Experimental measurement of nesting substrate preference in Caspian terns,

Published source details Quinn J.S. & Sirdevan J. (1998) Experimental measurement of nesting substrate preference in Caspian terns,. Biological Conservation, 85, 63-68.
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Summary

Provide artificial nesting sites for ground and tree-nesting seabirds

A before-and-after, site comparison study in 1993–1994 in Ontario, Canada (Quinn & Sirdevan 1998) reported that covering plots with sand, gravel or stones increased the number of Caspian tern Sterna caspia nests. This result is not based on assessments of statistical significance. In 1994, eighty-eight Caspian tern nests were initiated on the added substrates. Of the first 21 nests initiated, 20 were on the added substrates rather than the surrounding hard-packed ground. Across the whole breeding season, 50% of nests in the study area were on the added substrates (vs 24% in the same plots before substrates were added). The study also compared the different added substrates. More nests were initiated on sand (46) than on gravel (15) or stones (27). However, breeding success and productivity did not significantly differ between substrate types (see original paper for data). In spring 1994, artificial substrates were added to nine adjacent 9-m² plots. Three plots received each substrate: sand, smooth pea gravel, or sharp crushed stone. Nest initiation was monitored across the whole site (including adjacent hard-packed ground) before (1993) and after (1994) substrate addition. Nest performance was monitored on the added substrates in 1994.

A study in 1995–1997 in Ontario, Canada (Quinn & Sirdevan 1998) reported that sandy artificial islands attracted nesting Caspian terns Sterna caspia. The islands hosted 226 Caspian tern clutches in the first breeding season after construction, then 382 clutches in the second breeding season (319 early + 63 late-nesting or re-nesting attempts). This represented 86% and 96% respectively of the total number of clutches initiated in the wider study area (Hamilton Harbour). Each island was a 20 x 100 m mound covered with sand and some 1-cm diameter pea gravel. The islands were covered with plastic sheeting before terns arrived each year, to discourage gull nesting. Nest covers and chick shelters were also provided once nesting began.