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Fledging behavior—when and why baby birds leave the nest—is something scientists know very little about. Rarely is someone watching a nest at just the right moment to see fledging happen. To get around this, the researchers behind a new study from The Auk: Ornithological Advances deployed miniature video cameras to monitor over 200 grassland bird nests in Alberta, North Dakota, Minnesota, and Wisconsin, and they found that fledglings' decision-making process is more complex than anyone guessed.
Christine Ribic from the U.S. Geological Survey and her colleagues tested two competing hypotheses about fledglings' decision making. Birds might leave the nest early in the day to maximize the amount of time they have to find a safe place to hide from predators before nightfall. Alternatively, once their siblings start to leave, the remaining birds might decide to stay in the nest longer to take advantage of reduced competition for the food their parents provide, resulting in spread-out fledging times. Video data analyzed by Ribic and her colleagues showed that the more siblings in a nest, the longer it took for all of them to fledge, consistent with the idea that some young may stay behind to take advantage of reduced competition after the first nestlings leave. Ribic and her co-authors discovered that 20% of nests took more than one day to completely finish fledging. Fledging behavior also varied between species and over the course of the breeding season, for reasons that remain unclear.
Nestlings - Grassland - Birds - Demands - Hand
As they decide when to fledge, the nestlings of grassland birds are balancing two competing demands. On one hand, staying in the nest longer gives them more time to grow and develop before facing the risky outside world. On...
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