At this time of year petrel chicks are fledging and making their first tentative flights out to sea. Petrels are nocturnal and only active at night. When moonlight levels are low, or when the moon is obscured by cloud, the chicks may be attracted to artificial lighting on the base. Once on land they often seek shelter then become stranded. Everyone on the island makes a huge effort to reduce the amount of light emitted, but we still need to see!
In September and October, the ranger team patrols the periphery of all the buildings on the base looking for birds. This morning a petrel was discovered behind the gym. It was carefully caught and put in a dark box somewhere quiet until dusk. Releasing at this time of night means there are fewer predators around and this should give it a better chance of making it safely out to sea.
Bird bag made by Bailey Orr, age 11 - thanks!
This week, samples have been taken from the petrels to assist with Tom Black’s PhD research on the St Kilda Mouse. Surprisingly little is known about this small mammal and Tom is currently on island to investigate its breeding ecology, population dynamics and foraging ecology.
Mice eat a wide range of food items and there is some evidence that they scavenge or predate on petrel eggs. Tom has already taken tissue samples from the mice and potential prey items to use in stable isotope analysis but he needed samples from petrels to complete this aspect of work. Isotope analysis is complex but essentially prey have unique isotope ‘signatures’ that can be used to identify what the mice are eating.
Steve Votier (Tom’s co-supervisor) is on island to collect samples from the recently fledged petrels that we find around the base. In the next year or so, Tom should have some interesting results that will provide much needed information about the interactions between two of St Kilda’s most admired species.
Gina, Seabird and Marine Ranger