Evolution of tail fork depth in genus Hirundo.

Area of Science:

• Evolutionary biology
• Ornithology
• Animal behavior

Background:

• The deep fork tail of barn swallows (Hirundo rustica) was traditionally considered a sexually selected trait.
• Recent hypotheses suggest aerodynamic advantages, but lack detail on flight habits driving tail diversity.
• The evolutionary drivers of tail fork depth variation in hirundines remain debated.

Purpose of the Study:

• To investigate if differential flight habits explain the variation in tail fork depth within the Hirundo genus.
• To test the role of migration and foraging strategies in shaping tail morphology.
• To differentiate between sexual selection and flight-related advantages in tail evolution.

Main Methods:

• Phylogenetic comparative analysis across the Hirundo genus.
• Correlating tail fork depth with migratory status.
• Assessing the relationship between tail fork depth and bill size (as a proxy for prey size).

Main Results:

• Migratory species within the Hirundo genus exhibit deeper fork tails compared to non-migratory species.
• Migratory species also show less colorful plumage.
• Tail fork depth decreases with increasing bill size, suggesting shallower tails are favored when foraging on larger prey.

Conclusions:

• Differential flight habits, particularly migration, can explain the variation in tail fork depth in the Hirundo genus.
• Foraging on larger prey items may favor shallower fork tails.
• The evolution of deep fork tails in barn swallows may be primarily driven by aerodynamic advantages linked to flight, rather than sexual selection.