Main content area

Bobolink reproductive response to three hayfield management regimens in southern Ontario

Diemer, Kristen M., Nocera, Joseph J.
Journal for nature conservation 2016 v.29 pp. 123-131
agroecosystems, birds, breeding, breeding sites, farmers, fledglings, forage quality, grasslands, habitats, harvest date, hay, mortality, phenology, population dynamics, protein content, reproductive success, Ontario, Vermont
Incidental mortality of bobolinks (Dolichonyx oryzivorus) breeding in agricultural grasslands has long been known to contribute to population declines, though generalized recommendations for conservation that balance bird reproduction and farmer production needs have remained elusive. We evaluated three hayfield management strategies in southern Ontario by tracking hay quality, bobolink breeding success and phenology, and post-breeding dispersal from uncut fields, using sites that were (A) cut along a typical schedule at the manager's discretion, (B) harvested late, on or after July 15, and (C) harvested early, before June 1, and again after 65 days. First harvests on discretionally managed fields generally occurred during the nestling stage or while fledglings were mostly flightless (mean=June 23±2.45 SE), likely resulting in very low bobolink reproduction. On late harvested fields, most bobolinks dispersed from breeding sites before 15 July and had high reproductive success; however forage quality declines make this regimen generally infeasible for farmers, as hay protein content generally dropped below 10% in late June. No bobolinks (re)nested on early cut fields in the 65 days interim between harvests, in contrast to success with this strategy in Vermont. In southern Ontario, a modest delay in first harvest may be the most appropriate strategy to balance needs of breeding bobolinks and farmers, translating to small declines in hay quality and substantial increases in reproductive success. Our work highlights the need for geographically refined agro-ecosystem management approaches for supporting grassland birds due to regional differences in hay maturation timing, breeding bird phenology, and habitat availability.