Non-native invasive beetle alters structure of a riparian bird community in a biodiversity hotspot

Frontiers in Ecology and Evolution
By: , and 

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Abstract

A serious emerging threat to southern California riparian ecosystems is the invasive shot hole borer (Euwallacea spp.; SHB), a non-native beetle that cultivates a pathogenic fungus that kills trees of 66 reproductive host species. We examined the response of the bird community at the Tijuana River, California, to a massive SHB infestation in 2015 using data from a Monitoring Avian Productivity and Survivorship (MAPS) station operated during 7 pre-infestation (2009-15) and 7 post-infestation (2017-23) years. Species richness did not change between pre- and immediate (2017-18) post-SHB periods, but average annual adult captures declined by 27%. Among the species making up ≥ 5% of the total individuals caught in any one year (n=15), abundance declined by up to 76% in 10 species, including those most abundant at the station (Bushtit (Psaltriparus minimus), Song Sparrow (Melospiza melodia), Common Yellowthroat (Geothlypis trichas), Orange-crowned Warbler (Leiothlypis celata), and Wilson’s Warbler (Cardellina pusilla)). Mean annual abundance increased slightly for the endangered Least Bell’s Vireo (Vireo bellii pusillus) and Northern Yellow Warbler (Setophaga aestiva) and doubled for House Finch (Haemorhous mexicanus) and Western Warbling-Vireo (V. swainsoni). We compared species trends at the Tijuana River to those at a nearby uninfested MAPS station on the Santa Margarita River to isolate the effect of SHB from other factors influencing annual abundance. The contribution of SHB to changes in abundance post-SHB was high (63-80%) for 7 declining species, moderate (22-45%) for 4 species, and weakly to moderately positive (18-40%) for 3 species. By 2019, the SHB infestation at the Tijuana River had abated and canopy cover was recovering through resprouting of mature willows (Salix spp.) and seedling establishment. Bird abundance tracked this regrowth, with all of the species strongly affected by SHB increasing between 2019-23. The rapid recovery of the Tijuana River habitat and the associated response by the bird community are encouraging signs that the threat of the invasive shot hole borer to regional biodiversity may not be as great as originally anticipated.

Suggested Citation

Kus, B., Yee, J.L., and Mendia, S., 2026, Non-native invasive beetle alters structure of a riparian bird community in a biodiversity hotspot: Frontiers in Ecology and Evolution, v. 14, 1810966, 9 p., https://doi.org/10.3389/fevo.2026.1810966.

ISSN: 2296-701X (online)

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Publication type Article
Publication Subtype Journal Article
Title Non-native invasive beetle alters structure of a riparian bird community in a biodiversity hotspot
Series title Frontiers in Ecology and Evolution
DOI 10.3389/fevo.2026.1810966
Volume 14
Publication Date April 22, 2026
Year Published 2026
Language English
Publisher Frontiers Media
Contributing office(s) Western Ecological Research Center
Description 1810966, 9 p.
Country United States
State California
County San Diego County
Other Geospatial Tijuana River and Santa Margarita River Monitoring Avian Productivity and Survivorship (MAPS) stations
Additional publication details