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| Author |
Schuck-Paim, C.; Kacelnik, A. |
| Title |
Rationality in risk-sensitive foraging choices by starlings |
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Journal Article |
| Year |
2002 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
64 |
Issue  |
6 |
Pages |
869-879 |
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Normative models of choice usually predict preferences between alternatives by computing their value according to some criterion, then identifying the alternative with greatest value. An important consequence of this procedure is captured in the economic concept of rationality, defined through a number of principles that are necessary for the existence of an ordinal scale of value upon which organisms base their choices. Violations of these principles, such as some recently reported breaches of transitivity and regularity in birds and honeybees, have strong implications for the understanding of decision mechanisms in humans and nonhumans alike. We investigated rationality in risky choice using European starlings, Sturnus vulgaris. Birds had to choose between two or three food sources, each associated with a different variance in delay to reward. In three experiments, starlings were strongly risk prone, showing regular and consistent preferences in binary and trinary choices. Preferences also satisfied weak and strong stochastic transitivity. Our results extend the generality of previous research in risk-sensitive foraging to situations where more than two alternatives are present and suggest that violations of rationality in risk-sensitive choices may be expressed only under restricted sets of conditions. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved. |
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2106 |
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| Author |
Bateson, M.; Kacelnik, A. |
| Title |
Starlings' preferences for predictable and unpredictable delays to food |
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Journal Article |
| Year |
1997 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
53 |
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6 |
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1129-1142 |
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Risk-sensitive foraging theory is based on the premise that unpredictable runs of good or bad luck can cause a variable food source to differ in fitness value from a fixed food source yielding the same average rate of gain but no unpredictability. Thus, risk-sensitive predictions are dependent on the food intake from variable sources being not only variable but also unpredictable or `risky' in outcome. This study tested whether unpredictability is a component of the value that foraging starlings,Sturnus vulgarisattribute to food sources that are variable in the delay to obtain food. Two groups of birds chose between a fixed and a variable delay option; the variable option was unpredictable in the risky group and predictable in the risk-free group in the overall rate of intake it yielded. In both groups the fixed option was adjusted by titration to quantify the magnitude of preference for predictable and unpredictable variance. On negative energy budgets both groups were significantly risk-prone, with the risky group being significantly more risk-prone than the risk-free group. Switching the birds to positive budgets by doubling the size of each food reward had no significant effect on preference, and similar trends to those found with negative budgets were observed. These results are not readily explained by risk-sensitive foraging theory, but may be explained by the algorithm used by the birds to attribute value to average expected rewards. |
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2108 |
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Cuthill, I.; Kacelnik, A. |
| Title |
Central place foraging: a reappraisal of the `loading effect' |
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Journal Article |
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1990 |
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Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
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40 |
Issue |
6 |
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1087-1101 |
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Animals that provision a central place usually bring back larger loads when foraging far from home. This positive correlation between average load size and distance is typically explained as rate-maximizing behaviour in the face of a trade-off between travel costs and a decelerating rate of prey gain in food patches (the `loading effect'). By using feeders to provide wild parent starlings, Sturnus vulgaris, with constant rates of prey loading, a positive load-distance correlation was shown to exist in the absence of a loading effect (experiment I). However, in a laboratory simulation where no load was transported (experiment II). the average number of prey eaten in patch visits by self-feeding starlings was invariant with travel distance, so the explanation of the load-distance correlation in experiment I must lie in featues peculiar to central place foraging. Bottlenecks in ingestion by chicks and interruption by visual detection of nest disturbance (experiment III) were rejected as causes of the correlation. Risks of dropping prey in flight appeared low, but the risk of kleptoparasitism received weak support. The travel-load size correlation may be an adaptive response to load transport costs, as return travel times increased with the load size being carried (experiment IV). |
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2116 |
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Reboreda, J.C.; Kacelnik, A. |
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On cooperation, tit-for-tat and mirros |
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Journal Article |
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1990 |
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Animal Behaviour. |
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Anim. Behav. |
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40 |
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6 |
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1188-1189 |
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2117 |
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Cassini, M.H.; Kacelnik, A.; Segura, E.T. |
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The tale of the screaming hairy armadillo, the guinea pig and the marginal value theorem |
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Journal Article |
| Year |
1990 |
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Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
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39 |
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6 |
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1030-1050 |
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Foraging by screaming hairy armadillos, Chaetophractus vellerosus, and guinea pigs, Cavia porcellus, was studied in the laboratory. The main question was whether patch exploitation varies with overall capture rate as predicted by the marginal value theorem (MVT). Armadillos in experiment I and guinea pigs in experiment II experienced a single travel time between depleting patches of two kinds: good and poor. There were two treatments, which differed in the quality of poor patches. MVT predicts that within a treatment, more prey should be taken from good than from poor patches and between treatments, good patches should be exploited in inverse relation to the quality of poor patches and poor patches should be exploited in direct relation to their own quality. In experiment III, guinea pigs experienced three treatments which differed in the travel requirement, while the two patch types remained the same. MVT predicts that within a treatment more prey should be taken from good than from poor patches and that between treatments more prey should be taken from both patch types as travel requirement increases. The qualitative predictions were supported in the three experiments. The quantitative fit was good but there was a bias towards more severe patch exploitation than predicted. The results indicate that in these species patch exploitation depends on overall food availability as predicted by the MVT when overall food availability differs either because of patch type composition or because of differences in travel requirement between patches. |
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2120 |
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Kacelnik, A. |
| Title |
The foraging efficiency of great tits (Parus major L.) in relation to light intensity |
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Journal Article |
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1979 |
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Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
27 |
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Part 1 |
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237-241 |
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I report an experiment aimed at testing whether foraging efficiency of great tits is limited by light intensity at the time of the dawn chorus. Captive great tits hunting for prey under different luminance conditions were less successful in finding prey when foraging, hunted for a lower proportion of their time, and handled individual prey items for longer when luminance was under approximately 7 cd/m2. This luminance is not reached in the field until after the time of the dawn chorus, suggesting that in the early morning foraging is limited by light intensity. I suggest that a satisfactory functional explanation of the dawn chorus must take into account the comparatively low foraging opportunity early in the morning, as well as the factors affecting the opportunity for singing and other territorial activities. |
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2125 |
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Caraco, T.; Kacelnik, A.; Mesnick, N.; Smulewitz, M. |
| Title |
Short-term rate maximization when rewards and delays covary |
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1992 |
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Animal Behaviour. |
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Anim. Behav. |
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44 |
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Part 3 |
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441-447 |
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In nature foragers must exploit resources that vary randomly in both the energy acquired per item (reward) and the time required to pursue, capture and process an item (delay). Furthermore, rewards and delays associated with particular resources may often covary significantly. An analytical model asks how variance-covariance levels for rewards and delays could influence choice of resources when lack of information or cognitive limitation implies that a consumer attempts to maximize its short-term rate of energy gain. Both greater expected reward and reduced expected delay clearly should enhance preference for a resource. The model predicts that increased delay variance and reduced reward-delay covariance should increase a forager's preference for a resource. A forager should be risk-averse towards reward variance when the reward-delay covariance is positive, but should become risk-prone towards reward variance when the reward-delay covariance is negative. |
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2113 |
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Roberts, J.; Kacelnik, A.; Hunter, M.L. |
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A model of sound interference in relation to acoustic communication |
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Journal Article |
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1979 |
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Animal Behaviour. |
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Anim. Behav. |
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27 |
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Part 4 |
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1271-1273 |
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2124 |
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