Trends in Canadian shorebirds
Atlantic Maritime Ecozone+
The Atlantic Maritime Ecozone+ forms part of the Atlantic Northern Forest Bird Conservation Region (BCR 14 in Canada). Although this ecozone+ supports a number of breeding shorebird species, it is most important for migrant shorebirds, with coastal habitats – especially those around the Upper Bay of Fundy – of pivotal importance as key stop-over and refueling areas for various species, particularly the smaller sandpipers (Morrison, 1977; Morrison and Harrington, 1979; Hicklin, 1987). Trend estimates for migrant shorebirds are derived from the Atlantic Canada Shorebird Survey (ACSS) (previously Maritimes Shorebird Surveys (MSS)), while breeding shorebird trends can be estimated from BBS data from Canadian sites in the Atlantic Northern Forest BCR (Sauer et al., 2008).
Numbers of shorebirds passing through the Canadian Atlantic provinces have declined greatly since surveys were started in 1974 (Morrison et al., 1994; Morrison et al., 2001; Morrison and Hicklin, 2001; Bart et al., 2007). Updated analyses of ACSS data confirm this (Table 1). Between 1974 and 2006, for 15 species of shorebirds for which sufficient data were available, five species showed statistically significant negative trends, including Red Knot, Least Sandpiper (Calidris minutilla), Lesser Yellowlegs (Tringa flavipes), Black-bellied Plover (Pluvialis squatarola), and Ruddy Turnstone (Arenaria interpres). No other trends were statistically significant, but only two species (Semipalmated Plover (Charadrius semipalmatus) and Whimbrel (Numenius phaeopus)) showed positive trends, whereas 13 showed negative trends. These results show a significant tendency towards declines (χ2 = 8.07, df1, P<0.005) (Morrison and Collins, unpublished data).
(% per year)
|Red Knot||-10.9||P <0.05||11.2||9.1||3.3||-97.5||39.5|
|Least Sandpiper||-6.6||P <0.05||22.2||9.8||11.6||-88.8||80.7|
|Lesser Yellowlegs||-5.0||P <0.05||52.2||16.4||9.8||-80.6||29.2|
|Black-bellied Plover||-3.0||P <0.05||43.1||23.0||26.7||-62.3||51.0|
|Ruddy Turnstone||-2.8||P <0.01||10.9||11.4||4.2||-59.7||13.2|
Change is the percentage change over the entire period calculated from the overall trend (% per year).
Source: Morrison and Collins, unpublished data
Negative trends generally predominated during the 32 year period of the surveys: they outnumbered positive trends in the 1970s, 1990s, and 2000s, and were especially pronounced in the 1990s. The 1980s was the only decade in which positive trends outnumbered negative ones (Morrison and Collins, unpublished data).
Red Knots are considered a flagship species in shorebird conservation because of their long migrations between breeding and wintering areas and their tendency to concentrate in large numbers in a few favoured locations. Numbers in the Atlantic Provinces reached a peak in the late 1970s and early 1980s, but by the mid-1990s had fallen to very low levels (Figure 1). These declines reflect the declines that have occurred in Western Hemisphere populations of knots (Morrison et al., 2004). The populations wintering in Tierra del Fuego and Florida were assessed Endangered and Threatened, respectively, in 2007 (COSEWIC, 2007).
Figure 1. Trends in numbers of Red Knots migrating through the Atlantic Maritime Ecozone+, 1974-2006.
Long Description for Figure 1
This line graph shows trends in numbers of Red Knots migrating through the Atlantic Maritime Ecozone+ from 1974 to 2006. Numbers peaked in the late 1970s, early 1980s, and early 1990s, with abundance index value peaks of approximately 55 in 1977, 78 in 1979, 48 in 1981, and 49 in 1991. However, by the mid-1990s, abundance had fallen to very low levels where it remained below an abundance index of 8 for over a decade.
Source: Morrison and Collins, unpublished data
The reasons for the observed shorebird declines in Atlantic Canada are not completely understood. Changes, such as increases in raptors, have occurred in coastal habitats used by shorebirds that could affect use of historic shorebird staging sites, or how long the birds remain in those areas (length-of-stay), and might result in decreased counts of shorebirds at some migration areas (Hicklin, 2001), without a decrease in total population numbers. However, it is likely that the negative trends for at least some species reflect real population declines caused by factors in other parts of the migration ranges of the birds. Declines in Red Knots, for instance, are thought to be caused mainly by the birds being unable to gain sufficient weight during spring migration through Delaware Bay owing to overharvesting of horseshoe crabs (Limulus polyphemus), leading to a decline in crab eggs, the main food source of the knots (COSEWIC, 2007). The result was a steep decline in the survival of the knots (Baker et al., 2004).
Other potential causes of declines include: loss and degradation of coastal, wetland, and grassland habitat during wintering, climate (such as cooling eastern Arctic), changes in predator regimes (for example increased predation pressure due to a decrease in trapping of foxes or decline in DDT resulting in an increase in raptors), human disturbance, contaminants, and disease (Donaldson et al., 2000). Migrant shorebirds that are declining in eastern Canada include a diverse array of species of different sizes and ecology – such as plovers, sandpipers, yellowlegs, and turnstones – suggesting a variety of problems with wetland habitats used by the birds.
Relatively few species of shorebirds breed in the Atlantic Maritime Ecozone+. Nevertheless, trends can be calculated for the six species of shorebirds occurring on BBS routes (Figure 2). All six showed declines. Two species showed significant declines: Killdeer (-2.5% per year, P<0.001), a short distance migrant that is also declining significantly across its Canadian range (‑3.2% per year, P<0.001), and Wilson’s Snipe (Gallinago delicata) (-2.6% per year, P<0.01), which breeds in wetlands, but which shows a positive trend across Canada (0.5% per year, not significant) owing to population increases in the western part of its range. The decline of the other four species was not significant.
Figure 2. Trends in abundance of shorebirds breeding in the Atlantic Maritime Ecozone+.
Long Description for Figure 2
This line graph shows trends in abundance of shorebirds breeding in the Atlantic Maritime Ecozone+ from 1968 to 2006. Trends for six species of shorebirds occurring along the Breeding Bird Survey routes all indicate declines in abundance, although only Killdeer and Wilson’s Snipe declines are significant (-2.5% per year and -2.6% per year, respectively). Total declines in abundance levels during this period for each species are: Killdeer 62%, Upland Sandpiper 70%, American Woodcock 97%, Spotted Sandpiper 64%, Willet 71%, and Wilson’s Snipe 64%.
Change indicates the percentage change over the period of the surveys (1968-2006) calculated from the trend. Killdeer and Wilson’s snipe declines are significant (-2.5% per year, P<0.001 and -2.6% per year, P<0.01 respectively) Killdeer is a short distance migrant; Upland Sandpiper is a grassland bird, American Woodcock (Scolopax minor) is a successional/shrub bird; others are wetland birds
Source: Breeding Bird Survey (Sauer et al., 2008)
Mixedwood Plains Ecozone+
The Mixedwood Plains Ecozone+ is equivalent to the Lower Great Lakes/St. Lawrence Plain BCR (BCR 13), extending through southern Ontario north of the Great Lakes and into Quebec along the shores of the St. Lawrence River. Migrant shorebirds make use of lake and river shoreline habitats and associated wetlands, as well as sewage lagoons. Some information is available on trends from the OSS. Five species breed regularly in a variety of habitats and are covered by the BBS.
The only information currently available for migrant shorebirds in this ecozone+ is from the OSS for 1976 to 1997 (Ross et al., 2001). A summary of the results from these data is shown in Table 2. Shorebirds migrating through the ecozone+ form three broad groups: 1) species that breed in the Arctic and stop at the small-scale, relatively dispersed stop-over sites in southern Ontario en route to the east coast of North America; 2) species that breed to the north throughout the boreal forest; and 3) species with a widespread breeding distribution throughout Ontario, which include individuals from both local populations and those breeding farther north.
(% per year)
|Semipalmated Sandpiper||18||-4.97||= 0.5< P <0.1||Arctic|
|Wilson's Snipe||10||-15.26||= 0.5< P <0.1||Widespread|
|n negative trends||-||12||-||-|
|n positive trends||-||2||-||-|
Source: adapted from Ross et al., (2001)
Declines were widespread, occurring in all groups. Negative trends (14) significantly outnumbered positive trends (2); negative trend values tended to be high, but were not significant owing to high inter-year variation in counts and small sample sizes. Only the Semipalmated Sandpiper showed a significant negative trend, a phenomenon occurring in many other regions.
Five species of shorebirds, occupying a variety of habitats, were detected on BBSroutes (Figure 3). With the exception of Wilson’s Snipe, where no trend was detected, trends were negative, with Killdeer and Spotted Sandpipers (Actitis macularius) showing significant declines. Both species also showed significant negative Canada-wide trends (-3.2%per year, P<0.001; -2.0% per year, P = 0.005, respectively), as well as negative trends at migration areas (see Table 2).
Figure 3. Trends in abundance of shorebirds breeding in the Mixedwood Plains, 1968-2006.
Long Description for Figure 3
This lines graph shows trends in abundance of shorebirds breeding in the Mixedwood Plains Ecozone+ from 1968 to 2006. With the exception of Wilson’s Snipe, where no trend was detected, trends for shorebirds occurring along the Breeding Bird Survey routes indicate declines in abundance, although only Killdeer and Spotted Sandpiper declines are significant (-1.8% per year and -4.0% per year, respectively). Total declines in abundance levels during this period for the remaining species are: Spotted Sandpiper 80%, American Woodcock 64%, Upland Sandpiper 58%, and Killdeer 50%.
Percentages in brackets represent the change in abundance index between the 1970s and 2000-2006.
Guilds: short distance migrant (Killdeer); wetland (Spotted Sandpiper and Wilson’s Snipe);grassland (Upland Sandpiper), successional/shrub (American Woodcock).
Killdeer decline (-1.8% per year) is significant at P<0.001; Spotted Sandpiper decline (-4.0% per year) is significant at P<0.01; Upland Sandpiper decline (-2.2% per year), American Woodcock (-2.6% per year) and Wilson’s Snipe (0% change) are not significant.
Source: adapted from the Breeding Bird Survey (Sauer et al., 2008)
The Prairies Ecozone+ provides important habitat for both breeding and migrant shorebirds including eight species whose breeding range in Canada is primarily or entirely in the Prairies (American Avocet (Recurvirostra americana), Marbled Godwit (Limosa fedoa), Piping Plover, Wilson’s Phalarope (Phalaropus tricolor), Black-necked Stilt (Himantopus mexicanus), Willet (Tringa semipalmata), Long-billed Curlew (Numenius americanus), and Upland Sandpiper). In addition, the only reported (but rare) breeding occurrences of Mountain Plover (Charadrius montanus) and Snowy Plover (Charadrius alexandrinus) in Canada have been in this area. Thirty-one species of shorebirds regularly migrate through the Prairies, which provide important staging sites during both spring and fall. For migrants, from a national perspective, the Prairies are most important in the spring. Species such as Sanderling (Calidris alba), Red-necked Phalarope (Phalaropus lobatus) and White-rumped Sandpiper (Calidris fuscicollis) stage there in large numbers. In the fall, this region is important to Baird’s Sandpiper (Calidris bairdii), Pectoral Sandpiper (Calidris melanotos), Buff-breasted Sandpiper (Tryngites subruficollis), and Hudsonian Godwit (Limosa haemastica), and in both spring and fall to Stilt Sandpiper (Calidris himantopus), Lesser Yellowlegs, and Semipalmated Sandpiper (Gratto-Trevor et al., 2001). Populations of shorebird species usually number in the tens to hundreds of thousands, with a few in the low millions, compared to much higher numbers for many landbird and waterfowl species (Morrison et al., 2006). Shorebird species are also characterized by low annual reproduction (four eggs and often little renesting) and high adult survival, so any declining trend is of concern when it reflects declines in productivity or survival, and not changes in movement patterns.
The Prairies Ecozone+ is very important to shorebird migrants, many of which nest in the Arctic or boreal (Skagen et al., 1999). Based on abundance, this ecozone+ is most important during migration for the following species: Sanderling (spring), Red-necked Phalarope (spring), White-rumped Sandpiper (spring), Stilt Sandpiper (spring and fall), Baird’s Sandpiper (fall), Pectoral Sandpiper (fall), Buff-breasted Sandpiper (fall), Hudsonian Godwit (fall), Lesser Yellowlegs (spring and fall), and Semipalmated Sandpiper (Calidris pusilla: spring and fall) (Alexander and Gratto-Trevor, 1997; Gratto-Trevor et al., 2001).
Wetland conditions in the Prairies are prone to large inter- and intra-year variations in water levels. Since shorebirds forage in shallow wetlands, which are most affected by these changes, there is considerable variation in shorebird use of specific wetlands between seasons and years, as some become dry and others are too flooded (for example, Figure 4).
Figure 4. East side of Big Quill Lake Saskatchewan: beaches are >1 km wide in dry years (left), while virtually no shoreline habitat remained in the wet year of 2007 (right).
Long Description for Figure 4
Photos: East side of Big Quill Lake Saskatchewan Left: Beaches are more than 1km wide in dry years Right: Virtually no shoreline habitat remained in the wet year of 2007.
Photos © C. L. Gratto-Trevor
In some years some species (such as White-rumped Sandpiper) stage in prairie Canada in spring in very large numbers when conditions in the mid-western states are too dry. In other years, most White-rumped Sandpipers over-fly prairie Canada if conditions in the United States are favourable (Harrington et al., 1991). Therefore, although we have information from certain wetlands and years on numbers of specific shorebird species, we have no way of measuring population trends in prairie shorebird migrants at this time, and no surveys initiated to measure such trends in the future. Some trend information may be obtained from surveys elsewhere (such as in the Arctic) for particular species, but it is difficult to know whether they are examining the same populations that move through prairie Canada. A further complication is that one does not necessarily have birds from the same breeding area migrating through prairie Canada in the spring versus the fall. For example, spring Semipalmated Sandpipers originate from the central Canadian as well as western Arctic, while fall migrants are entirely of western Arctic origin, and the central Arctic birds move south through the Atlantic coast (Gratto-Trevor and Dickson, 1994).
However, declines in shorebirds elsewhere in Canada and the United States suggest a potential problem (Donaldson et al., 2000; Brown et al., 2001), and future climate change is likely to decrease numbers of shallow prairie wetlands.
While most North American shorebirds breed in the Arctic, the next highest number breed in interior grasslands and the breeding distribution of several species in Canada is restricted entirely to the Prairies. Of the seven priority prairie breeders noted in the Prairie Canada Shorebird Conservation Plan -- Piping Plover, Long-billed Curlew, Marbled Godwit, Willet (western subspecies), American Avocet, Wilson’s Phalarope, and Upland Sandpiper (Gratto-Trevor et al., 2001) – all but Piping Plover are covered to some extent by the BBS. That survey was not designed for non-singing, often wetland associated species however, so trend information from the BBS is more appropriate for some shorebird species than others. For the seven species listed above, trends for Upland Sandpipers are probably most accurate, and Long-billed Curlews (low numbers), American Avocet, and Wilson’s Phalarope (wetland species) least useful. Primarily this means that trends are unlikely to be statistically significant. Nevertheless, since no other consistent surveys for these species exist, BBS results for all (except Piping Plover) are shown in Figure 5.
Figure 5. Trends in abundance of priority Prairies Ecozone+ shorebird breeders, 1970s-2000s
Long Description for Figure 5
This line graph shows trends in abundance of priority Prairies Ecozone+ shorebird breeders from 1970s to 2000s. With the exception of Wilson’s Phalarope, which showed a 4% increase in abundance, trends for shorebirds occurring along the Breeding Bird Survey routes indicate declines in abundance, although only Marble Godwit declines are significant (-1.1% per year). Total declines in abundance levels during this period for the remaining species are: Upland Sandpiper 48%, Marbled Godwit 34%, Willet 28%, Long-billed Curlew 19%, and American Avocet 13%.
Percentages indicate change from the 1970s to 2000s.
Marbled Godwit is the only significant decline (-1.1% per year)
Source: Breeding Bird Survey (Sauer et al., 2008)
The only statistically significant decline is in Marbled Godwit, which is important as approximately 60% of the world population breeds in prairie Canada (Gratto-Trevor, 2000). All of the other upland breeding species (Upland Sandpiper, Willet, and Long-billed Curlew) show a decrease in the BBS Abundance Index between the 1970s and 2000s, although overall trends are not significant. This decline is thought to be related to continued loss of ephemeral wetland habitat, which is likely to be exacerbated by future climate change.
Trends in Piping Plovers (assessed as Endangered in Canada by COSEWIC), are determined by a census carried out every five years throughout the breeding range of the species (United States and Canada), starting in 1991 (Figure 6). The prairie Canada population was at a low in the 2001 census, but had increased again in 2006 to the 1996 level. The increase between 2001 and 2006 appears to be due to improvements in habitat conditions (fewer droughts, floods, and hail at hatch, plus management efforts in protecting nests with exclosures in some areas). Since 2006, conditions in Saskatchewan (where the majority of the prairie Canada population breeds) have been poor, and productivity low. One important breeding area, Big Quill Lake, has been flooded (a fifty year high) since 2007, and another, Lake Diefenbaker (a reservoir), flooded four years in a row (2005 through 2008) from run-off and rains in Alberta. A drought resulted in many Missouri Coteau wetlands (southern Saskatchewan) being dry in 2008. Shorebirds are often affected by flood and drought cycles in the west, as the wetlands they use for foraging and chick rearing are usually very shallow.
Figure 6. Trends in numbers of Piping Plovers in prairie Canada, 1991-2006.
Long Description for Figure 6
This line graph shows trends in the numbers of Piping Plovers in prairie Canada from 1991 to 2006. The primary axis shows Piping Plovers as a percentage of the global population and the western population, and the secondary axis shows the total population. The values follow a similar trend as population increased from roughly 1400 to almost 1700 between 1991 and 1995, only to drop to less than 1000 in 2001, and returning to around 1700 in 2006.
Ten year change is 1% increase in total number.
Secondary y-axis is population and is represented on brown dotted line
Sources: adapted from the following sources for specified years: 1991 (Haig and Plissner, 1993), 1996 (Plissner and Haig, 2000), 2001 (Ferland and Haig, 2002), and 2006 (Elliott-Smith et al., 2009)
Pacific Maritime Ecozone+
A comprehensive shorebird monitoring plan for the Pacific Maritime is still in development, although existing information suggests that species that breed within British Columbia are steady or declining, and that most wintering and migrating species show stable population trends (see below). However, the uncertainties and the limited scope of these surveys suggest that results should be interpreted with caution, and continued attention should be paid to shorebird species within this ecozone+.
Population trend estimates for 1999 to 2009 are available for some species in British Columbia. These trend estimates are derived from data from the BBS, the BC Coastal Waterbird Survey, spring migration monitoring in the Fraser River Delta, and fall migration monitoring in the Strait of Georgia. These data sources cover different areas and suites of species, but represent the best available data on trends in shorebird abundance in British Columbia during the breeding, wintering, and migration seasons. Although both the BBSand migration monitoring can provide trend information prior to 1999, the BC Coastal Waterbird Survey only provides information for 1999 to 2009, and we therefore restricted trend analyses to this time period to allow comparisons. No migration monitoring occurred in 1998, so data for migration monitoring were extended to 1997.
Migration monitoring in British Columbia has focused on counts during the spring at Brunswick Point on Roberts Bank in the Fraser River Delta and on fall counts of mudflats on Sidney Island in the Strait of Georgia. Numbers of Western Sandpipers counted on Brunswick Point vary widely from year to year, and have a non-significant trend (Table 1, Figure 7). Dunlin at Brunswick Point increased in abundance between 1997 and 2009. Fall migration counts of Western Sandpipers and Least Sandpipers did not show a significant trend between 1997 and 2009. While these results should be treated with caution because the areas surveyed only cover a small proportion of all sites used during migration, the results suggest no large population declines during this time period.
Figure 7. Shorebird migration monitoring in British Columbia, 1997-2009.
Long Description for Figure 7
This graphic presents four line graphs showing shorebird migration monitoring in British Columbia from 1997 to 2009. Western Sandpiper spring migration shows a slightly decreasing trend and fall migration shows an increasing trend, although both are non-significant. Dunlin spring migration shows a significant increasing trend, approximately 7,000 in 1997 to 23,000 in 2009. Least Sandpiper fall migration shows a slightly increasing, non-significant trend.
Spring migration monitoring is conducted at Brunswick Point on the Fraser River Delta near Vancouver. Fall migration monitoring is conducted at Sidney Island in the Strait of Georgia.
Vertical lines indicate ± 1 Standard Error on the mean count, solid red lines indicate significant trends (P<0.05), and dashed lines indicate non-significant trends.
Source: Lemon and Drever, unpublished data
The BBS is considered an adequate survey for a few shorebird species that can breed in accessible areas in proximity to road networks. The BBS provides reports for Bird Conservation Regions as well as for all of British Columbia, but these were similar to the provincial trends (Environment Canada, 2010), and so only provincial trends are reported here. For the time period 1999-2009, the BBS provides trends for four species in BC (Table 3), two of which show no trend (Greater Yellowlegs and Spotted Sandpiper). Two common species (Wilson’s Snipe and Killdeer) show significant declines. Wilson’s Snipe has wide population fluctuations, and temporal trends for this species vary widely throughout the country. In contrast, Killdeer have shown a steady decline that mirrors the range-wide decline of this species throughout Canada.
Table 3. Temporal trends in population counts for selected shorebird species in British Columbia during breeding, wintering, and migration periods, 1997-2009.
Source: Environment Canada (2010); Crewe et al. (2010); Lemon and Drever, unpublished data
The BC Coastal Waterbird Survey monitors waterbird species during the winter months (September to April) throughout large sections of British Columbia’s coastlines, and provides trend information for eight species (Crewe et al. 2010, Table 3). Of the eight species, six have no significant trend. Killdeer have a significantly negative trend, and Black Turnstone showed a positive trend. Despite the lack of significant trends, we note that trends for five of the six species had negative point estimates, which may reflect an underlying fragility in their population status. British Columbia has high jurisdictional responsibility for several of the rock intertidal species (Black Turnstone, Surfbird, and Black Oystercatcher) that have large proportions of their wintering range in the province, and therefore monitoring efforts for these species should be given high priority.
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