Diet shift induced rapid evolution of size and function in a predatory bird

Area of Science:

• Avian biology
• Evolutionary morphology
• Ecology

Background:

• Predator body size typically correlates with prey size.
• Dietary shifts necessitate adaptations in hunting strategies and traits.

Purpose of the Study:

• To investigate long-term trends in northern goshawk sternum size and shape.
• To correlate these changes with shifts in prey availability and hunting modes.

Main Methods:

• Geometric morphometrics applied to museum specimens of northern goshawks (1962-2008).
• Analysis of sternum size and shape in relation to sex, prey type, and cause of death (starvation vs. accidental).

Main Results:

• Goshawk body size decreased in both sexes, reflecting a shift from tetraonids to smaller avian prey.
• Sternum shape evolved towards a "Buteo-type" in both sexes, correlating with smaller prey and potentially indicating selection for agility.
• A "Buteo-type" sternum was more prevalent in "fit" individuals (accidental death) than starved individuals, suggesting selective advantage.

Conclusions:

• Observed morphological changes in goshawks are likely driven by directional selection due to dietary shifts towards smaller, more agile prey.
• Global warming may also contribute to body size decrease, making the scenarios inseparable.
• Museum collections are valuable for studying long-term phenotypic changes in large raptors.