I recently finished a 28-page summary report for the 2009 Colonial Wading Bird census effort. I will be periodically posting segments of that report here for all to see. I’ll start today by posting the “Summary” that gives you a quick overview of the effort and results…
Maine is home to several colonial wading birds during the spring and summer: great blue herons, snowy egrets, great egrets, and black-crowned night-herons, as well as occasional cattle egrets, little blue herons, tricolored herons, and glossy ibis. These magnificent birds build large stick nests in trees or shrubs and nest in groups. The great blue heron is the largest of Maine’s wading birds and nests in the greatest numbers both inland and along the coast.
As recent as 1995, there were as many as 14 coastal islands occupied by 644 pairs of nesting great blue herons. More recently we noticed that many of these colonies no longer existed or that the numbers of nesting birds had waned. There had not been a comprehensive wading bird survey of the coastal islands since the mid-1990s, and there had never been a comprehensive survey effort for the rest of the state.
With funding from State Wildlife Grants and the Oil Spill Recovery Fund, we set out to conduct a nearly statewide census for great blue herons and other colonial wading birds. With the help of pilots from the Warden Service and Forest Service, biologists conducted over 60 hours of aerial surveys. Over 180 historical locations were checked, and 73 new sites were discovered during the surveys or as a result of information provided by the public or other biologists. In addition to aerial surveys, biologists visited 38 colony sites on the ground to help verify colony locations and to gather more precise counts of active nests.
Survey efforts revealed 1,071 nesting pairs of great blue herons at 83 colonies, ranging in size from 1 to 120 active nests. A majority of the colonies were small in size (less than 10 nests) and located in beaver flowage settings. As in the past, the largest colonies were located on coastal islands, with the exception of a colony located on an island in Aziscohos Lake in Lynchtown. With approximately 65 active nests, the Aziscohos Lake colony is the largest inland colony in the state and has persisted for at least 23 years.
The coastal breeding population of great blue herons experienced a 46.7% decline between 1983 and 1995. Consideration of this decline, evidence of fewer active nests in recent years, and observations of predation by an increasing eagle population prompted Maine Department of Inland Fisheries and Wildlife (MDIFW) to list the great blue heron as a state Species of Special Concern in 2007. This year’s census revealed 430 pairs on 9 coastal islands, a 33.3% decrease from 1995, and a 64.4% decrease from 1983. While we are fairly certain we’ve thoroughly surveyed the coastal islands and have detected most colonies containing more than 1 pair, we expect there are many inland colonies that have gone undetected. Thus, it is difficult to make an accurate estimate of the statewide breeding population of great blue herons. Without consistent historical data for inland breeding sites, we intend to use this year’s survey results as a new baseline from which to detect breeding population trends in the future. Given the available data and trend analyses using Breeding Bird Survey and Christmas Bird Count data, Maine’s great blue heron population appears to be experiencing some level of decline, the causes of which are largely unknown.
Additional on-the-ground efforts included surveys of two coastal islands for nesting black-crowned night-herons, a species that was recently listed as Threatened in Maine. It was encouraging to find 87 active nests between these two islands. National Audubon also reported 21 nesting pairs on Stratton Island, bringing our known total to 108 pairs at these 3 sites. Black-crowned night-heron colonies can be difficult to detect from the air because they tend to nest beneath the canopy of deciduous trees or shrubs. Future efforts will be made to conduct on-the-ground surveys on additional islands.
This year’s survey effort was extremely time and labor intensive, and thus cannot be performed on an annual basis. To ensure that we continue to collect nesting data for great blue herons and other colonial wading birds, we began a volunteer adopt-a-colony program this year called the Heron Observation Network (or HERON for short). Seventy-eight people across the state signed up to be a part of HERON this year! More than half of these volunteers are tracking and reporting their time, which can be used as a match for federal funds for future research and monitoring. We plan to continue this program in the coming years, and appreciate all who have contributed thus far. If you know of a wading bird colony, we’d love to know about it too! Please don’t hesitate to contact Danielle D’Auria (email@example.com, 941-4478) with information about wading bird colonies, or if you’d like to sign up to be a HERON volunteer.