Interspecific competition between resident and wintering birds: experimental evidence and consequences of coexistence

Powell, Luke L.; Ames, Elizabeth M.; Wright, James R.; Matthiopoulos, Jason; Marra, Peter P.

Abstract

The contribution of interspecific competition to structuring population and community dynamics remains controversial and poorly tested. Specifically, interspecific competition has long been thought to influence the structure of migrant‐resident bird communities in winter, yet experimental evidence remains elusive. The arrival of billions of songbirds into Neotropical habitats, where they co‐exist with residents, provides a unique opportunity to assess interspecific competition and its consequences. Working in 15 ha of Jamaican black mangrove forest, we used removal experiments to test whether dominant resident Yellow Warblers compete interspecifically with subordinate wintering American Redstarts; we also used observational evidence (interspecific territorial overlap) to understand whether this coexistence influences physical condition, spring departure dates or annual return rates. Consistent with interspecific competition, after experimental removal of the resident, yearling male redstarts (but not females or adult males) immediately into vacated Yellow Warbler territories, increasing their overlap with the space by 7.3%. Yearling redstarts also appeared to adjust their territorial space use by actively avoiding Yellow Warblers; for example, redstarts departing the wintering grounds as yearlings and returning the following winter shifted such that their territories overlapped 32% less with those of Yellow Warblers. Adult redstarts showed no such territorial flexibility. Adult male redstarts also showed evidence supporting the consequences of coexistence: territorial overlap with Yellow Warblers was negatively correlated with body condition and annual return rates. Adult male redstarts with <25% territorial overlap with Yellow Warblers were more than three times as likely to return between seasons than those with 100% overlap. We propose that the territorial inflexibility of adult male redstarts produces these consequences, which may be due to their years‐long investment in that particular territory. More generally, the temporary nature of migrant‐resident interspecific competition is likely what allows coexistence during winter, the most resource poor time of year. Our observations suggest that interspecific competition and the consequences of coexistence are age‐ and sex‐specific and the product of intraspecific dominance hierarchy in redstarts. Our observations suggest that interspecific coexistence has measurable consequences, and our experiments support the long‐held, but previously untested belief that resident birds compete interspecifically with wintering migrants.

Citation

Powell, L. L., Ames, E. M., Wright, J. R., Matthiopoulos, J., & Marra, P. P. (2020). Interspecific competition between resident and wintering birds: experimental evidence and consequences of coexistence. Ecology, 102(2), Article 03208. https://doi.org/10.1002/ecy.3208

• Journal Article Type: Article
• Acceptance Date: Aug 7, 2020
• Online Publication Date: Jan 21, 2021
• Publication Date: 2020
• Deposit Date: Oct 15, 2020
• Publicly Available Date: Oct 15, 2020
• Journal: Ecology
• Print ISSN: 0012-9658
• Publisher: Ecological Society of America
• Peer Reviewed: Peer Reviewed
• Volume: 102
• Issue: 2
• Article Number: 03208
• DOI: https://doi.org/10.1002/ecy.3208
• Public URL: https://durham-repository.worktribe.com/output/1260004