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Abstract

We measure changes in occurrence (i.e., presence/absence) of three grassland bird species in the Carden Plain, between 2001 to 2005 and 2015 to 2016, by comparing point count results of the 2001–2005 Ontario Breeding Bird Atlas (OBBA) to repeated point counts at the same sites in the more recent period. We examine associations between changes of occurrence and habitat change and protection status of the survey locations for the three most commonly occurring species of Ontario grassland birds (Bobolink, Dolichonyx oryzivorus; Eastern Meadowlark, Sturnella magna; and Savannah Sparrow, Passerculus sandwichensis), all of which have experienced population declines in Ontario of between 2.75% and 3.87% annually between 1970 and 2019. There was no relationship between changes in the occurrence of these species and the protection designation of sites. Changes in occurrence had a significant association with change in habitat, for all three species with losses of occurrence between the two time periods associated with either shrub succession or conversion to row crops. For Bobolinks and Eastern Meadowlarks, all sites that were converted to row crops lost birds. For Bobolinks, sites experiencing shrub encroachment were also more likely to experience losses. Savannah Sparrows were present in the current period on three of the 10 sites that had been tilled since the OBBA. Gains of all three species were most likely when there had been no change in habitats between the two periods. We suggest targeted removal of trees and shrubs in the Carden Plain on sites where shrubs have not fully established, to help to maintain a healthy grassland bird community.

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