Foraging movements and migration in auks
Combining data from guillemots and razorbills will allow a comparison of the foraging behavioural ecology between the two species. This may help answer an outstanding question of Baltic Sea ecology around Stora Karlsö; why do razorbills breed later than guillemots? It does not appear to be due to different diets, as previous studies at the island suggest both species feed on clupeid species, both herring (Clupea harengus)and predominantly sprat (Sprattus sprattus).
Diving and flight abilities
GPS trackers and time-depth-recorders
Using GPS trackers and TDR, time-depth-recorder devices, we plan to follow razorbills’ behaviour during the chick rearing period. These devices will provide both spatial data on where and when birds are foraging, and detailed information on diving activity, including diving durations and depths. Together this information will provide a detailed picture of spatio-temporal foraging ecology in the species.
Affect on behaviour?
An important consideration in any study of wild animals is; does the method of observation affect the animal’s behaviour? If one wishes to investigate the natural behaviour of a species it is important that any observation effects are small. Several studies have looked at whether devices attached to seabirds affect their behaviour, however most of these have used fairly insensitive measures, such as breeding success; few have looked in detail at behaviour, and none on alcid species.
In this study, as two devices are used, the TDR and the GPS, we plan to attach only TDR devices to one group, and TDR with GPS to the other. With the TDR devices recording both temperature and pressure data (for dive depth) it is possible to broadly recognise behaviour types; flight, water surface resting, diving, and presence at the nest. Thus it is possible to compare the proportion of time spent on these behaviours between the two groups, and also fine scale diving measures, such as maximum dive depths, and the number of dives made in a diving bout.
Our plan is to deploy the TDR devices throughout the year; being small and attached to a leg ring this is possible. This will allow behaviour to be compared across the year. Especially interesting is the moult-period. For the first stage of the moult birds are flightless for several weeks, with reduced wing area from lost primary wing feathers. Measuring diving activity in this period could throw-light on trade-offs between diving and flight - fascinating as these birds are highly specialised in diving, able to dive to depths over 100 meters, and yet they can still fly; better than penguins!