String-Pulling Behavior in a Captive Harris Hawk (Parabuteo unicinctus)

Two Harris' hawks were trained to fly along horizontal and climbing flight paths, while carrying loads of various masses, to provide data for estimating available muscle power during short flights. The body mass of both hawks was about 920 g, and they were able to carry loads up to 630 g in horizontal flight. The rate of climb decreased with increasing all-up mass, as also did the climbing power (product of weight and rate of climb). Various assumptions about the aerodynamic power in low-speed climbs led to estimates of the maximum power output of the flight muscles ranging from 41 to 46 W. This, in turn, would imply a stress during shortening of around 210 kPa. The effects of a radio package on a bird that is raising young should be considered in relation to the food load that the forager can normally carry, rather than in relation to its body mass.

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BODY DRAG, FEATHER DRAG AND INTERFERENCE DRAG OF THE MOUNTING STRUT IN A PEREGRINE FALCON,FALCO PEREGRINUS

Journal of Experimental Biology ◽

10.1242/jeb.149.1.449 ◽

1990 ◽

Vol 149 (1) ◽

pp. 449-468 ◽

Cited By ~ 7

Author(s):

VANCE A. Tucker

Keyword(s):

The Body ◽

Peregrine Falcon ◽

Reference Area ◽

Drag Coefficients ◽

Minimum Drag ◽

Body Drag ◽

The Mean ◽

The Difference ◽

Parabuteo Unicinctus ◽

Crosssectional Area

1. The mean, minimum drag coefficients (CD,B) of a frozen, wingless peregrine falcon body and a smooth-surfaced model of the body were 0.24 and 0.14, respectively, at air speeds between 10.0 and 14.5 ms−1. These values were measured with a drag balance in a wind tunnel, and use the maximum crosssectional area of the body as a reference area. The difference between the values indicates the effect of the feathers on body drag. Both values for CD,B a r e lower than those predicted from most other studies of avian body drag, which yield estimates of CD,B up to 0.41. 2. Several factors must be controlled to measure minimum drag on a frozen body. These include the condition of the feathers, the angle of the head and tail relative to the direction of air flow, and the interference drag generated by the drag balance and the strut on which the body is mounted. 3. This study describes techniques for measuring the interference drag generated by (a) the drag balance and mounting strut together and (b) the mounting strut alone. Corrections for interference drag may reduce the apparent body drag by more than 20%. 4. A gliding Harris' hawk (Parabuteo unicinctus), which has a body similar to that of the falcon in size and proportions, has an estimated body drag coefficient of 0.18. This value can be used to compute the profile drag coefficients of Harris' hawk wings when combined with data for this species in the adjoining paper (Tucker and Heine, 1990).

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Problem-solving performance in wild Steller’s jays using a string-pulling task

Behaviour ◽

10.1163/1568539x-bja10057 ◽

2021 ◽

pp. 1-24

Author(s):

Derek P. Harvey ◽

Jeffrey M. Black

Keyword(s):

Individual Differences ◽

Problem Solving ◽

Social Interactions ◽

Broad Spectrum ◽

Food Reward ◽

Natural Habitat ◽

Species Problem ◽

String Pulling ◽

Free Ranging

Abstract Animals that exploit resources from human-modified environments may encounter unique problems when searching for food. Pulling a string tied to a food reward (string-pulling task) is one of the most widespread methods of testing a species’ problem-solving performance in non-human animals. Performance in problem-solving tasks may be influenced by an individual’s characteristics and social interactions, especially in its natural habitat. We examined problem solving by free-ranging Steller’s jays (Cyanocitta stelleri) when extracting food from a string-pulling task presented in their natural habitat. During the study, seven of 50 jays successfully solved the task on their first to eighteenth experimental opportunity; solvers differed from nonsolvers by showing higher levels of persistence by pulling the string in more trials. Of the successful jays, five birds solved without observing others, while two birds were present during successful trials and subsequently completed the task. All seven jays demonstrated improvement in the task by using less string pulls over additional successful trials. Nineteen other jays in the population interacted with the apparatus and pulled the string, but not enough to acquire the food. These 19 jays were significantly bolder (shorter latencies to approach), more explorative (contacted more parts of the apparatus), and had observed solvers more than the 24 individuals that did not pull the string. These results indicate a broad spectrum of individual differences in propensity for solving novel tasks in our population of Steller’s jays.

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