Related topics: Empty Forest

As birds go down, spiders go up on the island of Guam (and the press has a field day)

By Joshua Tewksbury

The forests of the island of Guam have been without birds for over 25 years, due to the invasion of the Brown Tree Snake. The consequence of this wholesale removal of birds from a tropical forest had received only a small amount of attention in the ecological literature. In a Paper out this week in in PLOSone, Haldre Rogers takes a big first step in filling this void. Haldre shows that during the wet season, when spider webs are rare in the forests of the Mariana Islands, spiders are 40 times more abundant on the island of Guam, compared to nearby islands with birds. They are also 2 to 4 times more abundant in the dry season. This response pretty much wipes out the strong seasonality seen in spider numbers on nearby islands. Highlights, details, and analysis all came out this week (get the article here). This may be the first whole-ecosystem-level examinations of top-down effects of bird loss on lower trophic levels, and both the size and shape of the response strongly suggest that the full system may comes into equilibrium at a different place than one would predict based on smaller scale experiments. There is no doubt we need experimental work to build a mechanistic understanding, but for the full measure of the impact, the study of full ecosystems undergoing large scale change appears critical. This is exactly what we set up the Ecology of Bird Loss Project (or EBL for short) to do, and more generally, perhaps we can see this as our responsibility as ecologists – to learn as much as possible from the changes we have imposed on ecosystems. In the case of bird loss, I think it is safe to say that there is simply no place in the world better suited than the Mariana Islands.


This is the first paper from to come out from EBL on the impacts of bird loss on lower trophic levels, and because it links invasive snakes to huge increases in spiders, the press has been having a field day. Check out some of the news coverage we have received, on NPR, CBS, NSF’s website, MSNBC, and elsewhere. And check out the video on the research on Slate (or click the embedded video above).

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