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Posted by Carlos Sanchez on 06:43:52 03/26/11
In Reply to: Some thoughts on low warbler count posted by Paul-the-other
Although severe, the only real impact Hurricane Wilma could have wrought on migrants would have been during its passing in the month of October. Most early migrants from August and September should have been spared as they would have already been already on their wintering grounds away from the storm's effects (unless of course they were wintering in the northeast Yucatan). Also, Hurricane Wilma was not powerful enough to destroy south Florida's tree canopy to impact future migrations long term. Not like Andrew, which leveled every tree in southern Miami-Dade in the middle of August just as migration was starting. What were the impacts, then?
Regardless, this does not explain the apparent universal decline Toe is implying. Birds are incredibly diverse in both migration timing and migration routes used that a natural disaster in a point in time could not have possibly impacted them all.
In any case, we are hard pressed to judge songbird numbers from our vantage point in south Florida. The migration periods are fickle due to the high variability that comes into play whether a bird stops over or not -- wind direction, visibility, precipitation, timing, etc.
For example, conditions that were conducive to a fallout in past years might not create a fallout this year. A large batch migrants might have taken advantage of the good conditions the previous day, and there weren't many migration ready birds to 'fallout' during the conducive (for us) conditions. The only thing we can do here is provide enough stopover habitat for those birds not strong enough to continue on their journey.
Breeding bird surveys and wintering bird surveys are much more effective for determining songbird numbers. What have our wintering warbler numbers been like in the past few years? Have they declined in numbers and diversity? Habitat loss in the tropics might be helping some birds like Swainson's Thrushes, Blackburnian Warblers, and Canada Warblers which seem to prefer secondary habitats over primary forest. Breeding grounds need to be a bit more pristine, however.
Carlos
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