Selectivity and ecological consequences of cavity nesters using natural vs. artificial nest sites

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Secondary cavity nesters will use nest boxes in lieu of tree cavities in managed forests. Information on use of artificial vs. natural cavities is fragmentary, but preference for boxes is sometimes observed. This may indicate variation in quality of nest sites regarding expected reproductive success. l observed nest-site choice by breeding birds in northern Arizona and offer an alternate hypothesis for nestsite preference. An alternative hypothesis is that relative densities of artificial vs. natural cavities can influence occupancy of a given nest type. Ratios of nest boxes to dead trees on the Dense, Thinned, and Open plots were approximately 1.5, 3.0, and 9.0, respectively. If boxes and natural cavities were used according to their availability, the frequency of box occupancy on the Dense and Thinned plots should have been similar. Yet, 94% of the nests on the Thinned plot were in boxes. I propose that prospective breeders "switch" to the most frequently encountered cavity type. About 70% of the boxes on the Dense plot were never occupied. Thick vegetation may have prevented their detection. Switching behavior could benefit birds attempting reproduction by reducing time spent searching for potential nest sites. Secondary cavity nesters, especially first-time breeders, often inspect many cavities prior to selection of a nest site. How birds locate cavities merits investigation. Field experiments that vary the ratio of artificial to natural cavities within similar habitats could test the hypothesis that selectivity is frequency dependent.

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Reference Code: A88BRA02IDUS

Full Citation: Brawn, J. D. 1988. Selectivity and ecological consequences of cavity nesters using natural vs. artificial nest sites. Auk 105(4): 789-791.

Location: ANIMAL EF: BIRDS