A long-term study of size variation in Northern Goshawk Accipiter gentilis across Scandinavia, with a focus on Norway

Changing climate and growing human impacts are resulting in globally
rising temperatures and the widespread loss of habitats. How species will
adapt to these changes is not well understood. The Northern Goshawk
(Accipiter gentilis) can be found across the Holarctic but is coming under
more intense pressure in many places. Studies of recent populations in
Finland and Denmark have shown a marked decline in body size of Northern
Goshawks over the past century. Here we investigate long-term changes to
Norwegian populations of Northern Goshawk by including material from the
Middle Ages. We measured 240 skeletons of modern Northern Goshawks from
Norway, Sweden, Denmark and Finland, and 89 Medieval Goshawk bones. Our
results show that Norwegian and Swedish female Goshawks have decreased in
size over the past century, whilst males showed little decline. Medieval
female Goshawks were larger than contemporary females. A decline in forest
habitats and a concomitant shift towards smaller prey likely drove a shift
to smaller body size in Northern Goshawks. Our study shows that
significant body size changes in birds can occur over relatively short
time spans in response to environmental factors, and that these effects
can sometimes differ between sexes.