Crossbills are specialist finches whose crossed bills are uniquely adapted to extracting seeds from conifer cones, with welfare tied to conifer mast cycles.
Crossbill welfare is highly dependent on conifer seed availability, which fluctuates dramatically between years. In boom years with abundant cone crops, crossbills breed prolifically regardless of season. In mast failure years, food scarcity causes starvation and drives irruptive movements of thousands of birds across Europe. Nest timing outside spring means breeding can coincide with poor weather, with welfare implications for egg and chick survival in cold winters. Conifer plantation management that removes mature seed-bearing trees reduces food availability. Scottish crossbill welfare is particularly precarious given dependence on Caledonian pine forest that occupies a tiny remnant of its original extent. Maintaining diverse age-structured native pine forest is essential for Scottish crossbill welfare.