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Regurgitative Food Transfer Among Wild Wolves


This study adds considerable detail to anecdotal reports that wolves transport food in their stomach and regurgitate it to nursing females and pups. It also confirms observations that in captive wolves, yearlings and adult pack members transfer food via regurgitation to the breeding female, pups, and nonbreeders, though the recipients are usually only the breeding female and pups, and that only the breeders regurgitate into caches (Fentress et al 1978; Fentress and Ryon 1982; Paquet et al. 1982).

Our results do not support the hypothesis that auxiliary wolves compete more than they contribute, at least during the first 2 months of pup development, (Harrington and Mech 1982; Ballard et al. 1991). Instances of auxiliaries receiving regurgitations from the breeding pair and other auxiliaries were infrequent during both the initial and the second transition phases of parental care, when pups actively solicited regurgitation and switched from milk to solid food (Packard et al. 1992). Rather, our auxiliaries appeared to have helped more than they hindered food transfer. Such help is in keeping with the kin-selection hypothesis (Williams 1966).

Assuming that, on average, 1.25 kg of food is delivered per regurgitation, an estimate of food delivered per bout would be 1.25-7.25 kg. Since the proportion of regurgitations per bout averaged 1.5, our best estimate of the amount of food per bout would be 2.2 kg. This calculation assumes that the amount regurgitated to pups is the same as the amount regurgitated into caches, but this assumption needs testing.

Fentress and Ryon (1982) hypothesized that wolves can selectively transfer food via regurgitation to whichever individuals they wish. Our data support this hypothesis in the probabilistic sense: given that a regurgitation was donated by a particular age-sex class, recipients were not equiprobable. More regurgitations by a breeding male were received by a breeding female and more regurgitations by a breeding female were received by the pups, than in the pattern shown by auxiliaries. However, such probabilities do not consider differential rates and intensities of solicitation which are difficult to quantify, so they do not demonstrate control in the sense of intentionality on the part of donors.

Integrating observations made in the field and in captivity, we hypothesize that (i) over the lifetime of a pair bond, male and female do not differ in regurgitation effort, although they may differ during specific years, (ii) the recipients are usually the breeding female and the pups, seldom the auxiliaries, and rarely, if ever, the breeding male, (iii) litter size affects regurgitation effort by the breeding female, and (iv) members of the breeding pair are more likely than auxiliaries to cache regurgitant matter during the initial phase of lactation, when pups are still in the den.

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