While negative effects of human disturbance on animals living above the ground have been widely
reported, few studies have considered effects on animals occupying cavities or burrows underground.
It is generally assumed that, in the absence of direct visual contact, such species are less vulnerable to
disturbance. Seabird colonies can support large populations of burrow- and cavity-nesting species and
attract increasing numbers of tourists. We investigated the potential effects of recreational disturbance
on the reproductive behaviour of the European storm petrel Hydrobates pelagicus, a nocturnally-active
cavity-nesting seabird. Reproductive phenology and outcome of nests subject to high and low levels of
visitor pressure were recorded in two consecutive years. Hatching success did not differ between disturbance
levels, but overall nestling mortality was significantly higher in areas exposed to high visitor pressure.
Although visitor numbers were consistent throughout the season, the magnitude and rate of a
seasonal decline in productivity were significantly greater in nests subject to high disturbance. This study
presents good evidence that, even when humans do not pose a direct mortality risk, animals may perceive
them as a predation risk. This has implications for the conservation and management of a diverse
range of burrow- and cavity-dwelling animals. Despite this reduction in individual fitness, overall colony
productivity was reduced by 61.6% compared with that expected in the absence of visitors. While the colony-
level consequences at the site in question may be considered minor, conservation managers must
evaluate the trade-off between potential costs and benefits of public access on a site- and species-specific
basis.
2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://