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Trends in Canadian shorebirds

Ecozones+

Boreal and Taiga Ecozones+

Information on boreal-breeding shorebirds is limited because their breeding habitat is remote, difficult and expensive to access, and techniques designed for more open ecozones+such as the Prairies or the Arctic, cannot be easily adapted to the densely-treed ecozones+ (Sinclair et al., 2004). An additional complication to assessing trends in boreal and taiga shorebirds is that they do not concentrate along migration routes, at stop-over sites, or on the wintering grounds. This makes them difficult to census and monitor throughout their annual cycle.

Species selected for reporting in this section are those outlined by Sinclair et al. (2004) as priority species for these ecozones+ (Table 4). The population estimates that are available for boreal and taiga shorebirds are reported with low or poor confidence for all species (Brown et al., 2001) making determination of trends difficult. The trend information provided by the BBS data reports low reliability for all shorebirds in the taiga and boreal Bird Conservation Regions (BCRs) -- BCR4 (Boreal and Taiga Cordillera ecozones+), BCR6 (Boreal and Taiga Plains ecozones+), BCR7 (Taiga Shield and Hudson Plains ecozones+), and BCR8 (Boreal Shield Ecozone+). From the BBS data as summarized by BCR from 1966 to 2007, only Lesser Yellowlegs shows a significant trend (decline; -8.7% change per year, P < 0.01) (Sauer et al., 2008). Trend information for boreal shorebirds in Quebec (Aubry and Cotter, 2007) shows most species are increasing or have stable populations. Only Wilson’s Snipe was found to have a significantly declining trend (Table 5). However, when compared with qualitative trend information for boreal species across Canada, most species are believed to be declining (Table 4) (Brown et al., 2001; Morrison, 2001). An assessment of various migration surveys separated into two major regions (North Atlantic BCR and Midwest BCR) found declining population trends for Solitary Sandpiper (Tringa solitaria) (-6.3% per year) in the North Atlantic Region (Table 6) (Bart et al., 2007).

Table 4. Population trend assessments for shorebirds breeding in the boreal and taiga regions.
SpeciesEcozones+ for which this is a Priority Species Footnote1
Plains
(Boreal)
Ecozones+ for which this is a Priority SpeciesFootnote1
Plains
(Taiga)
Ecozones+ for which this is a Priority SpeciesFootnote1
Shield
(Boreal)
Ecozones+ for which this is a Priority SpeciesFootnote1
Shield
(Taiga)
Ecozones+ for which this is a Priority SpeciesFootnote1
Cordillera
(Boreal)
Ecozones+ for which this is a Priority SpeciesFootnote1
Cordillera
(Taiga)
U.S. Shorebird Conser-vation PlanCanadian Wildlife Service Shorebird CommitteeTrend
SummaryFootnote2
Greater Yellowlegsxxxx  Not enough informationMixed trends
Lesser Yellowlegsxx xxxSignificant declineSignificant decline↓↓
Solitary Sandpiperxxx xxMixed trendsDecline
Short-billed Dowitcherxxxx  Significant declineSignificant decline↓↓
Wilson’s SnipexxxxxxSignificant declineSignificant decline↓↓

Source: adapted from (Brown et al., 2001; Morrison, 2001). Trend data are based on many localized data sets across the North America spanning 1970s-2000s as well as expert opinions

Footnotes

Footnote 1

Taken from Sinclair et al. (2004).

Return to footnote 1

Footnote 2

↓↓ significant declining population trend; ↓ probable or declining population trend, not statistically significant; ↔ not enough information to conclusively determine population trend (mixed trends); ↓? or ↓↓? conflicting information

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Table 5. Trends of boreal shorebirds occurring in Quebec.
SpeciesQuebecFootnote1
Spring Migration
(r)
QuebecFootnote1
Spring Migration
(P)
QuebecFootnote1
Spring Migration
Trend
QuebecFootnote1
Autumn Migration
(r)
QuebecFootnote1
Autumn Migration
(P)
QuebecFootnote1
Autumn Migration
Trend
CanadaFootnote2
Trend
Greater Yellowlegs0.3050.157Stable0.0170.938StableStable
Lesser Yellowlegs0.4430.034IncreasingFootnote**-0.0910.679StableDeclining^
Solitary Sandpiper0.3440.108Stable-0.1770.419StableDeclining
Wilson’s Snipe-0.3650.087DecliningFootnote*-0.6020.002DecliningFootnote**Declining^

Source: Quebec data from Aubry and Cotter, (2007); Canada data from Donaldson et al. (Donaldson et al., 2000)

Footnotes

Footnote 1

** strong (significant) trend P < 0.05; * weak trend 0.10 > P ≥ 0.05

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Footnote 2

“Declining^” denotes predominantly negative trends with significant declines in at least one region of Canada; “Declining” denotes predominately negative trends; “Stable” denotes both positive and negative trends have been calculated.

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Table 6. Estimated population trends for shorebirds expressed as the annual rates ofchange.
SpeciesEstimated Trend
North Atlantic
Estimated Trend
Midwest
Greater Yellowlegs0.9921.011
Lesser Yellowlegs0.9640.992
Solitary Sandpiper0.937Footnote**0.972
Short-billed Dowitcher1.0181.110
Wilson’s Snipe0.9661.038

A value less than 1 denotes a population decline where each 0.01 is 1% decrease per year (for example 0.98 mean a decline of 2% per year.
Source: data from Bart et al. (2007)

Footnotes

Footnote 8

P-value 0.01 to 0.049

Return to footnote*

Footnote 2

P-value < 0.01

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Intensive shorebird studies have been carried out in the Taiga Shield Ecozone+ near Yellowknife and Dettah, NWT (Johnston, 2000; Johnston et al., 2008a) and in the Taiga Plains Ecozone+ near Ft. Simpson and Wrigley, NWT (Johnston et al., 2008b) to determine if shorebirds in the boreal and taiga ecozones+ can be surveyed from a helicopter. Use of aerial surveys was recommended by the Boreal PRISM Committee as a potential tool for monitoring boreal and taiga shorebirds (Sinclair et al., 2004). Unfortunately, boreal and taiga shorebirds rarely flush and if they do, flush approximately ten seconds after the helicopter has passed so they are not properly recorded by the aerial surveyors, resulting in very low or incalculable detection ratios (estimated number of bird x seen from the air divided by the actual number of bird x on the ground). Thus, aerial surveys are an unsuitable method of obtaining absolute population estimates (Elliott and Johnston, 2009).

Large-scale, intensive, and costly ground studies will be required to get reliable population and trend estimates for boreal and taiga breeding shorebirds. However, since much is still unknown about the breeding ecology of these species, further research is required before an effective monitoring program can be designed (Howe et al., 2000; Bart et al., 2005). Suggestions by Sinclair et al. (2004) for potential research and monitoring which are in progress, include the use of combinations of existing protocols such as the North American BBS, off-road point counts with modified but complementary data to the BBS, ground-based breeding season surveys, and further examination of stop-over site data to assess its usefulness for boreal and taiga shorebird monitoring and trend assessment.

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Hudson Plains Ecozone+

The vast Hudson Bay Lowlands, lying behind the coastlines of James Bay and Hudson Bay, supports a number of breeding species of shorebirds. Very little information is available on population trends. Shorebirds have been studied extensively at Churchill, Manitoba, and nearly all studies have reported widespread declines in shorebirds and other birds (Jehl and Lin, 2001; Jehl, 2004). Declines were particularly notable in the Semipalmated Sandpiper, which used to be the most abundant breeding shorebird in the Churchill region up to the 1940s, but which by 2004 could no longer be found breeding in the area (Allen, 1945; Gratto-Trevor, 1994; Jehl, 2007). A similar situation was reported at Cape Henrietta Maria at the north end of James Bay, where the species was abundant in the 1970s but had become scarce by 2004/2005 (G. Peck and M. Peck in Peck and James, 1983; Cadman et al., 1987; Jehl, 2007). These results appear to be consistent with the declines reported for Semipalmated Sandpipers on migration in many other regions (for example Morrison et al., 1994; Morrison et al., 2001; Bart et al., 2007; and other work summarized by Jehl, 2007). Somewhat anomalous results were reported by Sammler et al. (2008) at a study area 60 km east of Churchill, where results of line transect surveys indicated an increase in Semipalmated Sandpipers between 1984 and 1999, though many other larger ground-nesting species declined. While the precise reasons for the decline in Semipalmated Sandpipers remain unclear, it did not appear to be linked to the extensive damage to coastal habitats caused by increasing populations of Lesser Snow Geese (Jehl, 2007; Sammler et al., 2008), and is more likely to be related to conditions outside the breeding grounds (Jehl, 2007).

The coastlines of Hudson Bay and James Bay are extremely important as migration corridors for many shorebirds breeding in the central Canadian Arctic en route to and from their nesting grounds (Morrison and Harrington, 1979). Many Hudsonian Godwits are thought to fly directly from the James Bay area to stop-over areas in South America (Morrison, 1984), and James Bay is also a key area for the Endangered Red Knot (COSEWIC, 2007). No trend information is available for shorebird migrants passing through the area.

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Arctic Ecozone+

The Arctic Ecozone+ is of great importance globally for shorebird production. Sixty percent of North American shorebirds breed in the Arctic. The Canadian Arctic alone provides 75% of the North American breeding range for 15 of the 49 species of shorebirds that are common to North America (Donaldson et al., 2000).

Globally, 44% of estimated population trends for Arctic-breeding shorebirds are declining (Figure 8) making the problem more widespread than was originally thought (Morrison et al., 2001). Overall, the Arctic breeders as a group are declining 1.9% per year (Bart et al., 2007).

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Figure 8. Summary of population trends for Arctic-breeding shorebirds, 2003.

graph

Long Description for Figure 8

This bar graph shows summary of population trends for Arctic-breeding shorebirds in 2003. For populations for which trends are known, 12% are increasing, 42% are stable, 44% are decreasing, and 2% are possibly extinct.

Globally, population trends have been estimated for 52% of Arctic-breeding shorebirds (100 biogeographical populations of 37 species). Of these, 12% are increasing, 42% are stable, 44% are decreasing and 2% are possibly extinct.
Source: Delany and Scott (2006)

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An analysis of fall migration count data was undertaken to determine if the declining numbers of birds recorded on migration counts could be explained by changes in migration routes or timing or by changes in detection rates (Bart et al., 2007). The authors concluded that migration counts most likely reflected a true reduction in population size. They found no evidence of major shifts in the number of birds migrating along specific routes and no major changes in variables related to detection. Annual rates of change were calculated over the period 1974 to 1998 in this study – results are shown in Figure 9 for Arctic-breeding shorebirds with sufficient survey counts in fall migration surveys conducted in the Canadian-United States North Atlantic or United States Midwest regions.

Figure 9. Estimated trends in Arctic-breeding shorebird fall migration counts, 1974-1998.

graph

Long Description for Figure 9

This bar graph shows estimated trends in Arctic breeding shorebird fall migration counts from 1974 to 1998. Annual decreasing trends with high significance include, Black-bellied Plover 5%, American Golden-plover 7.2%, and Pectoral Sandpiper 4.5%. Less significant annual decreasing trends include Hudsonian Godwit 3.5%, Semipalmated Sandpiper 4%, and Red-necked Phalarope 7.6%. Non-significant annual decreasing trends include, Whimbrel 3.3%, Ruddy Turnstone 12.3%, Red Knot 3.3%, Sanderling 3.3%, White-rumped Sandpiper 5.2%, Baird’s sandpiper 1%, and Dunlin 2.6%. A non-significant annual increase of 0.4% was found for Sempalmated Plover.

NA = North Atlantic migration survey; MW = Midwestern migration survey.
Source: data from Bart et al. (2007)

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Two major shorebird trend reviews by the U.S. Shorebird Conservation Plan Committee (in 2001 and 2004) and Canadian Wildlife Service Shorebird Committee (in 2001) assessed 18 species of Arctic-breeding shorebirds with very similar results (Table 7). Eight species were listed in both assessments as having significant population declines (Brown et al., 2001; Morrison et al., 2001; U.S. Shorebird Conservation Plan, 2004).

Table 7. Population trend assessments for Arctic-breeding shorebirds.
SpeciesTrend
summaryFootnote1
U.S. Shorebird
Conservation Plan
Canadian Wildlife Service
Shorebird Committee
Black-bellied Plover
↓↓
Significant declineSignificant decline
American Golden-Plover
↓↓
Significant declineSignificant decline
Semipalmated Plover
↓?
Not enough informationSignificant decline
Eskimo Curlew
↓↓
Significant declineLikely extinct
Whimbrel
↓?
Significant declineMixed trends
Hudsonian Godwit
Not enough informationDecline
Ruddy Turnstone
↓↓
DeclineSignificant decline
Red Knot
↓↓
Significant declineSignificant decline
Sanderling
↓↓
Significant declineSignificant decline
Semipalmated Sandpiper
↓↓
Significant declineSignificant decline
White-rumped Sandpiper
Not enough informationMixed trends
Baird’s Sandpiper
↓?
Not enough informationDecline
Pectoral Sandpiper
Not enough informationMixed trend
Purple Sandpiper
↓?
StableSignificant decline
Dunlin
↓↓
Significant declineSignificant decline
Buff-breasted Sandpiper
DeclineDecline
Red-necked Phalarope
↓↓
DeclineSignificant decline
Red Phalarope
↓↓
Significant declineSignificant decline

Source: extracted from the U.S. Shorebird Conservation Plan (2004); Brown et al.(2001); and Morrison et al. (2001)

Footnotes

Footnote 1

↓↓ significant declining population trend; ↓ probable or declining population trend, not statistically significant; ↔ not enough information to conclusively determine population trend (mixed trends); ↓? conflicting information     
Trend data are based on many local data sets across the North America spanning 1970s-2000s, as well as on expert opinion.

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What is of most concern is that over the past 30 years many species trends have changed from slightly declining to significantly declining, indicating that the decline is persistent and ongoing (Morrison et al., 2001; Delany and Scott, 2006). The declines are observed in species with a range of migration, habitat, and breeding strategies and needs. Preliminary investigations by Thomas et al. (2006a) and Bart et al. (2007) found no common factors among declining species.

In the U.S. Shorebird Conservation Plan (Brown et al., 2001), population trend information was combined with five other variables (relative abundance, threats during breeding season, threats during non-breeding season, breeding distribution, and non-breeding distribution) to create a conservation prioritization scheme. The scheme, adopted in the Canadian Shorebird Conservation Plan (Donaldson et al., 2000), is useful because species with stable or slightly downward-trending populations with threats on their wintering grounds and very specific breeding ground habitat requirements may be more at risk than species with significant population declines. The highest priority species were those designated ‘highly imperiled’. Using this prioritization scheme, the only Arctic species listed in 2001 as ‘highly imperiled’ (Eskimo Curlew) is believed to be extinct (Environment Canada, 2007).

In 2004, species were re-evaluated (U.S. Shorebird Conservation Plan, 2004) and the status of several species was upgraded (Table 8).

Table 8. Conservation status of tundra-nesting shorebirds as classified in the U.S. Shorebird Conservation Plan.
Highly imperiled (first priority)Species of high concern (second priority)
Eskimo Curlew (believed to be extinct)
Footnote*Buff-breasted Sandpiper (globally)
Footnote*Red Knot (Canadian Arctic-Atlantic Coast
population)
American Golden-Plover (globally)
Whimbrel (North American populations)
Hudsonian Godwit (globally)
Ruddy Turnstone (North American populations)
Red Knot (populations other than the Canadian
Arctic-Atlantic Coast population)
Sanderling (North American populations)
Footnote*Dunlin (Alaska-East Asian and Alaska-Pacific
Coast populations)

Source: U.S. Shorebird Conservation Plan (2004)

Footnotes

Footnote *

Upgraded species

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Local studies have recorded population declines over a range of periods. Analysis of the Atlantic coastal migration stop-overs from 1972 to 1983 (Howe et al., 1989) found significant declines for Black-bellied Plover (decreasing by 5.4% per year), Whimbrel (-8.3% per year) and Sanderling (-13.7% per year). Breeding populations of Red Phalarope (Phalaropus fulicarius), Black-bellied Plover, and American Golden-Plover decreased significantly, by 76, 87, and 79% respectively, in the Rasmussen Lowlands (Central Arctic) over a 20-year period (Gratto-Trevor et al., 1998). Given the long time interval between studies, natural fluctuation as a result of a series of poor breeding seasons rather than a persistent and continuous population decline could explain the differences between the two study periods, but it may represent a true decline in these species (Gratto-Trevor et al., 1998).

A study in the Foxe Basin (Prince Charles and Air Force Islands) found significant population declines for White-rumped Sandpiper (-61%) and Red Phalarope (-43%) over an eight-year time span (1989-1997) (Johnston and Pepper, 2009). For Red Phalarope the decline was even more pronounced at East Bay, Southampton Island, where there was a 93% decline over six years (1999-2005) (Pirie et al., 2012). All shorebird species (n = 5) at East Bay declined by more than 90% over the same interval. In 2007, there was a small rebound to about 33% of the original 1999 values. This coincided with a high lemming (and therefore low predation) year (Pirie et al., 2012).

Near Churchill Manitoba, a comparison of six qualitative bird abundance studies between 1930 and the 1990s found that Semipalmated Sandpiper, Stilt Sandpiper and Red-necked Phalarope experienced a ‘great decrease’, and Dunlin (Calidris alpina) a ‘decrease’ (Jehl and Lin, 2001). Huge declines were also noted at La Perouse Bay, Manitoba (40 km east of Churchill), for Semipalmated Sandpiper and Red-necked Phalarope (Gratto-Trevor, 1994).

One of the current major limitations to determining population trends for Arctic-breeding shorebird species is the lack of two reliable population estimates. In many cases intensive surveys of shorebirds on the Arctic breeding grounds have led to increases to the world population estimate for a given species (Johnston et al., 2000; Latour et al., 2005; Johnston and Pepper, 2009). This does not reflect an increase in world population size but instead is an indication that initial population estimates were probably low (Brouwer et al., 2003; Morrison et al., 2006). The large-scale PRISM, which has an Arctic component, is partway through a multi-year survey program that will produce continental population estimates for 19 species of shorebirds that breed in the North American Arctic. Once the first pass of surveys is complete, a second set is planned to assess species-specific as well as North American Arctic-wide population trends (Skagen et al., 2003; Bart and Earnst, 2004; Bart et al., 2005; Bart and Johnston (eds), 2012).

Proposed causes of shorebird population declines include: loss of migration stop-over sites, loss of wintering habitat, and life history characteristics (that is, migratory behaviour, life history, biogeography) which may predispose shorebirds to population decline. Future population decline is expected to be accelerated by habitat changes on the Arctic breeding grounds.

Since many shorebirds are long-distance migrants that tend to gather in very large numbers at relatively few sites, loss of one or two major stop-over sites could have a huge effect on shorebird populations. Declining food availability at existing stop-over sites can also have a large impact on populations because birds may not be able take in enough fuel to move to the next stop-over site, or may not be able to acquire the body stores essential for survival and successful reproduction (Senner and Howe, 1984; Donaldson et al., 2000; Morrison et al., 2001; Baker et al., 2004; Morrison et al., 2004; Morrison et al., 2007). Analysis of population trends of North American shorebirds found species that followed continental migration routes (as opposed to coastal or oceanic migration routes) were at higher risk of population decline because of ecosystem loss and alteration (Thomas et al., 2006a; Bart et al., 2007). Continental migrants use small, ephemeral ponds and wetlands that are scattered over a large area. These ponds and wetlands are difficult to delineate for conservation initiatives making it harder to preserve them as compared to larger stop-over sites (Thomas et al., 2006a). Little is known about Arctic stop-over sites because of their remoteness. Observations along a 200 km stretch of coast line in the Kivalliq Region (northwestern Hudson Bay) during the 2008 spring migration found hundreds of High Arctic nesting migrants feeding on insects in the wrack lines on their journey north to the breeding grounds (Johnston and Rausch, unpublished data). The importance of sites such as these to migration and subsequent breeding success is not known.

Loss or degradation of habitat on the non-breeding grounds from human activities such as oil pollution (Harrington and Morrison, 1980), mechanical dredging or fishing (Piersma et al., 2001), conversion of native grasslands and wetlands to agriculture (Isacch and Martinez, 2003; Shepherd et al., 2003) and tourism and development on marine beaches (Blanco et al., 2006) may be a cause of population decline (Thomas et al., 2006a). Complicating our assessment of the importance of wintering habitat is that little is known about food resources on the wintering grounds (Morrison et al., 2 004). Threats on the wintering grounds, however, have been found to have a weak influence on the likelihood of a species being in population decline (Thomas et al., 2006a).

The intrinsic biology of shorebird species may make them more susceptible to population decline. Migratory behaviour (such as distance and routes) is suspected to be the most influential intrinsic factor, with more continental migrants in population decline than coastal or oceanic migrants (Thomas et al., 2006a). Phylogenic characteristics such as body and clutch size, lifespan, and relatedness were found to be unimportant to population decline, but limited clutch sizes means that recovery following a decline is likely to be slow (Myers et al., 1987). Sexual selection may have an influence on declining populations since most socially polygamous species have declining populations while socially monogamous species have stable or increasing population trends – but the data are not conclusive. There are no clear intrinsic factors held in common by shorebird species with declining population trends and extrinsic factors are more likely to be the primary cause of decline (Thomas et al., 2006a; Thomas et al., 2006b; Bart et al., 2007).

Habitat changes in the Arctic caused by climate change are expected to have an exacerbating effect on the declining population trends of Arctic-breeding shorebirds (Bart et al., 2007). Arctic-breeding shorebirds are adapted to the annually variable weather conditions of the Arctic during the breeding season. However, their conservative life-history strategy (low reproduction and long lifespan) makes it difficult for them to adapt to accelerated climate change. This puts Arctic-breeding shorebirds more at risk of population decline than other groups (Donaldson et al., 2000; Meltofte et al., 2007). Effects of accelerated climate change on breeding habitat include: drying of tundra ponds (Walsh et al., 2005; Smol and Douglas, 2007), shrub encroachment (Callaghan et al., 2005), and asynchrony of insect-chick hatch (Tulp and Schekkerman, 2006).

The synchrony of shorebird chick hatch with the peak of insect emergence is not as critical as hatch occurring when there is sufficient food supply. The availability of the food supply is strongly influenced by weather and a sufficient supply is only available for 40% of the insect season (Tulp and Schekkerman, 2008). The peak date of insect emergence fell between 8 July and 23 July for 75% of the 33-year study period. These earliest and latest peak emergence dates were recorded in consecutive years, showing that the date of peak emergence is not advancing linearly with time. Overall, however, the date of peak insect emergence as well as the range of dates with sufficient food available for the normal growth of chicks is getting earlier in the season (Tulp and Schekkerman, 2008). Since Arctic shorebirds time nest initiation to occur as soon as the snow melts, the advancement in the timing of insect emergence is not critical for the survival of chicks hatched from the earliest nests. It could, however, be a serious problem for chicks from late nests, or from re-nests (clutches laid late to replace an earlier nest that was unsuccessful) because they will hatch too late in the season to obtain sufficient food resources (Meltofte et al., 2007). Further analysis is needed to determine if snow melt is advancing at the same rate as the timing of insect emergence, which would permit birds to nest earlier. It is not known whether shorebirds will be able to adjust their migration strategies to arrive on the breeding grounds sooner in response to an earlier snow-free season. Species which make the final jump to the breeding ground from latitudes closer to the Arctic may be more successful than species that use internal length-of-day cues to initiate migration from very distant wintering grounds (Tulp and Schekkerman, 2008).

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