Members and friends of Northumberland and Lone Pine Land Trusts attended Dr. Erica Nol’s talk on February 16 at the Cobourg Public Library entitled, “Can humans and songbirds coexist in southern Ontario.” Dr. Nol is a professor at Trent University and along with her graduate students, she studies influences on bird population dynamics.
Dr. Nol first put her talk in context; birds compete with humans for lands that are converted into more and more houses. Woodland song birds such as Veery and Rose-breasted Grosbeak are facing mild declines while grassland birds like Bobolink and Field Sparrows are showing steep declines. Common native birds such as Robins, Grackles, and Brown-headed Cowbirds are increasing. As examples, Dr. Nol expanded on various studies she has participated in that focus on songbirds in forests or grasslands including: Ovenbirds, the impact of trails on songbirds, Bank Swallows, Brown Creepers, and Bobolinks.
The ovenbird nests on the ground and their success is related to the abundance of their invertebrate food source. The research found that larger woodlots have more ovenbirds. This is related to lower temperature, higher moisture, and less wind in larger woodlots. Large woodlots are therefore better for maintaining ovenbird populations.
Next Dr. Nol highlighted research conducted in the Northumberland Forest that related trail width to abundance of forest-interior songbirds. When trails were wider, the researcher was less likely to hear songbirds, especially compared to areas that did not have trails. Nest success of Eastern Wood Peewee was less in pine plantations compared to deciduous forests and was positively influenced by forest gaps. Early thinning of pine plantations that results in faster deciduous regeneration is advantageous for this species.
The Bank swallow, a threatened species in Ontario, can reproduce in aggregate pits with appropriate soils. Compared to the Lake Ontario lakeshore, the abundance of nests was lower in aggregate sites but clutch and hatchling number were similar. Gull predation was higher at the lakeshore sites.
Brown Creepers nest under bark. A study conducted in Algonquin park found that any tree harvesting reduced numbers of creepers but populations were more likely to be sustained when yellow birch trees were left standing.
In a study examining rotational grazing effects on Bobolink, any grazing reduced the bobolink population by half (cattle were good at trampling nests). Cattle in larger fields with lower stocking densities had a lower impact but Bobolinks had the greatest reproductive success in hay fields that were cut after July 1.
I found Dr. Nol’s explanation of impacts of humans on various aspects of songbird success to be enlightening. The research examples presented demonstrated the myriad of ways that birds are influenced by our development.
While Dr. Nol did not truly answer whether humans and songbirds can coexist, it is clear that human choices have often unlikely impacts.