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Owl Wars: The Secret Behind Barred Owls' Domination Over Northern Spotted Owls

Dec 06, 2016 05:44 AM EST
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Barred owls have been encroaching on the territory of Northern spotted Owls, pushing the already endangered species even further from increasing their population in the Pacific Northwest. Researchers from Michigan State University have developed a model to shed light on the current situation of the Northern spotted owls in relation to the invasion of the barred owls.

"Our model estimates population abundance and demographic rates, such as survival and reproduction, from relatively 'cheap' data," explained Sam Rossman. A postdoctoral researcher with Michigan State University and Hubbs-SeaWorld Research Institute, Rossman is the study's lead author. "Typically, estimating these quantities requires intensive sampling efforts involving capturing, marking, releasing animals and then repeatedly tracking and recapturing them at later dates."

The model is intended to give wildlife conservationists a highly accurate, yet cost-effective tool to help shape management policies. Featured in Ecology, the study utilizes data on two simple factors: presence or absence of animals across space and time. The 'Dynamic N-occupancy' can provide accurate estimates of local abundance, survival rates and population gains. This includes reproduction and immigration and accounts for the fact that the presence of a species may be detected imperfectly during sampling.

"Simply put, the model is telling us the rate at which barred owl numbers are increasing and offering clues as to why that's happening. This, in turn, can help us understand how endangered spotted owl populations in the same region may respond," shared Sarah Saunders. A postdoctoral researcher from Michigan State University and a co-author of the study, Saunders elaborated, "Barred owls are bigger, more aggressive, maintain a smaller territory, produce more young and are even outcompeting spotted owls in old-growth forests, what was once thought to be spotted owl strongholds."

Barred owls have consistently high survival rates. With a strong positive relationship between regional population abundance and local-level reproduction and immigration, it was inevitable that their population would increase significantly. Based on the team's findings, the population of the barred owl in the study area has been slowing down for the last five years, possibly indicating population saturation.

Elise Zipkin, an integrative biologist and another co-author from Michigan State University, believes the model can work particularly well on tracking the increase of invasive species or the decrease of endangered species.

"We've developed a crucial tool in helping explain why populations are changing and at what costs," Zipkin said. "We are like wildlife detectives. People come to us when they can't solve their mysteries. We're able to quickly sift through extensive data sets, involve citizen scientists in data collection, and help them solve their problems."

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