Humpbacks Multitask for Mates


The trade-offs between rewards involved in either foraging or courting mates have likely plagued animals for millennia. The need to feed often competes with the requirement to reproduce . . . and yet one cannot successfully secure a mate and raise offspring without adequate resources. This dilemma means that animals must carefully balance the time and energy they allocate to each endeavor. Humans may be able to cruise for dates in the grocery store, but few other animals are so lucky.

Like many migratory species, humpback whales (Megaptera novaeangeliae) were long thought to have designated geographic areas along their migration routes for specific activities: a region for breeding, other regions for foraging and feeding, et cetera. One of the most lauded characteristics of humpback courtship is the complex “singing” behavior involved in their courtship displays (to hear one for yourself, see this video). A new study conducted by researchers from U.S. Naval Postgraduate School, the University of California-Santa Barbara and Duke University, however, suggests that humpbacks may emit courtship calls not only in their traditional breeding grounds, but outside of the “breeding zone” as well, and sometimes even perform these complex calls while in the process of making foraging dives (Stimpert et al. 2012).

 In order to study calling behavior during foraging, suction-cup tags were attached to ten individual humpbacks in the Western Antarctic Peninsula. This region of Antarctica is known to be a rich foraging ground, where humpbacks gather to consume masses of krill (Nowacek et al. 2011). Although there were previous reports of whales singing courtship songs outside of breeding areas, no one had yet either described individual songs from the Antarctic region’s rich feeding grounds or recorded what other activities the whale was doing at the time the song was produced. Thus, the new study by Strimpert et al. sought to address an important question: what is the behavioral context of courtship displays performed outside of traditional breeding regions?

Study region: West Antarctic Peninsula (Strimpert et al. 2012)

The suction-tag data showed that the whales did indeed emit calls outside of traditional breeding areas, and at least two individuals produced songs with acoustic qualities matching those used in courtship displays. One individual even appeared to manage the feat of producing these courtship calls while in the process of performing a deep (greater than 100 meters) foraging dive. Although there is a potential that the tag devices recorded calls from nearby whales rather than the individual to which the device was affixed, the researchers note that aggregated individuals usually engage in the same types of activities when together, and the call during a deep dive could not have been recorded from an individual remaining near the surface.

The primary takeaway from this study is: rather than strictly compartmentalizing their breeding and feeding behaviors into different geographic regions, humpbacks apparently are able to multitask. They were observed advertising their mating availability while also performing deep foraging dives in feeding areas thousands of miles from traditional warm-water breeding grounds.

The fact that whales can multitask in such a way is interesting from a behavioral as well as a physiological standpoint: producing the correct sounds while moving down in the water column likely requires tight vocal modulation in response to increasing water pressure. Another noteworthy finding was that the whales in this study produced songs while they were foraging in groups, which is unusual: on breeding grounds whales normally sing either while solitary or while escorting mother/calf pairs.

The significance of these findings should not be understated. The data essentially show that the paradigm of a strict breeding-feeding dichotomy is a simplistic and probably inaccurate way to frame humpback whale behavior. Multitasking allows whales much more complexity in their feeding behavior and social interactions, in addition to both their temporal and their spatial ecology. In addition, if this rigid trade-off pattern is not accurate for humpbacks, it is likely that many other species have much more complex, multi-faceted behavior patterns than traditional models might suggest.
ResearchBlogging.org
Alison K. Stimpert, Lindsey E. Peavey, Ari S. Friedlaender, Douglas P. Nowacek (2012). Humpback Whale Song and Foraging Behavior on an Antarctic Feeding Ground PLoS ONE, 7 (12)

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