Use of social attraction to restore ashy storm-petrels Oceanodroma homochroa at Orizaba Rock, Santa Cruz Island, California

Published source details McIver W.R., Carter H.R., Harvey A.L., Mazurkiewicz D.M. & Mason J.W. (2016) Use of social attraction to restore ashy storm-petrels Oceanodroma homochroa at Orizaba Rock, Santa Cruz Island, California. Marine Ornithology, 44, 99-112.
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Summary

Provide artificial nesting sites for burrow-nesting seabirds

A replicated, controlled study in 2008–2011 on Santa Cruz Island, California, USA (McIver et al. 2016) reported that artificial nests were used by ashy storm petrels Oceanodroma homochroa, with a similar breeding success and laying date to natural crevices. Over four years, 20 of 30 (67%) of artificial nests were visited by storm petrels. Eggs were laid in 11 (37%). Storm petrels also nested in nearby natural crevices. Artificial and natural nests had statistically similar breeding success (artificial: 52%; natural: 48% of nests fledged a chick) and average laying date (data not reported). Between 2008 and 2011, a total of 30 artificial nests were installed amongst coastal boulders. These were mostly made from concrete roof tiles with gravel floors and rocks to reduce entrance sizes. In 2011, some were replaced with custom-built ceramic nests. Ashy storm petrel calls were also played from speakers each breeding season.

Use vocalisations to attract birds to safe areas

A before-and-after, site comparison study in 2005–2011 on Santa Cruz Island, California, USA (McIver et al. 2016) reported that playing vocalizations (along with installing artificial nests) increased the size of the focal ashy storm petrel Oceanodroma homochroa colony, but reduced breeding success. Results summarized for this study are not based on assessments of statistical significance. In 2005–2007 (before intervention), Orizaba Rock supported 7–14 active storm petrel nests/year and 60% of nests fledged a chick. In 2008–2011 (after intervention), there were 24–33 active nests/year, but only 49% of natural nests and 52% of artificial nests fledged a chick. Meanwhile, at a nearby sea cave with no intervention, colony size was relatively stable (before: 19–28; after: 24–29 active nests/year) and breeding success increased slightly (before: 65%; after: 75%). Between 2008 and 2011, a total of 30 artificial nests were installed amongst coastal boulders at Orizaba Rock (≥21 available each year). These were mostly concrete roof tiles. From 2011, some were custom-built ceramic nests. During each breeding season, conspecific calls were also played from speakers (continuously during night hours; range 300 m). The study does not distinguish between the effects of these interventions.