Allee effects and conspecific cueing jointly lead to conspecific attraction

Conspecific attraction is the preferential settlement into habitat patches with conspecifics. To be a good proximate strategy, fitness gains from settling with conspecifics must outweigh the costs of higher conspecific densities, such as intraspecific competition. Two types of benefits have been proposed to explain conspecific attraction: Allee effects (i.e., positive density dependence) and conspecific cueing (using conspecifics as an indicator of habitat quality). I present empirical evidence for conspecific attraction in the settlement of the porcelain crab, Petrolisthes cinctipes Randall (Anomura: Porcellanidae). Previous work demonstrated that P. cinctipes experiences strong intraspecific competition and that both Allee effects and conspecific cueing are present in P. cinctipes life-history. I developed an empirically-based fitness model of the costs and benefits of settling with conspecifics. Based on this model, I simulated optimal settlement to habitat patches that varied in conspecific density and habitat quality, where the correlation between density and habitat quality determined the level of conspecific cueing. I tested whether Allee effects alone, conspecific cueing alone, or Allee effects and conspecific cueing together could provide an ultimate explanation for the proximate settlement behavior of P. cinctipes. The settlement simulation was consistent with empirical settlement only when Allee effects and conspecific cueing were both included. Three life-history features are critical to this conclusion: (1) fitness is maximized at intermediate density, (2) fitness depends on the decisions of previous settlers, and (3) conspecific density provides good information about habitat quality. The quality of information garnered from conspecifics determines whether conspecific attraction is a good proximate strategy for settlement. I present a graphical illustration demonstrating how Allee effects and conspecific cueing work together to influence fitness, providing a conceptual framework for other systems.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Reconciling social interaction with habitat selection in territorial species

The concept of habitat selection as the primary force in clustered distributions has been challenged by behavioral studies of conspecific attraction. This has lead to two conflicting explanations for settlement behavior, which we have integrated into one model. This model creates a range of fitness outcomes for different settlement strategies, encompassing the four combinations of positive and negative effects of the habitat selection and social interaction. It expands the ideal free distribution models (negative intra-specific interactions and positive habitat selection), to consider alternative situations where (1) beneficial social interaction increases fitness for clustered pairs in poor quality habitat, (2) neither habitat selection nor conspecific attraction can improve fitness, and (3) where both are beneficial and do not interfere with each other. The model does this by establishing an intrinsic fitness, where the effects of both habitat selection (h) and conspecific attractions (c) are neutral (h = c = 1) and do not influence settlement. Clustered distributions occur when h · c > 1 because the fitness in clusters is greater than intrinsic fitness. Dispersed distributions occur when h · c < 1 and fitness is lower than the intrinsic. The benefit of the model is that it allows conspecific attraction to be considered a positive force in fitness without rejecting the proven concept of ideal free distribution.     

Predation-Related Costs and Benefits of Conspecific Attraction in Songbirds—An Agent-Based Approach

Songbirds that follow a conspecific attraction strategy in the habitat selection process prefer to settle in habitat patches already occupied by other individuals. This largely affects the patterns of their spatio-temporal distribution and leads to clustered breeding. Although making informed settlement decisions is expected to be beneficial for individuals, such territory clusters may potentially provide additional fitness benefits (e.g., through the dilution effect) or costs (e.g., possibly facilitating nest localization if predators respond functionally to prey distribution). Thus, we hypothesized that the fitness consequences of following a conspecific attraction strategy may largely depend on the composition of the predator community. We developed an agent-based model in which we simulated the settling behavior of birds that use a conspecific attraction strategy and breed in a multi-predator landscape with predators that exhibited different foraging strategies. Moreover, we investigated whether Bayesian updating of prior settlement decisions according to the perceived predation risk may improve the fitness of birds that rely on conspecific cues. Our results provide evidence that the fitness consequences of conspecific attraction are predation-related. We found that in landscapes dominated by predators able to respond functionally to prey distribution, clustered breeding led to fitness costs. However, this cost could be reduced if birds performed Bayesian updating of prior settlement decisions and perceived nesting with too many neighbors as a threat. Our results did not support the hypothesis that in landscapes dominated by incidental predators, clustered breeding as a byproduct of conspecific attraction provides fitness benefits through the dilution effect. We suggest that this may be due to the spatial scale of songbirds’ aggregative behavior. In general, we provide evidence that when considering the fitness consequences of conspecific attraction for songbirds, one should expect a trade-off between the benefits of making informed decisions and the costs of clustering.     

Species interactions and population density mediate the use of social cues for habitat selection

1. The perspective that populations and communities are structured by antagonistic interactions among individuals has dominated much of ecology. Yet how animals use social information to guide decisions, such as habitat selection, may be influenced by both positive and negative interactions among individuals. Recent theory also suggests that the way animals use social information may be substantially influenced by population density, which alters the potential costs and benefits of such behaviours. 2. I manipulated cues of two competitors, the dominant least flycatcher Empidonax minimus (Baird & Baird) and the subordinate American redstart Setophaga ruticilla (Linnaeus), to assess the use of conspecific and heterospecific cues during habitat selection, and if population density influences these strategies. The experiment consisted of surveying birds during a pre-treatment year, which allows for the control and testing the effect of baseline densities, and a treatment year, in which treatments were applied just prior to settlement. Treatments included broadcasting songs of flycatchers and redstarts, and were compared with controls. 3. When controlling for pre-treatment densities, bird densities, and to a lesser extent arrival dates, during the treatment year suggested that flycatchers were attracted to both conspecific and heterospecific cues during settlement. Furthermore, attraction was strongest for flycatchers in plots with moderate pre-treatment densities. American redstarts were rare in the study area but showed apparent attraction to conspecifics and avoidance of heterospecifics. 4. These results provide experimental evidence for the use of multiple social cues in habitat selection and suggest that heterospecific attraction may operate under broader contexts than originally envisioned. In such instances, nontarget effects can potentially occur when manipulating social cues to elicit settlement in conservation strategies. The impact of population density on the use of social cues shown here can also influence our understanding of metapopulation dynamics by causing complex threshold effects on the likelihood of rescue, which may influence metapopulation stability and the likelihood of local extinction.     

Wood warblers copy settlement decisions of poor quality conspecifics: support for the tradeoff between the benefit of social information use and competition avoidance

Social information use in songbird habitat selection commonly involves a conspecific attraction strategy. Individuals copy the breeding‐site choices of conspecifics, that is, bias their own settlement decisions towards sites (tracts of spatially limited habitat with similar structure) already occupied by others. In order to be adaptive, social information use has to be discriminative. Especially the decisions of good quality individuals, i.e. measuring high at observable fitness correlates, should be copied more frequently than those of poor quality individuals. It is unknown, however, whether songbirds discriminatively use conspecific presence by evaluating the quality of information providers in habitat selection. We experimentally tested whether wood warblers Phylloscopus sibilatrix selectively copied settlement decisions of conspecifics in relation to the quality of observed individuals. We also tested whether the use of social cues was influenced by the population density at a particular site in the preceding year. We found that wood warblers selectively used intraspecific social information, but in a pattern opposite to that expected based on existing hypotheses. Wood warblers copied breeding‐site choices of poor quality conspecifics and despite temporary attraction to sites where the presence of good quality individuals was simulated, they did not ultimately settle near these individuals. Population density in the preceding year did not influence settlement patterns. We argue that when making settlement decisions, wood warblers assessed the expected level of local intraspecific competition and selectively copied breeding‐site choices of conspecifics or refused to settle, depending on competitive abilities of observed individuals. This adds a novel aspect to the patterns and processes of social information use proposed thus far, and provides support for the predicted negative effect of intraspecific competition on benefit of information. Moreover, it seems that habitat selection in wood warblers is a complex decision‐making process, in which initial decisions are adjusted after acquiring more accurate information. Synthesis Social information use in songbird habitat selection commonly involves copying the breeding‐site choices of conspecifics (so‐called conspecific attraction). To be adaptive, this strategy has to be discriminative, but almost no empirical studies have tested this assertion. Our study shows that birds may selectively use social information by copying settlement decisions of poor quality conspecifics, but avoid settling near good quality individuals, likely because of their high competitive abilities. This decision‐making pattern supports the predicted, yet not experimentally tested, tradeoff between information value and cost of competition in social information use. Our study highlights also that the use of social cues in settlement decisions may be both positively and negatively biased.     

A silver spoon for a golden future: long-term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)

1. Long-term effects of conditions during early development on fitness are important for life history evolution and population ecology. Using multistrata mark-recapture models on 20 years of data, we quantified the relation between rearing conditions and lifetime fitness in a long-lived shorebird, the oystercatcher (Haematopus ostralegus). We addressed specifically the relative contribution of short- and long-term effects of rearing conditions to overall fitness consequences. 2. Rearing conditions were defined by differences in natal habitat quality, in which there is a clear dichotomy in our study population. In the first year of life, fledglings from high-quality natal origin had a 1.3 times higher juvenile survival. Later in life (age 3-11), individuals of high-quality natal origin had a 1.6 times higher adult prebreeder survival. The most striking effect of natal habitat quality was that birds that were reared on high-quality territories had a higher probability of settling in high-quality habitat (44% vs. 6%). Lifetime reproductive success of individuals born in high-quality habitat was 2.2 times higher than that of individuals born in low-quality habitat. This difference increased further when fitness was calculated over several generations, due to a correlation between the quality of rearing conditions of parents and their offspring. 3. Long-term effects of early conditions contributed more to overall fitness differences as short-term consequences, contrary to common conceptions on this issue. 4. This study illustrates that investigating only short-term effects of early conditions can lead to the large underestimation of fitness consequences. We discuss how long-term consequences of early conditions may affect settlement decisions and source-sink population interactions.     

The nose knows: linking sensory cue use,settlement decisions,and post-settlement survival in a temperate reef fish

Habitat selection by animals that migrate or disperse ultimately determines the biotic and abiotic environment they will experience in subsequent life stages. Intuitively, for habitat selection to be adaptive, animals should respond positively to cues produced by habitat characteristics that will enhance their fitness in the new environment. However, there are many examples of dispersing animals where individuals are attracted to cues produced by factors that reduce their fitness after arrival. In this study, we use a temperate reef fish to examine the relative importance of habitat-associated cues in habitat selection decisions, and assess whether use of these cues is adaptive across early life stages. We used a series of laboratory- and field-based manipulative experiments to test: (1) what habitat-associated cues are likely used to locate suitable habitat; (2) whether in situ settlement patterns reflect the cue response tested in the laboratory; and (3) whether the aspects of the habitat that stimulate settlement are the same as those that maximize survival. We observed a positive response to multiple habitat-associated cues, with conspecific cues eliciting the strongest behavioral response in laboratory choice experiments, and a strong inverse density-dependent relationship at settlement. Macroalgal cues also elicited a positive response at settlement, but were associated with higher mortality after settlement, suggesting that habitat selection decisions are not always adaptive. We argue that this non-intuitive behavior may still be adaptive if it improves fitness at an earlier life stage, as habitat selection behavior is the result of tradeoffs in fitness costs across multiple stages.     

Effects of individual condition and habitat quality on natal dispersal behaviour in a small rodent

1. Individuals should benefit from settling in high-quality habitats, but dispersers born under favourable conditions have a better physical condition and should therefore be more successful at settling in high-quality habitats. 2. We tested these predictions with root voles (Microtus oeconomus) by a manipulation of individual condition through litter-size enlargement and reduction during lactation combined with a manipulation of habitat quality through degradation of the vegetation cover. We accurately monitored movements of 149 juveniles during a settlement and breeding period of 3 months. 3. The litter size treatment had long-lasting effects on body size, life-history traits and home range size, but did not influence dispersal behaviour. 4. Different stages of dispersal were influenced by habitat quality. In low-quality patches, females dispersed earlier, spent more time prospecting their environment before settling, and settlers had a smaller adult body size than in high-quality patches. Preference and competition for high-quality patches is likely adaptive as it increased fitness both in terms of survival and reproduction. 5. We found no interactive effect of individual condition and habitat quality on natal dispersal and habitat selection. 6. These findings suggest that immediate conditions are more important determinants of dispersal decisions than conditions experienced early in life.     

Conspecific attraction and nest site selection in a nomadic species,the zebra finch

Conspecific nesting density affects many aspects of breeding biology, as well as habitat selection decisions. However, the large variations in breeding density observed in many species are yet to be fully explained. Here, we investigated the settlement patterns in a colonial species with variable breeding density and where resource distribution could be manipulated. The zebra finch, Taeniopygia guttata, is a classic avian model in evolutionary biology but we know surprisingly very little about nest site selection strategies and nesting densities in this species, and in fact, in nomadic species in general. Yet, important determinants of habitat selection strategies, including temporal predictability and breeding synchrony, are likely to be different in nomadic species than in the non‐nomadic species studied to date. Here, we manipulated the distribution of nesting sites (by providing nest boxes) and food patches (feeders) to test four non‐exclusive habitat selection hypotheses that could lead to nest aggregation: 1) attraction to resources, 2) attraction to breeding conspecifics, and 3) attraction to successful conspecifics and 4) use of private information (i.e. own reproductive success on a site). We found that wild zebra finches used conspecific presence and possibly reproductive success, to make decisions over where to locate their nests, but did not aggregate around water or food within the study areas. Moreover, there was a high degree of inter‐individual variation in nesting density preference. We discuss the significance of our results for habitat selection strategy in nomadic species and with respect to the differential selection pressures that individuals breeding at different densities may experience.     

Evolution of heterospecific attraction: using other species as cues in habitat selection

We analyzed the ecological conditions that may favor a habitat selection process in which later arriving individuals (colonists) use the presence of earlier established species (residents) as a cue to profitable breeding sites (heterospecific attraction). In our model, colonists assessing potential breeding patches could select between high-quality source and low-quality sink patches. A proportion of the source patches were occupied by residents. Colonists could either directly sample the relative quality of the patches (termed samplers) or, alternatively, they could also use residents as a cue of patch quality (cue-users). Cue-users gained benefit from lowered costs when assessing occupied source patches. The cue-using strategy is an efficient way to choose the best possible patch not only when interspecific competition is intense, but also when benefits from social aggregation exceed the effects of competition. High relative cost of sampling empty patches increases the fitness of the cue-using strategy relative to samplers. The strongest attraction to heterospecifics was predicted when the benefit from aggregating with residents exceeded the effects of competition, and approximately half of the landscape consisted of occupied, high-quality source patches.     

Who is in the neighborhood? Conspecific and heterospecific responses to perceived density for breeding habitat selection

Theoretical models of habitat selection often incorporate negative density dependence. Despite strong negative density‐dependent effects on habitat selection, more recent studies indicate that animals settle near members of their own (conspecific) and other species (heterospecific) when selecting habitat with social cues. Social cue use for habitat selection is particularly common among songbirds, but few studies have investigated if songbirds use social cues to assess conspecific or heterospecific density (as opposed to just presence/absence) when making settlement decisions. We conducted a playback experiment to evaluate if yellow warblers (Setophaga petechia) and willow flycatchers (Empidonax traillii), two potential competitors for breeding habitat, use social cues to assess density (conspecific for warblers and heterospecific for flycatchers) when selecting breeding locations at two spatial scales. We simulated yellow warbler density to be high or low at multiple treatment plots (3.14 ha) with song playback and then evaluated settlement decisions by comparing yellow warbler and willow flycatcher abundances across plots (broad‐scale habitat selection) and individual space use within plots (fine‐scale territory establishment). Yellow warbler density treatments did not affect habitat selection by yellow warblers at the broad scale, but caused individuals to cluster territories at high‐density treatments. Willow flycatchers were most abundant at high‐density treatment plots, but yellow warbler density treatments did not affect territory locations. The results indicate that perceived density affects the habitat selection process for both conspecifics and heterospecifics.     

“Perchance to dream?”: Assessing the effects of dispersal strategies on the fitness of expanding populations

Unraveling the patterns of animals’ movements is crucial to understanding the basics of biogeography, tracking range shifts resulting from climate change, and predicting and preventing biological invasions. Many researchers have modeled animals’ dispersal under the assumptions of various movement strategies, either predetermined or directed by external factors, but none have compared the effects of different movement strategies on population survival and fitness. In this paper, using an agent-based model with a landscape divided into cells of varying quality, we compare the ecological success of three movement and habitat selection strategies (MHSSs): (i) Smart, in which animals choose the locally optimal cell; (ii) Random, in which animals move randomly between cells without taking into account their quality; (iii) Dreamer, in which animals attempt to find a habitat of dream whose quality is much higher than that of the habitat available on the map. We compare the short-term success of these MHSSs in good, medium and bad environments. We also assess the effect of temporal variation of habitat quality (specifically, winter harshness) on the success of each MHSS. Success is measured in terms of survival rate, dispersal distance, accumulated energy and quality of settled habitat. The most general conclusion is that while survival rate, accumulated energy and quality of settled habitat are affected primarily by overall habitat composition (proportions of different habitat types in the landscape), dispersal distance depends mainly on the MHSS. In medium and good environments, the Dreamer strategy is highly successful: it simultaneously outperforms the Smart strategy in dispersal distance and the Random strategy in terms of the other metrics.     

Beyond ecological traps: perceptual errors and undervalued resources

Ecological traps arise when animals choose to settle in poor-quality habitats, leading to a reduction in their survival or productivity. Although this phenomenon has received comprehensive theoretical treatment in the recent literature, the corollary of the ecological trap (when animals choose to avoid good-quality habitats) is rarely discussed. Failure to recognize high-quality sites could influence the ability of a population to reach its threshold size. An exploration of this phenomenon brings new insights into existing cases of ecological traps. By considering the full range of pitfalls faced during settlement, the relationship between habitat quality and population size might become clearer. We argue here that an improved understanding of factors determining the colonization of high-quality sites could aid conservationists in mitigating the damaging effects of maladaptive habitat selection.     

Conspecific cues and breeding habitat selection in an endangered woodland warbler

1.?Research on habitat selection has focused on the role of vegetative and geologic characteristics or antagonistic behavioural interactions. 2.?Conspecifics can confer information about habitat quality and provide positive density-dependent effects, suggesting habitat selection in response to the presence of conspecifics can be an adaptive strategy. 3.?We conducted a manipulative field experiment investigating use of conspecific location cues for habitat selection and consequent reproductive outcomes for the endangered golden-cheeked warbler (Setophaga chrysoparia). We investigated the response in woodlands across a range of habitat canopy cover conditions typically considered suitable to unsuitable and using vocal cues presented during two time periods: pre-settlement and post-breeding. 4.?Warblers showed a strong response to both pre-settlement and post-breeding conspecific cues. Territory density was greater than four times higher in treatment sample units than controls. The magnitude of response was higher for cues presented during the pre-settlement period. Positive response to conspecific cues was consistent even in previously unoccupied areas with low canopy cover typically considered unsuitable, resulting in aggregations of warblers in areas generally not considered potential habitat. 5.?Pairing and reproductive success of males was not correlated with canopy cover, as commonly thought. Pairing success and fledging success increased with increasing territory density suggesting that conspecific density may be more important for habitat selection decisions than the canopy cover conditions typically thought to be most important. These results suggest the range of habitat within which birds can perform successfully may be greater than is typically observed. 6.?Our results suggest the territory selection process may not be substantially influenced by competition in some systems. Settlement in response to conspecific cues produced aggregations within larger areas of similar vegetative characteristics. Understanding what cues drive habitat selection decisions and whether these cues are correlated with habitat quality is critical for conserving fitness-enhancing habitats, avoiding creation of ecological traps, generating accurate predictions of species distributions and understanding how occupancy relates to habitat suitability.     

Aggregations from using inadvertent social information: a form of ideal habitat selection

Social information in breeding site selection has received extensive study; however, few attempts have been made to link this process to pre‐existing models. We examine the importance of social information to three pertinent models of habitat selection that describe breeding aggregations and spatial patterns: 1) the ideal despotic distribution (IDD) which considers conspecific competition and habitat availability, 2) the perceptual constraints model which accounts for patch selection when animals experience a threshold of undetectable difference in quality, and 3) the “neighbourhood model” which predicts concordance between resources and settlers can be disrupted by conspecific attraction when resources are patchy. These models all predict initial settlers will select a high quality patch first. However, their predictions of subsequent settlement behaviour in remaining patches differ: the IDD predicts subsequent settlers will be distributed regularly, the perceptual constraints model predicts a random distribution, and the neighbourhood model predicts clustering from conspecific attraction. We examined which model best described settlement patterns of bobolink Dolichonyx oryzivorus and savannah sparrow Passerculus sandwichensis, in the context of social information. We observed settlement timing, quantified available resources, and determined where they occurred in the highest (local population “core”) and lowest densities (local population “periphery”). We then assessed whether individuals in the periphery settled in greater concordance with resources or conspecific presence. Core territories were clustered strongly on relevant resources, and these territory holders were older than in the periphery. Peripheral territories were likewise clustered but did not always co‐occur with the best available resources, matching the neighbourhood model prediction that social information may not always direct them to the best sites available. This suggests older individuals used their own experience to locate ideal habitat, whereas younger individuals attempted to aggregate on seemingly ideal habitat by using conspecific location; such information asymmetry due to age can be viewed as an “ideal aggregative distribution”.     

Conspecific Attraction is a Missing Component in Wildlife Habitat Modeling

Abstract Wildlife biologists use knowledge about wildlife-habitat relationships to create habitat models to predict species occurrence across a landscape. Researchers attribute limitations in predictive ability of a habitat model to data deficiencies, missing parameters, error introduced by specifications of the statistical model, and natural variation. Few wildlife biologists, however, have incorporated intra- and interspecific interactions (e.g., conspecific attraction, competition, predator-prey relationships) to increase predictive accuracy of habitat models. Based on our literature review and preliminary data analysis, conspecific attraction can be a primary factor influencing habitat selection in wildlife. Conspecific attraction can lead to clustered distributions of wildlife within available habitat, reducing the predictive ability of habitat models based on vegetative and geographic parameters alone. We suggest wildlife biologists consider incorporating a parameter in habitat models for the clustered distribution of individuals within available habitat and investigate the mechanisms leading to clustered distributions of species, especially conspecific attraction.     

Climate and density influence annual survival and movement in a migratory songbird

Assessing the drivers of survival across the annual cycle is important for understanding when and how population limitation occurs in migratory animals. Density‐dependent population regulation can occur during breeding and nonbreeding periods, and large‐scale climate cycles can also affect survival throughout the annual cycle via their effects on local weather and vegetation productivity. Most studies of survival use mark–recapture techniques to estimate apparent survival, but true survival rates remain obscured due to unknown rates of permanent emigration. This is especially problematic when assessing annual survival of migratory birds, whose movement between breeding attempts, or breeding dispersal, can be substantial. We used a multistate approach to examine drivers of annual survival and one component of breeding dispersal (habitat‐specific movements) in a population of American redstarts (Setophaga ruticilla) over 11 years in two adjacent habitat types. Annual survival displayed a curvilinear relation to the Southern Oscillation Index, with lower survival during La Niña and El Niño conditions. Although redstart density had no impact on survival, habitat‐specific density influenced local movements between habitat types, with redstarts being less likely to disperse from their previous year's breeding habitat as density within that habitat increased. This finding was strongest in males and may be explained by conspecific attraction influencing settlement decisions. Survival was lowest in young males, but movement was highest in this group, indicating that apparent survival rates were likely biased low due to permanent emigration. Our findings demonstrate the utility of examining breeding dispersal in mark–recapture studies and complement recent work using spatially explicit models of dispersal probability to obtain greater accuracy in survival estimates.     

Does attraction to conspecifics explain the patch‐size effect? An experimental test

Recent theory suggests that attraction to conspecifics during habitat selection can be one potential, yet untested, mechanism for animal sensitivity to habitat fragmentation. The least flycatcher Empidonax minimus , a highly territorial migratory bird, has previously been shown to be attracted to conspecifics and sensitive to patch size by avoiding small patches of riparian forest in Montana, USA. I used a large-scale field experiment in this region to test the conspecific attraction hypothesis for explaining sensitivity to patch size, and I supplemented this experiment by estimating whether vegetation structure, nest predation, or nest parasitism rates could better explain patterns of sensitivity to patch size. Vegetation structure did not vary consistently with patch size, based on a random sample of patches across 150  km of the Madison and Missouri Rivers, Montana. Nest predation and parasitism rates by brown-headed cowbirds Molothrus ater also did not vary with patch size during the experiment. However, when conspecific cues were simulated across a gradient of patch sizes, flycatchers settled in all patches – and their sensitivity to patch size vanished – providing strong support for the conspecific attraction hypothesis. These results provide the first experimental evidence that attraction to conspecifics can indeed help explain area sensitivity in nature and highlight how understanding the role of animal behavior in heterogeneous landscapes can aid in interpreting pressing conservation issues.     

Managing breeding forest songbirds with conspecific song playbacks

Recent studies confirm that several territorial songbird species use conspecific cues, including song, when selecting habitat. We conducted a controlled experiment with a population of black-throated blue warblers Dendroica caerulescens , a species of concern in boreal hardwood transition forests, to determine whether song playbacks influence settlement patterns. We tested whether conspecific song broadcast during spring arrival attracts black-throated blue warblers during territory establishment, and whether song playbacks shift territories from the previous year's breeding distributions. The results of our experiment demonstrate that song playbacks significantly increased territorial occupancy and shifted territories closer to the speakers. Loss of breeding habitat is implicated in population declines of many songbirds, and our results suggest that song playbacks should be further investigated as a tool for mitigating the effects of disruptive management actions. Additional work should consider the spatial arrangement of playback speakers to avoid attracting birds from safe areas. The demographic consequences of conspecific attraction must also be explored before this technique is widely implemented.     

Habitat selection in a fluctuating ground squirrel population: Density‐dependence and fitness consequences

Investigating individual‐based habitat settlement decisions is a central theme in ecology, yet studies that quantify density‐dependent habitat selection or tie fitness to resource selection decisions remain rare. We quantified habitat selection in golden‐mantled ground squirrels (Callospermophilus lateralis) across two spatial scales (home‐range placement, and occurrence within the home range) by using 11 consecutive years of data on individual space use, and we used resource selection functions and multilevel modeling to address how habitat preferences may be influenced by density or linked to fitness outcomes. Squirrels preferred dry meadow over other habitat types (wet meadow, aspen, spruce, and willow) at both spatial scales. Squirrels were more likely to use dry meadow that contained shorter vegetation and vision‐enhancing prominences such as rocks (“perches”). The use of dry meadow at each scale was not influenced by changes in density. The use of dry meadow did not lead to increased litter size, pre‐hibernation mass, or survival. However, squirrels that experienced a greater number of perches or lower local densities had higher survival rates. Our results suggest that a lack of visual obstruction, probably facilitating detection of predators, drives habitat selection in this system. Surprisingly, squirrels maintained their preference for dry meadow as density increased, and they experienced reduced survival as a result. This work furthers our understanding about the causes and consequences of changes in habitat use, informing wildlife management and conservation.