Thermoenergetic challenges and daytime behavioural patterns of a wild cathemeral mammal

The importance of auditory, olfactory, and visual cues for insect foraging in owl monkeys (Aotus nancymaae)

Nocturnal mammals have unique sensory adaptations to facilitate foraging at night. Owl monkeys (Aotus spp.) are pair-living nocturnal platyrrhines adept at capturing insect prey under low-light conditions. Owl monkeys use acoustic and chemical cues in intraspecific communication and use olfaction to detect fruit as they forage. We conducted an experiment to determine which cues (auditory, olfactory, and visual) Aotus nancymaae rely upon when foraging for insects. We scored the behavior of 23 captive owl monkeys during a series of trials in which monkeys were provided sensory boxes with insect cues either present (experimental box) or absent (control box). Each cue was tested alone and in combination with all other cues (multimodal cues). We used generalized linear mixed models to determine which cues elicited the greatest behavioral response. Owl monkeys approached and spent more time near experimental boxes than control boxes. Male owl monkeys were quicker than their female partners to approach the sensory boxes, suggesting that males may be less neophobic than females. The owl monkeys exhibited behaviors associated with olfaction and foraging (e.g., sneezing, trilling) during trials with multimodal cues and when only olfactory cues were present. When only visual or auditory cues were present, owl monkeys exhibited fewer foraging-related behaviors. After approaching a sensory box, however, they often touched boxes containing visual cues. A. nancymaae may rely on olfactory cues at night to detect a food source from several meters away and then rely more on visual cues once they are closer to the food source. Their use of sensory cues during insect foraging differs from nocturnal strepsirrhines, possibly reflecting physiological constraints associated with phylogeny, given that owl monkeys evolved nocturnality secondarily from a more recent diurnal ancestor.

The behaviour and activity budgets of two sympatric sloths; Bradypus variegatus and Choloepus hoffmanni

It is usually beneficial for species to restrict activity to a particular phase of the 24-hour cycle as this enables the development of morphological and behavioural adaptations to enhance survival under specific biotic and abiotic conditions. Sloth activity patterns are thought to be strongly related to the environmental conditions due to the metabolic consequences of having a low and highly variable core body temperature. Understanding the drivers of sloth activity and their ability to withstand environmental fluctuations is of growing importance for the development of effective conservation measures, particularly when we consider the vulnerability of tropical ecosystems to climate change and the escalating impacts of anthropogenic activities in South and Central America. Unfortunately, the cryptic nature of sloths makes long term observational research difficult and so there is very little existing literature examining the behavioural ecology of wild sloths. Here, we used micro data loggers to continuously record, for the first time, the behaviour of both Bradypus and Choloepus sloths over periods of days to weeks. We investigate how fluctuations in the environmental conditions affect the activity of sloths inhabiting a lowland rainforest on the Caribbean coast of Costa Rica and examined how this might relate to their low power lifestyle. Both Bradypus and Choloepus sloths were found to be cathemeral in their activity, with high levels of between-individual and within-individual variation in the amounts of time spent active, and in the temporal distribution of activity over the 24-hour cycle. Daily temperature did not affect activity, although Bradypus sloths were found to show increased nocturnal activity on colder nights, and on nights following colder days. Our results demonstrate a distinct lack of synchronicity within the same population, and we suggest that this pattern provides sloths with the flexibility to exploit favourable environmental conditions whilst reducing the threat of predation.

The ecological importance of the accuracy of environmental temperature measurements

The implications of logger accuracy and precision are rarely considered prior to their application in many ecological studies. We assessed the accuracy and precision of three temperature data loggers widely used in ecological studies (Hobo®, iButton® and TinyTag®). Accuracy was highest in TinyTags (95% of readings were within 0.23°C of the true temperature) and lowest in HOBOs and iButtons (95% of were readings within 0.43°C and 0.49°C of the true temperature, respectively). The precision (standard deviation of the repeat measurements) was greatest in TinyTags (0.04°C), followed by iButtons (0.17°C) and then HOBOs (0.22°C). As a case study, we then considered how modelled estimates of sea turtle hatchling sex ratios (derived from temperature), could vary as a function of logger accuracy. For example, at 29°C when the mean sex ratio derived was 0.47 female, the sex ratio estimate from a single logger could vary between 0.40 and 0.50 for TinyTags and 0.29 and 0.56 for both HOBOs and iButtons. Our results suggest that these temperature loggers can provide reliable descriptions of sand temperature if they are not over-interpreted. Logger accuracy must be considered in future ecological studies in which temperature thresholds are important.