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Abstract
The fostering behaviour of female New Zealand sea lions Phocarctos hookeri was studied to investigate simultaneously nursing of two or more pups. Surveys (n=44) documenting the frequency of this fostering behaviour found that it is uncommon with a mean of 6.0% (S.E.=0.5) of nursing females at any one time seen nursing two or more pups simultaneously. Most of the multiple suckling events (n= 149) observed were females simultaneously nursing two pups (78%), although three (20%) and four (2%) pups per female were also recorded. We used time spent nursing and a nursing index to investigate relative nursing times. Females seen to nurse more than one pup simultaneously (multiple nursers) spent significantly more time nursing and had a significantly higher nursing index than females seen to nurse only a single pup at any one time (single nursers). The impact of this on the female and her pup are unknown but could represent a significant increase in the cost of lactation over this period. Single nursers rejected almost all (95%) pups that attempted to suckle from them when there was already a pup suckling, while multiple nursers rejected less than half (46%) of the extra pups and appeared more tolerant of additional pups suckling. The mechanism through which this behaviour may have evolved has not been determined.
Notes
Present address: Conservation and Land Management, Locked Bag 104, Bentley Delivery Centre, WA 6983, Australia. Ph 61–8‐93340290 Fax 61–8‐93340278
