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El Portal, AZ, United States

Cooper W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Ethology | Year: 2016

A prey's body orientation relative to a predator's approach path may affect risk of fleeing straight ahead. Consequently, prey often turn before fleeing. Relationships among orientation, turn, and escape angles and between these angles and predation risk have not been studied in terrestrial vertebrates and have rarely been studied in the field. Escape angles are expected to lead away from predators and be highly variable to avoid being predictable by predators. Using approach speed as a risk factor, we studied these issues in the zebra-tailed lizard, Callisaurus draconoides. Lizards fled away from human simulated predators, but most did not flee straight away. Escape angles were variable, as expected under the unpredictability hypothesis, and had modes at nearly straight away (i.e., 0°) and nearly perpendicular to the predator's approach path (90°). The straight away mode suggests maximal distancing from the predator; the other mode suggests maintaining ability to monitor the predator or possibly an influence of habitat features such as obstacles and refuges that differ among directions. Turn angles were larger when orientation was more toward the predator, and escape angles were closer to straight away when turn angles were larger. Turning serves to reach a favorable fleeing direction. When orientation angle was more toward the predator, escape angle was unaffected, suggesting that turn angle compensates completely for increased risk of orientation toward the predator. When approached more rapidly, lizards fled more nearly straight away, as expected under greater predation risk. Turn angles were unrelated to approach speed. © 2016 Blackwell Verlag GmbH.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Behavioral Ecology and Sociobiology | Year: 2013

Escape latency theory models the tradeoff between maintaining crypsis by remaining immobile near an immobile predator versus moving to flee or engage in fitness-enhancing activities. The model predicts that latency to flee increases as cost of fleeing increases and decreases as cost of remaining immobile increases. As predation risk increases, cost of fleeing, primarily due to abandoning crypsis due to immobility, decreases. Predictions have been tested for few risks and a single cost of immobility factor in only two species of active foragers. To gauge the breadth of applicability of the model, we tested effects of four risk factors and two cost of immobility factors in ambush-foraging phrynosomatid lizards, which we selected for testing because foraging mode strongly affects many aspects of ecology and behavior of lizards. Latency to flee decreased as standing distance (predator-prey distance before fleeing) decreased, predator approach speed increased, directness of approach increased, and predator persistence increased. Latency to move was shorter in the presence of food and shorter for males in the presence of females. Lizards often moved toward food or females instead of fleeing. Latency was affected as predicted by all risk and by cost of remaining immobile factors. Our findings agree with previous results for the same four risk factors and the foraging cost of immobility. That social cost of immobility affects latency as predicted is a novel finding. The model is robust, applying to ecologically diverse prey and to a wide range of factors affecting costs of fleeing and of immobility. © 2013 Springer-Verlag Berlin Heidelberg.


Cooper W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Behaviour | Year: 2015

Flight initiation distance (FID = predator-prey distance when escape begins) increases as starting distance (predator-prey distance when approach begins) increases. The flush early and avoid the rush (FEAR) hypothesis proposes that this relationship exists because monitoring an approach is costly. Hypothesized causes are increase in assessed risk and decrease in obtainable benefits while monitoring as starting distance increases.We propose the delay risking emergence and avoid dying (DREAD) hypothesis: hiding time in refuge increases as starting distance increases because prey use risk assessed during approach to estimate risk upon emerging. In the lizard Callisaurus draconoides, FID increased as standardized starting distance increased at faster approach speeds, supporting the FEAR hypothesis. In its first test, the DREAD hypothesis was supported: hiding time in the lizard Sceloporus virgatus increased as standardized starting distance increased. No large benefits were attainable, suggesting that dynamic increase in assessed risk accounts for these findings. © 2015 Koninklijke Brill NV, Leiden.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Wilson D.S.,Southwestern Research Station
Herpetologica | Year: 2010

During encounters with predators, prey that flee into refuges decide how long to hide. Refuge use theory predicts that hiding time increases as the risk of emerging increases. Lizards that escape by autotomizing their tails incur costs, including temporary decrease in speed and loss of ability to use autotomy. Thus, risk of being captured upon emergence is greater after autotomy. Also, a predator that captures a prey may later be assessed as posing greater threat. We predicted that hiding time increases after a lizard has been captured or has undergone autotomy. A previous study of striped plateau lizards (Sceloporus virgatus) showed that the proportion of lizards that entered refuges increased after autotomy but not after earlier capture. To examine unstudied effects of autotomy and capture on hiding time, we conducted a 2 × 2 factorial field experiment with handling and autotomy as factors. The four groups were (1) unhandled intact controls; (2) unhandled autotomized; (3) captured (and handled) intact, but not autotomized; and (4) captured, handled and autotomized. Because entering cool refuges entails costly decrease in body temperature, hiding times are shorter in cooler refuges. We controlled this effect statistically by conducting analyses of covariance incorporating difference in air temperature inside and outside refuges as the covariate. As predicted, autotomy and handling led to longer hiding times. However, handling affected hiding time only in intact lizards. Our results add autotomy and capture to risk factors known to affect hiding time, augmenting a growing body of knowledge supporting the hypothesis that trade-offs between costs of emerging and remaining in a refuge guide decisions about hiding time. © 2010 by the Herpetologists' League, Inc.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Canadian Journal of Zoology | Year: 2010

Flight initiation distance (predator-prey distance when escape begins) increases as predation risk increases. Prey should have longer flight initiation distance when their background, movement, or current posture reduces crypsis. Flight initiation distance of ectotherms may increase at lower body temperature to compensate for slower running speed. However, for cryptic prey, fleeing might increase the probability of being detected. The Round-tailed Horned Lizard (Phrynosoma modestum Girard, 1852) is eucryptic and resembles small stones. We predicted that flight initiation distance by P. modestum is shorter among stones than on uniform sand. Because movement and upright posture disrupt crypsis, we predicted that flight initiation distance is greater after movement and when standing than when still and lying on the ground. As predicted, flight initiation distances were shorter on a rocky than sandy area, when lying flat than standing, and while immobile than after moving. We measured running speed and flight initiation distance to determine relationships among body temperature, speed, and escape decisions. Running speed and flight initiation distance were reduced at lower body temperature, suggesting that crypsis reinforced by immobility is more advantageous than longer flight initiation distance for cool, slow lizards. The lizards adjusted escape decisions to current effectiveness of crypsis and escape ability.

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