The migration of nearctic-neotropical birds is one of nature's greatest spectacles. In an earlier post, we discussed why birds migrate. This post will highlight some general aspects of stopover habitat around the Gulf of Mexico. GCBO is involved in initial research to create a landscape scale stopover habitat model to help in conservation efforts relating to stopover habitat. The map at the left is an illustration of stopover habitats in Bird Conservation Region 37 (Partners in Flight).
Following is a conceptual framework for considering stopover habitat:
"Fire Escape”: Like fire escapes in human habitations, these stopover sites are infrequently used, but are utterly vital when they are. Habitat quality may be too low to allow birds to gain significant mass, but at least they will survive, can take shelter, and may be able to get fresh water. Fire escape sites are typically adjacent to significant barriers such as deserts or large bodies of water.
"Convenience Store”: Forested patches, such as small parks or woodlots, in a non-forested matrix and located along migratory routes. These sites offer a place where birds can briefly rest and gain some mass easily, perhaps between short flights to higher quality sites, or when migrants’ fuel stores are moderate. A given Convenience Store may be better able to serve the needs of some species than others. Convenience Stores are found in various areas like city parks, and small woodlots near agricultural fields.
"Full-service Hotel”: Forested sites in a forested landscape. Full-service Hotels are places where all needed resources (food, water, shelter) are relatively abundant and available. These places serve many individuals of many species. Bottomland hardwood forests are a good example.
After an exhausting overnight flight across the Gulf of between 10 and 20 hours (depending on wind), birds must find habitat to stop, rest, and refuel. Recent research indicates that primary migration routes evolved in the last glacial period, 25,000 years ago, and are centered around 95 degrees west longitude (from just SW of Houston eastward to the central Louisiana coast). The precise landing zone for a trans-Gulf migrant however, is largely dependent on weather, especially wind speed and direction, and the energetic condition of the bird itself. A fat-depleted migrant, or one that encounters strong north winds or thunderstorms, will usually stop in a fire-escape (if the bird makes it ashore at all). In most cases, during favorable weather, migrants will fly inland and settle in a patch of hardwood forest (convenience store or full-service hotel). If the bird must use a fire-escape, it will usually spend the minimum time there necessary to regain strength (and possibly wait for favorable weather). What happens after landfall - and what strategy the bird uses to find resources - will be the subject of the next post.