A new study comparing bird communities six decades apart at five sites in Oregon’s Willamette Valley has documented the loss of roughly 50 percent of the bird species – yet at the same time, recorded almost the same number of new species.
The bottom line is that there has been little change in the number of species or diversity over 60 years, but a great deal of change in the specific bird species occupying the sites.
“Bird communities change naturally as the habitat changes,” noted Jenna Curtis, a doctoral student in fisheries and wildlife at Oregon State University’s College of Agricultural Sciences and lead author on the study. “Some of the change is natural, as plants grow, while in other instances the habitat is altered through agriculture, urbanization or other human activities.”
Birds increasing in association with human activity and favorable conditions include Anna’s hummingbird, European starling, brown-headed cowbird, and house finch.
Some of the birds that appear to be decreasing because of regional environmental changes include Nashville warbler, chipping sparrow, and the northern rough-winged swallow.
Some species have experienced little change in numbers from one master’s study to another over 60 years, including killdeer, several woodpecker species, American robins, song sparrows, red-winged blackbirds, Steller’s jays, American crows, and others.
Results of the research have been published in the journal, PeerJ.
The study is unusual because there are few highly detailed, historic surveys of bird communities on a local level – especially ones that looked at multiple habitats, including coniferous forest, oak woodland, marsh, mixed deciduous, riverine/riparian and brushy. But in 1953, Richard Eddy completed and published a master’s thesis at Oregon State in which he surveyed and documented bird species at six sites with 50 kilometers of Corvallis.
As part of her own master’s study, Curtis located five of Eddy’s original six sites and conducted a new survey, comparing the richness and diversity of bird species – during many of the same times of year as Eddy.
“Quite a bit has changed in six decades,” Curtis said. “One site, which used to be known as Murphy’s Beach, is now a sports recreation facility at Crystal Lake Park near Corvallis. It used to be very barren, with old roads and chest-high grass until a flood in the 1960s completely altered the landscape. Now there are large cottonwood trees and soccer fields. Bird populations change accordingly.”
Another site was off Bruce Road on Highway 99 between Corvallis and Monroe. When Eddy did his survey, much of the marsh was grazed by cattle. With new water management protocols, this area within Finley Wildlife Refuge is now a haven for waterbirds.
W. Douglas Robinson, the Mace Professor for Watchable Wildlife at OSU, has been conducting bird surveys in each county in Oregon to begin establishing new baselines for species diversity throughout Oregon by the year 2020. Human activities throughout western Oregon can influence bird populations at local sites, he said.
“There have been massive changes in agriculture resulting in larger fields and fewer pastures,” Robinson said. “As a result, species like pheasant, bobwhite, chipping sparrows and common nighthawks largely have disappeared throughout the valley. This study is wonderful because it is so rare to find such detailed information from 60 years ago and compare it to what is happening today. It helps us to better understand how birds respond to changes in landscape – both natural and human-caused.”
Curtis and Robinson say it isn’t clear whether climate change and drought have had a significant impact on bird species in western Oregon.
“That’s why we need to gather more baseline data,” Robinson said, “so that we know what is ‘normal’ and can identify deviations. There are some signals, for example, that there may be changes in the insect populations, which would affect a number of bird species. But we need more data there, too.”
Source: Oregon State University