The Chuck-will's-widow and the Whip-poor-will in a managed forest landscape: the effect of matrix habitats on distribution and abundance
Abstract
The Chuck-Will's Widow and the Whip-poor-will are nocturnal-insectivorous birds commonly known as "nightjars". Little information exists about their breeding ecology (including habitat requirements), in part, because their nocturnal habits are difficult to study. In fact, definitive survey methods have never been developed for these species. Both Whip-poor-wills and Chuck-Will's-widows appear to require forested habitat for nesting but frequently forage in open habitats. Because of this, these species may be sensitive to variation in intrinsic forest structure, as well as, the spatial context of forest patches. The purpose of this study was to investigate the influence of stand and landscape management on the distribution and abundance of nightjars within a managed forest system and to develop appropriate survey protocols. Nightjars were sampled between dusk and dawn within a network of 78 survey plots distributed throughout Weyerhaeuser's J&W management tract. The Whip-poorWill was overwhelmingly the most frequently encountered species (96% of all observations) being recorded within 87% of plots with an average density of 2.4 birds/lOOha. The Chuck-will's-widow was only detected within13% of plots and had an overall average density of0.3 birds/100ha. Landscape configuration had a significant influence on the abundance and distribution ofthe Whip-poor-will. Forested stands bordered by similar habitat supported lower bird densities compared to forested stands bordered by open (1-5 year old stands) or mid-rotation age (7-10 year old) stands. Whippoor- will's were more frequently encountered in mid-rotation age stands compared to forested stands. Results indicate that Whip-poor-wills responses to landscape structure were due to proximity and use of foraging habitats. The Chuck-will's Widow was not compared in this fashion because of a low number of detections. Lunar light intensity had a significant effect on the probability of detecting nightjars. The highest probability for detecting nightjars occurred when the moon was 75-100% illuminated. Future nighjar surveys should consider lunar phase and moon height above the horizon. In general, repeated surveys are needed to increase the probability of detecting all nightjars in a given area.
