Spring is the time when birds recover from the hard times of winter, build their nests and raise their young. Reproduction occurs in the spring because laying eggs and raising nestling requires highly nutritious foods and these are much more available in the spring than any other time of the year. Nutrients that are critical for breeding include protein, energy, calcium and lots of vitamins and minerals.
The availability of quality foods declines after spring. An early start at breeding makes it more likely that a pair of birds can raise several broods of chicks. Consequently many species of birds start breeding as soon as there are enough high quality foods to insure success. Insects are especially nutritious for nestlings and the first blooms of insects in the spring trigger a breeding frenzy.
Birds that have survived winter in good health are best suited for getting reproduction going as soon as possible. A wide variety of studies have shown that providing supplemental foods permit s birds to begin reproduction earlier in the spring with better success. The additional food helps them have more eggs per nest, bigger eggs, better hatchability, faster nestling growth, and lower nestling mortality. Supplemental feeding is especially helpful in years when bad weather shortens spring.
Many species feed their nestlings a diet of mostly insects until they are grown because insects are great sources of protein, energy, vitamins, and minerals that are needed for fast growth. When insects, such as meal worms, are provided at feeding stations, parents will use them to provision their young. When seeds are provided along with insects, parents may consume the seeds for their own nourishment and forage for insects to provide to their young.
Neither seeds nor insects have enough calcium for the formation of good eggs shells and bones. During reproduction, birds must seek out concentrated sources such as shells from snails and calcium containing pebbles. Some environments are so low in these high calcium sources that reproductive success is diminished. Providing a good calcium source, like crushed oyster shells, can be very valuable in these situations.
Article by Kirk Klasing. Dr. Klasing is a professor of Comparative Avian Nutrition in the Department of Animal Science, University of California, Davis
