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Spatial effects of artificial feeders on hummingbird abundance, floral visitation and pollen deposition

Abstract

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.

Zusammenfassung

Bruterfolg bei der Kohlmeise und ihr Zusammenhang mit Eigenschaften natürlicher Nisthöhlen in einem Urwald

Das Angebot künstlicher Nektarspender gefüllt mit Zuckerlösung für Kolibris ist eine gängige Praxis in ganz Nord-, Mittel- und Südamerika. Obwohl die Nektarspender das Nahrungssuchverhalten von Kolibris beeinflussen können, ist wenig bekannt über das Ausmaß dieses Effektes. Vielmehr ist zu überlegen, ob Nektarspender nicht negative Auswirkungen auf durch Kolibris bestäubte Pflanzen durch weniger Blütenbesuche und verringertem Pollentransfer in der Nähe der Futterstellen haben. Wir untersuchten die Effekte der Entfernung zu Nektarspendern in einer lokalen Kolibrigemeinschaft und die Bestäubung von Psychotria nuda (Rubiaceae), eine durch Kolibris bestäubte, endemische Pflanze im atlantischen Regenwald von Brasilien. Mit ansteigender Distanz (0–1000 m) zu einer Futterstelle, wo Kolibris seit 13 Jahren kontinuierlich gefüttert werden, quantifizierten wir die Kolibridichte sowie die Raten der Blütenbesuche und Pollenverbreitung von P. nuda. Es zeigte sich, dass die Dichte von Kolibris nicht verbunden war mit einer Entfernung von über ca. 75 m zu Futterstellen, stieg jedoch stark an in der Nähe von Futterstellen. Die einzige Ausnahme bildete die kleine Art Phaethornis ruber, die nicht an den Futterstellen anwesend war. P. nuda Pflanzen innerhalb von ca. 125 m zu den Nektarspendern wurden zunehmend mehr besucht, einhergehend mit einer höheren Kolibridichte, wobei die Besuchsrate jenseits von 125 m keinen distanzbezogenen Trend zeigte. Trotz dieser Beobachtung war die Pollenverbreitung nicht assoziiert mit der Entfernung zu den Futterstellen. Unsere Ergebnisse zeigen, dass künstliche Nektarspender lokal die Kolibridichte erhöhen können und möglicherweise auch die Artenzusammensetzung verändern. Sie müssen aber nicht zwangsläufig einen störenden Effekt auf die Bestäubungsleistung von Kolibris und die reproduktive Fitness der Pflanzen haben.

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Acknowledgments

This study is dedicated to Mr. Jonas d’Abronzo, whom we thank for hosting us and allowing us to conduct this study at Folha Seca. We also thank André Rodrigo Rech for assistance with pollen count techniques, Marina Wolowski for logistic help in the field, Tatsuya Amano for advice on the piecewise regression analysis, and João Afonso, Martins do Carmo, Felipe W Amorim and Vinicius L G Brito who helped to confirm information about the reproductive morphology of P. nuda. We also thank two anonymous reviewers for their useful comments that improved the manuscript. PK was supported by Svend G. Fiedler and wife’s Foundation and a PICA scholarship. PKM received a Ph.D scholarship from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico). JVB received a Ph.D scholarship and a PDSE scholarship (processo: 99999.008012/2014-08) from CAPES (Coordenaçãoo de Aperfeiçoamento de Pessoal de Nível Superior). JO’s visit to Brazil was supported by FAPESP. JS, PK, JVB, PKM and BD thank the Danish National Research Foundation for its support of the Center for Macroecology, Evolution and Climate. We state that this study complies with the current laws of Brazil.

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Correspondence to Jesper Sonne.

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Communicated by C. G. Guglielmo.

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Sonne, J., Kyvsgaard, P., Maruyama, P.K. et al. Spatial effects of artificial feeders on hummingbird abundance, floral visitation and pollen deposition. J Ornithol 157, 573–581 (2016). https://doi.org/10.1007/s10336-015-1287-1

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Keywords

  • Artificial feeding
  • Atlantic Rainforest
  • Hummingbirds
  • Pollination
  • Mutualistic interactions
  • Psychotria nuda
  • Rubiacea