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Résumé :
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The Red-vented Bulbul (Pycnonotus cafer) is native to southern Asia and is an established invasive species in several tropical Pacific islands, parts of the Middle East, Spain, and Houston (Texas, USA), the focal region presented herein. Here, we assess recent range expansion, density, and population size. We used locality databases and the Map Maker program to measure bulbul range expansion. The range expanded from 589 km2 before June 2012 to 4,606 km2 during the following decade. By counties, there were 215 bulbul reports in Harris County before June 2012 (and none in surrounding counties), and 6,543 in the following decade, along with nearly 50 records in adjacent counties. Mean distance of outliers from the central population doubled from 27 km before June 2012 to 53 km during the following decade. To estimate minimum density and population size we conducted transect surveys for bulbuls January—March 2024 at four sites, repeating each transect 10 times. We estimated a mean population density of 8.77 bulbuls/km2 and a total population of 466 (range = 144–955) individuals within the 53.18 km2 core area. Although range size of the Houston bulbul is indeed expanding, it is not expanding rapidly, growing at approximately 400 km2/year. Additionally, recent outliers have appeared as far as 68 km from the center of the bulbul’s range, suggesting that expansion trajectories are continuing. Natural barriers (e.g. rivers, intracoastal waterways) and some highways appear to inhibit continued bulbul range expansion, as additional records are absent beyond these features.
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