In the previous post, we discussed the different types of stopover habitat available to a trans-Gulf migrant on its journey to and from its wintering grounds in the tropics. This discussion will examine what happens when the migrant makes landfall.
Most trans-Gulf migrants reach the coast before dawn, and probably continue inland until forest is encountered after sunrise. Depending on the weather encountered during flight and the energetic condition of the bird, stopover options may be limited and birds may have to land immediately after reaching the coast. Regardless, birds will usually undertake a “morning flight” soon after arrival or after sunrise. These flights are of short duration, low altitude (often treetop to treetop), and in flocks (often mixed species). It is assumed that the birds are “evaluating” their immediate surroundings to determine the suitability of the habitat for feeding and resting. There is great pressure on the bird to find suitable habitat quickly – time spent in migration searching for optimum habitat is time that the bird is not on the breeding grounds and is not competing for a breeding territory. It is speculated (in most cases) that birds first stop based on gross habitat features like vegetation density. The decision to search for resources or move on may depend on more specific habitat features or on the behavior of other migrants. It’s important to realize again that most of these decisions are probably based on the migrant’s energetic condition – birds with remaining fat are most interested in finding a place to rest, while fat-depleted birds must find food quickly. The exact methods by which migrants make decisions about habitat use during stopover are poorly understood.
Bill
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