As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Sunday 26 November 2017

More stress and lower survival rates for birds in young, managed forests


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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