Exploration speed in captivity predicts foraging tactics and diet in free-living red knots.

Variation in foraging tactics and diet is usually attributed to differences in morphology, experience and prey availability. Recently, consistent individual differences in behaviour (personality) have been shown to be associated with foraging strategies. Bolder or more exploratory individuals are predicted to have a faster pace-of-life and offset the costs of moving more or in risky areas, with higher energetic gains by encountering profitable foraging opportunities and prey. However, the relationship between personality, foraging and diet is poorly understood. We investigated how exploratory behaviour in red knots Calidris canutus is associated with foraging tactics and diet by combining laboratory experiments, field observations and stable isotope analysis. First, we developed a mobile experimental arena to measure exploration speed in controlled settings. We validated the method by repeated testing of individuals over time and contexts. This setup allowed us to measure exploratory personality at the field site, eliminating the need to bring birds into captivity for long periods of time. After releasing birds within days of their capture, we asked whether exploration speed was associated with differences in foraging tactics and diet in the wild. We found that tactile foraging red knots mainly caught hard-shelled prey that are buried in the sediment, whereas visual foraging knots only captured soft preys located close to or on the surface. We also found that faster explorers showed a higher percentage of visual foraging than slower explorers. By contrast, morphology (bill length and gizzard size) had no significant effect on foraging tactics. Diet analysis based on δ15 N and δ13 C stable isotope values of plasma and red blood cells confirmed our field observations with slower explorers mainly consumed hard-shelled prey while faster explorers consumed more soft than hard-shelled prey. Our results show that foraging tactics and diet are associated with a personality trait, independent of morphological differences. We discuss how consistent behaviour might develop early in life through positive feedbacks between foraging tactics, prey type and foraging efficiency.

On the importance of accounting for alternative foraging tactics when assessing cognitive performance in wild animals.

Research Highlight: Reichert, S., Morand-Ferron, J., Kulahci, I. G., Firth, J. A., Davidson, G. L., Crofts, S. J., & Quinn, J. L. (2021) Cognition and covariance in the producer-scrounger game. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13551. When foraging in groups, individuals can either acquire their own resources, as producers, or profit from the work of other individuals, as scroungers. Individuals vary in how much they rely on one foraging tactic over the other. Yet, each of these foraging tactics presents unique cognitive challenges. Using a field experiment with a mixed-species flock of birds, Reichert et al. (2021) investigated how production learning (i.e. successfully feeding from their assigned rewarded feeder) and scrounging propensity (i.e. collecting food from a non-assigned feeders by following another individual) are related at an individual level, as well as the repeatability of both production learning and scrounging propensity. The authors show that overall, (a) individuals learned to scrounge, (b) individuals who rely more on scrounging took longer to learn their assigned feeder and (c) variation in each cognitive trait was mostly explained by individual behavioural flexibility rather than by consistent differences between individuals. Since learning was negatively correlated with the use of an alternative foraging tactic (i.e. scrounging), results of this study also suggest that individual choice of foraging tactics should be considered when evaluating cognitive abilities in wild animals.

Spatiotemporal heterogeneity in prey abundance and vulnerability shapes the foraging tactics of an omnivore.

Prey abundance and prey vulnerability vary across space and time, but we know little about how they mediate predator-prey interactions and predator foraging tactics. To evaluate the interplay between prey abundance, prey vulnerability and predator space use, we examined patterns of black bear (Ursus americanus) predation of caribou (Rangifer tarandus) neonates in Newfoundland, Canada using data from 317 collared individuals (9 bears, 34 adult female caribou, 274 caribou calves). During the caribou calving season, we predicted that landscape features would influence calf vulnerability to bear predation, and that bears would actively hunt calves by selecting areas associated with increased calf vulnerability. Further, we hypothesized that bears would dynamically adjust their foraging tactics in response to spatiotemporal changes in calf abundance and vulnerability (collectively, calf availability). Accordingly, we expected bears to actively hunt calves when they were most abundant and vulnerable, but switch to foraging on other resources as calf availability declined. As predicted, landscape heterogeneity influenced risk of mortality, and bears displayed the strongest selection for areas where they were most likely to kill calves, which suggested they were actively hunting caribou. Initially, the per-capita rate at which bears killed calves followed a type-I functional response, but as the calving season progressed and calf vulnerability declined, kill rates dissociated from calf abundance. In support of our hypothesis, bears adjusted their foraging tactics when they were less efficient at catching calves, highlighting the influence that predation phenology may have on predator space use. Contrary to our expectations, however, bears appeared to continue to hunt caribou as calf availability declined, but switched from a tactic of selecting areas of increased calf vulnerability to a tactic that maximized encounter rates with calves. Our results reveal that generalist predators can dynamically adjust their foraging tactics over short time-scales in response to changing prey abundance and vulnerability. Further, they demonstrate the utility of integrating temporal dynamics of prey availability into investigations of predator-prey interactions, and move towards a mechanistic understanding of the dynamic foraging tactics of a large omnivore.

Analyzing the proximity to cover in a landscape of fear: a new approach applied to fine-scale habitat use by rabbits facing feral cat predation on Kerguelen archipelago.

Although proximity to cover has been routinely considered as an explanatory variable in studies investigating prey behavioral adjustments to predation pressure, the way it shapes risk perception still remains equivocal. This paradox arises from both the ambivalent nature of cover as potentially both obstructive and protective, making its impact on risk perception complex and context-dependent, and from the choice of the proxy used to measure proximity to cover in the field, which leads to an incomplete picture of the landscape of fear experienced by the prey. Here, we study a simple predator-prey-habitat system, i.e., rabbits Oryctolagus cuniculus facing feral cat Felis catus predation on Kerguelen archipelago. We assess how cover shapes risk perception in prey and develop an easily implementable field method to improve the estimation of proximity to cover. In contrast to protocols considering the "distance to nearest cover", we focus on the overall "area to cover". We show that fine-scale habitat use by rabbits is clearly related to our measure, in accordance with our hypothesis of higher risk in patches with smaller area to cover in this predator-prey-habitat system. In contrast, classical measures of proximity to cover are not retained in the best predictive models of habitat use. The use of this new approach, together with a more in-depth consideration of contrasting properties of cover, could help to better understand the role of this complex yet decisive parameter for predator-prey ecology.

Efeito do tamanho do fragmento na dispersão de sementes de Copaíba (Copaifera langsdorffii Delf.) / Effect of fragment size on Copaifera langsdorffii seeds dispersal

A fragmentação de habitats pode afetar negativamente a relação mutualística entre plantas e animais, se estes tornarem-se localmente extintos nos fragmentos. No decorrer do processo de fragmentação há evidências de substituição de espécies especialistas por generalistas, adotando também sua função no ecossistema. Nós estudamos a frugivoria de Copaifera langsdorfii por aves para avaliar o efeito do tamanho do fragmento no potencial de dispersão das suas sementes. Durante o ano de 2008 foram selecionadas vinte plantas focais distribuídas em cinco remanescentes de Mata Atlântica (amplitude 29,2 a 104,8 ha) para descrever o comportamento de forrageamento de aves consumidoras e avaliar o potencial de dispersão de sementes de cada espécie através do método de observação focal. O potencial de dispersão variou entre as espécies, juntamente com o padrão de distribuição e abundância nos diferentes fragmentos. O tamanho dos fragmentos afetou positivamente o número de interações de espécies com bom potencial de dispersão (R2 = 0,85; p = 0,05). A riqueza de espécies com má qualidade de dispersão foi negativamente afetada pelo tamanho do fragmento, mas com significância marginal (R2 = 0,77; p= 0,08). Portanto a preservação de fragmentos de maior tamanho garante mais eventos de interação entre a C. langsdorfii e seus bons dispersores, e consequentemente favorece seu sucesso reprodutivo.

Effect of fragment size on Copaifera langsdorffii seed dispersal. Habitat fragmentation may cause functional disruption in seed dispersal, if the disperser species become locally extinct in the fragments. However during the fragmentation process, there is empirical evidence of replacement of specialist by generalist species, and these generalist species could also replace the functional activity of the specialists in the ecosystem. We studied bird frugivory on C. langsdorffii in order to evaluate the patch size effect on the potential of seed dispersal of this plant. During 2008 we chose 20 focal trees distributed in five Atlantic forest remnants (range 29.2 to 104.8 ha), looking for which bird species consumed the fruits, describing their foraging behavior and consequently evaluating the potential for seed dispersal. The results suggest that there was lower similarity of bird richness among the patches. The ability to disperse seeds also varied among birds and their patterns of distribution and abundance were related with patch size. The number of good disperser species and their interactions were positively related with patch size (R2 = 0.85; p = 0.05); in contrast, the poor dispersers had the opposite tendency (R2 = 0.77; p=0.08). Therefore the preservation of larger patch size increases the interaction events between C. langsdorffii and their good dispersers, and consequently improving their fitness.

The Chimango Caracara (Milvago chimango), an additional fisher among Caracarini falcons / O chimango (Milvago chimango), um pescador adicional entre os falcões Caracarini

The Caracarini falcons are among the most versatile birds of prey, and their variable diet includes fishes, which may be taken as carrion. However, fishing behaviour is described for two species. Here we describe the Chimango Caracara (Milvago chimango) fishing at an estuary in Chile, Pacific coast of South America. The caracara flew and glided close to water surface, hovering on occasions. After such a hovering, the bird plunged and attempted to snatch a prey with its talons. If successful, the caracara carried the fish in its talons and landed on an adjacent beach where the prey was torn apart and eaten. The 'glide-hover' technique of the Chimango Caracara differs slightly from the fishing recorded for the closely related Yellow-headed Caracara (Milvago chimachima), which plunges to the prey from a nearby perch ('perch to water'). The Black Caracara (Daptrius ater) picks up fish individually with its bill or talons while staying on a river bank ('ground foraging'). Thus, at least three fishing techniques are used by the Caracarini falcons, a group already known for its varied foraging techniques.

Os falcões da tribo Caracarini estão entre as aves de rapina mais versáteis e sua variada dieta inclui peixes, que podem ser apanhados mortos. Todavia, comportamento de pesca está descrito para duas espécies. Descrevemos aqui o chimango (Milvago chimango) pescando num estuário no Chile, costa pacífica da América do Sul. A ave voava e planava próximo à superfície da água, pairando de quando em vez. Após este pairar, o chimango baixava rapidamente e tentava apanhar uma presa com suas garras. Se bem sucedido, o chimango carregava o peixe em suas garras e pousava numa praia próxima, onde a presa era dilacerada e consumida. A tática de 'planar-pairar' do chimango difere ligeiramente da tática de pesca adotada pelo pinhé (Milvago chimachima), espécie relacionada, que se lança sobre a presa a partir de um poleiro. O gavião-de-anta (Daptrius ater) apanha peixes individualmente com o bico ou garras, enquanto pousado na margem de um rio. Portanto, pelo menos três táticas de pesca são usadas pelos falcões Caracarini, um grupo conhecido pelas suas variadas táticas de forrageio.

How foraging tactics determine host-plant use by a polyphagous caterpillar.

The use of multiple host-plant species by populations of insect herbivores can result from a variety of possible ecological and behavioral mechanisms. An understanding of the foraging mechanisms determining polyphagy in relation to local ecological conditions is therefore essential to understanding the evolutionary ecology of polyphagy. Here, we evaluate patterns of host-plant use by the polyphagous caterpillar Grammia geneura (Lepidoptera: Arctiidae) in relation to host-plant availability and foraging tactics of individuals. Field surveys of caterpillar feeding and plant abundance carried out across several sites, seasons, and years showed that: (1) G. geneura consistently preferred forbs to grasses and woody plants, (2) forb-feeding was opportunistic, supporting the idea that caterpillars sample locally available host-plants, and (3) there were consistent patterns of host-plant use that were not explained by host-plant availability (electivity). An independent set of 7-h observations of 11 caterpillars showed that electivity for a subset of caterpillar-host associations could be explained by variation in the probability of initiating feeding and the average duration of feeding bouts on different hosts but not by variation in the probability of encountering different hosts, thus providing a behavioral basis for the observed variation in host-plant use. The use of detailed foraging tactics by larvae to explain host-plant use at the population level is a novel contribution of this study.