Hair cortisol concentration (HCC) provides a long-term retrospective measure of hypothalamic–pituitary–adrenal axis activity, and is increasingly used to assess the life history, health and ecology of wild mammals. Given that sex, age, season and pregnancy influence HCC, and that it may indicate ongoing stress, we examined HCC in common marmosets (Callithrix jacchus) naturally inhabiting a hot and dry semi-desert like habitat, Caatinga, in northeastern Brazil. We trapped, measured, weighed, marked and collected shaved hair from the back of the neck of 61 wild marmosets during the wet and dry seasons. Using enzyme immunoassay, we found that HCC was higher in the dry season compared with the wet season among all age/sex classes. Females had significantly higher HCC than males, juveniles had higher HCC than adults, and reproductively active adult females and non-pregnant/non lactating adult females did not differ in HCC. There were no interaction effects of sex, age, group, or season on HCC. The magnitude of the effect of this extremely hot and dry environment (average yearly rainfall was only 271 mm) on HCC in common marmosets is difficult to ascertain as these animals are also experiencing a variety of other stressors. However, the elevated HCC seen in common marmosets during the 5–8 month dry season, suggests these primates face an extended period of heat, water and possibly nutritional stress, which appears to result in a high rate of juvenile mortality.
Understanding the set of factors that promote and constrain a species' ability to exploit ecologically distinct habitats is central for addressing questions of intraspecific variability in behavior and morphology. In this study, we compared newly collected data with published data on body measurements, group size and composition, daily path length, home range, and reproductive output in wild common marmosets naturally inhabiting two contrasting environments in northeastern Brazil: the Atlantic Forest (AF), which is characterized by high biodiversity and reduced seasonality in food availability and the Caatinga (CAT), which is characterized by a severe hot and dry season lasting from 5 to 11 months, drought-resistant plant species, and reduced primary productivity.Despite marked differences in ecological conditions, CAT marmosets and AF marmosets differed minimally in daily path length, home range, reproductive output, and infant survivorship. CAT marmosets were found to live in smaller groups containing fewer adult females than AF marmosets, and also were characterized by a greater surface area to body mass ratio, a trait that may represent an adaptation to the hot and dry conditions of the Caatinga. We propose that in conjunction with body mass reduction, minor adjustments in behavior, the exploitation of cacti as a source of water and nutrients, and access to exudates as a dependable year-round food resource, common marmosets successfully used the same adaptive pattern to maintain high reproductive output and infant survivorship in exploiting these two ecologically distinct environments. K E Y W O R D SAtlantic forest, Caatinga, intraspecific variability, phylogenetic constraints, surface area to body mass ratio
Several species of callitrichines (tamarins, marmosets, and callimicos) are reported to frequently leap between vertical supports when foraging and traveling in the forest understory. In the present study, we examine trunk-to-trunk leaping in a wild group of four habituated adult saddleback tamarins (Saguinus fuscicollis weddelli) in northern Bolivia. From June through July, 2011 we analyzed 200 leaps in which the tamarins moved between vertical supports. On average, takeoff height was 4.1 m (±1.3 m, range 1-7.5 m). During the airborne phase of travel the monkeys lost an average of 0.5 m (±0.5 m) at contact with the landing support, and the mean distance leapt was 1.4 m (± 0.7 m). We found no correlation between the diameter at breast height (DBH) of landing and takeoff supports, and either the distance leapt or height gained/lost during leaping. Across callitrichine taxa, it appears that ecological distinctions in diet, patterns of habitat utilization, and predator avoidance strategies have played an important role in understanding the frequency and context of trunk-to-trunk leaping behavior.
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