Bird diversity changes in Tervasaari, Savonranta, Finland from 1989 to 2023

Birds are sensitive to climate and environmental changes and monitoring the abundance and distribution of bird populations can be excellent barometers of the health of the environment. To investigate bird diversity changes, a hobby like birding was done from May 1989 until July 2023 on a forested island, at Lake Orivesi in Eastern Finland. The main observation area was some 1 km to all directions from the house mainly used for summer holidays. A total of 145 bird species were identified during the 34 years, 108 during the first period 1989–2000, 102 during the second 2001–2013 and 114 during the third period 2014–2023. Abundance classification listed 48% of species as common, 20% as rare and 32% as occasional. The population trend for 80% of bird species seen more than once or one year in 17% of species have upward trend, in 16% of species trend is downwards and the remaining 67% of species are not showing any clear changes. Bird feeding attracted 28% of species mainly during the winter but later also almost all year around. Interesting behaviour changes have been noted at individual and species levels during the feeding activity and in the use of the nest boxes.