There are many signs of spring that excite people here in northern New England. But perhaps the best sign in the bird world is male Red-winged Blackbirds. Each spring in March when I hear that first male calling in singing from the brown cattails around the pond I get terribly excited. For several days each year the Red-winged Blackbird, a very common bird, become my crown jewel. Males always arrive ahead of the females, trying to stake out the best territories to defend so they can attract the best females.
Spring arrival dates over many years and a broad geographic range can be great way for us to track and understand potential climatic effects on bird migration. For example, from 1960 to 2002 Kathleen Anderson recorded the first date each spring that migrating birds were seen on her property. Researchers at Boston University wanted to find out if a naturalist’s diary could be valuable for detecting potential changes in phenological events like spring migration.
For over 50 years Anderson has lived on a 100-acre farm just south of Boston. Everyday she is on her farm she records the birds, flowering plants, butterflies and amphibian choruses she encountered. Her observations were not systematic, but gathered as she enjoyed a walk or simply from the back porch.
Five bird species showed significantly earlier arrival dates including, Wood Duck, Ruby-throated Hummingbird, House Wren, Ovenbird, and Chipping Sparrow. The strongest trend was for Wood Ducks, which arrived on average 32 days earlier than they did when Anderson first began recording her sightings. Hummingbirds arrived 18 days earlier. Redwings arrived about 2.5 days earlier. Overall, 22 of the 24 species they examined showed trends toward earlier spring activity, an overall average of 8 days earlier.
A few years ago John Simpson gave me nearly 40 years of daily bird records that his late mother, Nancy Simpson, dutifully kept each day at her house in southern Vermont. I took a look at Red-winged Blackbird arrival dates from 1966 to 2004 in her bird diary. From 1966 to 1990 there was a trend toward earlier arrival dates at her house. Then, from 1990-2004 the trend changes to a later arrival time.
Redwings also have advanced their nesting times. An examination of nearly 5,000 nest records from across North America collected from 1951 to 2000 show that females are laying eggs 7.5 days earlier over the 50-year period.
This year, with record-breaking snows in Vermont, I saw my first red-winged blackbird a bit later than the past few years, March 10th. I saw the first one on March 7th in both 2009 and 2010. In 2008, another very snowy year, they didn’t arrive until March 11th. Someday perhaps my annual records will shed more light on the marvels of bird migration.