Z. Abramsky et al., THE EFFECT OF BARN OWLS (TYTO-ALBA) ON THE ACTIVITY AND MICROHABITAT SELECTION OF GERBILLUS-ALLENBYI AND GERBILLUS-PYRAMIDUM, Oecologia, 105(3), 1996, pp. 313-319
Predation plays an important role ill ecological communities by affect
ing prey behavior such as foraging and by physical removal of individu
al prey. In regard to foraging, animals such as desert rodents often b
alance conflicting demands for food and safety. This has been studied
in the field by indirectly manipulating predatory risk through the alt
eration of cues associated with increased risk such as cover or illumi
nation. It has also been studied by directly manipulating the presence
of predators in aviaries. Here, we report on experiments in which we
directly manipulated actual predatory risk to desert rodents in the fi
eld. We conducted a series of experiments in the field using a trained
barn owl (Tyto alba) to investigate how two species of coexisting ger
bils (Gerbillus allenbyi and G. pyramidum) respond to various cues of
predatory risk in their natural environment. The gerbils responded to
risk of predation, in tile form of owl flights and owl hunger calls, b
y reducing their activity in the risky plot relative to the control pl
ot. The strongest response was to owl flights and the weakest to recor
ded hunger calls of owls. Furthermore, when risk of predation was rela
tively high, as in the case with barn owl flights, both gerbil species
mostly limited their activity to the safer bush microhabitat. The res
ponse of the gerbils to risk of predation disappeared very quickly fol
lowing removal of the treatment, and the gerbils returned to normal le
vels of activity within the same night. The gerbils did not respond to
experimental cues (alarm clock), the presence of the investigators, t
he presence of a quiet owl, and recorded ''white noise''. Using traine
d barn owls, we were able to effectively manipulate actual risk of pre
dation to gerbils in natural habitats and to quantify how gerbils alte
r their behavior in order to balance conflicting demands of food and s
afety. The method allows assessment of aspects of behavior, population
interactions, and community characteristics involving predation in na
tural habitats.