Firstly, what are GUDs?
GUDs stands for “Giving up Densities” and represents the density of a patch at which an individual ceases foraging. How long an animal stays in a patch before deciding to forage elsewhere represents a trade-off between meeting energy demands and safety from predators.
The question we are addressing is: do samango monkeys deplete patches to lower levels when there’s no, or relatively less, perceived risk of predation?
We have established artificial food patches by suspending tubs filled with sawdust (the substrate) and peanuts (the food) at four different canopy heights. Our 6-day pilot phase took place in the home range of one of the two habituated study troops of samangos called Barn Troop, and consisted of 20 tubs hung on 5 trees at 0.1m, 2.5m, 5m and 7.5m above the ground. You can view a video of samango monkeys foraging on these patches below. We baited the tubs in the morning at 0600, and counted remaining peanuts in the evening at 1700.
As previous studies indicated that access to peanut halves was too easy for samango monkeys and consequently many patches had no food remaining, it was imperative for us to extend the amount of time required to forage in each GUD patch by reducing forager access to the tubs. By criss-crossing ropes in a grid pattern across the tops of the tubs, we were able to slow down monkeys’ foraging time at these artificial food patches. Our pilot data suggest that a grid of 9 cells is significantly more difficult than a grid of 4 and 6 cells (based on the number of peanuts left).
The larger objectives of this research are to determine if significant differences in GUDs are related to canopy height, and if we can manipulate samangos’ perceived risk by playing leopard growls or presenting visual stimuli such as fake snakes in the GUDs area. It is expected that predation risk will be higher at the lowest and highest tub heights, and prompt higher vigilance and co-feeding, i.e., individuals foraging in closer proximity. We hypothesize that GUDs will be raised following the presentation of predator stimuli.
Check back for an update in August!