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Technical Thematic Report No. 18. - Inland colonial waterbird and marsh bird trends for Canada

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Inland colonial waterbird and marsh bird trends for Canada

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D.V.C. WeselohFootnotea

Canadian Biodiversity: Ecosystem Status and Trends 2010
Technical Thematic Report No. 18
Published by the Canadian Councils of Resource Ministers

Library and Archives Canada Cataloguing in Publication

Inland colonial waterbird and marsh bird trends for Canada.

Issued also in French under title:
Tendances relatives aux oiseaux aquatiques coloniaux de l’arrière-pays et aux oiseaux de marais au Canada.
Electronic monograph in PDF format.
ISBN 978-1-100-21165-7
Cat. no.:  En14-43/18-2012E-PDF

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This report should be cited as:
Weseloh, D.V.C. 2011. Inland colonial waterbird and marsh bird trends for Canada. Canadian Biodiversity: Ecosystem Status and Trends 2010 Technical Thematic Report No. 18. Canadian Councils of Resource Ministers. Ottawa, ON. iv + 33 p.

© Her Majesty the Queen in Right of Canada, 2012
Aussi disponible en français

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Footnote a

Canadian Wildlife Service, Environment Canada, Downsview, ON

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The Canadian Councils of Resource Ministers developed a Biodiversity Outcomes FrameworkFootnote1 in 2006 to focus conservation and restoration actions under the Canadian Biodiversity Strategy.Footnote2 Canadian Biodiversity: Ecosystem Status and Trends 2010Footnote3 was a first report under this framework. It assesses progress towards the framework’s goal of “Healthy and Diverse Ecosystems” and the two desired conservation outcomes:

  • productive, resilient, diverse ecosystems with the capacity to recover and adapt; and
  • damaged ecosystems restored.

The 22 recurring key findings that are presented in Canadian Biodiversity: Ecosystem Status and Trends 2010 emerged from synthesis and analysis of technical reports prepared as part of this project. Over 500 experts participated in the writing and review of these foundation documents. This report, Inland colonial waterbird and marsh bird trends for Canada, is one of several reports prepared on the status and trends of national cross-cutting themes. It has been prepared by experts in the field of study and reflects the views of its author and contributors.

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G. Beyersbergen, S. Boyd, A. Breault, P. Brousseau, M. Drever, S.G. Gilliland, B. Jobin, B. Johns, V. Johnston, S. Meyer, R. Millikin, C. Pekarik, J. Rausch, D. Shervill, S.I. Wilhelm


I would like to thank all of the contributors for taking the time to send me their data, the pertinent references, and for providing further explanations where necessary.

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Ecological Classification System – Ecozones+

A slightly modified version of the Terrestrial Ecozones of Canada, described in the National Ecological Framework for CanadaFootnote4, provided the ecosystem-based units for all reports related to this project. Modifications from the original framework include: adjustments to terrestrial boundaries to reflect improvements from ground-truthing exercises; the combination of three Arctic ecozones into one; the use of two ecoprovinces – Western Interior Basin and Newfoundland Boreal; the addition of nine marine ecosystem-based units; and, the addition of the Great Lakes as a unit. This modified classification system is referred to as “ecozones+” throughout these reports to avoid confusion with the more familiar “ecozones” of the original frameworkFootnote5.

Ecological classification framework for the Ecosystem Status and Trends Report for Canada.


Long Description for Ecozones+ map of Canada

This map of Canada shows the ecological classification framework for the Ecosystem Status and Trends Report, named “ecozones+”. This map shows the distribution of 15 terrestrial ecozones+ (Atlantic Maritime; Newfoundland Boreal; Taiga Shield; Mixedwood Plains; Boreal Shield; Hudson Plains; Prairies; Boreal Plains; Montane Cordillera; Western Interior Basin; Pacific Maritime; Boreal Cordillera; Taiga Cordillera; Taiga Plains; Arctic), two large lake ecozones+ (Great Lakes; Lake Winnipeg), and nine marine ecozones+ (North Coast and Hecate Strait; West Coast Vancouver Island; Strait of Georgia; Gulf of Maine and Scotian Shelf; Estuary and Gulf of St. Lawrence; Newfoundland and Labrador Shelves; Hudson Bay, James Bay and Fox Basin; Canadian Arctic Archipelago; Beaufort Sea).

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The purpose of this report is to present data on temporal trends in populations and, where possible, vital rates for colonial waterbirds and marsh birds for Canada’s 16 terrestrial ecozones+. Unfortunately, these kinds of data could not be found for three ecozones+ -- the Taiga Cordillera, Taiga Shield, and Hudson Plains -- and therefore these ecozones+ are not included in this report. Historical data, sometimes extensive, were available for four ecozones+ -- Boreal Cordillera, Western Interior Basin, Montane Cordillera, and Prairies -- but there are no recent data with which to compare to determine trends. The other nine ecozones+ have one or more dataset of five or more years that can be used to give preliminary data; some of these have much more data than others. The results for these nine ecozones+ are summarized here.

  • Atlantic Maritime Ecozone+ – Data are reported for one species. The trend since the 1990s for the Great Blue Heron on the Magdalen Islands was stable.
  • Great Lakes Ecozone+ – 30-year trends are available for at least ten colonial waterbird species. Four (American White Pelican, Double-crested Cormorant, Great Egret, and Caspian Tern) are increasing, four (Ring-billed, Herring, and Great Black-backed Gulls, and Common Tern) are decreasing, and two (Great Blue Heron and Black-crowned Night Heron) are stable. Among marsh birds, Pied-billed Grebe, Virginia Rail, Common Moorhen/American Coot, Black Tern, and Red-winged Blackbird all declined significantly over the last 13 years.
  • Mixedwood Plains Ecozone+ – Black Tern populations in Quebec have shown a severe decline while the Ring-billed Gull have shown a slower decline. Five years of Marsh Monitoring data show preliminary declines for Sora and Virginia Rail and American Coot/Common Moorhen. The Great Egret is increasing while Great Blue Heron and Black-crowned Night-Heron are stable. A 36-year checklist database shows four species declining 46 to 77% and nine species increasing 40 to 80%.
  • Boreal Shield Ecozone+ – Long-term data are available for the Great Blue Heron but the large size of the ecozone+ makes it difficult to identify trends. Sandhill Crane numbers have been documented during Black Duck Surveys and show a dramatic increase since 1990. Herring Gull, Great Black-backed Gull, and Common Loon numbers have also been recorded on these surveys and show the loons to be significantly increasing while the gull populations are stable. Double-crested Cormorants have increased on the north shore of the Gulf of St. Lawrence. In the Newfoundland Boreal Ecozone+, data have been collected jointly with the Boreal Shield Ecozone+, and share stable Herring and Great Black-backed Gull populations and an increasing Common Loon population.
  • Boreal Plains Ecozone+ – A recent 5-year trend for Western Grebes in Alberta shows significant population declines and low reproductive success. American White Pelicans in Saskatchewan were surveyed for 16 years and have been removed from the “Threatened” list; presumably because the population had increased. Breeding Bird Surveys (BBS) showed that Black Terns declined at a significant rate of – 5.4% per year over a 28 year period, 1980 to 2007.However, the applicability of BBS surveys to adequately census colonial waterbirds is often questioned. Historical data are also available for selected species.
  • Taiga Plains Ecozone+ – A strong long-term increase for the Whooping Crane at the Aransas National Wildlife Refuge in Texas is apparent and it is assumed that this is due to an increase on the Canadian breeding grounds. These birds breed only in Canada’s Taiga Plains and this increase is reflective of habitat protection as well as favourable conditions on the plains. A long-term dataset (24 years) for a small geographical area near Yellowknife is also available that could yield local trends for Horned Grebes, but these data have not been analyzed for this report.
  • Arctic Ecozone+ – Nesting density of Sabine’s Gulls was lower in 1996 on Prince Charles Island than it was in 1984, but there are no recent data. Current population levels of several other species have been established but no trends are yet available.
  • Pacific Maritime Ecozone+ – Trends were analyzed for 58 species (including waterfowl) from the Coastal Waterbird Survey that was initiated in 1999.  Annual declines of -5 to -18% were found for Glaucous- winged, Herring, California and Bonaparte’s Gulls and a continuing decline for Western Grebes, while annual increases were found for Double-crested (3%) and Pelagic (4%) Cormorants.

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Introduction and Methods

The aim of this report is to present data on the trends in population numbers and other vital statistics for inland colonial waterbirds and marsh birds in Canada’s 16 terrestrial ecozones+. The data were solicited from members of the Inland Colonial Waterbird and Marsh Bird Chapter of the Canadian Waterbird Technical Committee and other waterbird biologists from across the country. There were surprisingly few long-term datasets identified, particularly for some ecozones+. Some ecozones+  had no data (Taiga Cordillera, Taiga Shield, and Hudson Plains), some had historical data but no current data (Boreal Cordillera, Western Interior Basin, Montane Cordillera, and  Prairies), some had data awaiting analysis, and some had recent but no historical data. Nine ecozones+ had one or more dataset of five or more years that was used to give preliminary data; some had much more data than others.

For each ecozone+, the availability of data is summarized and trends are presented for some species where data exists. In addition, for each ecozone+, potential or previously adopted indicator species are listed to draw attention to focal species which could, if sufficient data were available, provide an indication of ecosystem health for the ecozone+. Currently sufficient data do not necessarily exist to assess trends in all of these species.

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Inland Colonial Waterbirds

The use of inland colonial waterbirds, including gulls, terns, herons, several grebes, and cormorants, as indicators of ecosystem health has been extensively reviewed by Kushlan (1993). Most species are piscivores to a large extent and, as such, are at the top of the aquatic food web making them good indicators of perturbations in the ecosystem. Equally important is the fact that these birds usually nest in relatively large numbers in discrete colonies, enabling easy location, identification, access, and censusing of the nesting sites. This is in direct contrast to other inland waterbirds such as rails, bitterns, loons, and cranes that nest more solitarily or cryptically, making them much more difficult to locate and census.

The main metric used in assessing trends of inland colonial waterbirds is colony size, such as how many nests or nesting pairs are present in the colony. This is because once the phenology of the species is known, the question of colony size can usually be answered by a single well-timed visit to the site. Data on colony size are used to answer basic questions, such as how many nesting individuals are there and are their numbers increasing or decreasing. Although these basic questions are often easy to answer for a single colony (site), they become more difficult when applied to large geographical areas. Methods for censusing waterbird colonies in most habitats have been standardized (Erwin, 1981; Kushlan, 1986; Blokpoel and Tessier, 1996; Morris et al., 2003; Steinkamp et al., 2003; Soos, 2004) while methods for censusing in the boreal forest have been suggested but not yet implemented (Morris, 2006; Weseloh and Moore, 2010).

Once the size of the breeding population size is known, other useful metrics can include productivity, diet, contaminant concentrations, migration arrival and departure dates, and other life-history features. Nevertheless, for most of these metrics, multiple visits, expensive equipment, or tedious identifications are necessary. As a result, very few of them are tracked to the extent that temporal population trends are documented.

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Marsh Birds

Marsh-nesting birds are indicators of ecosystem health because they require wetland habitat to complete their life cycle. Wetlands, because of their unique location between upland/terrestrial and open water/pelagic habitats, are transitional ecosystems that are affected by terrestrial and aquatic environments. For example, water quantity and quality are affected by terrestrial attributes such as soil porosity which can lead to high sedimentation and turbidity through high runoff. In addition, land uses, such as agriculture within a watershed and adjacent to a wetland, affect wetland function through inputs such as fertilizer, herbicides, and pesticides (Environment Canada and Central Lake Ontario Conservation Authority, 2004; Great Lakes Coastal Wetlands Consortium, 2008). Similarly, aquatic effects such as invasive species and water-level regulation affect wetland function by significantly altering biotic communities (Timmermans et al., 2008). These stressors degrade wetland function and impair wildlife habitat. Marsh-nesting birds, as ecosystem indicators, reflect these habitat changes.

Many monitoring programs and conservation initiatives use marsh-nesting birds as ecosystem indicators. For example, State of the Lakes Ecosystem Conferences, which report on the health of the Great Lakes every three years, use marsh-nesting bird data from the Great Lakes Marsh Monitoring Program – a volunteer-based program administered by Bird Studies Canada in partnership with Environment Canada with funding support from the U.S. Environmental Protection Agency. A Prairie and Parkland Marsh Monitoring Program in the prairie provinces and administered by Bird Studies Canada began with a pilot study in 2008 and more extensive monitoring and site distribution in 2009-10. Regional and wetland-specific monitoring programs have implemented Indices of Biotic Integrity, which use a number of parameters, or metrics, to assess the health of a wetland or how well conservation efforts are working (Environment Canada and Central Lake Ontario Conservation Authority, 2004; Archer et al., 2006; Great Lakes Coastal Wetlands Consortium, 2008; Meyer and Grabas, 2008). These monitoring activities, in conjunction with stewardship activities (for example wetland restoration), facilitate the conservation of marsh-nesting bird populations, and other wildlife, by providing information to guide adaptive management as well as inform people about the important ecological goods and services that wetlands and marsh birds provide to society.

In assessing the value of different marsh-nesting bird species as ecosystem indicators for this report, the following criteria were used:

  1. Abundant species that are characteristic of the ecozone+;
  2. Species for which population or other biological indicator data are available for multiple years;
  3. Species that require marshes for nesting (marsh-nesting obligates such as grebes, rails, and bitterns);
  4. Species that are marsh-nesting generalists; and,
  5. Hierarchy in the food chain (species on the high end).

Among a variety of biological measures commonly utilized to monitor marsh-nesting birds, the following are particularly useful for assessing the state of the ecosystem:

  • Population trends;
  • Community structure and composition (loss or gain of some species);
  • Changes in timing of breeding (an indicator of climate change effects); and,
  • Reproductive success and nestling growth (an indicator of possible habitat contamination and food web changes).

Population changes integrate information on survival over the entire year. For migratory species, population trends may reflect conditions in both their non-breeding and breeding range. Consequently, population changes of migratory species should be examined in relation to other communities (such as, resident species) and abiotic conditions.

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Footnote 1

Environment Canada. 2006. Biodiversity outcomes framework for Canada. Canadian Councils of Resource Ministers. Ottawa, ON. 8 p.

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Footnote 2

Federal-Provincial-Territorial Biodiversity Working Group. 1995. Canadian biodiversity strategy: Canada's response to the Convention on Biological Diversity. Environment Canada, Biodiversity Convention Office. Ottawa, ON. 86 p.

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Footnote 3

Federal, Provincial and Territorial Governments of Canada. 2010. Canadian biodiversity: ecosystem status and trends 2010. Canadian Councils of Resource Ministers. Ottawa, ON. vi + 142 p.

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Footnote 4

Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch. Ottawa/Hull, ON. 125 p. Report and national map at 1:7 500 000 scale.

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Footnote 5

Rankin, R., Austin, M. and Rice, J. 2011. Ecological classification system for the ecosystem status and trends report. Canadian Biodiveristy: Ecosystem Status and Trends 2010, Technical Thematic Report No. 1. Canadian Councils of Resource Ministers. Ottawa, ON. 

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