A relatively simple — and familiar to most of us — kind of seasonal and reversible body-modeling occurs in bears preparing for hibernation, beavers getting ready for snoozing in their lodges or deer anticipating food shortages in winter.<\/p>\n
These species all put on fat in fall, becoming distinctly more portly. Come spring, they are more svelte, having burned up that winter fat. Humpback whale females migrating from Hawaii to the food-rich northern waters are much slimmer than in fall when on their way south. Similarly, migrating birds typically put on fat before they migrate and arrive at their seasonal destinations in trimmer condition.<\/p>\n
Sometimes the reversible remodeling occurs in internal organs. Bar-tailed godwits and other birds that migrate very long distances without feeding on the way markedly reduce their digestive organs and regenerate them and resume feeding upon arrival. Chickadees, jays, nuthatches and nutcrackers get bigger brains in fall; the part of the brain associated with processing spatial information is the hippocampus, which actually acquires more neurons. The temporarily larger hippocampus allows them to remember the widely scattered locations where they have stored seeds and retrieve them during the winter.<\/p>\n
[Seeing Red: Highbush cranberries in the snow]<\/ins><\/a><\/p>\n Brood-parasitic birds, which lay eggs in other birds’ nests, also have improved spatial memories — just in the nesting season. Two species of cowbirds in which the females monitor the locations of potential host nests have enlarged brains (hippocampus) in the nesting season. But in a third species of cowbird, in which both male and female monitor host nests, both sexes have seasonal changes in brain size.<\/p>\n Males of other birds (for example, starlings), get temporarily enlarged brains, especially the parts associated with singing, in spring, when males sing to advertise territory and attract females. European titmice that engage in strongly seasonal singing have corresponding seasonal changes in brain size, while those that vocalize year-round do not. Captive house sparrow males kept near females sang more often and had bigger brains than those isolated from females. These studies have focused on male birds and the production of song, but what about the females that listen to those songs?<\/p>\n