Multidimensional natal isotopic niches reflect migratory patterns in birds.

Area of Science:

• Ecology
• Zoology
• Biogeochemistry

Background:

• Stable isotope ratios in animal tissues indicate trophic position and ecological niche.
• Migratory bottlenecks provide opportunities to sample diverse populations and species across continental scales.

Purpose of the Study:

• To investigate migratory strategies and niche breadth using stable isotopes in 21 bird species at an Italian Alps migratory bottleneck.
• To compare dietary and breeding origin niche breadth among long-distance trans-Saharan (TS), short-distance intra-Palearctic (IP), and irruptive (IR) migrants.
• To assess the correlation between niche breadth and reported population trends.

Main Methods:

• Measurement of stable isotopes (δ²H, δ¹⁸O, δ¹³C, δ¹⁵N) in juvenile bird feathers.
• Analysis of isotopic trends in relation to capture date and migratory strategies (Type-I migration).
• Comparison of niche breadth (dietary and breeding origin) among different migratory groups (TS, IP, IR).

Main Results:

• δ²H values indicated that TS migrants have broader breeding ranges extending further north than IP and IR migrants.
• TS migrants exhibited wider breeding origin niche breadth, suggesting a link between long-distance migration and broader ecological niches.
• No significant relationship was found between breeding niche breadth and European population trends.

Conclusions:

• Stable isotope analysis at migratory bottlenecks is valuable for studying large-scale life-history phenomena in birds.
• Long-distance migration in birds is associated with wider breeding ecological niches.
• Breeding ground conditions, as inferred by isotopes, are not the sole factor determining long-term species persistence.