Soon after the last brood of young vacates the nest, most birds begin to travel more frequently outside the territory which they claimed earlier in the season. The strong territorial instincts that existed in nearly all species prior to and throughout the breeding period quickly fade as the young fledge. This can be noted by the absence of the songs that are commonly used to proclaim ownership to a particular location.
Occasionally, a person may still detect the sound of a white-throated sparrow, a black-capped chickadee, or some other species announcing its presence, yet the abundance of melodious tunes that filled the morning air only a few months ago are now absent. When hiking, or picking berries, you can still hear the short, soft and less musically appealing notes given when a bird is alarmed over another creature’s presence, yet even these sounds are far less prevalent as the asters start to bloom.
Acquiring food becomes the number one order of business for all birds during the latter part of summer as a layer of fat becomes essential to these feathered creatures. While birds do not appear to expand their girth during this time of year, they must form a fair amount of fat in order to fuel their bouts of long distance travel. A huge caloric expenditure is required by these animals to sustain their marathon periods of flight, which typically occur at night when the wind is from the north. Without the appropriate fat reserves, migration would be impossible. Non-migratory birds also start to form fat reserves by the end of summer to help insulate them against the cold and provide them with energy during those periods in winter when their food intake is insufficient to maintain an adequate internal body temperature.
Birds also require extra nourishment at the end of summer in order to grow the new layer of plumage that will serve them during the coming months. All birds experience a molting process in which new feathers replace the ones that currently cover their body. In some cases, only a partial molt involving only the feathers on the head and the core of their body occurs. A total molt, which replaces all of the plumage including the much larger feather on their wings and tail, is experienced annually. Although the time at which a complete molt occurs depends upon the species, most happen after the nesting season is completed and before migration begins.
In their search for food, birds often venture into many areas well away from the location of their nest. In this way, individuals are able to gain information on the relative abundance of food in surrounding areas. While most adult birds are known to return to the same site each spring to nest, juveniles that have not yet nested are exposed to a variety of new surroundings, some of which they may elect to return to in their attempt to establish a territory of their own next spring.
When exploring the general area, many birds tend to gather into flocks, which helps better provide for their safety. It becomes extremely difficult for a predator to sneak up on a single bird if there are dozens or hundreds of others around, all scanning different sections of the area for danger. Once one individual detects a threat and takes to the air, all of the birds immediately react, regardless of whether or not they also spot the intruder.
While some birds, like the cliff swallows and male hummingbirds have already departed the Adirondacks for warmer areas, others like the ovenbird, yellowthroat and broad-winged hawk will be leaving in the next several weeks.
It is difficult to say what species are the last to leave, as there are always stragglers that remain well past the dates of their general migration period. Typically, any seasonal resident that fails to leave the Adirondacks before the first prolonged bout of subzero weather is doomed. These procrastinating migratory individuals are those that probably failed to develop the necessary fat reserves to undertake the long trip south, and will never survive until the nesting season comes again here in the Adirondacks.
Photo courtesy EPA.