Occupancy modeling reveals territory-level effects of nest boxes on the presence, colonization, and persistence of a declining raptor in a fruit-growing region

Abstract

Nest boxes for predators in agricultural regions are an easily implemented tool to improve local habitat quality with potential benefits for both conservation and agriculture. The potential for nest boxes to increase raptor populations in agricultural regions is of particular interest given their positions as top predators. This study examined the effects of cherry orchard nest boxes on the local breeding population of a declining species, the American Kestrel (Falco sparverius), in a fruit-growing region of Michigan. During the 2013–2016 study, we added a total of 23 new nest boxes in addition to 24 intact boxes installed previously; kestrels used up to 100% of our new boxes each season. We conducted temporally-replicated surveys along four roadside transects divided into 1.6 km × 500 m sites. We developed a multi-season occupancy model under a Bayesian framework and found that nest boxes had strong positive effects on first-year site occupancy, site colonization, and site persistence probabilities. The estimated number of occupied sites increased between 2013 and 2016, which correlated with the increase in number of sites with boxes. Kestrel detections decreased with survey date but were not affected by time of day or activity at the boxes themselves. These results indicate that nest boxes determined the presence of kestrels at our study sites and support the conclusion that the local kestrel population is likely limited by nest site availability. Furthermore, our results are highly relevant to the farmers on whose properties the boxes were installed, for we can conclude that installing a nest box in an orchard resulted in a high probability of kestrels occupying that orchard or the areas adjacent to it.

Nest sites as a key resource for population persistence: A case study modelling nest occupancy under forestry practices

“…The results of the present study show that nests are important breeding resources for forest raptors and should be preserved as part of forestry practice. Our conclusions agree with previous studies of other raptor species [ 16 , 62 , 64 ], as well as cavity-nesting species [ 11 , 17 , 23 , 65 ]. Moreover, our results corroborate previous studies in our study system that state that all nest trees should be kept in order to preserve an adequate supply of breeding sites for raptors [ 4 ].…”

“…Other management measures such as the provision of artificial nest sites [ 72 ] have been successfully applied in the case of secondary cavity-nesting birds (mostly insectivorous birds and raptors) such as kestrels [ 16 ]. However, some birds use dense forests where these artificial structures may not improve populations; for example, these nests may function as ecological traps in the case of forest-dwelling raptors [ 41 ].…”

“…In several bird species, the same nest can be maintained and reused over long periods of time [ 7 , 8 , 9 ], and interspecific competition may occur when this breeding resource is limited [ 10 ]. Indeed, nests are a key resource for population persistence and the conservation of many species, and the availability of nesting platforms and cavities is essential for long-term territorial occupancy [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

Falcons using orchard nest boxes reduce fruit‐eating bird abundances and provide economic benefits for a fruit‐growing region

“…Our bird survey results, combined with the high kestrel reproductive rates observed for boxes in the study region (Shave & Lindell, ), indicate that orchard nest boxes are effective tools that can enhance regulating ecosystem services while also sustaining or increasing the local kestrel breeding population (Shave & Lindell, ). Kestrel presence was particularly valuable in deterring fruit‐eating birds in sweet cherry orchards and also significantly reduced fruit‐eating bird abundance in tart cherries.…”

“…For this and other reasons, box occupancy rates will undoubtedly vary across landscapes and regions (Smallwood et al., ). However, costs to install and maintain boxes are small and, even if box occupancy rates are low, boxes can direct kestrel activity to particular places in agricultural landscapes (Shave & Lindell, ) where they can reduce pest bird activity. Thus, the potential benefits in fruit crops greatly outweigh the costs of this pest management strategy.…”