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The power curve provides a basis for predicting adjustments that animals make in flight speed, for example in relation to wind, distance, habitat foraging quality and objective. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed and power allocation through modifications in climb rate and perceived predation risk. We equipped homing pigeons (Columba livia) with high-frequency loggers to examine how flight speed, and hence effort, varies in relation to topography and land cover. Pigeons showed mixed evidence for an energy-saving strategy, as they minimized climb rates by starting their ascent ahead of hills, but selected rapid speeds in their ascents. Birds did not modify their speed substantially in relation to land cover, but used higher speeds during descending flight, highlighting the importance of considering the rate of change in altitude before estimating power use from speed. Finally, we document an unexpected variability in speed and altitude over fine scales; a source of substantial energetic inefficiency. We suggest this may be a form of protean behaviour adopted to reduce predation risk when flocking is not an option, and that such a strategy could be widespread.

Many animals have colour patterns that appear to change dynamically when the animal moves. Experiments have suggested that such colour patterns, termed 'dynamic flash' coloration, can reduce predatory attacks by misrepresenting the prey's location. However, the conditions that make this coloration effective are not known. We here tested the influence of two factors, target size and unpredictable movement, on the efficacy of dynamic flash coloration. Both these factors have independently been shown to affect the predator's ability to attack a moving prey accurately, but whether they interact with prey coloration remains unclear. Using a virtual predation experiment with human participants, we found that the effectiveness of dynamic flash coloration, when compared to background-matching coloration, declined as the size of the target increased, but only when the target movement was linear (i.e. predictable). However, when the movement was unpredictable (i.e. when the target adopted a 'protean' motion), we found dynamic flash coloration to be effective in reducing the number and accuracy of attacks irrespective of target size. Under most conditions, the effectiveness of dynamic flash coloration did not differ from that of a uniform luminance-matched grey target. Our results suggest that the efficacy of dynamic flash coloration is limited by prey size, but animals can overcome this constraint by employing an unpredictable movement trajectory. The study also provides direct empirical evidence that protean antipredator behaviour influences the effectiveness of prey coloration that works in motion. • Dynamic change in prey colour during motion may reduce predatory attacks. • We tested the factors affecting the effectiveness of dynamic coloration. • When movement was linear, dynamic coloration was effective only in small targets. • It was effective irrespective of size when the movement path was unpredictable. • Its evolution might be affected by prey size and escape trajectory. [ABSTRACT FROM AUTHOR]

The escape paths prey animals take following a predatory attack appear to be highly unpredictable - a property that has been described as 'protean behaviour'. Here, we present a method of quantifying the escape paths of individual animals using a path complexity approach. When individual fish (Pseudomugil signifer) were attacked, we found that a fish's movement path rapidly increased in complexity following the attack. This path complexity remained elevated (indicating a more unpredictable path) for a sustained period (at least 10 s) after the attack. The complexity of the path was context dependent: paths were more complex when attacks were made closer to the fish, suggesting that these responses are tailored to the perceived level of threat. We separated out the components of speed and turning rate changes to determine which of these components contributed to the overall increase in path complexity following an attack. We found that both speed and turning rate measures contributed similarly to an individual's path complexity in absolute terms. Overall, our work highlights the contextdependent escape responses that animals use to avoid predators, and also provides a method for quantifying the escape paths of animals. [ABSTRACT FROM AUTHOR]

Small crustaceans, such as the rockpool prawnPalaemon elegansRathke, respond to the approach of predators by executing a version of the crustacean tail-flip response, known as the ‘jack-knife’. We used two types of stimulus to investigate the escape behaviour ofP. elegans, specifically the escape trajectories taken by individual prawns. The first stimulus consisted of mechanosensory cues, while the second stimulus included visual and mechanosensory cues. Responses to the two stimulus types differed, with the combined cues from the second stimulus type resulting in escapes over longer distances, and with greater directionality, compared to those following purely mechanosensory stimulation. Altering the direction of approach of the ‘predator’ affected the proportion of escapes that were to the side opposite from the eliciting stimulus and strongly influenced escape trajectories. Such unpredictability in the escape direction ofP. elegansmay be an example of so-called ‘Protean’ behaviour. [ABSTRACT FROM AUTHOR]

Longfin squid, Loligo pealeii, were exposed to two predators, bluefish, Pomatomus saltatrix, and summer flounder, Paralichthys dentatus, representing cruising and ambush foraging tactics, respectively. During 35 trials, 86 predator–prey interactions were evaluated between bluefish and squid, and in 29 trials, 92 interactions were assessed between flounder and squid. With bluefish, squid predominantly used stay tactics (68.6%, 59/86) as initial responses. The most common stay response was to drop to the bottom, while showing a disruptive body pattern, and remain motionless. In 37.0% (34/92) of interactions with flounder, squid did not detect predators camouflaging on the bottom and showed no reaction prior to being attacked. Squid that did react, used flee tactics more often as initial responses (43.5%, 40/92), including flight with or without inking. When all defence behaviours were considered concurrently, flight was identified as the strongest predictor of squid survival during interactions with each predator. Squid that used flight at any time during an attack sequence had high probabilities of survival with bluefish (65%, 20/31) and flounder (51%, 18/35). The most important deimatic/protean behaviour used by squid was inking. Inking caused bluefish to startle (deimatic) and abandon attacks (probability of survival=61%, 11/18) and caused flounder to misdirect (protean) attacks towards ink plumes rather than towards squid (probability of survival=56%, 14/25). These are the first published laboratory experiments to evaluate the survival value of antipredator behaviours in a cephalopod. Results demonstrate that squid vary their defence tactics in response to different predators and that the effectiveness of antipredator behaviours is contingent upon the behavioural characteristics of the predator encountered. [Copyright &y& Elsevier]

The power curve provides a basis for predicting adjustments that animals make in flight speed, for example in relation to wind, distance, habitat foraging quality and objective. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed and power allocation through modifications in climb rate and perceived predation risk. We equipped homing pigeons ( Columba livia ) with high-frequency loggers to examine how flight speed, and hence effort, varies in relation to topography and land cover. Pigeons showed mixed evidence for an energy-saving strategy, as they minimized climb rates by starting their ascent ahead of hills, but selected rapid speeds in their ascents. Birds did not modify their speed substantially in relation to land cover, but used higher speeds during descending flight, highlighting the importance of considering the rate of change in altitude before estimating power use from speed. Finally, we document an unexpected variability in speed and altitude over fine scales; a source of substantial energetic inefficiency. We suggest this may be a form of protean behaviour adopted to reduce predation risk when flocking is not an option, and that such a strategy could be widespread., (© 2021 The Authors.)