Perch-Mounted Camera Traps Record Predatory Birds in Farmland
Artificial perches can attract raptors to farmland, where the raptors perform an ecosystem service by consuming insect or rodent pests; however, such perches have not enjoyed widespread use. We used an improved camera trap installation method to record birds on perches, and to test perch height preference of raptors and other species. Our study area was in a mosaic agriculture system, the typical farming environment in Asia. Our “double-branch” perches consisted of a main pole with a branch at the top and in the middle, 8 and 4 m from the ground, respectively. Each branch was equipped with a camera trap, with the focus adjusted to close range. From April to July 2020, the installations at five different crop fields provided a total of 83,740 photographs with birds, including 27 avian species. Photographs of raptors and insectivorous birds accounted for 80.1% to 99.7% in each field. The most frequently recorded raptors were the Black-winged Kite (Elanus caeruleus) and the Collared Scops-Owl (Otus lettia). The most frequently recorded insectivorous birds were the Black Drongo (Dicrurus macrocercus) and the Brown Shrike (Lanius cristatus). The kites preferred to stand on the upper branches, whereas the owls and most of the insectivorous birds tended to choose the lower branches. By our method, numerous clear photographs of birds can be obtained and used to analyze visit frequency, activity patterns, and captured prey. Moreover, we showed that different species used artificial perches of different heights. Artificial perches could be more widely used for enhancing and quantifying avian ecosystem services, and promoting raptor-friendly farming. Cámaras Trampa Montadas en Posaderos Registran Aves Depredadoras en Tierras Agrícolas Los posaderos artificiales pueden atraer aves rapaces a las tierras agrícolas, donde las aves rapaces realizan un servicio ecosistémico al consumir plagas de insectos o roedores; sin embargo, estos posaderos no han gozado de un uso generalizado. Usamos un método mejorado de instalación de cámaras trampa para registrar aves en posaderos y para probar las preferencias de altura de los posaderos de las rapaces y otras especies. Nuestra área de estudio estuvo ubicada en un sistema de agricultura en mosaico, el entorno agrícola típico en Asia. Nuestros posaderos de “doble rama” consistieron en un poste principal con una rama en la parte superior y otra en el medio, a 8 y 4 m del suelo, respectivamente. Cada rama estuvo equipada con una cámara trampa, con el enfoque ajustado a corta distancia. De abril a julio de 2020, las cámaras instaladas en cinco campos de cultivo diferentes proporcionaron un total de 83.740 fotografías con aves, incluyendo 27 especies de aves. Las fotografías de aves rapaces y aves insectívoras representaron del 80.1% al 99.7% en cada campo. Las rapaces registradas con mayor frecuencia fueron Elanus caeruleus y Otus lettia. Las aves insectívoras registradas con mayor frecuencia fueron Dicrurus macrocercus y Lanius cristatus. E. caeruleus prefirió pararse en las ramas superiores, mientras que O. lettia y la mayoría de las aves insectívoras tendieron a elegir las ramas inferiores. Con nuestro método, se pueden obtener numerosas fotografías claras de aves y utilizarlas para analizar la frecuencia de las visitas, los patrones de actividad y las presas capturadas. Además, mostramos que diferentes especies usaron posaderos artificiales de diferentes alturas. Los posaderos artificiales podrían usarse de forma generalizada para mejorar y cuantificar los servicios ecosistémicos proporcionados por las aves y promover una agricultura amigable con las aves rapaces. [Traducción del equipo editorial]ABSTRACT
RESUMEN
(a) The double-branch perch set up in field D. (b) The camera trap setup, showing the perch deterrents placed on the branch and the camera. (c) A polyvinyl chloride (PVC) water pipe was buried in the ground to facilitate the insertion and withdrawal of the main pole of the perch. (a) and (c) were taken by Shiao-Yu Hong, and (b) was taken by Yun-Chieh Hunag.
Average percentages of photographs taken per species per day in each field. Totals shown represent photographs taken by the cameras on the upper and lower branches combined. The numbers in parentheses on the x-axis indicate the average number of photographs taken per day in each field. The solid and patterned segments of the bars represent raptors and insectivorous birds, respectively. The segments with dots represent the granivorous, frugivorous, and omnivorous birds. The open segments denote species that accounted for <2% of the photographs taken in each field. Species names: Black-winged Kite (Elanus caeruleus), Collared Scops-Owl (Otus lettia), Black Drongo (Dicrurus macrocercus), Brown Shrike (Lanius cristatus), Savanna Nightjar (Caprimulgus affinis), Plain Prinia (Prinia inornata), Gray Treepie (Dendrocitta formosae), Eurasian Tree Sparrow (Passer montanus), Light-vented Bulbul (Pycnonotus sinensis), Red Turtle-dove (Streptopelia tranquebarica).
Sample photographs of the most frequently recorded bird species. (a) Black-winged Kite in field B. (b) Collared Scops-Owl in field A. (c) Black Drongo in field C. (d) Brown Shrike in field E. (a) and (b) were taken using the KeepGuard 795, whereas (c) and (d) were taken using the Ereagle E1B.
The mean number (bars) and SD (brackets) of photographs taken per day of the four most frequent raptors and insectivorous birds by camera traps placed on the upper and lower branches of artificial perches. We included only species that appeared on >10 d per field, when both the upper and lower camera traps were operating. The brackets after each study field (n) show the number of days analyzed by paired t-tests (*** indicates P < 0.001, ** P < 0.01). For results on less common species, see Fig. S3.
Contributor Notes
1 Email address: ysun@mail.npust.edu.tw
Associate Editor: Ian G. Warkentin