WIKIMEDIA COMMONS, B. NAVEZ
Female elephant seals avoid brutes
In southern elephant seal colonies, females return each year to the beach where they were born to give birth and mate again before returning to the sea for the rest of the year. Males arrive a few weeks early to duke it out for territory and gain access to a harem of females. The females benefit by getting to breed with strong males that will protect them from unwanted attention from a crowd of others. But they can also sometimes get caught in the cross-fire of males defending their territory.
In a study published September 1 in Animal Behavior, researchers found that more than half of females periodically skip a breeding season at their usual beach. Even so, they would often show up pregnant the next year, indicating that they had mated in the ocean. With 75 percent of males also failing to show up at the beaches, the logical conclusion is that they are finding better opportunities elsewhere, a tactic that perhaps benefits the weaker males that can’t win a beach fight. The new data shows that females exert more choice than was originally thought in a breeding system that has been touted as a textbook example of polygyny.
Dolphins get crafty
In 1984, researchers spotted bottlenose dolphins using tools, the first marine mammals found to do so. A female dolphin in Shark Bay Australia had torn loose a basket sponge and fit it over its nose like a mitten. It then shoveled its nose through the rough sediments on the ocean floor, scaring up prey while protecting itself from scrapes. In July, researchers at Georgetown University in Washington, DC, published in PLoS ONE that they mimicked the dolphin’s behavior and found that the fish scared up by the technique are more nutritious than non-bottom-dwellers, reports ScienceNOW. Most of the species also lack swim bladders and are therefore rendered nearly invisible to the dolphin’s typical mode of finding prey—echolocation.
Over a decade after the original discovery, other dolphins were observed carrying conch shells containing hiding fish to the surface and shaking out the prey directly into their mouths. Over time, researchers have seen both behaviors spread, as mothers taught their daughters the prey-catching tricks, though rarely their sons. It’s possible, the researchers hypothesized, that the technique is useful to dolphin moms who must spend up to 5 years raising their offspring and don’t always have time to roam for prey like males do. But now, researchers at the University of Zurich, Switzerland, and Murdoch University in Australia have documented more examples of the conch shell tool use in the last season than they have in the last decade, according to a paper published in Marine Mammal Science. “It is a tantalizing possibility that this behavior could spread before our very eyes—over a field season or two—and that we could track that spread,” said Simon Allen, a researcher at Murdoch University’s Cetacean Research Unit, in a press release. (Hat tip to Wired Science.)
Wild spotted hyenas and primates both react to the calls of potential intruders by becoming more alert and attentive to the sound, reports Nature. And they become more alert when they hear the calls of multiple unknown individuals. Hyenas appear to be able to distinguish the calls of up to three intruders; primates can distinguish up to six or seven. In other words, these animals can count.
When researchers at Michigan State University in East Lansing played the calls of unfamiliar hyenas through a speaker, a lone hyena would become more alert as the number of different calls increased. The observation supports the hypothesis that animals in social communities develop more complex cognitive abilities and evolve bigger brains in order to keep track of the intricate relationships within their group, such as hierarchies and familial ties. Previous studies have shown that hyenas have more cognitive abilities than animals that live in smaller social group such as lions. But primates are still the smartest, even though their social groups are very similar in size and structure to hyena populations. So the authors acknowledge that other factors must also be important in shaping cognitive abilities and brain size.
Wasps dive-bomb to lay eggs
Parasitic European wasps that inject their eggs into the bodies of living ants have been caught on film for the first time—yielding insights as to how they perform their airborne attacks. Two of the four wasp species described in the study, published last month (August 26) in Zoo Keys, are brand new to science. Three of the species lay their eggs in the abdomens of adult ants by diving down from above, briefly grasping the ant’s abdomen, and injecting their eggs either through the thin membrane that connects the ant’s abdominal segments, or through the anus. The fourth species injects ant larvae while they are being transported outside of the nest by worker ants.
The videos of the other three sneak-attack tactics can be viewed at Wired Science.
Ostriches experience ancient sleep
Ostriches, the most ancient of bird species, experience a unique set of sleep patterns that is most closely related to the platypus—one of the most ancient living mammals, according to a study published last month (August 24) in PLoS ONE. Rather than having two distinct states of sleep—rapid eye movement (REM) and slow wave sleep (SWS)—that is common in most other birds and mammals, ostriches experience only a single sleep state that combines elements of REM and SWS. This observation suggests that the phenomenon of separate sleep states evolved more recently than once was thought and separately in birds and in mammals.
The single sleep state is marked by rapid eye movements, reduced muscle tone, and head twitches that are characteristic of REM sleep, but with the unusual occurrence of some brain wave activity being generated by the frontal lobe—typical during SWS—rather than by the brain stem as during REM. The ostriches’ eyes are shut and the head—which the animals hold in the air during sleep, and do not bury in the sand—bobbles around sleepily, but occasionally the eyes will open and the head remains still, giving the impression that they are awake. Ostriches and platypuses also share another similarity—they both get more REM sleep than any other birds or mammals in their lineages. The evolution of distinct sleep patterns on at least two different occasions raises the question of what advantages it gives an animal.