Reproductive success of three parid species in managed boreal forests

Anthropogenic impacts, such as forestry and land use practices, can
deteriorate habitat quality, affecting reproductive success and leading to
population decline. The boreal willow tit (Poecile montanus) population
has dramatically declined in Finland. In contrast, great tits (Parus
major) and blue tits (Cyanistes caeruleus), both of temperate origin, have
expanded their ranges and increased in numbers in Northern Finland. It has
been suggested that the decline in the willow tit population is mainly
caused by the reduction of breeding sites and wintering areas resulting
from habitat loss and degradation. We investigated whether forest
management influences the reproductive success of willow tits, great tits,
and blue tits, including recruitment across years, while considering other
factors such as possible intra- and interspecific competition. We combined
long-term breeding data (1990-2020) from Oulu, Finland, with spatial data
on forest management activities and analysed the data using (generalized)
linear mixed-effect models. Results varied depending on the breeding
parameter, species, and forest management method. Forestry had no
significant effect on clutch size. We found negative effects of thinnings
on nestling survival and growth in great and blue tits, with
clear-cuttings negatively affecting blue tit nestling growth. However,
recent clear-cuttings had positive effects on willow tit nestling survival
and growth. Despite these benefits, clear-cuttings near nesting sites were
associated with reduced willow tit local recruitment probability, leading
to an overall negative impact on the population. These findings may arise
from forest management influences on food availability; certain stages
following clear-cutting may improve the food availability for boreal
willow tit nestlings, yet thinnings may reduce foraging opportunities for
great tits and blue tits. While some positive effects of forestry on
willow tits were recorded, they may not be enough to offset the
well-established negative impacts of forestry on the loss of optimal
wintering and breeding habitats.