Determining When Bobolink Finish Breeding to Time Agricultural Activity in Nesting Refuges

Conservation actions are ongoing for the federally and provincially threatened bobolink (Dolichonyx oryzivorus) in Ontario, Canada because of population declines. One conservation action being implemented in agricultural grasslands is the delay of hay harvesting and livestock grazing until 15 July, a general guideline for when bobolink finish breeding. Efficient methods to assess when breeding ceases could benefit bobolink and farmers engaged in conservation by ensuring nesting is finished before agricultural activity occurs and enabling agricultural activity earlier when breeding is finished before 15 July. We conducted field surveys to assess if low-intensity surveys (i.e., transect surveys, point counts, roadside counts) could accurately detect when bobolink finish breeding compared to intensive monitoring (i.e., spot mapping and nest monitoring). We monitored 29 pastures in 2017 in eastern Ontario and 9 hay fields, 10 restored grasslands, and 6 fallow fields in 2018 in southern Ontario. The date breeding finished varied across fields in 2017 from 13 June to 29 July and in 2018 from 24 June to 30 July, based on spot mapping and nest monitoring. Transect surveys and point counts were good predictors of breeding in a field, as confirmed through spot mapping and nest monitoring, based on generalized linear mixed models. We recommend using transect surveys or point counts as an efficient field method to assess when bobolink finish breeding in a field targeted for bobolink conservation. Our results suggest that 2 consecutive visits that fail to detect evidence of breeding in early July are needed to reasonably infer that breeding has likely finished, leaving a small probability (i.e., <0.01) that breeding may still be occurring. Determining when bobolink finish breeding in fields intended to provide nesting refuges can help maximize conservation benefits and minimize negative effects on agricultural production. (c) 2020 The Wildlife Society.