Grosbeak’s evening drop is evident on the college campus

The Evening Grosbeak, a noisy and charismatic songbird, once arrived at Oregon State University during the spring of an immense OSU statistics professor who estimated there were up to a quarter of a million birds on campus every day.

However, the time had passed when there were so many birds that students, staff, and teachers felt the need to hide from the dirt.

An Oregon State study published in the journal Diversity shows the number of Evening Grosbeaks using the campus as a migration stop-over site has dropped an average of 2.6% per year over the past four decades. The bird is experiencing decades of decline across it, which includes most of the United States, said Douglas Robinson of the OSU College of Agricultural Sciences.

It’s not yet known, Robinson said, why there are fewer Evening Grosbeaks than ever before. It may be related to disease, climate change, or changes in land use, or some combination of those, or other factors not yet discovered by scientists.

“Planned surveys designed to take advantage of the opportunities presented by spring stop-over sites will improve our understanding of population change over time,” Robinson said. “Our observations suggest that further attention should be focused on risk assessments and hypothesized explanations for the decline of this charismatic bird species.”

People hardly notice the birds

The research led by Robinson produced a day -high number of 1,442 birds during 117 surveys that took place on the Oregon State campus from 2013 to 2015. In total, the researchers counted 8,407 grosbeaks.

“The numbers that used to appear here every spring are in the hundreds of thousands,” said Robinson, who was the Mace Watchable Wildlife Endowed Chair at OSU during the study. “Now we come down to a few thousand at most, sometimes just a few hundred. We came from student newspaper reports in the 1970s carrying umbrellas in the sunny day so as not to remove bird droppings from their heads to people who barely noticed that the birds were around. ”

The Evening Grosbeak, a black, white, and bright yellow member of the finch family, is a disturbing species – if there is little food in the winter, it will migrate south. But it’s also moving to predictable schedules, especially during the spring, allowing populations to be tracked at stop-over locations like OSU’s Corvallis campus.

“They eat elm seeds here before moving to their forest breeding ground in June,” Robinson said. “They’re usually here for a few weeks in April and May.”

Evening Grosbeaks abounded in the 1970s

Admired by their sheer number, Fred Ramsey, an OSU professor of statistics from 1966 to 2003, used a randomized sampling technique to count birds on selected elm trees. Ramsey, who throughout his career has made major contributions to the field of wildlife population estimation, calculated that on a single spring day in the mid -1970s there were 150,000 to 250,000 birds looking for food on campus.

Ramsey has played many roles in estimating wildlife abundance and has participated in bird population surveys on many Pacific islands, although his estimate in Evening Grosbeak was not part of a scientific article.

“But Ramsey is a professional statistician, and even if in the unlikely event he loses by an order of magnitude, it seems safe to conclude that Evening Grosbeak’s numbers are much lower than they were 45 years ago. that was ago on our study site, ”Robinson said. “When we compare the lower value from Ramsey’s estimate-150,000-to our maximum daily number of 1,442, that’s an average annual decrease of 2.6%. Meanwhile, decreases across the entire range of Evening Grosbeaks according to North American Breeding Bird Survey data volume show a decrease of 2.5%.

Is bird rejection associated with Dutch elm disease?

The number of elm trees on campus has also declined since the Ramsey era, though the connection of tree decline to the grosbeak population is uncertain.

Elms were planted throughout campus beginning at 35 in 1913 and eventually became the dominant canopy tree on campus, numbering more than 330 mature trees, Robinson said.

“In 1978, Dutch elm disease spread throughout North America, and there were concerns that the advent of the disease would cause widespread deaths of elms, leaving the campus without shade trees,” he said. “That led to the removal of the elms to ensure that the root connections between the infected trees would not allow the disease to spread too quickly.”

Within 10 years, all endangered elms were cut down and replaced with disease -resistant elm species or other tree species; today the campus features 143 mature elms. Robinson does not know of any evidence that disease-resistant elms produce food that is less plentiful or desirable than grosbeaks but notes that may be a possibility.

It is unlikely, however, that the grosbeaks simply moved their foraging sites to other parts of Corvallis or the Willamette Valley, he said. Data from eBird from 2004 to 2021 showed some higher numbers from around Corvallis than observed on campus, but the highest single day number was less than 2,000 birds, he said.

Most high numbers are between 90 and 500 birds, with similarly small numbers reported throughout the Willamette Valley.

Four Oregon State University students, who are now at other research institutions after their graduation, participated in the study: Jessica Greer (University of California Davis), Juliana Masseloux (Zoological Society of London), Tyler Hallman ( Swiss Ornithological Institute) and Jenna Curtis (Cornell Lab of Ornithology). Greer and Masseloux were undergraduates, and Curtis and Hallman were doctoral students.

Thanks to Oregon State University for providing this news.

Where to find Evening Grosbeaks