Dec
10
2008

Seasonal patterns of nesting success

Many bird populations across North America have declined in recent years and researchers have been busy trying to determine why populations of birds are declining.
Dusky flycatcher nest: These dusky flycatcher eggs might be safe when it comes to researchers, but something is still amiss here: those speckled eggs are brown-headed cowbirds, not dusky flycatchers. When they hatch, they'll outcompete the flycatcher chicks for food.
Dusky flycatcher nest: These dusky flycatcher eggs might be safe when it comes to researchers, but something is still amiss here: those speckled eggs are brown-headed cowbirds, not dusky flycatchers. When they hatch, they'll outcompete the flycatcher chicks for food.Courtesy West Coast Birding

My research focuses on factors that could affect survival of birds during the breeding season. The breeding season is an important time for birds because this is the time when individuals have an opportunity to raise young and the ability to successfully raise young can have a big effect on the bird population. However, producing young can be quite difficult for birds. In fact, the number one factor that affects the ability of birds to raise young is nest predation. Nest predation occurs when a predator, such as a chipmunk or squirrel eats the eggs or young in a bird’s nest. But do all birds have an equal chance of survival during the breeding season? Research suggests that the chance of survival for a bird’s nest is not equal and chances for survival change during the breeding season. Why might survival change during the breeding season? I have some ideas or hypotheses that might explain why survival changes during the breeding season. I am investigating whether plant cover, food resources for predators, temperature, or number of predators affects the ability of songbirds to raise their young.
When birds build their nests, they often hide them in plants to reduce the chance that a predator will find their nest. But many birds begin building their nests early in the spring and in early spring we often notice that plants and flowers in the forest are just starting to grow. So birds building their nests during this time have fewer plants to hide their nests in which could make their nests more visible to predators, such as chipmunks and squirrels. Because plant cover may be a key factor preventing predators from eating the eggs or young in a bird’s nest, I experimented with plant cover to test the importance of plant cover. I removed plant cover around Wilson’s Warbler nests and compared the fate (i.e., were the parents able to raise their young) of these nests to nests that did not have plant cover removed. I also measured plant cover at nests of Wilson's Warblers and Dusky Flycatchers and compared the amount of plant cover to the fate of each nest.
In addition to seasonal changes that we see in plants, the amount of food available in the forest for critters to eat also changes as we move from spring to summer to fall. Early in the summer, there may be less food available for the predators because pine cones and seeds from other plants are not yet available. If predators such as chipmunks, mice, or jays have less to eat they spend more time looking for food to eat in the forest. The increase in time spent searching for food could also increase the chance that one of these predators will find a bird nest and eat the eggs or young in the nest. Because the amount of food available might affect survival of a bird’s nest I conducted another experiment to find out if this was the case. I provided food (sunflower seeds and corn) to predators to see if providing extra food to predators will increase the ability of birds to raise their young.
Determining how both vegetation and food affect survival of bird’s nests during the breeding season is challenging but fun because I am able to experiment with nature and find out what happens. As a scientist I am like a detective trying to figure out why bird populations are declining. Finding the answer is challenging and exciting, but hopefully we will find an answer that will prevent further losses of our bird populations.

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