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No abstract

We examined mass-specific activity patterns among overwintering cotton rats (Sigmodon hispidus) in northeastern Kansas. We livetrapped animals for a 24-h period, checking traps every 2 h. Trapping occurred every 2 weeks for 5 months. We estimated probability of capture for each mass class, time class, and date, then tested for differences in probability of capture (i.e., activity levels) using a General Linear Model with temperature as a covariate. Large cotton rats were significantly less active than small and intermediate-sized cotton rats. Activity of small cotton rats increased with decreasing temperature, whereas larger cotton rats were less responsive to temperature. Finally, activity levels of large and small cotton rats did not vary significantly with time of day, but intermediate-sized cotton rats were significantly less likely to be captured during the night than at dusk.Résumé : Nous avons examiné les patterns d'activité spécifique à la masse chez des Rats-cotonniers hirsutes (Sigmodon hispidus) dans le nord-est du Kansas, en hiver. Nous avons procédé à la capture d'animaux vivants pendant des périodes de 24 h au cours desquelles nous relevions les pièges toutes les 2 h. Ces piégeages ont eu lieu toutes les 2 semaines pendant 5 mois. Nous avons estimé la probabilité de capture pour chaque classe de masse, chaque classe de temps, chaque date, et éprouvé les différences des probabilités de capture (i.e., intensité des activités) au moyen d'un modèle linéaire général où la température servait de covariable. Les rats-cotonniers de grande taille étaient significativement moins actifs que les animaux de taille petite ou intermédiaire. L'activité des petits rats-cotonniers augmentait lorsque la température diminuait, alors que les rats-cotonniers plus gros étaient moins affectés par la température. Enfin, l'intensité de l'activité chez les gros et les petits animaux ne variait pas significativement en fonction du moment de la journée, mais les rats-cotonniers de taille intermédiaire étaient moins susceptibles d'être capturés durant la nuit qu'au crépuscule. [Traduit par la Rédaction]

We experimentally determined that the lizard Pedioplanis namaquensis engages in area-restricted searching (=ARS, localized searching after encounters with food) while foraging and that prey characteristics influence ARS. Single prey items were introduced to free-ranging lizards, and their subsequent search effort was characterized using first passage times (=FPT, time required for an animal to cross a circle of a given radius). Three prey types were used: termites, flies, and rice (control). FPTs were longer following termite encounters than following fly or control encounters. Control treatments produced no change in FPT, while lizards searching for termites showed the greatest change. The use by Pedioplanis namaquensis of ARS was most pronounced for the typically aggregated prey type.

The whiptail lizard Aspidoscelis uniparens searches for fossorial prey using a series of moves and pauses punctuated by bouts of digging. We examined the effect of predation risk on foraging A. uniparens in outdoor enclosures, observing their behavior in the presence and absence of the predatory lizard Gambelia wislizenii. Predator presence led to changes in activity patterns and foraging behavior. When predators were present, A. uniparens reduced both the proportion of time active and time moving, shifted activity periods, reduced their movement rate, and changed the duration of moves. There were no apparent changes in digging effort, but the likelihood of successfully digging for food decreased when a predator was present.