Chapter 4 - Results Part II: Introduction to Species Accounts
To this point, we have been lumping all species together, which could give the impression that all species behave the same way when approaching their annual migration. In reality, there were many behavioral and evolutionary strategies observed during Connecticut River Valley migration that help a bird advance its species to the next generation.
One strategy is to arrive very early on the breeding grounds, if the problem of a dependable food supply can be solved. Early April in the forested hills of Massachusetts, New Hampshire, and Vermont often means deep snow cover, freezing temperatures and resultant delays in insect hatches and tree flower blooming. Those are staples in the diets of many migrants. However, for the Yellow-bellied Sapsucker, which arrives before the first survey count, the early supply of tree sap provides a high-energy food supply at a time when the majority of migrants have yet to enter the Connecticut River Valley.
Even with the presence of the Yellow-bellied Sapsucker, the late April count was lonely and quiet for the alert surveyor looking to record birds. The calls and partial songs of a flock of Yellow-rumped Warblers was a welcomed break in the silence. Like the non-migratory Black-capped Chickadee, the Yellow-rumped Warbler is less dependent on warming temperatures, insect emergence and blooming flowers because it forages on persistent seeds and fruits. Yellow-rumps begin appearing early in Connecticut, and as their migration progresses up the valley, their numbers decrease in Connecticut while increasing in Massachusetts. Their numbers also diminish in the Connecticut River Valley as they disperse to higher elevations and northern coniferous forest breeding grounds.
The American Redstart is a mid-season migrant whose population in Connecticut is relatively small in early May, but increases rapidly from mid to late May when both insects and tree flowers become more abundant. Redstarts begin their Connecticut River Valley migration in Connecticut using predominately main stem “A” sites, and as spring and migration progress they begin using “B” sites along tributaries. Late in migration, as winter lifts, their use of “B” sites becomes dominant in the higher elevations of the tributaries and territories become suitable for breeding.
In contrast, the Red-eyed Vireo foregoes all the early or mid season variability in weather and food supply and simply does not appear in the Connecticut River Valley until mid to late May. It shows a bias toward the higher elevation upland forests where food is now abundant and breeding territories await. By migrating later in the season, when winter is long gone, Red-eyed Vireos are not bound to the milder climate lower in the valley near the main river.
Although all four of these species migrate, their behavior, timing of migration, food sources, and habitat use varies considerably. These differences help define each species, and reflect evolutionary responses to the environmental challenges their ancestors faced, and the genetic material those ancestors passed along. In the Selected Species Index and Links that follows, species accounts are provided for 33 species that were recorded during spring migration, over the course of the three-year study. These accounts provide insights into the rich lives of birds as they migrate within and through the Connecticut River Valley.