Athene noctua), on the structure of a cavity-nesting bird community including mesopredators and primary prey under variable levels of competition for nest holes. Competitors sharing top predators with the callers and prey of the callers interpreted alarm and non-alarm calls differently. Competitors chose preferentially alarm and non-alarm patches over control patches to breed, while prey selected alarm patches. In contrast, competition for nest sites affected habitat selection of prey species more than that of competitors of the callers. This study provides support for a changing value of alarm calls and competition for nest sites for distinct receivers related to niche overlapping among callers and eavesdroppers, therefore, calling attention to possible cascading effects by the use of information in natural communities.

Nest-site interference competition with House Sparrows affects breeding success and parental care in Great Tits

Although interspecific competition is suggested to be one of the major forces dictating community structure, interspecific interference competition for nest sites in birds has been reported mainly from observational studies. Here, we asked whether interference by the larger House Sparrow (Passer domesticus) could reduce breeding success and parental behavior in the smaller Great Tit (Parus major) following clutch completion, by experimentally allowing House Sparrows to access half of the Great Tit nest boxes. Significantly more tit pairs failed to raise young in nest boxes that House Sparrows were able to enter during their breeding period compared to those that were not able to do so, because House Sparrows usurped 77.8% of the Great Tit nests. Great Tits also increased the duration of nest defense in the presence of House Sparrows. As the outcome of interference competition may lead to breeding failure, birds should necessarily evolve ways to avoid nest competitors either by selecting nests that restrict access to their larger competitors and/or by initiating breeding earlier. Conservation efforts should be directed toward attaching a metal restrictor plate around the entrance of nest boxes to prevent woodpeckers from enlarging the entrance and larger species from entering nests.

IInteractions between Australian Ravens and raptors in a pastoral area of New South Wales: Interspecific aggression and nest-site spacing

This study, near Tamworth, New South Wales, investigated the interactions within a diurnal raptor and Australian Raven Corvus coronoides community. The Australian Raven (hereafter ‘Raven’) is an abundant breeding resident here, is the only corvid that breeds in the area, and is known to have a close association with many raptor species. It is known to interfere with nests, provide frequent harassment and decrease the breeding productivity of several nesting raptor species, yet few studies have been completed on this issue, and its significance remains unknown. The abundance of raptors and Ravens and diversity of raptor species were determined from weekly surveys along a fixed 60-km transect in autumn to late spring 2016. A negative association was found between raptor species diversity and Raven abundance. The density and distribution of active or potential raptor and Raven nests were also recorded along the transect: active raptor nests had significantly more active stick nests of other species (raptors and Ravens) nearby (within 500 m), whereas active Raven nests had fewer such active nests within 500 m. Intruding Ravens and Wedge-tailed Eagles Aquila audax elicited significantly higher rates of defensive interactions from nesting Black Falcons Falco subniger than did other diurnal raptor species; Ravens triggered the highest rate of response. An increased understanding of the factors responsible for shaping community structure is useful for the management of threatened species. The raptor assemblage around Tamworth includes five threatened species, at least four of which are known to breed there, making competition for nest-sites here worthy of research.

Behavioral Differences among Eastern Bluebird Populations Could Be a Consequence of Tree Swallow Presence: A Pilot Study

Aggressive interference competition for limited resources is frequently observed among animals. However, these behavioral interactions within (intraspecific) and between (interspecific) species are costly as they can be energetically expensive and cause injury or death. To avoid these agonistic interactions, numerous species alter their behaviors and resource requirements. Spatial variation in nest site competition allows for investigation of concurrent variation in territorial defense behavior. Further, among species with bi-parental nest defense, behavioral similarity in territorial defense may benefit pairs. Here, we studied territorial aggression between two eastern bluebird (Sialia sialis) populations (North Carolina and Alabama, USA) that differ in avian community structure; those in North Carolina have recently begun to experience strong interspecific competition for nesting cavities by tree swallows (Tachycineta bicolor), a competitive pressure that is relatively new for North Carolina bluebirds (~35-40 years) and is absent in Alabama populations. We found that bluebirds in North Carolina are more aggressive to simulated territorial intrusions compared to their Alabama counterparts. Behavioral similarity (here, in aggression) between partners is strong and similar in both populations. These results suggest that bluebirds in North Carolina may have to maintain higher baseline aggression during territory establishment and nest construction to co-occur with highly aggressive tree swallows, but that, in both populations, behavioral similarity between partners may be adaptive. Finally, we acknowledge the preliminary nature of this study and the need for expanding the behavioral studies to other sites in the southeastern United States. Greater regional coverage would exclude the possibility of alternative drivers of the observed behavioral differences between the North Carolina and Alabama populations.

Conflict over non-partitioned resources may explain between-species differences in declines: the anthropogenic competition hypothesis

Human alterations of habitats are causing declines in many species worldwide. The extent of declines varies greatly among closely related species, for often unknown reasons that must be understood in order to maintain biodiversity. An overlooked factor is that seasonally breeding species compete for nest sites, which are increasingly limited in many anthropogenically degraded environments. I used evolutionary game theory to predict the outcome of competition between individuals that differ in their competitive ability and timing of nesting. A range of species following evolutionarily stable strategies can co-exist when there are sufficient nest sites, but my model predicts that a reduction in nest site availability has greater impacts on late-nesting species, especially the stronger competitors, whereas early-nesting, stronger species decline only slightly. These predictions are supported by data on 221 bird and 43 bumblebee species worldwide. Restoration and provision of nest sites should be an urgent priority in conservation efforts. More broadly, these results indicate a new ecological principle of potentially widespread importance: rapid reductions in the abundance of resources for which species’ preferences have not diversified will result in unprecedented conflicts that reduce the potential for species co-existence.Significance statementUnderstanding the causes of species declines is crucial to preventing the losses. Whilst much work on species vulnerability shows broad scale effects, an enduring mystery is the variation in population trends between closely related species. I combined evolutionary modelling with three global-scale long-term data sets to reveal that competition for scarce nest sites causes variation in declines. The impact of the loss of nest sites on differential declines among closely related species from very different taxa indicates a new ecological principle of widespread importance: the effect of habitat degradation on competition among species. A lack of differentiation of nest site preferences means that—now nest sites are more limited—some species may be driving others to extinction. This phenomenon is likely to occur for any other non-partitioned resources that rapidly, on an evolutionary timescale, are now limiting population sizes.

A comparative study of insect abundance and reproductive success of barn swallows Hirundo rustica in two urban habitats

Few studies have quantified the relative reproductive success of passerines in urban habitats. I studied food availability and reproductive success of barn swallows Hirundo rustica in two urban habitats during 2012–2015. Barn swallows breeding in the town center experienced lower insect densities than those in the town periphery. Lower food availability resulted in reduced feeding rates per capita, lower nestling body mass, longer nestling periods, longer inter‐clutch intervals, fewer first and second brood fledglings and a lower total number of fledglings produced during the breeding season in comparison to barn swallows breeding in the town periphery. I hypothesize that the lower intra‐specific competition for nest sites and fitness advantages linked to the solitary breeding in urban habitats balanced the apparent costs of reproduction in more urbanized habitats.

‘The early bird catches the nest’: possible competition between scops owls and ring‐necked parakeets

AbstractCompetition for critical resources is one of the key mechanisms through which invasive species impact on native communities. Among birds, the widely introduced ring‐necked parakeet Psittacula krameri locally affects cavity‐nesting communities through competition for suitable tree cavities, although it remains unclear to what extent such competition translates into population declines of native species. Here, we studied the potential for nest site competition between ring‐necked parakeets and the native scops owl Otus scops, a small nocturnal migratory raptor, by comparing the spatial distribution of the nest site locations of the raptor before (2002) and after (2015) the parakeet invasion. Pre‐invasion nesting sites of scops owls (2002) strongly coincided with those selected by ring‐necked parakeets, but although both parakeet and scops owl populations increased during the study period, this was no longer true for 2015. Ring‐necked parakeets took over several cavities formerly occupied by scops owls, and land‐use data suggest that because of the higher overall breeding densities in 2015, scops owls were forced to occupy suboptimal breeding habitats to minimize nest site competition with invasive parakeets. Ring‐necked parakeets start breeding early in the season, a behaviour enabling them to secure the best nest sites first, before the owls return from their wintering grounds. Our study highlights that locally observed competition not necessarily impacts on population dynamics of competing species and thus warns against uncritical extrapolation of smaller scale studies for assessing invasive species risks at larger spatial scales. Nonetheless, given the increasing number of studies demonstrating its competitive capacities, monitoring of ring‐necked parakeet populations is prudent and mitigation measures (such as mounting of man‐made nest‐boxes, which are used by scops owls, but not by parakeets) may be justified when the parakeets are likely to invade areas harbouring cavity‐nesters of conservation concern.

Heterospecific Infanticidal Behavior by Southern House Wrens (Troglodytes aedon musculus) Suggests Nest Site Competition

ABSTRACT Destruction of conspecific and heterospecific eggs and nestlings occurs in several species of passerines. Two main hypotheses have been proposed to explain the adaptiveness of this behavior: as a mechanism to avoid competition or to gain access to reproductive opportunities. In Colombia, Southern House Wrens (Troglodytes aedon musculus) broke eggs and/or killed nestlings of Spectacled Parrotlets (Forpus conspicillatus, 24 cases), Apical Flycatcher (Myiarchis apicalis, one case) and of other House Wrens (four cases). Wrens attacked parrotlet nests in three contexts: 1) wrens took over and used a parrotlet nestbox within their territory, 2) wrens with an active nest attacked a neighboring parrotlet nest, or 3) the attacker was unknown but was inferred to be a wren. Wrens also attacked trial nests with natural and artificial wren eggs that were placed near active wren nests. These observations suggest that infanticidal behavior by wrens at this locality may be driven by competition for nest sites. I...

Genetic structure of native ant supercolonies varies in space and time.

Ant supercolonies are the largest cooperative units known in nature. They consist of networks of interconnected nests with hundreds of reproductive queens, where individuals move freely between nests, cooperate across nest boundaries and show little aggression towards non-nestmates. The combination of high queen numbers and free mixing of workers, queens and brood between nests results in extremely low nestmate relatedness. In such low-relatedness societies, cooperative worker behaviour appears maladaptive because it may aid random individuals instead of relatives. Here, we provide a comprehensive picture of genetic substructure in supercolonies of the native wood ant Formica aquilonia using traditional population genetic as well as network analysis methods. Specifically, we test for spatial and temporal variation in genetic structure of different classes of individuals within supercolonies and analyse the role of worker movement in determining supercolony genetic networks. We find that relatedness within supercolonies is low but positive when viewed on a population level, which may be due to limited dispersal of individuals and/or ecological factors such as nest site limitation and competition against conspecifics. Genetic structure of supercolonies varied with both sample class and sampling time point, which indicates that mobility of individuals varies according to both caste and season and suggests that generalizing has to be carried out with caution in studies of supercolonial species. Overall, our analysis provides novel evidence that native wood ant supercolonies exhibit fine-scale genetic substructure, which may explain the maintenance of cooperation in these low-relatedness societies.

Nest-site competition between invasive and native cavity nesting birds and its implication for conservation

Nesting cavities are often a limited resource that multiple species use. There is an ongoing discussion on whether invasive cavity nesting birds restrict the availability of this key limited resource. While the answer to this question has important conservation implications, little experimental work has been done to examine it. Here, we aimed to experimentally test whether alien cavity nesting birds affect the occupancy of cavities and the resulting breeding success of native cavity breeders in a large urban park located in Tel Aviv, Israel. Over three breeding seasons, we manipulated the entry size of nest boxes and compared the occupancy and breeding success of birds in nest boxes of two treatments. These included nest boxes with large-entrance and small-entrance holes. The large-entrance holes allowed access for both the native and invasive birds (the two main aliens in the park are the common mynas and rose-ringed parakeets). The smaller-entrance boxes, on the other hand, allowed only the smaller sized native cavity breeders (great tits and house sparrows) to enter the boxes but prevented the alien species from entering. We found that the large-entrance nest boxes were occupied by five different bird species, comprising three natives (great tit, house sparrow, Scops owl) and two invasive species (common myna, rose-ringed parakeet) while the small-entrance boxes were only occupied by the two native species. The alien common mynas and rose-ringed parakeets occupied 77.5% of the large-entrance nest boxes whereas native species, mainly great tits, occupied less than 9% of the large-entrance boxes and 36.5% of the small-entrance boxes. When examining the occupancy of those cavities that were not occupied by the aliens, natives occupied both the small and large-entrance nest boxes equally. Three quarters (78%) of the great tits breeding in the large-entrance boxes were usurped by common mynas during the breeding season and as a result breeding success was significantly lower for great tits breeding in the large-entrance boxes compared with the small-entrance boxes. The results of this study suggests that the invasive alien species can reduce the breeding potential of native cavity breeders both by exploiting the limited breeding resource (nest cavities) and by directly usurping cavities already occupied by the native species. Since the majority of large-entrance nest boxes were occupied by the larger alien birds, less native species bred in the limited number of unoccupied large-entrance nest boxes because of exploitation competition. We propose that for management purposes, nest-box programs that alter the entrance size of available natural cavities may be a practical approach, reducing the competition between native cavity breeders and alien invasive birds, and especially benefiting the smaller native cavity breeders.

Evaluation of nest site preferences of a nest dismantler, the Hair-crested Drongo (Dicrurus hottentottus) in Dongzhai National Nature Reserve of central China

The Hair-crested Drongo (Dicrurus hottentottus) exhibits a unique nest-dismantling behavior after the fledging of the young. One hypothesis explaining this behavior is dismantling one’s own nest may reduce potential competition for nest sites in the following breeding season because suitable breeding habitat might be limited, and sites are often reused. By comparing the habitat features at nest and random locations, we determined the nest habitat preference of the Hair-crested Drongo within Dongzhai National Nature Reserve, Henan, China. We also compared habitat features with nesting success to determine if any trends could be detected. We found that nest tree height, diameter at breast height, live crown ratio, tree rank, and presence of overstory were significantly higher at nesting locations than random locations; slope, leaf litter cover percentage and depth, presence of understory and midstory, and number of trees per hectare were significantly lower at nest sites than random sites. Drongos preferred to use some tree species, such as Metasequoia glyptostroboides, Castanea mollissima, and Pterocarya stenoptera for nesting. Failed nests were often associated with habitat with higher percentage of leaf litter on the ground. Our data support that selection of nest sites does occur for this species at this site and therefore support the hypothesis that breeding habitat limitation could be one of the driving forces for the development of the nest-dismantling behavior in this species.

First Documentation of a “Double-Decker” Cerulean Warbler (Setophaga cerulea) Nest

ABSTRACT Construction of nests containing multiple layers or “stories” has been observed in a number of passerine species. These atypical nest structures are frequently a response to brood parasitism, wherein the host female will bury the parasite’s egg under a new layer of nesting material. They may also occur as a result of either intra- or interspecific competition for limited nest sites, with one individual usurping another’s nest and adding new material on top. However, such structures have not previously been documented in the Cerulean Warbler (Setophaga cerulea), a Neotropical migrant species that breeds in the eastern U.S. and Canada. Here, we report our observations of an unusual “double-decker” nest that was constructed in 2014 in Brown County, southern Indiana. A female Cerulean Warbler first built a typical nest, and several days later we discovered a second visibly distinct nest superimposed on top of the original one. Subsequent retrieval and inspection of the two-story nest revealed no buri...

Nest-site competition between bumblebees (Bombidae), social wasps (Vespidae) and cavity-nesting birds in Britain and the Western Palearctic

Capsule There is no evidence of widespread significant nest-site competition in Britain or the Western Palearctic between cavity-nesting birds and bumblebees or social wasps.Aims To investigate competition between cavity-nesting birds and bumblebees and wasps, particularly the range-expanding Tree Bumblebee, Saxon Wasp and European Hornet in Britain, and review evidence throughout the Western Palearctic.Methods We compared field data from English and Polish studies of tits and woodpeckers breeding in nest-boxes and/or tree holes to assess nest-site competition with bumblebees and wasps. We reviewed the literature quantifying nest-site competition between birds and these insects in the Western Palearctic.Results Bumblebees and wasps are capable of usurping small passerines from nests. In England, these insects commandeered a mean annual 4.1% of tit nests initiated in nest-boxes; occurrence of hornets showed a long-term increase, but not other wasps or bumblebees. Across the Western Palearctic, insect occupation of nest-boxes was generally low, and was lower in England than in Poland. No insects were discovered in tree cavities, including those created by woodpeckers (Picidae).Conclusion Nest-site competition between cavity-nesting birds and bumblebees and wasps appears to be a ‘nest-box phenomenon’, which may occasionally interfere with nest-box studies, but appears negligible in natural nest-sites.

Latitudinal variation in behaviors linked to risk tolerance is driven by nest-site competition and spatial distribution in the ant Temnothorax rugatulus

Geographic range has long been noted to be associated with many organismic and ecological traits such as body size and species richness. However, much less is known about whether and how ecological variation across latitudinal gradients reflects behavioral variation. Ant colonies may also show behavioral variation, and Temnothorax rugatulus show a colony-level behavioral syndrome that seems to reflect risk tolerance across their North American range. While it is presumed that this pattern is the result of adaptation to local environmental conditions, which ecological factors are driving this variation are unknown. Here, we test if colony risk tolerance is affected by competition, predation, resource availability, or environmental stress at each site. Our results show that increased competition, specifically for nest sites, as well as increased spatial clustering of colonies predicts higher risk tolerance. Additionally, the spatial clustering of colonies influences the structure of the risk-taking syndrome, i.e., which colony-level behaviors are correlated and how strongly. This emphasizes the need for understanding large-scale geographic variation in behavior, as it may explain how ecological factors drive the evolution and maintenance of intraspecific behavioral variation across populations.

Do American dippers obtain a survival benefit from altitudinal migration?

Studies of partial migrants provide an opportunity to assess the cost and benefits of migration. Previous work has demonstrated that sedentary American dippers (residents) have higher annual productivity than altitudinal migrants that move to higher elevations to breed. Here we use a ten-year (30 period) mark-recapture dataset to evaluate whether migrants offset their lower productivity with higher survival during the migration-breeding period when they occupy different habitat, or early and late-winter periods when they coexist with residents. Mark-recapture models provide no evidence that apparent monthly survival of migrants is higher than that of residents at any time of the year. The best-supported model suggests that monthly survival is higher in the migration-breeding period than winter periods. Another well-supported model suggested that residency conferred a survival benefit, and annual apparent survival (calculated from model weighted monthly apparent survival estimates using the Delta method) of residents (0.511 ± 0.038SE) was slightly higher than that of migrants (0.487 ± 0.032). Winter survival of American dippers was influenced by environmental conditions; monthly apparent survival increased as maximum daily flow rates increased and declined as winter temperatures became colder. However, we found no evidence that environmental conditions altered differences in winter survival of residents and migrants. Since migratory American dippers have lower productivity and slightly lower survival than residents our data suggests that partial migration is likely an outcome of competition for limited nest sites at low elevations, with less competitive individuals being forced to migrate to higher elevations in order to breed.