Testing problem solving in turkey vultures (Cathartes aura) using the string-pulling test

Abstract

To examine problem solving in turkey vultures (Cathartes aura), six captive vultures were presented with a string-pulling task, which involved drawing a string up to access food. This test has been used to assess cognition in many bird species. A small piece of meat suspended by a string was attached to a perch. Two birds solved the problem without apparent trial-and-error learning; a third bird solved the problem after observing a successful bird, suggesting that this individual learned from the other vulture. The remaining birds failed to complete the task. The successful birds significantly reduced the time needed to solve the task from early trials compared to late trials, suggesting that they had learned to solve the problem and improved their technique. The successful vultures solved the problem in a novel way: they pulled the string through their beak with their tongue, and may have gathered the string in their crop until the food was in reach. In contrast, ravens, parrots and finches use a stepwise process; they pull the string up, tuck it under foot, and reach down to pull up another length. As scavengers, turkey vultures use their beak for tearing and ripping at carcasses, but possess large, flat, webbed feet that are ill-suited to pulling or grasping. The ability to solve this problem and the novel approach used by the turkey vultures in this study may be a result of the unique evolutionary pressures imposed on this scavenging species.

Bajan Birds Pull Strings: Two Wild Antillean Species Enter the Select Club of String-Pullers

“…Taken together, these data suggest that motor trial-and-error learning was occurring, at least in some individuals. The gradual improvement leading to success over trials and the latency reduction following repeated successes is also seen in the majority of other string-pulling investigations in birds [ 9 , 12 , 15 , 32 , 33 ]. Because our birds were wild-caught, we cannot exclude that differences in individual experience in the field might have affected performance, facilitating for instance the rapid success of the birds that solved in their first trials.…”

“…First, most birds used in the studies were raised in captivity, be it in laboratories or zoos. Familiarity with (and often hand-raising by) humans might facilitate solving of the string problem, with, for example, conspecific tutoring [ 11 ] or long periods of acclimatization [ 15 ] sometimes included in the protocol. Notable exceptions are the work of Taylor and colleagues [ 12 , 13 ] on wild-caught crows Corvus moneduloides studied in aviaries in their native New Caledonia, as well as that of Millikan and Bowman [ 16 ] on seven species of Darwin's finches.…”

Functional morphology of vertebrate claws investigated using functionally based categories and multiple morphological metrics

“…aura is most certainly not a scansorial species and it is unclear why it might be misclassified as such as it occupies a position near dead center in the linear discriminant plots for both analyses (Figure 4a,c). Their feet are not well suited for grasping (Ellison et al, 2015) but instead are more adapted for terrestrial locomotion (Wink, 1995) which is more consistent with their scavenging lifestyle. Porphyrio porphyrio , on the other hand, occupies a space in both linear discriminant plots trending toward flatter, less curved claws with relatively large base depths (Figure 4a,c).…”

Azure-winged magpies solve string-pulling tasks by partial understanding of the physical cognition

“…In previous studies, birds have generally been tested on vertical strings (Jacobs and Osvath 2015). A horizontal string can be reeled in with a single pull, whereas a vertical string requires more complex coordination, such as reaching down, grasping and pulling, creating a loop, and repetition of these processes (Werdenich and Huber 2006; Ellison et al. 2015).…”