The usefulness of top predators as biodiversity surrogates indicated by the relationship between the reproductive outputs of raptors and other bird species

Abstract

Given the global reduction in biodiversity, conservation actions must occur even with only a partial understanding of the distribution and abundance of species in various locales. The concept of surrogate species, those whose protection affords the protection of other species, is considered a conservation short-cut. Although surrogate species have been used as practical conservation tools, whether they serve as indicators of the reproductive output of other species is still unknown. We hypothesized that the reproductive output of the eastern marsh harrier (Circus spilonotus) can serve as a surrogate for both the adult abundance and reproductive output of sympatric birds. In a fragmented wetland landscape (approximately 211.60km2), we measured the reproductive output of harriers for 3years and conducted replicated counts of the adults and juveniles of other wetland bird species in wetland patches that varied in harrier reproductive output. We used playbacks of mobbing calls in replicated counts and accounted for imperfect detection using an N-mixture model. We modeled adult and juvenile abundances for 10 and 7 species, respectively, and showed that the reproduction-based habitat quality of the marsh harrier (cumulative numbers of both years occupying the habitat and chicks produced) was positively associated with adult abundances in four species and with juvenile abundances in five species. We suggest that areas with high reproductive output of several sympatric bird species could be selected based on the reproduction-based habitat quality of the marsh harrier. Furthermore, the approach combining the playback of mobbing calls and N-mixture models enabled us to estimate juvenile abundances for many bird species on a landscape scale over a short period of time.