Sargassum Invasion: a Boon for Birds?

By now St. Martiners are plenty familiar with the huge influx of sargassum that has washed up on our eastern shores. You may have also noticed how abundant shorebirds and other birds are on those same beaches right now. Is there a connection and perhaps a silver lining to this smelly nuisance?

The starting point for a possible connection is the impact of the sargassum on invertebrates that scavenge vegetation on our beaches. Although I can’t be sure, it seems highly likely that isopods, insects and other small, coastal detritivores are experiencing a population explosion due to the large increase in available food and shelter. Shorebirds are obviously foraging on these mounds of rotting algae, and other birds like the barn swallow are feasting on flying insects in these areas. But are we seeing more birds right now? If so, how could that be?

Probably the total bird population has not increased. After all, unlike insects, most of these birds only breed once a year, so it is too early to see much of an impact in overall bird numbers. It’s possible that some birds that might have starved in a normal year would have survived with this extra food available, but that’s probably a relatively small number.

On the other hand, we are in the middle of a pretty busy time for migration, with many species either arriving to or leaving the island between August and October. Perhaps it is possible that some birds would stay here a little longer than they otherwise would, increasing the local population. Presumably the extra food wouldn’t encourage birds to fly here earlier than usual, because they would have no idea that the extra food is here. I think it is possible that if some birds delay their annual departure and others take longer visits as they fly over, this could be noticeable, particularly when combined with the normal seasonal arrival of other species.

Another possibility, which seems pretty likely and may be happening at the same time, is that bird populations on the island have gravitated towards the impacted eastern beaches to take advantage of the resources there. In this case, people (like me) may be more apt to notice the large numbers of birds on some beaches while not noticing that other areas have fewer birds than normal.

Of course, maybe nothing special is happening at all. Shorebirds arrive on the island at this time of year every year, and unless you’re counting, it’s hard to tell if there’s really any difference this year. Unless someone is actually studying this on one of the affected islands, we probably won’t know. It’s too bad school is out for the summer, because this would be a pretty great science fair project.

Below are some photos from Baie de l’Embouchure. Right now you can go there and see a lot of sargassum and lots of shorebirds.

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