Movement has important consequences for individual and population-level processes, but methods are only starting to become available for quantifying fine-scale movement paths of smaller animals. New techniques for inferring behavioral states and their relation to social and environmental factors provide a powerful way to test the influence of such factors on individuals. One such technique that has recently gained popularity is the use of hidden Markov models, which link time series of movement variables and the underlying behavioral states of individuals. We used hidden Markov models to evaluate behavioral states and their relation to environmental, seasonal, and social factors in the cooperatively breeding red-cockaded woodpecker (Picoides borealis) while accounting for individual heterogeneity with discrete random effects. We identified 2 distinct behavioral states, resting and foraging, which were related to covariates in our models. Using this approach, we concluded that woodpecker step lengths tended to be longest in winter, larger groups of woodpeckers tended to spend less time foraging and more time resting when compared with smaller groups, and woodpeckers foraged more and rested less when in higher-quality habitat. Our results demonstrate the impact that social and environmental factors can have on movement in a social species and, thus, reinforce the importance of including these factors in animal movement studies. The extensions of basic hidden Markov models considered here may prove valuable in forthcoming studies that involve highresolution tracking to understand behavior of birds and other small animals.
Sex ratios can influence mating behaviour, population dynamics and evolutionary trajectories; yet the causes of natural sex ratio variation are often uncertain. Although secondary (birth) sex ratios in guppies (Poecilia reticulata) are typically 1:1, we recorded female-biased tertiary (adult) sex ratios in about half of our 48 samples and male-biased sex ratios in none of them. This pattern implies that some populations experience male-biased mortality, perhaps owing to variation in predation or resource limitation. We assessed the effects of predation and/or inter-specific resource competition (intraguild predation) by measuring the local catch-per-unit-effort (CPUE) of species (Rivulus killifish and Macrobrachium prawns) that may differentially prey on male guppies. We assessed the effects of resource levels by measuring canopy openness and algal biomass (chlorophyll a concentration). We found that guppy sex ratios were increasingly female-biased with increasing CPUE of Macrobrachium, and perhaps also Rivulus, and with decreasing canopy openness. We also found an interaction between predators and resource levels in that the effect of canopy openness was greatest when Macrobrachium CPUE was highest. Our study thus also reveals the value of simultaneously testing multiple environmental factors that may drive tertiary sex ratio variation.
Climate change is affecting behaviour and phenology in many animals. In migratory birds, weather patterns both at breeding and at non-breeding sites can influence the timing of spring migration and breeding. However, variation in responses to weather across a species range has rarely been studied, particularly among populations that may winter in different locations. We used prior knowledge of migratory connectivity to test the influence of weather from predicted non-breeding sites on bird phenology in two breeding populations of a long-distance migratory bird species separated by 3,000 km. We found that winter rainfall showed similar associations with arrival and egg-laying dates in separate breeding populations on an east-west axis: greater rainfall in Jamaica and eastern Mexico was generally associated with advanced American redstart (Setophaga ruticilla) phenology in Ontario and Alberta, respectively. In Ontario, these patterns of response could largely be explained by changes in the behaviour of individual birds, i.e., phenotypic plasticity. By explicitly incorporating migratory connectivity into responses to climate, our data suggest that widely separated breeding populations can show independent and geographically specific associations with changing weather conditions. The tendency of individuals to delay migration and breeding following dry winters could result in population declines due to predicted drying trends in tropical areas and the tight linkage between early arrival/breeding and reproductive success in long-distance migrants.
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