"The traditional view was that the leaves exploited by howler monkeys were an abundant food source - but this is not the case," said Dunn.
"The monkeys rely much more heavily on fruit than previously believed, and when turning to foliage for food - as they are increasingly forced to do they have to be highly selective in the leaves they consume, visiting lots of different trees. This leads to the increased 'travel time' and consequent high levels of stress we are seeing in these primates as their habitats disintegrate."
As trying to catch the howlers to examine them would in itself be highly stressful for the animal, the best way of evaluating stress levels in wild primates is by analysing their faeces for glucocorticoid stress hormones, which are general to all vertebrates.
Through statistical modelling, the researchers were able to determine that it is the 'travel time' - rather than the increased foliage intake - causing high levels of stress.
"Monkeys in disturbed habitats suffering high levels of stress is in itself unsurprising perhaps, but now we think we know why, the root cause from the primates perspective. Our results also highlight the importance of preserving and planting fruit trees - particularly those species such as figs that can produce fruit during periods of general fruit scarcity - for the conservation of howler monkeys said Dr Jurgi Cristbal-Azkarate, also from Cambridge, who led the research in collaboration with Dr Joaquim Vea from the University of Barcelona.
The authors say that further studies are required to fully understand the significance of increases in stress in howler monkeys living in disturbed habitats. "Determining the full rel
|Contact: Fred Lewsey|
University of Cambridge