Senescence in Wild Populations of Mammals and Birds

This chapter reviews research undertaken to understand senescence in birds and mammals in the wild. Increasing age-specific mortality in adulthood is widely used as the gold standard of senescence, both in natural and in laboratory populations. Both reproductive and survival senescence can be difficult to detect in the presence of infectious disease. The relationship between senescence and disease is complex. Decreased reproductive performance near the very end of life might as easily reflect infectious status as senescence per se. A potentially useful way of envisioning demographic senescence is to assess the maintenance of adaptive tradeoffs between reproduction and somatic survival as they occur in young adults. Senescence could potentially be seen as well in reduced ability to provide nourishment to offspring. Mammary glands themselves may senesce because of a decreasing replicative capacity of mammary epithelial cells with age. The ability to defend a territory declines with age in a number of species. In small passerine birds, the great tit, male territory size increases until 4 years of age and then decreases from 5 years throughout the rest of life.