JOSIP TURKALJ – June fieldwork

After a long, long travel from Zagreb, we have arrived on Lastovo island, to Pasadur. It is the beginning of June, period when Yelkouan shearwater and Audouin’s gull nesting is in a full swing, while Scopoli’s shearwater are soon going to incubate the eggs. It is a perfect time to visit the foraging areas, as well as the nesting grounds.

We start early in the morning, take our boat and leave the area of Nature part Lastovsko otočje, but not too far. We steer our boat around the border area of the Park and watch the birds if they feed there or only fly. You might ask why? Well, we want to know which exact areas around the island is these sea birds use as feeding grounds or only for commuting. Not every area is rich with food resources and equally peaceful, and birds prefer only certain locations for that matter. It takes us several days to visit all the wanted locations since the summer is coming, and due to the heat, it will not be possible to work all day but only during those “colder” hours.

Next couple of days we spend at the sea looking at the birds flying just a few millimetres above the sea surface, using the airflow we barely notice to help them cruise. Even though, we spent most of our days at the open sea, during the night we visit Zaklopatica, an island next to the village it shares the name with. The largest known Yelkouan shearwater colony in Croatia is right on that island. For the past couple of months, we have tagged around 20 birds with GPS tags and now it was time to collect the equipment and data. Yelkouan shearwater were now nesting, and our task was to find the tagged adults on those nights and remove tags from them which was our biggest challenge since they could be foraging and not sitting on nests. That was the reason it took us couple of nights to locate them and finish our task.

After we finished most of our sea transects, we started our search around the Lastovo island for the Scopoli’s shearwater nests. They usually nest on smaller islands around Lastovo, and on each island or islet it was necessary to spend couple of hours to find all potential nesting locations and to determine the number of couples. On some islands that was much easier than on others. Just as Yelkouan shearwater, Scopoli’s shearwater nest in crevices and holes and it was sometimes very difficult to notice birds in incubation. Apart from searching for nests, we tried to determine the presence of ship rats that are one of the main threats for young birds. Unfortunately, all islands that we visited had indications of rat presence, which was visible from biting traces on olive pits or traces of their feaces. Last activity in June was setting acoustic recording devices. We have set them on familiar locations that are also potential nesting places for Scopoli’s shearwater so we can determine potential number of couples. To estimate the number, it was necessary to set at least one recording device on an island or on a location that we thought it would be the best spot for the estimation. Based on recordings from that location, it is possible to estimate the number even on other locations. We have set 20 recording devices on 14 islands that will continuously record the sound during the whole nesting season or until mid-September.

Measuring Scopoli’s shearwater, Author: Goran Šafarek