All animals secrete odors which can be picked up by others. This odor is a cue, a product that will always be present in nature. Animals know the scent of their predators and prey, assisting them in consumption or avoiding consumption. When predator odors are identified, the prey will exhibit anti-predator behaviors. Performing these anti-predator behaviors take time and energy to perform, taking the animals “focus” away from other tasks such as foraging or mating.
Huailing Guo and colleagues set up an experiment in the Laboratory of Animal Behavior, at Gansu Agricultural University in Gansu Province, China to examine the trade-offs between defensive responses and foraging [1]. Specifically, they investigated the anti-predator behavioral and hormonal effects on the plateau zokor (Eospalax baileyi) when exposed to various amounts of eagle owl (Bubo bubo) feces.
The plateau zokor is a subterranean rodent that inhabits the Qinghai-Tibetan Plateau and lives the large majority of its life underground in complicated tunnels. Over the course of evolution, the vision of the plateau zokor has diminished and they must rely strongly on olfaction and hearing. This means that when above ground, they are much more vulnerable to aerial and terrestrial predation.
To perform the experiment, 80 adult plateau zokors from the Qinghai-Tibetan Plateau were transported to a room meant to imitate their natural environment and fed at a rate they would have foraged in the wild to reduce stress. The zokors were randomly divided into four groups of 20. The four groups were exposed to either distilled water as the control group, 1g of feces, 3g of feces, or 6g of feces. The predator odor, eagle owl feces, was obtained from the Lanzhou Zoo, Gansu Province, China and kept fresh until use. The testing apparatus was a glass box for viewing with an opaque pipe in the back called the “hiding tunnel”. The front corners consisted of a food cup and odor cup. Zokors were exposed to the empty apparatus the day prior to the experiment. During the experiment, the appropriate amount of feces was added to the odor cup and the zokor was placed in the middle of the box, left to move about for 30 minutes.
While in the box, the quantity of food contacted (smelling or biting food), freezing (immobilization), rearing (raised on hind legs), contact with feces, hiding (entire body in the hiding tube), and head out (head sticking out of hiding tube) were recorded. Afterwards, twelve zokors from each group were selected to provide blood to obtain serum levels of the adrenocorticotropic hormone and corticosterone which are produced during periods of stress.
As you may have predicted, the presence of feces causes the plateau zokor to adapt a more defensive behavior and spend less time foraging. They found that food contacting and amount of food consumed decreased from the control, however the amount of feces present did not have a significant difference. The amount of times zokors hid or stuck their head out of the “hiding hole” was insignificant across the groups. When it came to contract with feces, the only significant group was the 1g of feces which was unexpected. The behaviors that most resembled their hypothesis was that of freezing and rearing as they significantly increased as higher amounts of predator feces were present.
You would have also expected the zokor to experience more stress when under the impression there is a predator nearby. This can be seen in the analysis of the hormones present after exposure. The adrenocorticotropic hormone levels were significantly higher in the groups exposed to feces that those without, however the amount of feces had no effect. The corticosterone levels were significant to that of the control, however the groups of 3g and 6g were also significant to that of the 1g group.
The results confirm that the presence of eagle owl feces would reduce foraging since the zokor was largely concerned with defense. Strangely, the zokors did not greatly alter their foraging between low and high risk which contradicts the risk allocation hypothesis. They only altered their foraging behavior between risk and no risk. Guo points out in their paper that it is important to remember that the zokor primarily lives underground so it is possible that any amount of feces is enough to indicate the presence of danger. More research is necessary to determine if other predatorial signals such as sound could influence the anti-predator behavior of zokors.
Work Cited:
[1] Guo, H., Hegab, I.M., Tan, Y., Yao, B., Wang, C., Cai, Z., Ji, W., Su, J., Exposure to eagle owl feces induces anti-predator behavior, physiology, and hypothalamic gene responses in a subterranean rodent, the plateau zokor (Eospalax baileyi). Behav Ecol Sociobiol 74, 145 (2020). https://doi-org.libproxy.kenyon.edu/10.1007/s00265-020-02934-w
Recent Comments