Observers Don’t Change Ultimate Fate of Sage-Grouse Nests

(February 18, 2015, The Auk: Ornithological Advances)—Visits by researchers may cause some nesting Greater Sage-Grouse (Centrocercus urophasianus) females to abandon their nests, but those nests were likely to fail anyway, according to a new paper in The Auk: Ornithological Advances. Daniel Gibson and James Sedinger of the University of Nevada Reno, Erik Blomberg of the University of Maine, and Michael Atamian of the Washington Department of Fish and Wildlife used eight years of data from sage-grouse nesting grounds in Nevada to determine whether observing nests affected their fate. They found that while females who were flushed from their nests by researchers were more likely to abandon their eggs, this did not ultimately change the overall rates of nest failure.

Scientists who study birds typically use two different numbers to measure how well nests do. Nest success is simply the probability that chicks will successfully leave a nest or not, that is, the nest’s ultimate fate. Nest survival is more complicated and measures how long a nest is active before failing (due to predation, abandonment, or other factors) or hatching. Gibson and his colleagues found that observer effects influenced nest survival, but not nest success. In other words, visits by researchers caused some nests to fail earlier in the season than they would have otherwise, but the nests would have likely failed anyway.

To determine why this was the case, the study’s authors analyzed the characteristics of abandoned nests, resulting in the first study to link female quality with observer-related nest abandonment. Younger, less experienced females and those who occupied poor-quality nest sites were most likely to abandon their nests after being flushed by researchers. “Our study found that a small proportion of females, about 16%, abandoned their nests after we flushed them, causing the nest to fail.  However, we also found those same females had other characteristics, such as poor nest quality, that made them likely to fail even if we hadn’t flushed them in the first place,” explains lead author Daniel Gibson. “We believe this suggests that low quality females are more prone to abandon, whereas high quality females are unlikely to. Earlier nest failures by low quality females that were flushed caused us to underestimate nest survival even though there was very little effect on the ultimate fate of the nest.”

This paper “is important from both ethical and management perspectives, especially given current concerns for the status of the species,” says Dr. Jay Rotella of the Montana State University, a population ecology expert not affiliated with the study. “Moreover, the work provides not only an excellent example of how researchers can evaluate possible investigator impacts; it also provides an excellent example of interpreting estimated effects in a way that puts them in a broader context of the net impact.”

A Greater Sage-Grouse nest with eggs. Photo credit: S. Beh

A Greater Sage-Grouse nest with eggs. Photo credit: S. Beh

Observer effects strongly influence estimates of daily nest survival probability but do not substantially increase rates of nest failure in Greater Sage-Grouse is an open-access paper available at http://www.aoucospubs.org/doi/full/10.1642/AUK-14-197.1. Contact: Daniel Gibson, dnonne@gmail.com.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology. The journal has been the official publication of the American Ornithologists’ Union since 1884. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years, and currently holds the top impact factor among ornithological journals.

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