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New meta-analysis on the impact of researcher presence on nest predation: you may actually be doing those birds a favor!

By Ellen Paul

Have you been worrying that your presence may cause the birds you study to have a lower rate of breeding success? Well, for some species and in some conditions, you may actually be helping them to increase their breeding success by deterring predation!
Three researchers from the University of Granada have questioned the long-standing assumption that investigator presence negatively impacts breeding success.

Juan D. Ibáñez-Álamo, Olivia Sanllorente, and Manual Soler conducted a meta-analysis on 18 studies of investigator impact on natural nests. Of the 101 papers they found on this subject, only these 18 were experimental and met the criteria for the meta-analysis. Even with current technology such as remote cameras, it would be difficult, if not impossible, to study breeding success without any investigator presence, but this meta-analysis considered observations through binoculars to be the equivalent of a non-visit. In addition, this meta-analysis used the extent of disturbance as the measure of the impact of investigator presence. When a causal relationship exists, there should be an exposure-response such that increased exposure produces an increased response. Therefore, if investigator presence affects breeding success, increased presence should have greater impact than does less frequent presence or presence of shorter duration.

The meta-analysis looked at the extent of the impact by as reflected by the number of depredated and successful nests under a high perturbation treatment vs. low perturbation and non-perturbation treatments, habitat type, and the study methods (frequency of visits, visit v. non-visit, touched vs. untouched).

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Overall, Passeriformes showed a marginally significant effect of researcher disturbance in that researcher presence was associated with a reduction in nest predation. However, there was no significant effect (positive or negative) for Charadriiformes. Sample size for the other four orders was not sufficient for the analysis. As to some aspects of avian traits, researcher presence actually had a positive effect. For ground-nesting birds, researcher presence apparently had a negative effect on predators, resulting in greater breeding success. However, no difference was seen on colonially nesting species. The negative impact on predators was found for coastal species but not for grassland birds.

The depression of predation rates was not found in studies measuring visit vs. non-visit, perhaps because even with binoculars, the researcher is still physically present at a distance close enough to assess breeding success, which is still relatively close to the nest.

The negative effect on nest predation was strong enough that the authors caution those studying nest predation rates to take into account the impact of their own presence on the results.

This article summarizes information in this publication:

Ibáñez-Álamo, Juan D., Olivia Sanllorente, and Manual Soler. 2011. The impact of researcher disturbance on nest predation rates: a meta-analysis. Ibis (pre-publication version first published online on 7 November 2011).

Photo credits:
Black rat snake predation event by Andrew Cox.
Great Tit nestling by jamesmorton on Flickr, used here under license CC BY-NC-ND 2.0.