The role of information transfer under different food patterns: a simulation study

The aim of this paper is to address the question of how informationtransfer affects foraging efficiency in a colonial breedingsituation. By creating computer simulations, we attempt to modelinformation transfer of food location by individuals withinthe colony. Three kinds of foraging strategy were modeled: searcher–noinformation transfer (solo foraging), watcher–limitedinformation transfer (local enhancement), and a mixture of watcherand follower–full information transfer (information center).The predictability of food was changed by varying patchiness(ratio of food patches) and duration of food patches. When thefood occurs in many randomly distributed patches and the fooddensity in each is low, the solitary searcher strategy givesthe best foraging efficiency. The significance of informationtransfer strategies and colonial breeding on foraging efficiencyincrease when food becomes more clumped. The solitary watcherstrategy is the best at intermediately clumped food distribution.Colonial breeding gives the best foraging efficiency when theinformation center operates and there are some high-densityfood patches.     

Spatial-concentration effects and the importance of local enhancement in the evolution of colonial breeding in seabirds

The information center hypothesis (ICH) suggests that birds breed in colonies because this behavior favors information exchange at the colony about the location of food patches. However, the complex suite of behaviors the ICH requires implies that information center following is more likely to evolve after colonial breeding has become established than to promote its initial development. A simpler hypothesis to explain the evolution of colonial breeding is that coloniality concentrates foragers in space, which leads to more rapid discovery of food patches and, by means of local enhancement, more efficient transfer of information about the location of patches than if foragers bred in a dispersed fashion. To assess the effects of breeding dispersion on foraging success, I simulated the foraging behavior of cliff-breeding seabirds (nesting either solitarily or colonially) searching for patchily distributed prey. Results show that colonial breeding is favored when food patches are sufficiently large or short-lived that competition for food is ameliorated. Conversely, dispersed nesting is favored when patches are small or long-lived. Individuals playing a colonial breeding strategy can invade a population of solitarily breeding birds, and once a colonial breeding strategy becomes established, it generally is resistant to invasion. These findings suggest that the spatial-concentration model is a plausible mechanism for the initial development of coloniality.     

Does predation select for or against avian coloniality? A comparative analysis

Some studies have supported predation as a selective pressure contributing to the evolution of coloniality. However, evidence also exists that colonies attract predators, selecting against colonial breeding. Using comparative analyses, we tested the reduced predation hypothesis that individuals aggregate into colonies for protection, and the opposite hypothesis, that breeding aggregations increase predation risk. We used locational and physical characteristics of nests to estimate levels of species' vulnerability to predation. We analysed the Ciconiiformes, a large avian order with the highest prevalence of coloniality, using Pagel's general method of comparative analysis for discrete variables. A common requirement of both hypotheses, that there is correlated evolution between coloniality and vulnerability to predation, was fulfilled in our data set of 363 species. The main predictions of the reduced predation hypothesis were not supported, namely that (1) solitary/vulnerable species are more prone to become colonial than solitary/protected species and (2) colonial/protected species are more likely to evolve towards vulnerability than solitary/protected species. In contrast, the main predictions of the increased predation hypothesis were supported, namely that colonial/vulnerable species are more prone (1) to become protected than solitary/vulnerable species and/or (2) to become solitary than colonial/protected species. This suggests that the colonial/vulnerable state is especially exposed to predation as coloniality may often attract predators rather than provide safety.     

Public information affects breeding dispersal in a colonial bird: kittiwakes cue on neighbours

Habitat selection and dispersal behaviour are key processes in evolutionary ecology. Recent studies have suggested that individuals may use the reproductive performance of conspecifics as a source of public information on breeding patch quality for dispersal decisions, but experimental evidence is still limited for species breeding in aggregates, i.e. colonial species. We addressed this issue by manipulating the local breeding success of marked individuals and that of their neighbours on a series of breeding patches of a colonial seabird, the black-legged kittiwake (Rissa tridactyla). Based on previous observations in this species, we predicted that individuals that lost their eggs on successful patches would attend their nest and come back to it the year after at a higher rate than individuals that lost their eggs on patches where their neighbours were also in failure. As predicted, the attendance of breeders and prospectors was strongly affected by the local level of breeding success, resulting in differential site fidelity and recruitment. This suggests that individuals used information conveyed by conspecific breeding performance to make decisions relative to breeding site selection. This process can amplify the response of these populations to environmental change and may have contributed to the evolution of colonial breeding.     

Ecological and Phylogenetic Effects on Song Sharing in Songbirds

As a consequence of vocal learning, the songs of male songbirds often vary geographically. We examined three proximate hypotheses that predict variation in the incidence of local song sharing among species: the annual cycle, breeding season duration, and epiphenomenon hypotheses. To test these hypotheses, we compiled data from the literature on local song sharing, annual cycle, breeding location isophane (an index of breeding season duration), repertoire size, and phylogenetic relationships of 65 populations in the family Fringillidae. Mapping characters on the phylogenetic tree revealed that local song sharing, migratory status, and breeding location isophane were randomly distributed on the phylogeny. Breeding isophane and migratory status were themselves correlated and had significant effects on the probability of sharing local songs. As predicted by the annual cycle and breeding season duration hypotheses, males in sedentary populations and populations breeding at low isophanes were more likely to share local songs. In subsets of the data, the annual cycle hypothesis received more support than did the breeding season duration hypothesis. Neither hypothesis explained more than 17% of the variation in the incidence of song sharing, and we suggest that detailed information on song function, male dispersal, and constraints on the timing of song learning will be needed to better predict the occurrence of local song sharing.     

The evolution of coloniality: the emergence of new perspectives

The evolution of group living remains an outstanding question in evolutionary ecology. Among the most striking forms of group living are the enormous assemblages of breeders that occur in many colonial marine birds and mammals, with some colonies containing more than a million individuals breeding in close contact. Coloniality is an evolutionary puzzle because individuals pay fitness costs to breed in high densities. Despite numerous potential benefits proposed to overcome these costs, we still lack a general framework to explain coloniality. Several new hypotheses involving breeding habitat and mate selection create promising approaches for studying this enigma.     

Differential sensitivity of planktonic trophic levels to extreme summer temperatures in boreal lakes

The stress–size hypothesis predicts that smaller organisms will be less sensitive to stress. Consequently, climate warming is expected to favour smaller taxa from lower trophic levels and smaller individuals within populations. To test these hypotheses, we surveyed zooplankton communities in 20 boreal lakes in Killarney Provincial Park, Canada during 2005 (an anomalously warm summer) and 2006 (a normal summer). Higher trophic levels had larger responses to warm temperatures supporting the stress–size hypothesis; however, rather than imposing negative effects, higher density and biomass were observed under warmer temperatures. As a result, larger taxa from higher trophic levels were disproportionately favoured with warming, precluding an expected shift towards smaller species. Proportionately greater increases in metabolic rates of larger organisms or altered biotic interactions (e.g. predation and competition) are possible explanations for shifts in biomass distribution. Warmer temperatures also favoured smaller individuals of the two most common species, in agreement with the stress–size hypothesis. Despite this, these populations had higher biomass in the warm summer. Therefore, reduced adult survivorship may have triggered these species to invest in reproduction over growth. Hence, warmer epilimnions, higher zooplankton biomass and smaller individuals within zooplankton populations may function as sensitive indicators of climate warming in boreal lakes.     

How to make methodological decisions when inferring social networks

Social network analyses allow studying the processes underlying the associations between individuals and the consequences of those associations. Constructing and analyzing social networks can be challenging, especially when designing new studies as researchers are confronted with decisions about how to collect data and construct networks, and the answers are not always straightforward. The current lack of guidance on building a social network for a new study system might lead researchers to try several different methods and risk generating false results arising from multiple hypotheses testing. Here, we suggest an approach for making decisions when starting social network research in a new study system that avoids the pitfall of multiple hypotheses testing. We argue that best edge definition for a network is a decision that can be made using a priori knowledge about the species and that is independent from the hypotheses that the network will ultimately be used to evaluate. We illustrate this approach with a study conducted on a colonial cooperatively breeding bird, the sociable weaver. We first identified two ways of collecting data using different numbers of feeders and three ways to define associations among birds. We then evaluated which combination of data collection and association definition maximized (a) the assortment of individuals into previously known “breeding groups” (birds that contribute toward the same nest and maintain cohesion when foraging) and (b) socially differentiated relationships (more strong and weak relationships than expected by chance). This evaluation of different methods based on a priori knowledge of the study species can be implemented in a diverse array of study systems and makes the case for using existing, biologically meaningful knowledge about a system to help navigate the myriad of methodological decisions about data collection and network inference.     

Floater interference reflects territory quality in the Spanish Imperial Eagle Aquila adalberti: a test of a density‐dependent mechanism

We report on an 11‐year study of floater interference in a population of Spanish Imperial Eagles Aquila adalberti. We analysed changes over the years in the productivity of 15 territories to test predictions of two hypotheses of density‐dependent productivity in relation to the presence of floaters (birds without territories). According to the ‘interference' hypothesis, the frequency of intrusion by floaters increases with density, resulting in a decrease in productivity. Thus, in a high‐density population a negative relationship between floater intrusions and productivity of the territory is expected. In contrast, under the ‘habitat heterogeneity' hypothesis, as density increases a higher proportion of individuals is forced to occupy lower quality habitats. Support of this hypothesis requires that floaters detect differences in quality among territories and preferentially visit the better quality territories. Consequently, a positive relationship between floater intrusions and productivity is expected. Results showed that floaters tended to visit their natal area at the beginning of the breeding season. Among floater Eagles, males made significantly more intrusions per day than did females, but females stayed in the natal population for longer each year than males. Floater intrusions and productivity were highly positively correlated, supporting the ‘habitat heterogeneity' hypothesis; individuals were apparently able to assess the quality of a territory and, at the frequencies observed, their interference with the breeding pair had no obvious negative effect on productivity.     

Cooperative breeding in birds: a comparative test of the life history hypothesis

In approximately 3.2% of bird species individuals regularly forgo the opportunity to breed independently and instead breed cooperatively with other conspecifics, either as non-reproductive ''helpers'' or as co-breeders. The traditional explanation for cooperative breeding is that the opportunities for breeding independently are limited owing to peculiar features of the species'' breeding ecology. However, it has proved remarkably difficult to find any common ecological correlates of cooperative breeding in birds. This difficulty has led to the ''life history hypothesis'', which suggests that the common feature of cooperatively breeding birds is their great longevity, rather than any particular feature of their breeding ecology. Here, we use a comparative method to test the life history hypothesis by looking for correlations between life history variation and variation in the frequency of cooperative breeding. First, we find that cooperative breeding in birds is not randomly distributed, but concentrated in certain families, thus supporting the idea that there may be a common basis to cooperative breeding in birds. Second, increases in the level of cooperative breeding are strongly associated with decreases in annual adult mortality and modal clutch size. Third, the proportion of cooperatively breeding species per family is correlated with a low family-typical value of annual mortality, suggesting that low mortality predisposes cooperative breeding rather than vice versa. Finally, the low rate of mortality typically found in cooperatively breeding species is associated with increasing sedentariness, lower latitudes, and decreased environmental fluctuation. We suggest that low annual mortality is the key factor that predisposes avian lineages to cooperative breeding, then ecological changes, such as becoming sedentary, further slow population turnover and reduce opportunities for independent breeding. As the traditional explanation suggests, the breeding habitat of cooperatively breeding species is saturated, but this saturation is not owing to any peculiar feature of the breeding ecology of cooperative breeders. Rather, the saturation arises because the local population turnover in these species is unusually slow, as predicted by the life history hypothesis.     

A review of the evolutionary causes of rodent group-living

I analyze and summarize the empirical evidence supporting alternative hypotheses posed to explain the evolution of rodent group-living. Eight hypotheses are considered: two rely on net fitness benefits to individuals, five rely on ecological and life-history constraints, and one uses elements of both. I expose the logic behind each hypothesis, identify its key predictions, examine how the available evidence on rodent socioecology supports or rejects its predictions, and identify some priorities for future research. I show that empirical support for most hypotheses is meager due to a lack of relevant studies. Also, empirical support for a particular hypothesis, when it exists, comes from studies of the same species used to formulate the original hypothesis. Two exceptions are the hypothesis that individual rodents live in groups to reduce their predation risk and the hypothesis that group-living was adopted by individuals to reduce their cost of thermoregulation. Finally, most hypotheses have been examined without regard to competing hypotheses and often in a restricted taxonomic context. This is clearly an unfortunate situation given that most competing hypotheses are not mutually exclusive. I suggest that in the future comparative approaches should be used. These studies should examine simultaneously the relevance of different benefits and constraints hypothesized to explain the evolution of rodent sociality.     

The evolutionary history of division of labour

Functional specialization, or division of labour (DOL), of parts within organisms and colonies is common in most multi-cellular, colonial and social organisms, but it is far from ubiquitous. Several mechanisms have been proposed to explain the evolutionary origins of DOL; the basic feature common to all of them is that functional differences can arise easily. These mechanisms cannot explain the many groups of colonial and social animals that exhibit no DOL despite up to 500 million years of evolution. Here, I propose a new hypothesis, based on a multi-level selection theory, which predicts that a reproductive DOL is required to evolve prior to subsequent functional specialization. I test this hypothesis using a dataset consisting of the type of DOL for living and extinct colonial and social animals. The frequency distribution of DOL and the sequence of its acquisition confirm that reproductive specialization evolves prior to functional specialization. A corollary of this hypothesis is observed in colonial, social and also within multi-cellular organisms; those species without a reproductive DOL have a smaller range of internal variation, in terms of the number of polymorphs or cell types, than species with a reproductive DOL.     

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.     

Dispersal in Kin Coalition Throughout the Non‐Breeding Season to Facilitate Fine‐Scale Genetic Structure in the Breeding Season: Evidence From a Small Passerine

Evidence shows that social cooperation among kin may evolve even in birds with extensive dispersal. In such cases, maintaining kinship during dispersal is essential to the subsequent expression of kin cooperation. This hypothesis has not been examined for most bird species. We addressed it in the ground tit (Parus humilis), a passerine where kin frequently interact in terms of cooperative polygamy and extra‐pair mating despite fast annual turnover of the breeding population. Pedigree and genotype data showed that while groups varied in composition throughout the non‐breeding season due to continual individual emigration and immigration, they always contained kin coalitions consisting of either local or immigrant individuals of different age and sexes. The first‐order kin coalitions, according to the information from local individuals, stemmed from single‐family lineages (siblings and their parents), and the lower‐order ones from neighbouring, related family lineages that merged after fledging. It was probable that immigrants had formed kin coalitions in similar ways before dispersing. Groups broke up in the breeding season. Pairing between unrelated individuals from different coalitions within a group was more likely, whereas related individuals from the same coalition tended to nest near each other. The resulting fine‐scale population genetic structure is expected to facilitate breeding interactions among kin. Our findings give clues to understanding the evolution of social cooperation in relation to dispersal.     

Habitat selection rules in breeding mallards (Anas platyrhynchos): a test of two competing hypotheses

Ideal preemption and conspecific attraction are alternative hypotheses of the habitat selection rules used by individuals. According to the former an occupied site is assumed to be preempted and therefore not available for later arriving individuals, whereas according to the latter individuals are assumed to be attracted by conspecifics to occupied sites, rather than avoiding them. We studied these competing hypotheses in breeding mallards (Anas platyrhynchos) by a cross-over experiment in 2 years, introducing birds onto lakes before migratory wild mallards arrived. If mallards use the ideal preemptive rule, breeding density of wild mallards in experimental lakes should be lower and they should be occupied less frequently than control lakes, but if mallards use the conspecific attraction rule the reverse should be true. Our results allowed us to reject the ideal preemptive rule whereas the conspecific attraction rule was to some extent supported. We discuss these findings in relation to population limitation. The results suggest that the local breeding population studied is not limited by spacing behaviour related to habitat selection. Received: 14 July 1997 / Accepted: 17 November 1997     

Influence of density‐dependent competition on foraging and migratory behavior of a subtropical colonial seabird

Density‐dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central‐place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while little is known about whether density‐dependent resource depletion influences individual migratory behavior outside the breeding season. Using breeding colony size as a surrogate for intraspecific resource competition, we tested for effects of colony size on breeding home range, nestling health, and migratory patterns of a nearshore colonial seabird, the brown pelican (Pelecanus occidentalis), originating from seven breeding colonies of varying sizes in the subtropical northern Gulf of Mexico. We found evidence for density‐dependent effects on foraging behavior during the breeding season, as individual foraging areas increased linearly with the number of breeding pairs per colony. Contrary to our predictions, however, nestlings from more numerous colonies with larger foraging ranges did not experience either decreased condition or increased stress. During nonbreeding, individuals from larger colonies were more likely to migrate, and traveled longer distances, than individuals from smaller colonies, indicating that the influence of density‐dependent effects on distribution persists into the nonbreeding period. We also found significant effects of individual physical condition, particularly body size, on migratory behavior, which in combination with colony size suggesting that dominant individuals remain closer to breeding sites during winter. We conclude that density‐dependent competition may be an important driver of both the extent of foraging ranges and the degree of migration exhibited by brown pelicans. However, the effects of density‐dependent competition on breeding success and population regulation remain uncertain in this system.     

When to stay,when to disperse and where to go: survival and dispersal patterns in a spatially structured seabird population

Dispersal is a key process for the population dynamics of spatially structured populations (at local and metapopulation levels), so the understanding of the mechanisms underlying the movement of individuals in space and time is important for evolutionary and ecological studies. Here we analyzed, for the first time, a long‐term (1992–2009) multi‐site capture– recapture database collected at four local populations of a long‐lived seabird, the Audouin’s gull Larus audouinii, covering 90% of its total world population. Those local populations show different ecological and demographic features that allow us to assess the influence of several key factors involved in breeding dispersal patterns at large spatio‐temporal scales. A recently developed analytical tool in mark–recapture modelling, the multi‐event approach, allowed us to obtain separate departure and settlement probabilities and test different biological hypotheses for each step of the dispersal process. Our results revealed that site fidelity was the most common strategy among breeders, and dispersal was only high from the site with the lowest population size and habitat quality. However, departures from the two largest local populations increased over the study period in response to severe ecological perturbations. Dispersers chose different settlement patches depending on their site of origin, with settlement choices determined by the population size of the destination colony rather than by the local reproductive performance, foraging area (a proxy of food availability) or distance to the destination site. Our results indicate that a breeding site is not abandoned by breeders unless a series of cumulative perturbations occur; once dispersing, settlement is directed towards densely populated sites, with dispersers using population size to rapidly assess the quality of the breeding patch.     

Behavioral mechanisms leading to improved fitness in a subsidized predator

General mechanisms underlying the distribution and fitness of synanthropic predators in human-influenced landscapes remain unclear. Under the consumer resource-matching hypothesis, synanthropes are expected to distribute themselves among habitats according to resource availability, such that densities are greater in human-subsidized habitats, but mean individual fitness is equal among habitats because of negative density dependence. However, “under-matching” to human food resources can occur, because dominant individuals exclude subordinates from subsidized habitats and realize relatively high fitness. We integrated physiological, behavioral, and demographic information to test resource-matching hypotheses in Steller’s jays (Cyanocitta stelleri), a synanthropic nest predator, to understand how behavior and social systems can influence how synanthropes respond to food subsidies. Jays consumed more human foods at subsidized (park campground) sites than jays at unsubsidized (interior forest) sites based on stable isotope analyses. Jays that occurred at higher densities were in better body condition (based on feather growth bars and lipid analyses), and had greater reproductive output at subsidized than unsubsidized sites. Jays with breeding territories in subsidized sites maintained relatively small home ranges that overlapped with multiple conspecifics, and exhibited a social system where dominant individuals typically won contests over food. Thus, jays appeared to be under-matched to prevalent resource subsidies despite high densities and behaviors expected to lead to resource matching. Our results also indicate that local resource subsidies within protected areas can result in source habitats for synanthropes, potentially impacting sensitive species over broader spatial scales.     

Inferring geographic origin, population structure and migration routes of a wintering population of Mediterranean gulls from resightings data

Winter congregations of migratory birds are made by individuals of different origins and generally assumed to be variable across space and time, but the demographic characteristics of these temporal populations are poorly known. We used 2,216 observations of 472 colour-ringed individuals to estimate the annual local survival of Mediterranean gulls Larus melanocephalus wintering in NE Spain. In addition, by gathering the ringing information on the 19,856 individuals marked as fledglings in 18 countries between 1990 and 2009, we were able to infer the composition of population in relation to the country of origin. We coupled these estimates with geographic information to contrast hypotheses on the migratory pattern most likely used by the gulls in their first migration from their natal colonies to the wintering area. The probability of reaching the study area was negatively associated with the distance from the natal colony. Data were consistent with a migratory strategy that combines fluvial and coastal routes in an optimal way, seeking minimal distance along favourable terrain. We found that, after the first year, annual local survival at the wintering site (0.81 on average) was comparable with the one estimated at the breeding colonies, indicating a high individual fidelity to the areas used in winter. Our work shows that winter groupings may behave as real populations, shaped by breeding output and survival, and that the geographic origin of wintering birds can be explained by a simple model. The study of winter congregations can help understand a species’ population structure and movement strategies.     

Competition between Homophily and Information Entropy Maximization in Social Networks

In social networks, it is conventionally thought that two individuals with more overlapped friends tend to establish a new friendship, which could be stated as homophily breeding new connections. While the recent hypothesis of maximum information entropy is presented as the possible origin of effective navigation in small-world networks. We find there exists a competition between information entropy maximization and homophily in local structure through both theoretical and experimental analysis. This competition suggests that a newly built relationship between two individuals with more common friends would lead to less information entropy gain for them. We demonstrate that in the evolution of the social network, both of the two assumptions coexist. The rule of maximum information entropy produces weak ties in the network, while the law of homophily makes the network highly clustered locally and the individuals would obtain strong and trust ties. A toy model is also presented to demonstrate the competition and evaluate the roles of different rules in the evolution of real networks. Our findings could shed light on the social network modeling from a new perspective.