Minnesota Department of Natural Resources 2021 Minnesota Colonial Waterbird Surveys

Abstract

The Minnesota colonial waterbird surveys began in 2004 in an effort to document the distribution and abundance of colonial nesting waterbirds in the state. The Minnesota Department of Natural Resources (MN DNR) partnered with researchers at the University of Minnesota to initiate monitoring efforts at colony sites of target waterbird species across the state (Table 1; Cuthbert and Hamilton 2016). The monitoring initially focused on documenting the number and distribution of two focal species, American White Pelican (Pelecanus erythrorhynchos) and Double-crested Cormorant (Phalacrocorax auritus), due to public concerns about the potential impacts of perceived population increases on recreation activities (e.g., fishing; Wires and Cuthbert 2006). The goal of monitoring was to evaluate efficacy of Double-crested Cormorant control efforts and document the status of American White Pelicans, which are a state-listed Species of Special Concern and Species in Greatest Conservation Need (SGCN; MN DNR 2016). Since the initial MN DNR waterbird surveys, conducted in 2004 and 2005, the intent was to conduct statewide surveys every five years. Surveys were conducted as planned in 2010 and 2015, but due to Covid-19 related work and travel restrictions, it was only possible to conduct a partial survey in 2020. Therefore, the primary objective of the 2021 survey was to complete the fourth census and provide a summary of the combined 2020–2021 survey results to MN DNR. The 2020 surveys were conducted by researchers at the University of Minnesota - Twin Cities campus and the 2021 surveys were conducted by researchers in the Avian Ecology Lab at the Natural Resources Research Institute (NRRI), Duluth, MN. The broad aim of this report is to provide a description of how sites were selected in 2020/21, which species were included as targets, and to provide recommendations for future monitoring efforts in the state. We include site-specific estimates of abundance for primary and secondary (when possible) target species for the combined 2020–2021 surveys. We also provide abundance and distribution estimates for primary target species for the current (2020–2021) and past census efforts at priority monitoring locations and focus on how future monitoring objectives and survey methodologies can best be tailored to maximize efficiency while providing necessary detail to effectively document population status of waterbirds breeding in Minnesota. Several additional waterbird species listed as SGCN in Minnesota include: Common Tern (Sterna hirundo), Black Tern (Chlidonias niger), Forster’s Tern (Sterna forsteri), Piping Plover (Charadrius melodus), Franklin’s Gull (Leucophaeus pipixcan), and Black-crowned Night-Heron (Nycticorax nycticorax). These species also require long-term monitoring to assess population status and associated habitat conditions, which are poorly monitored by other non-targeted surveys (MN DNR 2016; Cuthbert and Hamilton 2016). There are ongoing concerns for two additional colonial nesting species: Great Blue Heron (Ardea herodias) and Great Egret (Ardea alba). Although they are not state-listed species, the number of Great Blue Heron nesting colonies appears to have declined by ~30% since 1985, and the number of Great Egret nesting colonies remains low throughout the state. Overall, little is known about colony persistence or changes in the distribution and abundance of these species throughout the state (Pfannmuller et al. 2017). For these reasons, in 2021 we implemented additional surveys at secondary sites in an attempt to obtain information about the status of these species in the state.