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Regurgitative Food Transfer Among Wild Wolves

Results

We recorded 168 regurgitations in 114 bouts (Table 2). Usually, when a foraging wolf returned to the den area it was eagerly met by the pups and often by all the members present. When it regurgitated, sometimes more than one class of pack members fed. In 76% of the bouts, arriving wolves regurgitated where they were met, and in another 11% they were followed by the recipient(s) for 10-50 m before regurgitating. At other times they were followed up to 800 m. Wolves regurgitated only once in 61% of the bouts, twice in 24%, and three to five times in 12%, over periods of 5-35 min. Often subsequent regurgitations followed solicitation by recipients, but at other times the regurgitator spontaneously re-approached recipients as though inviting solicitation. The number of regurgitations per bout matched the number of recipients in only 7 of 114 bouts. Although the number of regurgitations per bout ranged from 1 to 5, the proportion of regurgitations to bouts did not vary among individuals. Individuals of all classes, the breeding male and female and auxiliaries occasionally reingested their own regurgitations.

Table 2. Numbers^a of regurgitations by wolves of various classes.
Year	Female	Breeders^a		Auxiliaries
Year	Female	Male	Female	Male	Total
1988	46^b (47)	18^c (18)	21 (21)	13^c (13)	98
1990	2 (10)	15 (75)	3 (15)	—	20
1991	3 (38)	4 (50)	1 (13)	—	8
1992	6 (50)	6 (50)	—	—	12
1994	0	8 (40)	3(15)	6 (30)	17
1996	4 (31)	9 (69)	—	—	13
Total	64	60	28	19	168
Mean^d	10 (27)	10 (27)	7 (19)	10 (26)	9
Mean^e	6 (24)	7 (31)	5 (20)	6 (24)	6
Note: A few regurgitations in a given bout may have been missed because of occasional visual obstruction during observation. Values in parentheses are percentages.
^a No significant difference between male and female over 6 years (Wilcoxon's signed-rank test, z = -0.67, P = 0.5). ^b Value contributed to significance of χ² goodness-of-fit test (χ² = 26.49, P= <0.001); higher than expected by chance (Freeman-Tukey deviate, z = 3.69). ^c Values lower than expected by chance (z < 12.961). ^d Average number of regurgitations per wolf per year. ^e Average number of regurgitation bouts per wolf per year.

Regurgitation into caches was rare (4 of 171 events). The masses of four regurgitations recorded from three caches were as follows: 2.5 kg (two regurgitations including 30 chunks averaging 80 g), and 1.1 kg by the breeding male and 1.4 kg by the breeding female. Thus, the average was 1.25 kg per regurgitation. The breeding male's caching took place during the first half of summer.

Overall, the number of regurgitations by individuals of both sexes and both roles were similar (Table 2). The pups were the main recipients of regurgitations (81%; Fig. 1), receiving more than the breeding female (14%) or auxiliaries (6%). We never saw the breeding male soliciting regurgitation.

Fig. 1. Distribution of donors and recipients of regurgitations in a wolf pack observed for 6 summers. Donors as denoted as follows: the breeding female by solid bars; the breeding male by open bars; and auxiliaries by shaded bars. Recipient distribution differed from random (G² = 30.76, 4 df, P > 0.001). The breeding female regurgitated more to the pups (z = 2.88) and the breeding male regurgitated more to the breeding female (z = 4.4)

The breeding female and auxiliaries regurgitated mostly to the pups, but the breeding female also regurgitated to auxiliaries and into a cache (Fig. 1). Only a few times did we see the auxiliaries regurgitating to other auxiliaries or to the breeding female. Auxiliaries sometimes partook of the regurgitated food delivered by others to pups, littermates, and the breeding female. Approximately 57% of the regurgitations by the breeding male were to pups, 32% to the breeding female, 5% to auxiliaries, and 5% into caches. The breeding male regurgitated more often to the pups in late summer (74%) than in early summer (41%), when he fed the female more ( = 6.10; P = 0.01; n = 56).

Across 6 years, the ratio of regurgitations by the breeding female to total regurgitations for all pack members was positively correlated with litter size (Kendall's τ = 0.93, P = 0.01), but not to pack size (Kendall's τ = -1.49, P = 7.1). Apparently the presence of more auxiliaries did not reduce the regurgitation effort by the breeding female.

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