Observed heterospecific clutch size can affect offspring investment decisions

Ecological and evolutionary consequences of selective interspecific information use

Recent work has shown that animals frequently use social information from individuals of their own species as well as from other species; however, the ecological and evolutionary consequences of this social information use remain poorly understood. Additionally, information users may be selective in their social information use, deciding from whom and how to use information, but this has been overlooked in an interspecific context. In particular, the intentional decision to reject a behaviour observed via social information has received less attention, although recent work has indicated its presence in various taxa. Based on existing literature, we explore in which circumstances selective interspecific information use may lead to different ecological and coevolutionary outcomes between two species, such as explaining observed co-occurrences of putative competitors. The initial ecological differences and the balance between the costs of competition and the benefits of social information use potentially determine whether selection may lead to trait divergence, convergence or coevolutionary arms race between two species. We propose that selective social information use, including adoption and rejection of behaviours, may have far-reaching fitness consequences, potentially leading to community-level eco-evolutionary outcomes. We argue that these consequences of selective interspecific information use may be much more widespread than has thus far been considered.

Size of an interspecific competitor may be a source of information in reproductive decisions

Animals use inter-specific cues as a source of information in decisions-making, but the full costs and benefits of inter-specific information use are unknown. We tested whether pied flycatchers use the body size and clutch size of great tits as cues in their reproductive decisions and what are the possible fitness consequences as a function of great tit size. The size of great tit females associated positively with flycatcher's probability to settle near a tit nest over a territory further away. Flycatcher egg mass was positively correlated with great tit female size regardless of flycatcher territory choice. However, in flycatchers that had chosen to nest near great tits, the size of nestlings decreased in relation to increasing great tit female size. Our results demonstrate the use of size of inter-specifics as a cue in reproductive decisions and the trade-off between the value of information and costs of competition information users face when using inter-specific information in decision-making.

Conceptual preferences can be transmitted via selective social information use between competing wild bird species

Concept learning is considered a high-level adaptive ability. Thus far, it has been studied in laboratory via asocial trial and error learning. Yet, social information use is common among animals but it remains unknown whether concept learning by observing others occurs. We tested whether pied flycatchers (Ficedula hypoleuca) form conceptual relationships from the apparent choices of nest-site characteristics (geometric symbol attached to the nest-box) of great tits (Parus major). Each wild flycatcher female (n = 124) observed one tit pair that exhibited an apparent preference for either a large or a small symbol and was then allowed to choose between two nest-boxes with a large and a small symbol, but the symbol shape was different to that on the tit nest. Older flycatcher females were more likely to copy the symbol size preference of tits than yearling flycatcher females when there was a high number of visible eggs or a few partially visible eggs in the tit nest. However, this depended on the phenotype, copying switched to rejection as a function of increasing body size. Possibly the quality of and overlap in resource use with the tits affected flycatchers' decisions. Hence, our results suggest that conceptual preferences can be horizontally transmitted across coexisting animals, which may increase the performance of individuals that use concept learning abilities in their decision-making.

The Role of Cognition in Social Information Use for Breeding Site Selection: Experimental Evidence in a Wild Passerine Population

In spatio-temporally variable environments, individuals are known to use information for making optimal decisions regarding where and when to breed. Optimal decision making can be complex when relying on multiple information sources with varying levels of reliability and accessibility. To deal with such complexity, different cognitive abilities such as learning and memory might enable individuals to optimally process and use these information sources. Yet, the link between information use and cognitive ability remains unexplored in natural populations. We investigated whether learning performance on a problem-solving task was related to the use of an experimentally manipulated source of social information for nest site selection in wild collared flycatchers (Ficedula albicollis). Collared flycatchers are known to use heterospecific information from their main competitors, the great tits (Parus major). Here, we created a local apparent preference by tits for an artificial nest site feature (a geometric symbol attached to nest boxes occupied by tits) and recorded whether flycatcher pairs chose to settle in nest boxes displaying the same feature as tits (i.e., copied tit apparent preference). Using a problem-solving task requiring opening a door temporarily blocking the nest box entrance, we then measured flycatchers' learning performance during nestling rearing as the number of entrances required to solve the task and enter the nest box twice in a row below a given efficiency threshold. We found that the probability to copy tit preference decreased with decreasing learning performance in females, particularly yearling ones: fast learning females copied tit preference, while slow learning ones rejected it. Male learning performance did not affect copying behavior. Our results showed that learning performance might play an important role in the ability to optimally use information for nest site selection in females: both fast and slow learning females could process this heterospecific information source but used it differently. This could partly explain the link between cognitive abilities and reproductive success reported in previous studies. Whether cognitive abilities may modulate condition-dependent costs of using different information remains to be explored.

Behavioural traits modulate the use of heterospecific social information for nest site selection: experimental evidence from a wild bird population

The use of social information for making decisions is common but can be constrained by behavioural traits via, for example, the ability to gather information. Such constrained information use has been described in foraging habitat selection; yet it remains unexplored in the breeding habitat selection context, despite potentially strong fitness consequences. We experimentally tested whether three behavioural traits (aggressiveness, boldness and neophobia) affected the use of heterospecific social information for nest site selection in wild collared flycatchers Ficedula albicollis. Flycatchers have previously been found to copy or reject an artificial apparent preference of tits (their main competitors) for a nest site feature: they preferred nest-boxes with the same or a different feature, depending on tit early reproductive investment. Here, we confirmed this result and showed that shy individuals and less aggressive old males (i.e. 2 years old or older) copied tit apparent preference, while more aggressive old males rejected the tit preference. Aggressiveness and boldness may allow males to access more information sources or affect males' interactions with dominant tits when selecting a nest site. Our study highlights the links between variation in behaviours and social information use for breeding habitat selection and calls for further work to explore underlying mechanisms.

Information collected during the post-breeding season guides future breeding decisions in a migratory bird

Breeding habitat choice and investment decisions are key contributors to fitness in animals. Density of individuals is a well-known cue of habitat quality used for future breeding decisions, but accuracy of density cues decreases as individuals disperse from breeding sites. Used nests remain an available information source also after breeding season, but whether such information is used for breeding decisions is less well known. We experimentally investigated whether migratory, cavity-nesting pied flycatchers (Ficedula hypoleuca) prospect potential breeding sites after breeding season and use old nests as a cue for future breeding decisions. In late summer 2013, forest sites were assigned to four treatments: (1) sites including nest boxes with old nests of heterospecifics (tits), (2) sites including suitable but empty nest boxes, (3) sites with unsuitable nest boxes, or (4) sites without any nest boxes. In the following year, we investigated pied flycatcher habitat choice and reproductive investment according to these "past" cues while also controlling for additional information sources present during settlement. Flycatchers preferred sites where tits had been perceived to breed in the previous year, but only if great tits were also currently breeding in the site and had a relatively high number of eggs. Old flycatchers avoided sites previously treated with suitable but empty cavities, whereas young flycatchers preferred sites where tits had apparently bred in the previous year. Also egg mass, but not clutch size or clutch mass, was affected by the combination of past treatment information and current tit abundance.

Interspecific information on predation risk affects nest site choice in a passerine bird

Background

Breeding site choice constitutes an important part of the species niche. Nest predation affects breeding site choice, and has been suggested to drive niche segregation and local coexistence of species. Interspecific social information use may, in turn, result in copying or rejection of heterospecific niche characteristics and thus affect realized niche overlap between species. We tested experimentally whether a migratory bird, the pied flycatcher Ficedula hypoleuca, collects information about nest predation risk from indirect cues of predators visiting nests of heterospecific birds. Furthermore, we investigated whether the migratory birds can associate such information with a specific nest site characteristic and generalize the information to their own nest site choice.

Results

Our results demonstrate that flycatchers can use the fate of heterospecific nesting attempts in their own nest site choice, but do so selectively. Young flycatcher females, when making the decision quickly, associated the fate of an artificial nest with nest-site characteristics and avoided the characteristic associated with higher nest predation risk.

Conclusions

Copying nest site choices of successful heterospecifics, and avoiding choices which led to failed attempts, may amplify or counter effects of nest predation on niche overlap, with important consequences for between-species niche divergence-convergence dynamics, species coexistence and predator-prey interactions.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1301-3) contains supplementary material, which is available to authorized users.

Nest site preference depends on the relative density of conspecifics and heterospecifics in wild birds

Background

Social learning allows animals to eavesdrop on ecologically relevant knowledge of competitors in their environment. This is especially important when selecting a habitat if individuals have relatively little personal information on habitat quality. It is known that birds can use both conspecific and heterospecific information for social learning, but little is known about the relative importance of each information type. If provided with the choice between them, we expected that animals should copy the behaviour of conspecifics, as these confer the best information for that species. We tested this hypothesis in the field for Pied Flycatchers Ficedula hypoleuca arriving at their breeding grounds to select a nest box for breeding. We assigned arbitrary symbols to nest boxes of breeding pied flycatchers (conspecifics) and blue and great tits, Cyanistes caeruleus and Parus major (heterospecifics), in 2014 and 2016 in two areas with different densities of tits and flycatchers. After ca 50% of flycatchers had returned and a flycatcher symbol was assigned to their nest box, we gave the later arriving flycatchers the choice between empty nest boxes with either a conspecific (flycatcher) or a heterospecific (tit) symbol.

Results

As expected, Pied Flycatchers copied the perceived nest box choice of conspecifics, but only in areas that were dominated by flycatchers. Against our initial expectation, flycatchers copied the perceived choice of heterospecifics in the area heavily dominated by tits, even though conspecific minority information was present.

Conclusions

Our results confirm that the relative density of conspecifics and heterospecifics modulates the propensity to copy or reject novel behavioural traits. By contrasting conspecific and heterospecific ecology in the same study design we were able to draw more general conclusions about the role of fluctuating densities on social information use.

Information-Mediated Allee Effects in Breeding Habitat Selection

Social information is used widely in breeding habitat selection and provides an efficient means for individuals to select habitat, but the population-level consequences of this process are not well explored. At low population densities, efficiencies may be reduced because there are insufficient information providers to cue high-quality habitat. This constitutes what we call an information-mediated Allee effect. We present the first general model for an information-mediated Allee effect applied to breeding habitat selection and unify personal and social information, Allee effects, and ecological traps into a common framework. In a second model, we consider an explicit mechanism of social information gathering through prospecting on conspecific breeding performance. In each model, we independently vary personal and social information use to demonstrate how dependency on social information may result in either weak or strong Allee effects that, in turn, affect population extinction risk. Abrupt transitions between outcomes can occur through reduced information transfer or small changes in habitat composition. Overall, information-mediated Allee effects may produce positive feedbacks that amplify population declines in species that are already experiencing environmentally driven stressors, such as habitat loss and degradation. Alternatively, social information has the capacity to rescue populations from ecological traps.

Catch the wave: prairie dogs assess neighbours' awareness using contagious displays

The jump-yip display of black-tailed prairie dogs (Cynomys ludovicianus) is contagious, spreading through a prairie dog town as 'the wave' through a stadium. Because contagious communication in primates serves to assess conspecific social awareness, we investigated whether instigators of jump-yip bouts adjusted their behaviour relative to the response of conspecifics recruited to display bouts. Increased responsiveness of neighbouring town members resulted in bout initiators devoting a significantly greater proportion of time to active foraging. Contagious jump-yips thus function to assess neighbours' alertness, soliciting social information to assess effective conspecific group size in real time and reveal active probing of conspecific awareness consistent with theory of mind in these group-living rodents.

Observed fitness may affect niche overlap in competing species via selective social information use

Social information transmission is important because it enables horizontal spread of behaviors, not only between conspecifics but also between individuals of different species. Because interspecific social information use is expected to take place among species with similar resource needs, it may have major consequences for the emergence of local adaptations, resource sharing, and community organization. Social information use is expected to be selective, but the conditions promoting it in an interspecific context are not well known. Here, we experimentally test whether pied flycatchers (Ficedula hypoleuca) use the clutch size of great tits (Parus major) in determining the quality of the observed individual and use it as a basis of decision making. We show that pied flycatchers copied or rejected a novel nest site feature preference of great tits experimentally manipulated to exhibit high or low fitness (clutch size), respectively. Our results demonstrate that the social transmission of behaviors across species can be highly selective in response to observed fitness, plausibly making the phenomenon adaptive. In contrast with the current theory of species coexistence, overlap between realized niches of species could dynamically increase or decrease depending on the observed success of surrounding individuals.

Flycatchers copy conspecifics in nest-site selection but neither personal experience nor frequency of tutors have an effect

Using the behavior of others in guiding one's own behavior is a common strategy in animals. The prevailing theory predicts that young age and the inexperience of an individual are expected to increase the probability of adopting the behaviors of others. Also, the most common behavior in the population should be copied. Here, we tested the above predictions by examining social information use in the selection of nest-site features with a field experiment using a wild cavity nesting bird, the collared flycatcher (Ficedula albicollis). We used an experimental design in which geometric symbols depict nest-site features. By manipulating the apparent symbol choices of early settled individuals and monitoring the choices of later arriving birds, we can study social information use without bias from learned or innate preferences. Flycatchers were found to use social information in the selection of nest-site features, with about 60% of the population preferring the manipulated conspecific choices. However, age and experience as explanatory factors suggested by the social information use theory did not explain the choices. The present result, in concert with earlier similar experiments, implies that flycatchers may in some situations rely more on interspecific information in the selection of nest-site characteristics.