2.1. Study sites
This study was carried out in 2020 in two different habitats: an urban
parkland and a deciduous forest. The study sites are located
~ 10 km apart and are separated by the city of Łódź. The
urban parkland study site (51º45’N; 19º24’E) consists of Łódź Botanical
Garden, which covers a total area of approximately 67 ha. It is mainly
of anthropogenic origin and has fragmented tree and bush cover with very
few remnants of natural stands including birches (Betula
pendula ), beeches (Fagus sylvatica ) and numerous alien species
planted intentionally by garden administrators (Glądalski et al., 2016).
The forest study site (51°50’ N;19°29’ E) is an area of approximately
145 ha located in the interior of a rich, mature mixed deciduous forest
called the Łagiewniki Forest (1250 ha in total). Oaks (Quercus
robur and Q. petrea ) are the dominant tree species in the
forest. Both study sites were supplied with standard wooden nest boxes,
each made of pinewood (200 in the parkland area and 300 in the forest
area). After each breeding season in mid-October, each nest box was
cleaned with a wire brush, so there were no visible nest remnants.