MOTHERS HAVE IT ROUGH. Their young need to be fed, require near-constant vigilance and have to be taught all the things they’ll need to know when it’s time to explore the world on their own. This is a particularly challenging task for humpbacks in Southeast Alaska, where an unattended calf is easy prey for hungry killer whales. So how can a lactating mother balance her own needs with those of her calf?
Dr. Szabo spent several field seasons observing humpback whale mother-offspring pairs in Southeast Alaska. These pairs tend to remain close to one another so mom can both nurse her calf and drive away hungry killer whales that might be looking for a meal. But young calves can’t dive as often or as long as their foraging mothers, so sometimes the two must separate. Dr. Szabo revealed that early on females sacrifice their own foraging needs by returning to the surface often to attend to their calves. But as the season progresses and the demands of lactation grow, calves are increasingly left to fend for themselves. Not wanting to be left behind and undoubtedly wanting to continue to nurse, the hungry calf soon begins to follow and is forced to begin supplementing its milk diet with food, such as krill, that it must catch itself.
Dr. Szabo cast these observations of changing priorities in light of a broad evolutionary theory called parent-offspring conflict. This theory suggests that at some point mothers should stop allocating energy to their present offspring and start conserving energy for their next one. Although the timing differs among different species, it always occurs at an age where juveniles can fend for themselves and mortality risk is low. However, this comes sooner than the offspring, who is more concerned with its own survival than its future siblings, might like. In some animals, the ensuing “conflict” is obvious; many hooved mammals can be seen forcibly driving their young away from their teats or actively avoiding their them. But until now, no instance of conflict has been observed among baleen whales.