November 14, 2017
Birds experience less stress
during the winter months when they shelter in old forests rather than in
younger, managed plantations suggests new research. The study in Springer's
journal The Science of Nature was led by Indrikis Krams of the
University of Latvia and the University of Tartu in Estonia.
Forestry activities are
increasingly causing the fragmentation and deterioration of old growth forests,
and these affect the diversity of plant and animal species. In Northern Europe,
for example, a decrease in old, natural forests has been linked to the
population decline of many insect-eating forest bird species because their
typical wintering and breeding habitats are disrupted. Having enough food to
eat and being in good physical condition is crucial if birds are to survive
cold spells and snow storms.
Krams' team focused on willow
tits (Poecile montanus), a small type
of insect-eating bird found widely throughout temperate and subarctic Europe
and Northern Asia. During the non-breeding winter periods, willow tits flock
together in coniferous trees to feed on arthropods such as insects and spiders.
Previous research has shown that the canopies of mature coniferous trees
contain more food than younger ones because arthropods prefer older branches
that have more needles attached to them.
This study was conducted in south
eastern Latvia in young, managed Scots pine plantations between 35 and 55 years
old and unmanaged forests up to 155 years old of mostly Norwegian spruce. The
98 birds from different flocks included in the study were caught twice: once
during mild conditions, and again when temperatures were very low. They were
weighed and banded, and the researchers evaluated the amount of underskin fat
and the condition of their breast muscles. Blood samples were taken immediately
after the birds were caught, and then again twenty minutes later to ascertain
the effect of being handled. This was done to measure the levels of the stress
hormone plasma corticosterone (CORT) in the blood.
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