![]() ![]() Selva agreed that the higher stress levels may be a response to the competition occurring in these groups, with the increased stress hormones triggering a boost of energy use. So those adult males without mates likely would be very stressed, Stöwe said, and it would be interesting to see their stress hormone levels at other times of the year. The samples were taken in January and February, a time when the ravens are pairing up and territories are secured. "So it might well be that the hormone content in the droppings (at least in some of them) reflects a stress response to previous events (fights etc.)." "We never know what the birds experienced before showing up at the carcass," Stöwe, who wasn't involved in the study, told LiveScience in an e-mail. Mareike Stöwe, a researcher at University of Veterinary Medicine, in Austria notes that stress hormone levels could be influenced by earlier events experienced by the birds, so it's difficult to truly know the baseline levels. In youth, though, the detrimental effects of the increased stress seem to be worth it in exchange for the safety in numbers from being in a flock. The flock is likely a stressful place because of the aggressive interactions that occur in competition for food and a place on the dominance hierarchy, he said. "They live in a much more stable and predictable environment than the nonbreeders and hence I would have expected that their life is less demanding." While Selva didn't expect these lower levels, Wolfgang Goymann, of the Max-Plank Institute for Ornithology, who wasn't involved in the study, says he thinks it makes sense. Also, the territory-based females had much lower hormones than their mates, which the researchers say might be due to their increased energetic demands on the males to defend the territory. "By logic, we would think that to maintain a territory would be much more stressful," Selva said, because these birds have to fight for their land. ![]() ![]() The flock-living ravens had higher stress levels than those paired up. They also tested the samples to determine the sex of the animal and if it was infected by parasites. They tested the samples for the levels of a stress hormone, called corticosterone, which regulates a bird's use of fuel, its immune health and its stress response. To get a better understanding of the bird's lifestyles, the researchers collected fecal samples from wild ravens that were either from young adults living in a flock, or from the territory of older birds living with a mate. ![]()
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