The ability to fly allows birds access to every corner of the globe. This ability comes at a great price however, as flight places major constraints on a bird’s . The most obvious hurdle that and migratory birds must overcome is that of keeping a very low body weight, while still being able to generate the power to keep themselves aloft. This remarkable balance is achieved by a number of that anchors powerful flight adaptations, including a simplified muscles to the rib cage. Some shorebirds, that fly non-stop over 6,000 miles of ocean, allow their internal organs including intestines, kidney and liver to atrophy before the flight, further reducing their weight.
Ruby-throated hummingbird Image from Thayer Birding Software
Despite all of these adaptations, migration still provides a unique challenge that calls for extreme preparation. As the late summer days begin to shorten, hormonal changes are triggered that cause birds to dramatically increase the amount of food they eat. In a period of several weeks birds can nearly double their body weight in fat, the critical fuel they will burn on long migratory flights.
Today it is hard to imagine navigating without maps, compasses, and Global Positioning Systems, yet birds have been accurately charting their migratory journeys for millennia without such aids. A number of environmental cues, however, are available to a migrating bird. The simplest form of navigation involves following known features such as rivers, coastlines and mountain ranges. Some birds are able to use a variety of more subtle cues including the stars, solar position, sense of smell, and even the earth’s magnetic field to navigate. With this combination of tools, birds are able to navigate with remarkable accuracy. Researchers studying of Red-eyed Vireos (Vireo olivaceus), a common breeding bird in eastern , discovered that individual males returned to the same West Virginia territories for five years in a row. Considering that Red-eyed Vireos winter in the western Amazon Basin and northern South America, this is truly remarkable.
HUMANS AND NEOTROPICAL MIGRANTS
Humans have certainly noticed and appreciated birds for thousands of years. This appreciation most likely focused primarily on the culinary and costume potential of birds. Exploitative of birds for food and fashion raised concerns about bird populations as early as the 1840’s. This concern was warranted, as evidenced most tragically by the extinction of the Passenger Pigeon (Numenius borealis). Laws passed in the early 1900’s provided legal protection for all of our native . Now it is illegal to possess feathers, nests or eggs of any of these protected species. Several other southeastern bird species were also driven to extinction through overhunting or habitat loss. These include the Carolina Parakeet (Conuropsis carolinensis)and Bachman’s Warbler (Vermivora bachmanii).
Carolina Parakeets were killed as agricultural pests