Contrasting responses of lizard occurrences to burrowing by a critically endangered seabird

© Akadémiai Kiadó, Budapest. Seabirds are considered ecosystem engineers, because they facilitate ecosystem functioning (e.g., nutrient cycling), crucial for other marine and terrestrial species, including reptiles. However, studies of seabird-reptile interactions are limited. Here, we assessed the influence of the ‘Critically Endangered’ Whenua Hou Diving Petrel (Pelecanoides whenuahouensis) on the occurrence of two threatened skinks, Stewart Island green skink (Oligosoma aff. chloronoton) and Southern grass skink (O. aff. polychroma). We surveyed skinks for 26 consecutive days at 51 sites with and 48 sites without Diving Petrel burrows in the dunes on Codfish Island (Whenua Hou), New Zealand. We used occupancy modelling to assess the influence of burrows on the occurrence of skinks, while accounting for other factors affecting occupancy (Y) and detection probabilities (p). Diving Petrel burrows had a contrasting effect on the occurrence of skinks. On average, Y of Stewart Island green skinks was 114% higher at sites with burrows compared to sites without, while Y of Southern grass skinks was only 2% higher. Occurrence of both skinks was negatively influenced by the presence of the other skink species. On average p were low: 0.013 and 0.038 for Stewart Island green and Southern grass skinks, respectively. Stewart Island green skinks appear attracted to burrows, which might facilitate thermoregulation (i.e., shelter from temperature extremes). The larger Stewart Island green skinks May subsequently exclude the smaller Southern grass skinks at burrows, causing the contrasting relationships. We suggest that these interspecific interactions should be considered when implementing conservation management, e.g., through the order of species reintroductions.