In 2013, the ornithological journal Avian Conservation and Ecology published a special issue documenting human-related sources of bird mortality in Canada. Since Maine abuts Canada, the Canadian research has broad applicability to Maine. I will devote the next three columns to a discussion of some of the papers as Earth Day approaches.
A variety of human or human-enabled impacts result in significant bird deaths or injury. These impacts are usually additive to natural deaths. In other words, the human-related factors caused the demise of birds that would have otherwise survived. The value of the work published in the ACE special issue is that the relative importance of the various human impacts is evaluated. These rankings will allow conservationists and environmental managers to most effectively target their efforts and resources to reduce bird mortality stemming from human direct and indirect effects.
In Canada, several billion birds of more than 400 species nest each year. These birds breed in a broad range of habitats, each of which may have its own particular human-related threats.
Sebastien Rioux and colleagues examined the importance of crashes with transmission lines on bird mortality. Getting accurate estimates of this impact is difficult because of the dearth of studies and the certain underestimate of mortality, because some of the birds killed by collisions are scavenged by foxes and other animals before they can be found and counted.
The high level of uncertainty is evident in a recent study in the United States where estimates of bird deaths from power line strikes ranged from hundreds of thousands to 175 million. Rioux and colleagues presented their most realistic estimates for Canadian bird mortality from these strikes as 2.5 million to 26.5 million birds per year. At the high end, those deaths kill about 0.7 percent of Canadian birds each year.
Some groups of birds are particularly susceptible to crashing into transmission lines, particularly during migration. Birds at most risk include grebes, waterfowl, shorebirds and cranes. Some waterfowl species are increasing in population size in Canada. While regrettable, line crashes do not seem to be limiting population growth of those waterfowl. But a line-related death for an endangered whooping crane is a major blow.
MAINE BUTTERFLY SURVEY
The volunteer-based Maine Butterfly Survey (mbs.umf.maine.edu) has the goal of mapping the distribution of Maine butterflies and skippers at the level of townships. We are beginning the next-to-last year of atlasing. As one of the coordinators, I am asking you to join this citizen-science project.
The survey is a voucher-based program, so records must be either based on a collected specimen or a photograph. To join the survey, you need to attend a six-hour training workshop. We will provide lectures on basic butterfly biology and give details on MBS record-keeping. All participants will be given a butterfly net and collecting equipment, an MBS manual and data forms.
The next workshop will be held Saturday, May 17, at Colby College. A free hot lunch will be provided. Prospective participants should email me. Workshop participants need to be at least 18 years old. I hope you will help us in our effort to map the distribution of these magnificent insects.
Since the formal part of the survey began in 2008, volunteers have provided more than 20 records of the giant swallowtail, a species that had not been seen in Maine for over a century. In 2012, we had three records of the long-tailed skipper, the first occurrences of this species in the state. Finally, a caterpillar of the short-tailed swallowtail was collected in northern Aroostook County. This find represents not only a first for Maine but also a first for the United States; earlier records were all from Canada. Consider joining the MBS team and help us to increase our understanding of Maine’s butterflies.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at: