The effect of familiarity with a neighborhood on territory acquisition

Asymmetric competition and floater dynamics

In territorial species, nonterritorial floaters may be critical to population dynamics. One theoretical framework, based on the assumption that floating is a strategic decision to forego reproduction, predicts that selection maintains an abundant floater population even if low-quality territories are available. However, existing models make two critical assumptions: all individuals have equal competitive ability, and every individual in a population has access to every available territory. We assess the consequences of relaxing these assumptions in a model of asymmetric competition with a trade-off between investment in competitiveness and reproductive success. Our results demonstrate that selection for greater competitiveness eliminates floater production unless the outcome of territorial contests has a strong stochastic component. Next, we suppose individuals can compete for territories only within a fixed neighborhood. If this constraint is sufficiently strong, our model predicts that a population will produce floaters. Finally, we show that our model makes novel predictions regarding the maintenance of trait variation and the relationship between this variation and the distribution of competitors among unequal territories.

Early-life foraging: Behavioral responses of newly fledged albatrosses to environmental conditions

In order to survive and later recruit into a population, juvenile animals need to acquire resources through the use of innate and/or learnt behaviors in an environment new to them. For far‐ranging marine species, such as the wandering albatross Diomedea exulans, this is particularly challenging as individuals need to be able to rapidly adapt and optimize their movement strategies in response to the highly dynamic and heterogeneous nature of their open‐ocean pelagic habitats. Critical to this is the development and flexibility of dispersal and exploratory behaviors. Here, we examine the movements of eight juvenile wandering albatrosses, tracked using GPS/Argos satellite transmitters for eight months following fledging, and compare these to the trajectories of 17 adults to assess differences and similarities in behavioral strategies through time. Behavioral clustering algorithms (Expectation Maximization binary Clustering) were combined with multinomial regression analyses to investigate changes in behavioral mode probabilities over time, and how these may be influenced by variations in day duration and in biophysical oceanographic conditions. We found that juveniles appeared to quickly acquire the same large‐scale behavioral strategies as those employed by adults, although generally more time was spent resting at night. Moreover, individuals were able to detect and exploit specific oceanographic features in a manner similar to that observed in adults. Together, the results of this study suggest that while shortly after fledging juvenile wandering albatrosses are able to employ similar foraging strategies to those observed in adults, additional skills need to be acquired during the immature period before the efficiency of these behaviors matches that of adults.

Application of large-scale parentage analysis for investigating natal dispersal in highly vagile vertebrates: a case study of American black bears (Ursus americanus)

Understanding the factors that affect dispersal is a fundamental question in ecology and conservation biology, particularly as populations are faced with increasing anthropogenic impacts. Here we collected georeferenced genetic samples (n = 2,540) from three generations of black bears (Ursus americanus) harvested in a large (47,739 km²), geographically isolated population and used parentage analysis to identify mother-offspring dyads (n = 337). We quantified the effects of sex, age, habitat type and suitability, and local harvest density at the natal and settlement sites on the probability of natal dispersal, and on dispersal distances. Dispersal was male-biased (76% of males dispersed) but a small proportion (21%) of females also dispersed, and female dispersal distances (mean ± SE  =  48.9±7.7 km) were comparable to male dispersal distances (59.0±3.2 km). Dispersal probabilities and dispersal distances were greatest for bears in areas with high habitat suitability and low harvest density. The inverse relationship between dispersal and harvest density in black bears suggests that 1) intensive harvest promotes restricted dispersal, or 2) high black bear population density decreases the propensity to disperse. Multigenerational genetic data collected over large landscape scales can be a powerful means of characterizing dispersal patterns and causal associations with demographic and landscape features in wild populations of elusive and wide-ranging species.

Sex-biased dispersal: a result of a sex difference in breeding site availability

Sex-biased dispersal is often explained by assuming that the resource-defending sex pays greater costs of moving from a familiar area. We hypothesize that sex-biased dispersal may also be caused by a sex bias in breeding site availability. In avian resource-defense mating systems, site availability is often more constrained for females: males can choose from all vacant sites, whereas females are restricted to sites defended by males. Using data on breeding dispersal of a migratory passerine, we show that average number of available breeding options and availability of the previous year's territory was greater for males than females. The female bias in site unavailability may explain the female bias in probability of breeding dispersal because there was no sex bias in dispersal among birds with their previous year's territory available. We suggest that sex biases in the availability of breeding options may be an important factor contributing to observed variation in sex-biased dispersal patterns.

Natal dispersal patterns are not associated with inbreeding avoidance in the Seychelles warbler

In this study, we test whether patterns of territory inheritance, social mate choice and female-biased natal dispersal act as inbreeding avoidance mechanisms in the cooperatively breeding Seychelles warbler. Our results show that Seychelles warblers do not reduce the likelihood of inbreeding by avoiding related individuals as mates. The occurrence of natural and experimentally induced territory inheritance did not depend on whether the remaining breeder was a parent of the potential inheritor or an unrelated breeder. Furthermore, dispersing individuals were no less related to their eventual mates than expected given the pool of candidates they could mate with. The female bias in natal dispersal distance observed in the Seychelles warbler does not facilitate inbreeding avoidance because, contrary to our prediction, there was no sex difference in the clustering of related opposite sex breeders around the natal territories of dispersers. As a result, the chance of females mating with relatives was not reduced by their greater dispersal distance compared with that of males.

Habitat exploration and use in dispersing juvenile flying squirrels

1. Variation in behaviours involved in habitat selection is important for several evolutionary and ecological processes. For example, habitat use during dispersal may differ from breeding habitat use, and for dispersers the scale of habitat familiarity is determined by exploratory behaviour. We studied habitat use and exploration of 56 radio-collared juvenile flying squirrels Pteromys volans L. within natal home range and during dispersal, and compared habitat use between juveniles and 37 adults within breeding home range. 2. Before dispersal, young flying squirrels actively moved around the natal site. Surprisingly, long-distance dispersers explored less than short-distance dispersers, but philopatric individuals explored similar distances as dispersers. Females explored less than males, although females are the more dispersive sex in flying squirrels. 3. For most of the individuals the settlement area was unfamiliar due to long dispersal distance. Consequently, direction and distance of exploration were not very strong predictors of settlement location. However, individuals familiar with the settlement area concentrated exploration to that area. Exploration did not correlate with short-term survival. 4. Dispersers preferred breeding habitat while dispersing, but were found more often in matrix habitat than juveniles within natal, or adults within breeding, home ranges. 5. We conclude that familiarity does not determine settlement as much as, for example, availability of the habitat for flying squirrels. Based on our results, it also seems clear that data on adult habitat use are not enough to predict habitat use of dispersing individuals. In addition, our results support the recent view that short- and long-distance dispersers may need to be analysed separately in ecological and evolutionary analyses.

Dispersal range analysis: quantifying individual variation in dispersal behaviour

A complete understanding of animal dispersal requires knowledge not only of its consequences at population and community levels, but also of the behavioural decisions made by dispersing individuals. Recent theoretical work has emphasised the importance of this dispersal process, particularly the phase in which individuals search the landscape for breeding opportunities. However, empirical advances are currently hampered by a lack of tools for quantifying these dispersal search tactics. Here, we review existing methods for quantifying movement that are appropriate for the dispersal search process, describe several new techniques that we developed for characterising movement and behaviour through an individual's dispersal range, and illustrate their use with data from Australasian treecreepers (Climacteridae). We also describe how the quantitative parameters we discuss are calculated in a freely available computer software package that we designed. Specifically, we present methods for calculating the area searched during dispersal, search rate, thoroughness, intensity, philopatry of search, timing of exploration, and surreptitiousness. When we applied this approach to the study of dispersal in treecreepers, we found that search area, philopatry and timing of exploration showed the greatest individual variation. Furthermore, search area, search rate, thoroughness and philopatry of search were all correlated, suggesting they may be useful parameters for further research on the causes and consequences of different dispersal search tactics. Finally, we make recommendations for modifying radiotracking protocols to facilitate more accurate assessment of individual variation in the dispersal process, and suggest future directions for this type of empirical work at the interface of population and behavioural ecology.

Changes in exploration from courtship to the breeding state in red-rumped parrots (Psephotus haematonotus)

Animals explore their environment to gather information about feeding areas, resting places, or suitable territories for reproduction. During the annual cycle seasonal variation in exploration occurs at least in some species. In this study, exploratory behaviour of red-rumped parrots (Psephotus haematonotus) was investigated during part of the reproductive period including courtship and incubation. On 2 test days 14 pairs in either the courtship or the breeding state were confronted with three unknown objects in their familiar aviary for 6 h on each of 2 days. Test days were separated by a 2-day pause. Exploration by the males did not change from courtship to breeding, whereas in females latency to first contact increased, and duration of exploration and the number of objects touched decreased from courtship to breeding state. Considering the pair as a unit, the total duration of exploration was shorter in breeding pairs than in pairs during courtship. Changes in exploration from the first to the second day of object exposure occurred in both sexes. Males explored longer on the second day, females contacted the objects significantly later on the second day but showed no significant changes in duration of exploration. The changes in exploration might be due to changed cost/benefit considerations during courtship and breeding.

Asymmetric territorial contests in the European robin: the role of settlement costs

A widespread feature of territorial systems is that residents almost invariably defeat challengers. This phenomenon has been explained by the existence of value asymmetries, variations in resource-holding potential or an 'owners always win' convention. Removal-replacement experiments were performed on 75 robins, Erithacus rubeculato test these hypotheses. The settling behaviour of newcomers was also examined in order to identify energetic costs incurred during territory establishment. In winter, dominance shifted gradually from removed owners to newcomers with increasing time of newcomer residence, and there was a peak in contest duration at 4-7 days. Removals of newcomers, followed by replacement with another newcomer, confirmed that dominance was determined by the time newcomers were in residence rather than the time original owners were absent. These results support the hypothesis that asymmetries in territory value govern the outcome of contests. It is proposed that high singing rates and low foraging rates of newcomers settling boundaries with neighbours contribute to this asymmetry, skewing outcomes in favour of original owners until replacements are fully established. The key result in this study is that the time at which dominance tends to reverse (5-6 days in winter) is predicted by the time taken for newcomers to settle territory boundaries and achieve base-line foraging effort. In spring, original owners become subordinate almost immediately after removal. Reductions in settlement cost for newcomers, and increases in territory value, are proposed to accelerate dominance reversal. Age and sex effects on dominance suggest that the value asymmetry rule is modified by variations in resource-holding potential.

Exploring territory quality in the North American red squirrel through removal experiments

If territory quality affects the fitness of its holder, then relatively unsuccessful individuals should relocate if given the opportunity to appropriate a higher quality territory. Relocation by these animals, however, may be prevented by habitat saturation, poor competitive ability, or the costs of relocating. We conducted two removal studies that created numerous territory vacancies in a population of the North American red squirrel (Tamiasciurus hudsonicus), thus providing favourable conditions for relocation. In both experiments, we tested whether nonbreeding females were more likely to relocate than breeding females, presumably because they (the nonbreeders) occupied relatively poor-quality territories. In our first experiment we permanently removed most of the squirrels from a study site and monitored the relative proportions of the remaining nonbreeding and breeding females that relocated. In our second experiment we monitored the response of squirrels to vacant territories that had been previously held by nonbreeding and breeding females, as well as by males. We also monitored the behaviour of squirrels that did not hold territories (dispersing offspring), as these individuals would not experience the same costs of relocation as adults. Our experiments showed that neither category of female was likely to relocate, regardless of the type of territory available. Both residents and dispersing offspring displayed no biases towards vacant territories that previously belonged to nonbreeding or breeding females or to males. Relocation does not appear to be a strategy for a female in this system to increase her reproductive opportunities. This suggests that either territory quality is inconsequential or the costs of relocation are prohibitive. Dispersing offspring also may be unable to select certain territories because of the premium placed on acquiring a territory, regardless of its quality.