Model explains barred owls' domination over northern spotted owls

Date: December 1, 2016

Source: Michigan State University

Barred owls -- unrivaled nocturnal predators and procreators -- are moving into the Pacific Northwest. They're encroaching on northern spotted owl territories and outcompeting this smaller, threatened cousin.

A model developed at Michigan State University shows how it's happening and gives wildlife conservationists a highly accurate, yet cost-effective tool to help shape management policies.

"Our model estimates population abundance and demographic rates, such as survival and reproduction, from relatively 'cheap' data," said Sam Rossman, postdoctoral researcher with MSU and Hubbs-SeaWorld Research Institute and the paper'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 MSU model is featured in the current issue of Ecology and uses data on two simple factors: presence or absence of animals across space and time. While the input may be simple, the model is not. "Dynamic N-occupancy" is capable of providing accurate estimates of local abundance, survival rates and population gains -- including reproduction and immigration -- while accounting 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," said Sarah Saunders, MSU postdoctoral researcher and one of the paper's co-authors. "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."

Continued