Utilizing artificial nesting platforms as a management tool: enhancing breeding productivity of Western Flycatchers ( Empidonax difficilis occidentalis ) in southwestern Colorado and southern Arizona, USA

Abstract

Artificial nesting substrates have been added around the world for many cavity-nesting bird species, but this has not been undertaken as extensively for crevice-nesting birds. The Western Cordilleran Flycatcher (Empidonax difficilis occidentalis) is a migratory, crevice-nesting flycatcher that is nest-site limited, breeding in higher elevation riparian habitats throughout intermountain western North America. We tested the effectiveness of multiple artificial nesting platform types that this flycatcher would accept for nesting, and then utilizing the successful design established an experimental array of platforms in southwestern Colorado and southern Arizona. From 2008 to 2022 we documented Cordilleran Flycatcher breeding and the influence of nesting platforms on productivity of young and adult numbers. Breeding behaviors did not differ significantly between natural nest sites and platform nests, except that the nestling period was an average of 16.73 (+/-0.98) days on platforms as compared to 15.92 (+/-0.71) on human structures and 15.67 (+/-0.48) days in natural locations. Platform nests had lower predation rates and greater rates of successful fledging when compared to natural locations. At both study locations platform nests doubled the number of young fledged each year. In Colorado, where Western Cordilleran Flycatchers were initially absent from areas, adult numbers increased following introduction of platforms, but in Arizona adult flycatcher numbers were not affected. Our findings demonstrate that the addition of artificial nesting platforms can enhance productivity and numbers of Western Cordilleran Flycatchers, and we hope that our findings will prove useful for the conservation of other crevice-nesting bird species.RESUMEN. Los sustratos de anidamiento artificiales han sido usados alrededor del mundo para muchas especies de aves que anidan en cavidades, pero no se han empleado para aves que anidan en grietas. El Mosquero Cordillerano (Empidonax difficilis occidentalis) es un atrapamoscas migratorio que anida en grietas, y que está limitado por sitios de anidamiento, reproduciéndose en hábitats ribereños a mayor elevación a lo largo del oeste inter-montañoso de Norte América. Nosotros evaluamos la efectividad de múltiples tipos de plataformas de anidamiento artificiales que este atrapamoscas podría aceptar para anidar; y luego, utilizando el diseño exitoso, se estableció un arreglo experimental de plataformas en el suroeste de Colorado y el sur de Arizona. Desde 2008 a 2022 documentamos la reproducción del Mosquero Cordillerano y la influencia de las plataformas de anidamiento en la productividad de números de juveniles y adultos. Los comportamientos de reproducción no variaron significativamente entre nidos naturales y nidos en plataformas, excepto que el periodo de anidamiento fue en promedio de 16.73 (+/-0.98) días en plataformas en comparación con 15.92 (+/-0.71) días en estructuras humanas y 15.67 (+/-0.48) días en sitios naturales. Los nidos en plataformas tuvieron tasas de depredación más bajas y...