Dall's porpoises display rare strategy

Written by Tessa Danelesko

As summer nears, scientists along British Columbia’s coast are dusting off their research equipment in anticipation of the upcoming field season. In B.C. research teams head out into their study areas to take advantage of friendlier weather and longer days. Sometimes the result of field work can be unexpected discoveries.  One such research team published a study a few years ago about a rare reproductive strategy called mate guarding. While this behavior is often observed in terrestrial species, it is considered uncommon amongst cetaceans (dolphins, whales, and porpoises). In the study, researchers observed mate guarding in Dall’s porpoises, shedding light on a species of which little is known about its mating behavior.

Risky behavior has pros and cons

Competition for mates is one of the most widespread phenomena on the planet, and males from many species have developed incredible techniques to secure their paternity. From the impeccably decorated nests of the male Bower bird to the time many human males spend at the gym, it’s safe to say men dedicate a lot of time prepping and searching for their perfect mate. So what happens when they find one? Well, it depends on the species.

For some species, males may try to hold onto their partner by mate guarding.  Such behavior occurs when the male monitors his mate’s movements in close proximity, and challenges any potential rivals. While this behavior can increase the chance that a specific male will successfully mate with the female he guards, it has its downsides as well.  Mate guarding requires the male to closely attend to his mate, reducing the amount of time the male may otherwise spend feeding. Aggressive interactions between males can also result from mate guarding, as many males may battle over a single female.  Regardless of the consequences, recent research has indicated mate guarding may be an important part of the mysterious reproductive strategies of Dall’s porpoises.

Defensive Dall’s

The study, published by Pamela M. Willis and Lawrence M. Dill in the journal Ethology, is among the first to observe mate guarding in Dall’s porpoises. After obtaining data on 87 pairs of Dall’s porpoises, they concluded males were more likely to surface in synchrony with a female counterpart, and maintain closer and longer associations with females versus males. Additionally, males paired with females were observed aggressively interacting with other adult males, suggesting the males were defending their mates against rivals. Although these observations provide major insight into the mating habits of Dall’s porpoises, the authors of the study agree more research into the reproductive strategies of these cetaceans will allow for a broader understanding of their mysterious underwater lives.

Not uncommon along our coast

If you’re out on the water, keep your eyes out for Dall’s porpoises; they can be found along our coast year round. At this time of year you may be lucky enough to observe some of the robust males guarding their slightly smaller mates. By contributing your sightings to our database you are supporting important research and contributing to the conservation of B.C.’s marine life. Report your sightings of Dall’s porpoises, or any other cetacean or sea turtle, to the B.C. Cetacean Sightings Network by calling 1-866-I-SAW-ONE or online here.

Reference

Willis, P. M. & Dill, L. M. (2007). Mate Guarding in Male Dall’s Porpoises. Ethology, 113, 587-597.

Lance Barrett-Lennard

Researchers studied groups of Dall's porpoises and observed interactions between individuals.

Vancouver Aquarium

Scientists looked for unique markings to track individual porpoises.

Lance Barrett-Lennard

Studying the surface behavior of Dall's porpoises allowed researchers to observe mate guarding in the species.