Red‐winged blackbirds nesting nearer to yellow warbler and conspecific nests experience less brood parasitism

• Published in: Ecology and evolution Vol. 13; no. 2; pp. e9818 - n/a
• Main Authors: Lawson, Shelby L., Enos, Janice K., Gill, Sharon A., Hauber, Mark E.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.02.2023; John Wiley and Sons Inc; Wiley
• Subjects: Antiparasitic agents; Behavioural Ecology; Birds; Brood parasitism; brown‐headed cowbirds; Communications systems; Conspecifics; Eavesdropping; Eggs; Nature Notes; neighboring species; Nesting; Nests; Parasites; Parasitism; Probability; red‐winged blackbird; referential alarm calls; Regression analysis; yellow warbler; brown‐headed cowbirds; referential alarm calls; yellow warbler; neighboring species; red‐winged blackbird
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.9818

In functionally referential communication systems, the signaler's message intended for a conspecific receiver may be intercepted and used by a heterospecific eavesdropper for its own benefit. For example, yellow warblers (Setophaga petechia) produce seet calls to warn conspecifics of nearby brood parasitic brown‐headed cowbirds (Molothrus ater), and red‐winged blackbirds (Agelaius phoeniceus) eavesdrop on and recruit to seet calls to mob the brood parasites. Prior work found that warblers nesting closer to blackbirds were less likely to be parasitized, suggesting that blackbirds may even be the target of warbler's seet calls to assist with antiparasitic defense. Here we discovered for the reverse to apply too: blackbirds nesting closer to yellow warblers also experienced lower probability of brood parasitism. Concurrently, we also found that blackbirds nesting closer to other blackbirds also experience lower parasitism rates. Although these are strictly correlational results, they nonetheless suggest that blackbirds are better able to defend their nest against cowbirds when also listening to nearby warblers' referential alarm calls. Yellow warbler hosts of brood parasitic brown‐headed cowbirds respond to parasites with referential alarm calls. Red‐winged blackbirds respond to these alarm calls with anti‐cowbird defenses. We discovered that nests of blackbirds that are closer to warblers have lower parasitism rates.