Chapter 21 - Recent changes in bird migrations

Abstract

Records indicate that many bird species have changed some aspects of their migratory behavior during the last century or more, in response to changed conditions with earlier arrival in spring, earlier or later departure in the autumn, shortening or lengthening of migratory routes, directional changes, and reduced or enhanced migratoriness. Many of the changes in migratory behavior witnessed in recent decades, which parallel changes in climate or food supplies, could therefore be facultative in nature. Changes from migratory to sedentary and sedentary to migratory are explained in the chapter. Short-stopping has occurred in many species as more food has become available at higher latitudes in the wintering range, either through human activities or climate change. Changes in migratory directions, time, lengthening of routes are all explained in the chapter with the help of relevant examples and graphs. Most of the studies cited in it were dealt with particular species or suites of similar species most changes in migratory behavior are likely to start as facultative responses which become genetically entrenched as selection comes to act in a consistent manner from year to year. The next step is to identify the genes that control migration behavior, and the constraints to further adaptive change. The potentially rapid evolutionary change in movement patterns may be a key factor buffering migratory species against extinction during periods of climatic or other change, including the present.