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Technical Thematic Report No. 8. - Trends in breeding waterfowl in Canada

Methodology

 

Data Sources

Western ecozones+

CWS/USFWS Waterfowl Breeding Population and Habitat Survey

The best source of data for waterfowl population estimates for the purpose of this report come from the joint Canadian Wildlife Service (CWS) and U.S. Fish and Wildlife Service (USFWS) Waterfowl Breeding Population and Habitat Survey (U.S. Fish and Wildlife Service, 2007). This survey was initiated experimentally in 1947 and became operational in 1955 with cooperative surveys carried out every year since 1955. The primary purpose of the survey is to provide information on spring population size and trajectory for certain North American duck species. These data are used extensively in the annual establishment of hunting regulations in the United States and Canada and in providing long-term time series data critical to effective conservation planning. For more information on the survey see Smith (1995).

The traditional survey area only covers part of the country (Figure 1). Ecozones+ covered by it (Prairies, Boreal Plains, and Taiga Plains) are referred to as "western ecozones+" and data from this survey was used exclusively in the analysis for these ecozones+ in this report. We identified strata from the survey that were entirely contained within an ecozone+ and discarded any strata which straddled two or more ecozones+.

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Figure 1. Strata and transects of the traditional CWS/USFWS Waterfowl Breeding Population and Habitat Survey and the more recent USFWS Airplane Transect Survey. USFWS Airplane Transect Survey is described below.
Map

Source: U.S. Fish and Wildlife Service (2007)

Long Description for Figure 1

This map of Canada and the northern United States shows the strata and transects of the traditional Canadian Wildlife Service (CWS) and U.S. Fish and Wildlife Service (USFWS) waterfowl breeding population and habitat survey area and the more recent USFWS Airplane Transect survey area. The traditional CWS/USFWS survey area covers the Prairies, Boreal Plains, and Taiga Plains, referred to as the "western ecozones+." The USFWS Airplane Transect Survey area covers the Atlantic Maritime, Mixedwood Plains, Newfoundland Boreal, Boreal Shield, and Taiga Shield, referred to as the "eastern ecozones+."

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Eastern ecozones+

Additional surveys in eastern Canada were initiated independently by CWS and USFWS much later (around 1990). These include the USFWS Airplane Transect Survey (Figure 1), the CWS Boreal Helicopter Plot Survey, the Southern Ontario Waterfowl Ground Survey, and the Québec Basses Terres survey. Recently, considerable effort has been made to integrate these surveys into a single survey. The results of this integration were used to generate estimates for the "eastern ecozones+" (Atlantic Maritime, Mixedwood Plains, Newfoundland Boreal, Boreal Shield, and Taiga Shield) for this report. The four data sources used to derive population estimates for each eastern ecozone+ are summarized in Table 1 and described in more detail below.

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Table 1. Sources of data used for waterfowl population estimates for the eastern ecozones+.
Data sourceSite area
(km²)
# of sitesEastern
ecozones+

Taiga

Shield
Eastern
ecozones+

Boreal

Shield
Eastern
ecozones+

Mixedwood

Plains
Eastern
ecozones+

Atlantic

Maritime
Eastern
ecozones+

Nfld.

Boreal
CWS Boreal
Helicopter Plot
25320 -X-XX
USFWS
Airplane Transect
11.65/ segment118XXXXX
Québec
Basses TerresTable 3, Footnote*
4125- X-
Southern Ontario
Ground
0.64349-XX--
Footnotes
Footnote *

The Québec Basses Terres survey covers areas in BCR 13 (Mixedwood Plains) and areas near Abitibi and Lac St Jean. Only the portion of the data in Mixedwood Plains was included in this analysis.

Return to table 3, footnote* referrer

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CWS Boreal Helicopter Plot Survey

The CWS Boreal Helicopter Survey is based on 5 km² plots run in a rotational design. The survey is run every year with each individual plot surveyed every five years in the rotational pattern. For this analysis, we included the boreal plots and some plots in the Appalachian region of Québec. In Ontario and Québec, the plots are placed systematically and can thus be partitioned into any necessary strata for analysis. In Nova Scotia, New Brunswick, and Newfoundland, the plots are not a systematic sample but did not require further stratification for this analysis because each plot is contained entirely within an individual ecozone+. In Labrador, there are plots in both the Taiga Shield and Boreal Shield ecozones+.

Surveys in some plots were initiated only recently and were therefore discarded for this analysis. These are:

  • Newfoundland      plot 49-57       started 2004 or later
  • Labrador             plot 43            run in 2003 and 2004
  • Appalachian         plot 1A12        started 2004

There was only one plot in BCR 13 (Mixedwood Plains). It was discarded from the analysis.

USFWS Airplane Transect Survey

The USFWS Airplane Transect Survey design partitions eastern Canada into 17 strata (Figure 2). Within each strata, the survey is based on a random selection of transects which are further subdivided into segments. The segments are 18 miles (~29 km) long and 0.25 miles (~0.4 km) wide. The number of segments within each transect varies. While surveys of most strata were initiated in 1996, Strata 51 to 54 were added after 1990, and Strata 58 and 59 were started in 2005 and 2006, respectively.

Figure 2 . Strata for eastern USFWS Airplane Transect Surveys of waterfowl.
Map

Source: U.S. Fish and Wildlife Service (2007)

Long Description for Figure 2

This map of eastern Canada shows the strata for the U.S. Fish and Wildlife Service Airplane Transect Surveys of waterfowl. Eastern Canada is partitioned into 17 strata numbered from 51 to 58 (around the Great Lakes and the west side of the James Bay) and 62 to 72 (along the Atlantic coast and the east side of the James Bay).

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The strata were developed to partition eastern Canada by province, grouping areas with similar habitat and areas which were practical for airplane transects. The resulting strata fit well into the ecozone+ framework, although some strata extend over more than one ecozone+. The relationship of the USFWS Airplane Transect Survey strata to ecozones+ is shown in Table 2. Individual transects also occasionally pass through different ecozones+. In these cases since the raw data on transect segments were available, we assigned each segment to an ecozone+ by comparing the segment length with the maps of ecozones+.

Table 2. Sampling intensity of USFWS Airplane Transect Survey, by stratum and ecozone+.
Ecozone+  ProvinceUSFWS
stratum
Area(Table 2, Footnotea) (km²)Sample area
(Table 2, Footnoteb) (km²)
Extrapolation
factor
Atlantic MaritimeQC56 (part)24,621(Table 2, Footnotec)256.396
Atlantic MaritimeQC7240,850----
Atlantic MaritimeNB6372,195570.5126
Atlantic MaritimeNS6454,850547.6100
Atlantic MaritimePEI655,76258.299
Mixedwood PlainsON5310,903104.8104
Mixedwood PlainsON5458,200512.6114
Mixedwood PlainsQC56 (part)24,303(Table 2, Footnotec)326.275
Newfoundland BorealNF66109,425792.2138
Boreal ShieldON51198,544885.4224
Boreal ShieldON5253,475372.8143
Boreal ShieldON57 (part)(Table 2, Footnoted)0--
Boreal ShieldQC68 (part)-1,386.4252(Table 2, Footnotef)
Boreal ShieldQC69 (part)-69.9370(Table 2, Footnoteg)
Boreal ShieldQC7084,393244.6345
Boreal ShieldQC7187,529----
Boreal ShieldLB67 (part)-116.5267(Table 2, Footnotee)
Taiga ShieldQC68 (part)-0--
Taiga ShieldQC69 (part)-967.0370(Table 2, Footnoteg)
Taiga ShieldLB67 (part)-710.6267(Table 2, Footnotee)
Footnotes
Footnote a

stratum area used by USFWS

Return to table 2, footnote a referrer

Footnote b

sample area derived after standardizing the transects to include the same segments each year

Return to table 2, footnote b referrer

Footnote c

based on Québec total area for BCR 13 (24,303) and BCR 14 (65,471). The result is 6,681 km² less then USFWS area for stratum 56. This is possibly due to a portion of the Québec area being assigned to the shoreline survey or to differences between USFWS strata and ecozone+ boundaries.

Return to table 2, footnote c referrer

Footnote d

area of Boreal Shield ecozone+ in this USFWS stratum is small so area was deleted.

Return to table 2, footnote d referrer

Footnote e

USFWS stratum 67 area (221,221 km²) divided by total sample area for all ecozones+

Return to table 2, footnote e referrer

Footnote f

USFWS stratum 68 area (364,739 km²) divided by total sample area for all ecozones+

Return to table 2, footnote f referrer

Footnote g

USFWS stratum 69 area (405,979 km²) divided by total sample area for all ecozones+

Return to table 2, footnote g referrer

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The sampling intensity for each stratum by ecozone+ was calculated as an extrapolation factor (Table 2). Strata within the same ecozone+ with similar extrapolation factors could be pooled for analysis purposes.

Comparable sample intensity for the CWS Boreal Helicopter Plot Survey is shown in Table 3.

Table 3. Sampling intensity for the CWS Boreal Helicopter Plot Survey for each USFWS stratum.
Ecozone+ProvinceUSFWS stratumArea(Table 3, Footnotea) (km²)Sample area (Table 3, Footnoteb) (km²)Extrapolation factor
Atlantic MaritimeQC56 (part)24,621(Table 3, Footnotec)25098
Atlantic MaritimeQC7240,850125327
Atlantic MaritimeNB6372,1951,00072
Atlantic MaritimeNS6454,85075073
Atlantic MaritimePEI655,762---
Mixedwood PlainsON5310,903---
Mixedwood PlainsON5458,200---
Mixedwood PlainsQC56 (part)24,303 (Table 3, Footnotec)---
Newfoundland BorealNF66109,425800137
Boreal ShieldON51198,544850234
Boreal ShieldON5253,475125428
Boreal ShieldON57 (part)(Table 3, Footnoted)---
Boreal ShieldQC68 (part)350,000(Table 3, Footnotef)2,625133
Boreal ShieldQC69 (part)----
Boreal ShieldQC7084,393400210
Boreal ShieldQC7187,529675130
Boreal ShieldLB67 (part)31,000(Table 3, Footnotee)175177
Taiga ShieldQC68 (part)----
Taiga ShieldQC69 (part)----
Taiga ShieldLB67 (part)190,000(Table 3, Footnotee)325584
Footnotes
Footnote a

stratum area used by USFWS

Return to table 3, footnote a referrer

Footnote b

total area of sample plots

Return to table 3, footnote b referrer

Footnote c

based on Québec total area for BCR 13 (24,303) and BCR 14 (65,471). This result is 6,681 km² less then USFWS area for stratum 56. This is possibly due to a portion of the Québec area being assigned to the shoreline survey or to differences between USFWS strata and ecozone+ boundaries.

Return to table 3, footnote c referrer

Footnote d

The area of Boreal Shield in this USFWS stratum is small so area was deleted.

Return to table 3, footnote d referrer

Footnote e

USFWS stratum 67 area (221,221 km²) apportioned across ecozones+ by transect sample area

Return to table 3, footnote e referrer

Footnote f

USFWS stratum 68 area (364,739 km²) apportioned across ecozones+ by transect sample area

Return to table 3, footnote f referrer

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Québec Basses Terres

The Basses Terres Survey is based on 2 km² plots flown by helicopter. The survey is run in the St. Lawrence Lowlands, Abitibi, and Lac St. Jean regions. Most of the plots in the St. Lawrence Lowlands are in BCR 13 (Mixedwood Plains) but there are a few plots in BCR 12 (Boreal Shield). The BCR 12 plots were discarded for this analysis. The surveys in the Abitibi and Lac St-Jean regions were also discarded because they would need to be treated as new strata and only cover a relatively small area.

Southern Ontario Waterfowl Ground Survey

The Southern Ontario Waterfowl Ground Survey is partitioned into two strata – high and low waterfowl density – and is based on 0.8 km² plots surveyed on the ground. The survey was initiated in 1974 and was run approximately every three years. Recently, the survey was changed to a rotating design with approximately one third of the plots run each year.

The stratum areas within each Bird Conservation Region (BCR) and the assignment of plots to BCRs are known and were used to assign the data to the Boreal Shield and Mixedwood Plains ecozones+. Because it is difficult to use this stratification with that used by the USFWS Airplane Transect Survey, only data from the Southern Ontario Waterfowl Ground Survey were used for southern Ontario.

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Summary of data availability

Table 4 summarizes data availability for each ecozone+ (organized by USFWS stratum) from all surveys from 1970 to 2006.

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Table 4. Summarizes data availability for each ecozone+ (organized by USFWS stratum) from all surveys from 1970 to 2006.
Stratum1970-899091929394959697989900010203040506
Atlantic Maritime------------------
56AM-XXXXXXXXXXXXXXXXX
72-XXXXXXXXXXXX-XXXX
63Table 4, Footnote*----XXXXXXXXXXXXXX
64-XXXXXXXXXXXXXXXXX
65 (dropped for this report)-------XXXXXXXXXXX
Data used in this report----XXXXXXXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Newfoundland Boreal------------------
66-------XXXXXXXXXXX
Data used in this report-------XXXXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Mixedwood Plains------------------
5354-XXXXXXXXXXXXXXXXX
56MW-XXXXXXXXXXXXXXXXX
Data used in this report-XXXXXXXXXXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Boreal Shield------------------
51-XXXXXXXXXXXXXXXXX
52-XXXXXXXXXXXXXXXXX
68BS-XXXXXXXXXXXXXXXXX
69BS (dropped in report)---------XXXXXXXXX
70-XXXXXXXXXXXXXXXXX
71-XXXXXXXXXXXXXXXXX
67BS-XXXXXXXXXXXXXXXXX
24XXXXXXXXXXXXXXXXXX
36XXXXXXXXXXXXX-XXXX
Data used in this report-XXXXXXXXXXXX-XXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Taiga Shield------------------
69TS---------XXXXXXXXX
67TS-XXXXXXXXXXXXXXXXX
16XXXXXXXXXXXXXXXXXX
18XXXXXXXXXXXXXXXXXX
Data used in this report---------XXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Taiga Plains------------------
15XXXXXXXXXXXXXXXXXX
17XXXXXXXXXXXXXXXXXX
Data used in this reportXXXXXXXXXXXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Boreal Plains------------------
20XXXXXXXXXXXXXXXXXX
22XXXXXXXXXXXXXXXXXX
25XXXXXXXXXXXXXXXXXX
75 (dropped for this report)-------XXXXXXXXXXX
76 (dropped for this report)-------XXXXXXXXXXX
Data used in this reportXXXXXXXXXXXXXXXXXX
Table 4. Continued
Stratum1970-899091929394959697989900010203040506
Prairies------------------
26XXXXXXXXXXXXXXXXXX
27XXXXXXXXXXXXXXXXXX
28XXXXXXXXXXXXXXXXXX
29XXXXXXXXXXXXXXXXXX
32XXXXXXXXXXXXXXXXXX
33XXXXXXXXXXXXXXXXXX
34XXXXXXXXXXXXXXXXXX
35XXXXXXXXXXXXXXXXXX
38XXXXXXXX-XXXXXXXXX
39XXXXXXXXXXXXXXXXXX
40XXXXXXXXXXXXXXXXXX
Data used in this reportXXXXXXXX-XXXXXXXXX
Footnotes
Footnote *

data from New Brunswick for 1990-1992 missing due to observer change.

Return to table 4, footnote * referrer

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Data Analysis

Western ecozones+

The analysis for the western ecozones+ was straight forward and used only the CWS/USFWS Waterfowl Breeding Population and Habitat Survey. We added the reported population estimates for all stratums within each ecozone+ and then calculated: 1) the annual averages by decade; 2) the percent change between the first and last decade; and 3) the trend from a simple regression over the period of the survey. Calculation of the regression line used estimates converted to the log scale. The standard error (SE) for the log of the index for each year was approximated from the reported SE using a Taylor approximation. The SE of the trend was calculated as a weighted combination of the SE for individual years. In cases where the index was zero, the SE of the log was also set to zero. If a species was not seen in an ecozone+ in a given year but there had been surveys run in each stratum then the annual index was set to zero. To accommodate this in the log-transform, we set the value to one half the smallest non-zero count for any year for the trend calculation.

The trend in log scale was calculated as:

Formula

Where Formula= natural log of the annual Index for year j
Formula= jth year

This slope was converted to other variables:

1) annual percentage change:Formula
2) total percentage change over a time period of k years:Formula

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Eastern ecozones+

The analysis for eastern ecozones+ was carried out using a custom written C++ program based on the assumption that all surveys in the same strata were measuring the same population and thus year to year differences were consistent among different surveys. A Poisson model was fitted separately for each stratum, taking into account the effects of site and year, with a log link function. The site area was used as an offset term in the model, so that site effects were measures of population density. The average observed density for each survey by stratum combination was estimated from the fitted model. The relative detection rates among surveys were then estimated by designating certain surveys as effective complete counts and assuming other surveys in the same strata detected a proportion of the birds observed. (See Calculation of relative detection rates section on page 10 for further explanation of relative densities and detection rates). The site effects from the Poisson model were then adjusted by the relative detection rate and a stratum by year population density was calculated for each stratum as a weighted average across surveys, with the weighting based on the among site variability within each survey.

Annual indices and densities were calculated for each eastern ecozone+ by summing across all strata within the ecozone+. If estimates were not available for all strata within the ecozone+ in an individual year, then no estimate was calculated for the ecozone+. The individual strata were summed to provide an overall eastern Canada estimate. A simple regression of the log annual index against year was also calculated at the stratum, ecozone+, and eastern Canada level. The SE of all estimates was calculated using a jackknife procedure.

Stratification

The USFWS Airplane Transect Survey dictated much of the stratification for the analysis; however, it was necessary to further partition these strata into smaller areas in order to match the ecozones+.

  • Stratum 56 is partitioned into 56AM and 56MW
  • Stratum 67 is partitioned into 67BS and 67TS
  • Stratum 68 is partitioned into 68BS, 68TS and 68HP (the latter was not used in this analysis)
  • Stratum 69 is partitioned into 69BS and 69HP (the latter was not used in this analysis)
  • There were no segments in 69TS and the potential stratum was discarded
  • Strata 53 and 54 had the same sampling intensity and were merged.
  • Stratum 58 was only run in 2005 and 2006 and was discarded.

The Southern Ontario Waterfowl Ground Survey analysis is based on two strata (Table 5)   Stratum 5354 was replaced with strata 13HI and 13LO, while stratum 52 was replaced with strata 12HI and 12LO. These new strata have somewhat different areas than the original strata. This is probably due to the USFWS strata not being aligned with the BCRs or ecozones+.

Table 5. Availability and assignment of all survey strata to each ecozone+.
Ecozone+USFWS
Stratum
  ProvinceArea
(km²)
Data Source

USFWS
Transect
Data Source

CWS
Plot
Data Source

Southern
Ontario
Data Source

Basses
Terres
Atlantic Maritime56AMQC24,621XX--
Atlantic Maritime72QC40,850-X--
Atlantic Maritime63NB72,195XX--
Atlantic Maritime64NS54,850XX-
Atlantic Maritime65PEI5,672X---
Mixedwood Plains13HION51,353-(Table 5, Footnoteb)X-
Mixedwood Plains13LOON26,890--X-
Mixedwood Plains56MWQC24,303X--X
Newfoundland Boreal66NF109,425XX--
Boreal Shield51ON198,544X---
Boreal Shield12HION14,376--X-
Boreal Shield12LOON34,095--X-
Boreal Shield68BSQC350,000(Table 5, Footnotea)XX--
Boreal Shield69BSQC26,000(Table 5, Footnotea)X---
Boreal Shield70QC84,393XX--
Boreal Shield71QC87,529-X--
Boreal Shield67BSLB31,000(Table 5, Footnotea)XX--
Taiga Shield68TSQC0(Table 5, Footnotea)(Table 5, Footnotec)---
Taiga Shield69TSQC358,500(Table 5, Footnotea)X---
Taiga Shield67TSLB31,000(Table 5, Footnotea)X---
Footnotes
Footnote a

area estimated as proportional to sampled area by transects;

Return to table 5, footnote a referrer

Footnote b

discarded from analysis (only one plot);

Return to table 5, footnote b referrer

Footnote c

no segments

Return to table 5, footnote c referrer

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Available estimates

Table 5  shows the availability of data by data source, stratum, and ecozone+. In most cases, there are multiple strata within an ecozone+. A total population estimate can only be calculated for a given year for an ecozone+ if data from all the individual strata within the ecozone+ are available. If some strata are missing, then the ecozone+-wide estimate was not calculated for that year. For individual species there may be few available estimates if the species was never recorded in a stratum by year combination.

Calculation of relative detection rates

The different survey platforms detect different proportions of the population. In order to combine the different platforms one survey was selected as the standard and estimates from the other survey were scaled to provide the same density. This scaling factor is the relative detection rate. The relative detection rate was estimated through maximum likelihood for all strata and years where both surveys were run. The survey with the highest observed density was used as the standard survey.

In the Mixedwood Plains, the Basse Terres Survey was used as the standard because it provided the highest observed density. In all other ecozones+, the eastern waterfowl survey was used as the standard survey. The USFWS transect survey was used as the standard survey for Canada Geese. While the CWS Helicopter Plot survey and Basse-Terres surveys were used as the standard for all other species.

The estimated relative detection rates are shown in Table 6a. Table 6b shows the results for the analysis in which the Basses Terres data were assumed to be complete for stratum 56MW and the combination of CWS Helicopter Plot and USFWS Airplane Transect data were assumed to be complete for all other strata.

Table 6. Estimated relative detection rates.
a) USFWS Airplane Transect Survey relative detection rates
SpeciesRelative detection rateStandard Error (SE)
Mallard0.430.037
American Black Duck0.340.036
Ring-necked Duck0.230.023


b) Relative detection rates for CWS Helicopter Plot/USFWS Airplane Transect and USFWS Airplane Transect/Basses Terres surveys
SpeciesCWS Plot/Transect

Relative detection rate
CWS Plot/Transect

SE
Transect/Basses Terres

Relative detection rate
Transect/Basses Terres

SE
Canada Goose0.620.180.110.024

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Species Selection

Species selection for each ecozone+ was determined using two criteria: 1) data availability, defined as the ability of the surveys to provide reliable estimates for a decade to derive trends; and 2) the importance of a given species to the ecozone+, defined by the priority species of the North American Waterfowl Management Plan (NAWMP) implementation plans and from the perspective of significance to biodiversity.

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Data Availability

The USFWS Airplane Transect Survey limits which species can be analyzed. The standard operating procedures for this survey doesn't differentiate many species. For example, mergansers, scaup, and scoters are reported as species groups, not to the species level.

For the eastern ecozones+, a set of 15 species from the USFWS Airplane Transect Survey were initially examined as potential species to highlight. Six species, Northern Shoveler, Redhead, Canvasback, Long-tailed Duck, Ruddy Duck, and American Coot are observed too infrequently for an effective trend analysis to be run and were therefore not used in the analysis for this report.

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Priority species

The NAWMP partners, including the Science Support Team, Joint Ventures, and biologists from Canada, Mexico, and the United States, have prioritized species based on socioeconomic importance and population trend or vulnerability to population decline (North American Waterfowl Management Plan, 2004). A detailed description of the NAWMP prioritization process can be found in NAWMP Plan Committee (2004) and in various implementation plans for respective Joint Ventures. The NAWMP priorities were identified at continental and regional scales. At the continental scale two main criteria were used, continental population trends and importance to harvest. Criteria used at the regional scale include, relative density during breeding and non-breeding periods of the Waterfowl Conservation RegionFootnote6 (compared to other Waterfowl Conservation Regions) and threat to the habitat (North American Waterfowl Management Plan, 2004).

Species selection for this report were based primarily on the importance of an ecozone+ to a given species for breeding since only surveys from the breeding period were used for this analysis.

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Footnotes

Footnote 6

The regional scale was tailored to ecological regions with relatively homogeneous waterfowl communities, habitats, species-habitat relationships, and threats to habitats. Consequently, "Waterfowl Conservation Regions" were created for NAWMP's geographic units. These Waterfowl Conservation Regions are essentially subdivisions of  Bird Conservation Regions (BCR), which have been widely accepted in the avian conservation and management community as planning units. Not surprisingly, BCR delineations (or combination of several BCRs) closely match those of ecozones+ as both systems are variations of the national ecological classification system.

Return to footnote 6 referrer