Ninja owl; Gerbils over-anticipate an unexpected flying predator.

Foragers make decisions based on cues, information collected from their environment, processed into strategic behaviours. This information, processed in multiple regions of the brain, ultimately result in the production of stress hormones and visible changes in behaviour of animals - both reflexively to avoid depredation and strategically to avoid an encounter with the predator. In a common-garden experiment we tested how imperfect information from visual cues of a predator impacts foraging and apprehension of a desert rodent, the Egyptian gerbil (Gerbillus pyramidum). The gerbils were exposed to predation by barn owls (Tyto alba), one camouflaged on dark nights using black dye. Gerbils' response to the owls was measured using patch-use measured in giving-up densities (GUDs) and time spent in vigilance activity. Owl lethality was extrapolated from mean times spent in attacks and number of attempted strikes. Dyed owls attack-rate was lower and attack duration greater than those of the white owls. During the full moon, when dyed owls were visible, gerbils responded with extreme vigilance and minimal foraging (high GUDs). During the new moon when the owls were most stealthy, the gerbils showed low vigilance coupled with a similar high GUD. The inconsistency between gerbils' foraging and vigilance behaviours, suggest a likely mismatch between perceived risk and actual measurement of predator lethality gathered by the gerbils' observations in real time.

Divergent behavior amid convergent evolution: A case of four desert rodents learning to respond to known and novel vipers.

Desert communities world-wide are used as natural laboratories for the study of convergent evolution, yet inferences drawn from such studies are necessarily indirect. Here, we brought desert organisms together (rodents and vipers) from two deserts (Mojave and Negev). Both predators and prey in the Mojave have adaptations that give them competitive advantage compared to their middle-eastern counterparts. Heteromyid rodents of the Mojave, kangaroo rats and pocket mice, have fur-lined cheek pouches that allow them to carry larger loads of seeds under predation risk compared to gerbilline rodents of the Negev Deserts. Sidewinder rattlesnakes have heat-sensing pits, allowing them to hunt better on moonless nights when their Negev sidewinding counterpart, the Saharan horned vipers, are visually impaired. In behavioral-assays, we used giving-up density (GUD) to gauge how each species of rodent perceived risk posed by known and novel snakes. We repeated this for the same set of rodents at first encounter and again two months later following intensive "natural" exposure to both snake species. Pre-exposure, all rodents identified their evolutionarily familiar snake as a greater risk than the novel one. However, post-exposure all identified the heat-sensing sidewinder rattlesnake as a greater risk. The heteromyids were more likely to avoid encounters with, and discern the behavioral difference among, snakes than their gerbilline counterparts.

Everybody loses: intraspecific competition induces tragedy of the commons in Allenby's gerbils.

Interference competition may lead to a tragedy of the commons in which individuals driven by self-interest reduce the fitness of the entire group. We investigated this hypothesis in Allenby's gerbils, Gerbillus andersoni allenbyi, by comparing foraging behaviors of single vs. pairs of gerbils. We recorded strong interference competition within the foraging pairs. Competition reduced the amount of time the gerbils spent foraging, as well as foraging efficiency since part of the foragers' attention was directed toward detecting competitors (apparent predation risk). Single gerbils harvested significantly more food than the combined efforts of two gerbils foraging together. Competition reduced the success of both individuals within a pair by more than 50%, making this a case of the tragedy of the commons where each individual's investment in competition reduces the success of all individuals within the group, including its own. Despite their great costs, competitive behaviors will be selected for as long as one individual achieves higher fitness than the other. In nature, interspecific interactions, such as predation risk, may act to reduce and regulate the deleterious effects of intraspecific competition.

To dare or not to dare? Risk management by owls in a predator-prey foraging game.

In a foraging game, predators must catch elusive prey while avoiding injury. Predators manage their hunting success with behavioral tools such as habitat selection, time allocation, and perhaps daring-the willingness to risk injury to increase hunting success. A predator's level of daring should be state dependent: the hungrier it is, the more it should be willing to risk injury to better capture prey. We ask, in a foraging game, will a hungry predator be more willing to risk injury while hunting? We performed an experiment in an outdoor vivarium in which barn owls (Tyto alba) were allowed to hunt Allenby's gerbils (Gerbillus andersoni allenbyi) from a choice of safe and risky patches. Owls were either well fed or hungry, representing the high and low state, respectively. We quantified the owls' patch use behavior. We predicted that hungry owls would be more daring and allocate more time to the risky patches. Owls preferred to hunt in the safe patches. This indicates that owls manage risk of injury by avoiding the risky patches. Hungry owls doubled their attacks on gerbils, but directed the added effort mostly toward the safe patch and the safer, open areas in the risky patch. Thus, owls dared by performing a risky action-the attack maneuver-more times, but only in the safest places-the open areas. We conclude that daring can be used to manage risk of injury and owls implement it strategically, in ways we did not foresee, to minimize risk of injury while maximizing hunting success.

What do predators really want? The role of gerbil energetic state in determining prey choice by Barn Owls.

In predator-prey foraging games, predators should respond to variations in prey state. The value of energy for the prey changes depending on season. Prey in a low energetic state and/or in a reproductive state should invest more in foraging and tolerate higher predation risk. This should make the prey more catchable, and thereby, more preferable to predators. We ask, can predators respond to prey state? How does season and state affect the foraging game from the predator's perspective? By letting owls choose between gerbils whose states we experimentally manipulated, we could demonstrate predator sensitivity to prey state and predator selectivity that otherwise may be obscured by the foraging game. During spring, owls invested more time and attacks in the patch with well-fed gerbils. During summer, owls attacked both patches equally, yet allocated more time to the patch with hungry gerbils. Energetic state per se does not seem to be the basis of owl choice. The owls strongly responded to these subtle differences. In summer, gerbils managed their behavior primarily for survival, and the owls equalized capture opportunities by attacking both patches equally.

Predator facilitation or interference: a game of vipers and owls.

In predator-prey foraging games, the prey's reaction to one type of predator may either facilitate or hinder the success of another predator. We ask, do different predator species affect each other's patch selection? If the predators facilitate each other, they should prefer to hunt in the same patch; if they interfere, they should prefer to hunt alone. We performed an experiment in a large outdoor vivarium where we presented barn owls (Tyto alba) with a choice of hunting greater Egyptian gerbils (Gerbillus pyramidum) in patches with or without Saharan horned vipers (Cerastes cerastes). Gerbils foraged on feeding trays set under bushes or in the open. We monitored owl location, activity, and hunting attempts, viper activity and ambush site location, and the foraging behavior of the gerbils in bush and open microhabitats. Owls directed more attacks towards patches with vipers, and vipers were more active in the presence of owls. Owls and vipers facilitated each other's hunting through their combined effect on gerbil behavior, especially on full moon nights when vipers are more active. Owls forced gerbils into the bushes where vipers preferred to ambush, while viper presence chased gerbils into the open where they were exposed to owls. Owls and vipers took advantage of their indirect positive effect on each other. In the foraging game context, they improve each other's patch quality and hunting success.

The role of indigenous bacterial and fungal soil populations in the biodegradation of crude oil in a desert soil.

The biodegradation capacity of indigenous microbial populations was examined in a desert soil contaminated with crude oil. To evaluate biodegradation, soil samples supplemented with 5, 10 or 20% (w/w) of crude oil were incubated for 90 days at 30 degrees C. The effect of augmentation of the soil with vermiculite (50% v/v) as a bulking agent providing increased surface/volume ratio and improved soil aeration was also tested. Maximal biodegradation (91%) was obtained in soil containing the highest concentration of crude oil (20%) and supplemented with vermiculite; only 74% of the oil was degraded in samples containing the same level of crude oil but lacking vermiculite. Gas chromatograms of distilled fractions of crude oil extracted from the soil before and after incubation demonstrated that most of the light and part of the intermediate weight fractions initially present in the oil extracts could not be detected after incubation. Monitoring of microbial population densities revealed an initial decline in bacterial viable counts after exposure to oil, presumably as a result of the crude oil's toxicity. This decline was followed by a steep recovery in microbial population density, then by a moderate increase that persisted until the end of incubation. By contrast, the inhibitory effect of crude oil on the fungal population was minimal. Furthermore, the overall increased growth response of the fungal population, at all three levels of contamination, was about one order of magnitude higher than that of the bacterial population.