Behavior Brief

A round-up of recent discoveries in behavior research

Aug 23, 2011
Bob Grant

The rock hyrax, Procavia capensis, abhors a heirarchyWIKIMEDIA, AMADA44

Equality for all...hyraxes

For rock hyraxes, small herbivores that are distant evolutionary cousins of elephants, it's not the size of their social networks that matter—it's the level of egalitarianism that exists in those networks, report researchers working in Israel. Tel Aviv University zoologist Amiyaal Ilany and colleagues observed populations of the social mammals in an Israeli nature reserve, and found that the animals formed interconnected groups of different types: some networks were characterized by more equality, with each individual sharing a similar number of relationships of roughly equal strength, while other groups were dominated by few individuals with larger and stronger networks. Ilany and his coauthors published their results in PLoS ONE last month, reporting that hyraxes in more egalitarian groups lived several years longer on average than individuals living in less equal societies. The authors suspect that stress is the main factor contributing to decreased longevity of hyraxes living in socially unequal groups. "In a more egalitarian group things may be more calm, as there is less harassment," Ilany told Wired Science.

Weasels ferret away food

The tayra, Eira barbara

Tayras, Central and South American relatives of weasels, pick unripe plantains and stash them until they're ripe and ready to eat, according to a study published this month in Naturwissenschaften. This behavior, which the researchers discovered after observing the animals clambering up trees to retrieve ripe plantains from hiding spots in a Costa Rican forestry plantation, may mean that the mammals are planning for the future, an ability only shown in primates and some birds thus far. Though some other animals—like squirrels hiding a store of nuts—cache food, it's thought that this is done with leftovers that the critters can't consume at the time. The plantains that tayras are stashing, however, aren't yet edible. "It's like knowing that it's going to be food in the future," study coauthor Fernando Soley told Science.

Fond finches

Monogamous zebra finches form and maintain same-sex pair bonds that are every bit as strong as the ties that male and female birds share with each other, new research suggests. The study, published on Behavioural Ecology and Sociobiology's website this month, also found that the birds will form more same-sex pairs in conditions where opposite-sex partners are in short supply. When the authors of the study purposely skewed sex ratios in captive populations of zebra finches, more than half the birds formed same sex pairs, in which partners shared nests, preened, and sang to each other. Additionally, the researchers discovered that when female birds were introduced to a group of pair-bonded males, five out of eight pairs of males were not interested in mating with female partners. University of California, Berkeley, researcher Julie Elie, first author on the paper, suggested that for some species, finding a mate may be more complicated than simply securing a reproductive partner. "A pair-bond in socially monogamous species represents a cooperative partnership that may give advantages for survival," she told the BBC. "Finding a social partner, whatever its sex, could be a priority."

Big mama

A plesiosaur model in the National Museum of Scotland, Edinburgh

Plesiosaurs, extinct reptiles that swam the seas more than 65 million years ago, might have carried, birthed, and nurtured their offspring much like modern mammals. The revelation came this month after researchers determined that a giant fossil plesiosaur nicknamed Poly, which was found in Kansas more than 20 years ago, was pregnant. The finding, which the researchers report in Science this month, is the first record of a pregnant plesiosaur and suggests that the species gave birth to one, large offspring at a time—a reproductive strategy more like marine mammals alive today than dinosaurs and most extant, egg-laying lizards. Marshall University paleontologist F. Robin O'Keefe, lead author on the paper, told ScienceNOW that the ancient species may have developed such a strategy because its environment was steady and supportive, much like that of some species of Australian skinks, which live in family groups of up to 17 relatives and also bear live young. "It is plausible that plesiosaurs lived in some fairly stable environments in which they didn't move around too much," he said.

Leaping gibbons

A new study, published earlier this month on the website of Biology Letters, delves into the mysterious and impressive jumping abilities of gibbons, primates that bound through tropical and subtropical forests in Asia. The authors studied the performance of gibbons leaping more than 3.5 meters (the animals are capable of jumps exceeding 10 meters!) and found that they transfer more energy relative to their body weights (that's mass-specific work for you physics buffs) than any other animal studied thus far. They also showed that gibbon can reach speeds of up to 8.3 meters per second, or about 18.5 miles per hour, in a single bound. The researchers chalk the astounding jumping ability up to the unique physiology and body proportions of gibbons, which have long arms, legs, hands, and feet, but relatively short, muscular trunks.

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