I started to work on my MSc thesis in 2022, which evolved to my PhD project in 2023 at the Lammi Biological Station. Since then, me and my supervisor, Juha Tiainen have spent three summers busy with catching birds and collecting insects from lakes and forests.
Long-term flood in a small forest lake increases nutrient leaching from the surrounding terrestrial ecosystem. This increases biological production in the food web of the lake, which is seen in, e.g., bigger numbers and biomass of invertebrates emerging to the above-water environment. Such a years-lasting flood is often induced by beavers.
The changes of the lake ecosystem resulting from beaver-induced eutrophication is well studied in the Evo region. Research has been made on duck numbers and offspring production as well as bat numbers in various kind of flooded and non-flooded lakes. However, nothing is known about the flood-induced impact on terrestrial bird populations. Therefore, we designed a study to investigate the impact of beavers on a small passerine species, the pied flycatcher.
The study design composed of sets of four study plots in Evo area, one at a beaver lake, one at a non-beaver lake, and terrestrial control plots for both lakes. Pied flycatchers were provided with nest boxes along shore lines or road sides, either 20 boxes in each study plot (one set; studied in 2022–2024) or 10 boxes in each study plot (two sets; studied in 2024). Hence, the total number of nest-boxes is 160.
We aimed to investigate differences in breeding performance of the pied flycatcher between study plots and to find out how the differences are related to food (as insects) quantity and quality for birds.
Invertebrates were collected from lakes and forest areas every week from the beginning of May to the end of July. Aquatic emerging macroinvertebrates were caught with emergence traps from the surface of lakes, while terrestrial insects were collected with window traps from shorelines and forests. After collection, we sorted, identified and dry-weighed the insects in the laboratory of Lammi Biological Station. These insect samples are used in fatty-acid composition analyses to determine the difference and importance between aquatic and terrestrial originated food items for the birds.
Pied flycatchers, breeding monitoring
When establishing study plots, the nest-boxes were put in rows at ca. 50-m distances from each other. To ensure that boxes were available for pied flycatchers at arrival from migration, their entrances were opened not before the second week of May. The boxes were closed in the autumn to prevent tit accommodation during the winter.
The goal was to get sufficient information from each study plot and for each year about the number of nests, timing of breeding, clutch size, hatching and fledging success, and nestling growth as we measured wing length and mass.
All the boxes were checked once or twice every week throughout the whole breeding season from mid-May to mid-July. All the females were caught, measured and ringed, and many males were treated similarly.
Analyses of fatty-acid composition of invertebrates and bird blood samples
During the season, we also took blood samples from the parents and nestlings in 2023 and 2024. We carefully collected ~70 microlitre of blood from the birds, which is less than the amount of one small capillary tube. After sampling, we separated blood plasma and red blood cells in the lab, and I am going to use the plasma to find out the fatty acid composition of the birds’ blood. When we compare these results with the findings of the same analyses with the insect samples, we will be able to tell how much aquatic-food they eat and we can describe the importance of aquatic habitats for terrestrial consumers.
After over a year now, that I (Eszter) call LBS my home as well, I have met many amazing people here and I have learnt a lot from them. This place is a home for very diverse research, but also for friendships and great community. So here, I would like to thank those people, who have effortlessly helped and supported me during my fieldwork campaigns, especially the interns, without whom I could have not succeeded. You are huge pillars of our research; and great friends too!
And for me (Jussi), having started with Phylloscopus warblers and pied flycatchers at the station area in 1972, this jump to Evo forests has been an enjoyable hard job (excepting the fight with horseflies) and recovery of old interests.
Lastly, we would like to thank LBAYS for supporting us, the grants were essential for this research to be carried out.