Back in November 2013, during my research and teaching trip to Brazil, I discussed an amazing garden that we visited in which the owner had set up around a dozen hummingbird feeders that were attracting hundreds of individual birds from over 20 species. As I mentioned, one of the owner’s concerns was that by feeding the birds he might be negatively affecting the reproduction of hummingbird-pollinated plants in the surrounding forest. I thought it unlikely but there have been very few tests of this idea, and none in that part of South America.
After I left, a Master’s student called Jesper Sonne, based at the Center for Macroecology and Climate in Copenhagen, worked with my Brazilian and Danish colleagues on collecting data to address this question. Between us we analysed and wrote up the results, and have recently published the paper in the Journal of Ornithology under the title “Spatial effects of artificial feeders on hummingbird abundance, floral visitation and pollen deposition“.
The abstract is below and if anyone wants a PDF, please drop me a line. But the take home message is that although these feeders have a significant local effect on hummingbird abundance, there’s no evidence that they affect plant reproduction in the vicinity. It’s nice when predictions prove correct….
Providing hummingbirds with artificial feeders containing sugar solution is common practice throughout the Americas. Although feeders can affect hummingbird foraging behavior and abundance, it is poorly understood how far this effect may extend. Moreover, it remains debated whether nectar-feeders have a negative impact on hummingbird-pollinated plants by reducing flower visitation rates and pollen transfer close to the feeders. Here, we investigated the effects of distance to nectar-feeders on a local hummingbird assemblage and the pollination of Psychotria nuda (Rubiaceae), a hummingbird-pollinated plant endemic to the Brazilian Atlantic Rainforest. At increasing distance (0–1000 m) from a feeding-station, where hummingbirds have been fed continuously for the past 13 years, we quantified hummingbird abundance, and rates of flower visitation and pollen deposition on P. nuda. We found that hummingbird abundance was unrelated to distance from the feeders beyond ca. 75 m, but increased steeply closer to the feeders; the only exception was the small hummingbird Phaethornis ruber, which remained absent from the feeders. Plants of P. nuda within ca.125 m from the feeders received increasingly more visits, coinciding with the higher hummingbird abundance, whereas visitation rate beyond 125 m showed no distance-related trend. Despite this, pollen deposition was not associated with distance from the feeders. Our findings illustrate that artificial nectar-feeders may locally increase hummingbird abundance, and possibly affect species composition and pollination redundancy, without necessarily having a disruptive effect on pollination services and plants’ reproductive fitness. This may apply not only to hummingbirds, but also to other animal pollinators.