Wild Species 2005: chapter 10
Bird - A feathered, warm-blooded vertebrate of the class Aves, having a beak and wings, laying eggs and usually able to fly - The Canadian Oxford Dictionary.
- There are approximately 10 000 species of birds worldwide, of which 653 have been found in Canada.
- Each spring, up to 3 billion birds of more than 300 species migrate north to breed in Canada's boreal forest!
- Arctic Terns make an annual migration from their breeding grounds in the Canadian Arctic to their Antarctic wintering grounds, a round-trip of approximately 35 000 km.
- Christmas Bird Counts have been used to survey North American birds since 1900. During the 2004 - 2005 count, 11 829 Canadian volunteers counted 3.05 million birds, of 300 species.
- The majority of bird species have Canada general status ranks (Canada ranks) of Secure (55%) or Accidental (30%). In addition, 6% of bird species have Canada ranks of Sensitive, 4% have Canada ranks of At Risk, 2% have Canada ranks of May Be At Risk, and less than 1% have Canada ranks of Extinct or Extirpated.
- Of the 629 species of birds that were ranked in both 2000 and 2005, the Canada ranks of 9% have been altered (55 species). 38% of the changes moved species into a category with a higher level of risk, 36% of the changes moved species into a category with a lower level of risk, and 25% of the changes moved species out of the Undetermined or Not Assessed categories Changes in Canada rank have not led to substantial changes in the proportion of bird species within each general status rank.
From the delicate Ruby-throated Hummingbird (Archilochus colubris) to the majestic Golden Eagle (Aquila chrysaetos), birds are arguably the best known and most popular group of species covered in this report. Birds show incredible diversity of shape, size, behaviour and ecology, but they are united by their adaptations for powered flight. These adaptations have shaped every aspect of the biology of birds, from the modification of forelimbs into wings, to the development of a highly efficient one-way breathing system.
Feathers are as unique to birds as hair is to mammals. Whether feathers originally evolved for use in flight, or to aid with insulating and/or cooling of the body (thermoregulation) is uncertain. However, in modern birds, feathers are used for a variety of purposes including the creation of a stream-lined body shape, flight, insulation, and for display. In addition, many bird species have feathers that are specially adapted for particular purposes, such as producing sound during display flights (e.g. Wilson's Snipe, Gallinago delicata) and improving hearing. Species of owls, like the Barn Owl (Tyto alba), have a facial ruff, hidden beneath their soft facial feathers. The facial ruff is a concave surface, made of stiff, dense feathers, that channels sound into the owl's ears, enhancing its sensitive hearing and allowing it to accurately locate its prey by sound alone.
Flight gives birds the flexibility of moving over large distances to take advantage of different habitats and resources. Canadian winters are harsh and food is often in short supply, particularly for insect-eating birds, so every fall billions of birds migrate south to take advantage of warmer weather and more abundant food supplies. Although most migrants travel south to the United States, the Caribbean and South America, others head to Australasia or Europe. Migrant species are diverse, ranging from tiny songbirds, such as the Blackpoll Warbler (Dendroica striata), to waterfowl like the Snow Goose (Chen caerulescens), seabirds like the Arctic Tern (Sterna paradisaea) and raptors like the Swainson's Hawk (Buteo swainsoni). The most spectacular group of migrants is probably the shorebirds. Some shorebirds, such as the Red Knot (Calidris canutus) regularly breed in the Arctic and migrate as far south as the southern tip of South America! Non-migratory birds, or birds that only move short distances, have adaptations to enable them to survive the winter, such as the Grey Jay (Perisoreus Canadensis) and the Clark's Nutcracker (Nucifraga columbiana) both of which store food to help avoid food shortages, and the White-tailed Ptarmigan (Lagopus leucura), which is found in the Arctic and buries itself under the snow to keep warm at night.
Birds need a large, consistent food supply to fuel their warm-blooded metabolism, and they use a wide variety of foods to supply this demand, including seeds, fruit, nectar, tree sap, invertebrates and vertebrates. Because the fore-limbs of birds are highly adapted to flight, their bills and talons are very important in feeding. The shape of a bird's bill can tell you much about their diet, from the large sturdy bill of seed-eating finches, to the hooked bills of hawks and owls. Even bird's tongues vary depending on what they eat. For example, the tongue of a Northern Flicker (Colaptes auratus) is sticky, and very long - more than 12 cm from base to tip - to allow it to reach into anthills and extract the ants on which it feeds.
For centuries people have been inspired by the beautiful songs of song birds like the American Robin (Turdus migratorius) and the Varied Thrush (Ixoreus naevius). Male birds typically use song both to attract a mate (courtship) and to defend their territory from other males. In addition, bird song helps to ensure that mating occurs between individuals of the same species (species recognition). This can be particularly important for groups of species that look very similar, such as the Empidonax flycatchers (genus Empidonax). Although song is one of the most important ways that birds attract a mate, it is by no means the only one. For example, many species of duck use visual displays to attract a mate. Studies of Long-tailed Ducks (Clangula hyemalis) have identified at least a dozen distinct displays performed by courting males, including head-shaking, neck-stretching and wing-flapping. Duck courtship displays are usually confined to the water, but more aerodynamic birds display in air. One of the most spectacular display flights is the cartwheel display of the Bald Eagle (Haliaeetus leucocephalus), during which the pair lock talons high in the sky, and tumble towards the earth, before separating at the last moment to avoid hitting the ground. More practical methods of courtship include nest building (e.g. Marsh Wren, Cistothorus palustris) and providing food (e.g. Arctic Tern, Osprey, Pandion haliaetus). Because courtship is fundamental to the breeding biology of birds, bird courtship has been well studied, leading to many new theories and discoveries, particularly in the areas of evolution and sexual selection (selection based on secondary sexual characteristics).
Status of knowledge
Birds are perhaps the best studied group covered in this report. Major reasons for this include the relative ease with which many bird species are surveyed, their economic importance, and their popularity with scientists, naturalists and the public. In general, the basic biology and physiology of birds are well understood, and the distribution of birds in Canada is probably better understood than for any other group of wildlife in the country. In addition, regular, long-term surveys, such as the Breeding Bird Survey (BBS), the Maritime Shorebird Survey and the National Harvest Survey, allow the population size and population trends to be estimated for a range of different bird species. To complement surveys that monitor population sizes and trends, other regional and nationwide surveys, such as nest-record schemes and the Monitoring Avian Productivity and Survivorship (MAPS) program, provide information on the life history and reproductive success of many different bird species.
Although huge progress has been made in studying bird distribution, populations and ecology, some groups of birds have proven difficult to sample adequately. In particular, birds breeding in northern Canada are not well surveyed by important schemes such as the Breeding Bird Survey, due to the vast area, and difficulty in accessing much of northern Canada. Other schemes, such as the Christmas Bird Count (CBC) and the Canadian Migration Monitoring Network, which survey birds in the winter and during migration respectively, go part way to filling this gap, but more work is needed to understand the distribution, population sizes and trends of northern birds. In addition, secretive raptors, such as the Cooper's Hawk (Accipiter cooperii) and species such as the crossbills (genus Loxia) and the redpolls (genus Carduelis), whose breeding density and/or patterns of movement are governed by cycles in their food sources, are difficult to survey and monitor. An additional problem is the difficulty of analysing large-scale volunteer based surveys, such as the CBC and the BBS, in a statistically rigorous and consistent manner. Although birds are arguably the best known group covered in this report, on-going improvement of survey techniques and analysis are needed to ensure we have the best possible data on the widest range of species possible.
Richness and diversity in Canada
A total of 653 bird species have been found in Canada; bird species richness is highest in western and central Canada, peaking in British Columbia (491 species) and Ontario (478 species, Figure 2-9-i, Table 2-9-i). Species richness is lower in the three territories than in the provinces, but the territories provide core breeding habitat for a range of bird species, particularly shorebirds.
Compared to the other species groups covered in this report, the proportion of bird species ranked Accidental is high across the country, reflecting the highly mobile and migratory nature of many bird species (Figure 2-9-ii). Accidental occurrences often result from bad weather conditions, which blow migrating birds off-course, or when juvenile birds get lost and appear many kilometres from their normal migration routes. The percentage of species ranked Accidental peaks in the maritimes (35% - 44%), which receive Accidental species from the rest of North America, Europe and Africa, as well as wandering sea birds.
Species spotlight - Atlantic Puffin
Atlantic Puffins, Fratercula arctica, are pigeon-sized seabirds, easily recognized by their striking black and white plumage, and large, colourful bills. As their name suggests, Atlantic Puffins are found in the northern Atlantic Ocean where they breed on the east coast of Canada, and the northeast coast of the United States as well as the coasts of Greenland, Europe and Russia. Atlantic Puffins typically breed in dense colonies on grassy slopes or cliff-tops of small islands. Colonies consist of many pairs of puffins, each with their own nesting burrow, which the pair defends vigorously. Adult puffins dig the burrows with their large bills, strong feet and sharp claws, and burrows may be re-used by the same pair for many years. The female lays one egg at the back of the tunnel, and both parents take turns incubating the egg, and eventually feeding the chick. Once the young is independent, Atlantic Puffins leave the land and spend the rest of the year feeding at sea. Atlantic Puffins typically breed for the first time when they are five years old, and can live up to about 25 years.
Atlantic Puffins feed on small marine fishes, captured underwater. Using their short wings as paddles, they 'fly' through the water, capturing fish one at a time from large schools of Capelin (Mallotus villosus), herring (family Clupeidae) or other small fish. In flight, puffins flap their wings extremely fast (300-400 times per minute!). Wing size for this bird (and other diving birds) is a compromise between flight (where large wings are better) and swimming (where small wings are better).
Like other seabirds, Atlantic Puffins have low rates of reproduction and long-lived adults that reproduce many times during their life. These life history traits mean that many seabirds are particularly vulnerable to increased rates of adult mortality. In the past puffins were harvested for food and for their feathers, leading to population declines in Canada and the United States, but this pressure has now largely been removed. Today, Atlantic Puffins and other seabirds are vulnerable to pollution (including oil spills and other environmental contamination), reduced food supply, drowning in fishing nets, and predation and competition from gulls. Atlantic Puffins are difficult to monitor, because their breeding grounds are remote and because they nest underground. Nevertheless, standardized surveys have shown that the Canadian population as a whole appears to be stable or increasing, despite differing trends among colonies. Atlantic Puffins have a Canada General Status Rank (Canada rank) of Secure.
Species spotlight - Western Screech-Owl, Megascops kennicotti
Western Screech-Owls, (Megascops kennicottii, are small, nocturnal owls, with large eyes and ear tufts. They have a diverse diet of insects and small mammals and have even been observed catching and eating crayfishes and bats! Like many other owls, Western Screech-Owls have numerous adaptations to nocturnal hunting. Their excellent eyesight and hearing help them to detect their prey, while the leading edge of their flight feathers is serrated, allowing them to fly silently, so that prey are not aware of their approach. Also, their strong sharp talons are adapted for grasping and carrying heavy prey. Owls swallow their prey whole, but they can't digest the bones, fur or feathers of their prey. These are separated from the meat, and coughed back up as an owl pellet. Scientists study the distribution and contents of owl pellets to learn what habitats the owls are using, and what they are eating.
Western Screech-Owls do not migrate; instead, they spend the whole year defending their territory with their mate. Western Screech-Owls nest in natural tree cavities, old woodpecker holes or nest-boxes. Males and females share the nesting duties; females incubate the eggs and guard the nest, while males bring food for both the female and the young. Like many species of owls, young Western Screech-Owls leave the nest before they can fly, and the parents must spend several more weeks feeding the young before they are independent. Western Screech- Owls nest in deciduous and mixedwood forests, and reach their highest densities in riparian habitat (close to rivers or other water sources).
Within Canada, Western Screech-Owls are found primarily in British Columbia, although a few records exist in Alberta and Saskatchewan. The two subspecies of the Western Screech-Owl known to occur in Canada were both were assessed by COSEWIC in 2002. The macfarlanei subspecies (Megascops kennicotti macfarlanei) was assessed as Endangered, and the kennicottii subspecies (Megascops kennicotti kennicottii) was assessed as Special Concern. Western Screech-Owl has a Canada rank of Sensitive, which has changed from Secure in 2000, due to the new COSEWIC reports.
Species spotlight: Red-headed Woodpecker
Red-headed Woodpeckers, Melanerpes erythrocephalus, are medium-sized, colourful woodpeckers that live in southeast Canada, southcentral Canada and the eastern United States. This noisy and intriguing species has a varied diet of insects and plant matter including seeds nuts, corn, berries and fruit. One of the Red-headed Woodpecker's favourite methods for catching insects is known as 'fly-catching' (flying out from a perch to capture insects in mid-air), a behaviour usually considered more typical of flycatchers, like the Eastern Kingbird (Tyrannus tyrannus), than woodpeckers! Red-headed Woodpeckers are one of the few species of woodpeckers known to regularly store food, and the only woodpecker species known to cover stored food with wood or bark.
Red-headed Woodpeckers typically nest in open deciduous forest, where trees are spaced fairly widely and where there are lots of dead trees (snags) for nesting and feeding. Red-headed Woodpeckers are known as 'primary cavity nesters' because they excavate their own nest hole, usually in dead wood. Once they have finished with their cavity, it is often re-used by other animals, ranging from squirrels to American Kestrels (Falco sparverius). Red-headed Woodpeckers defend their nest vigorously against members of their own species and other possible competitors such as Pileated Woodpeckers (Dryocopus pileatus), European Starlings (Sturnus vulgaris) and Red-bellied Woodpeckers (Melanerpes carolinus). In the fall, most Redheaded Woodpeckers migrate south to spend the winter in the United States. Their winteringareas are not fixed, but vary from year to year, depending mainly on the availability of their winter foods (primarily beechnuts and acorns).
Red-headed Woodpeckers have undergone fairly large fluctuations in population size since European settlers first arrived in North America. The small-scale clearing of forests by early settlers created forest edges and clearings, which provided good breeding habitat for Redheaded Woodpeckers. However, as huge tracts of forest in eastern North America were logged, the winter food supply of Red-headed Woodpeckers (beechnuts and acorns) declined, as did Red-headed Woodpecker populations. More recently, large-scale die-offs of Elm trees (genus Ulmus) and American Chestnut trees (Castanea dentata) in the middle of the last century left behind numerous large, decaying trees. This probably benefited Red-headed Woodpeckers by providing suitable nesting and feeding sites. Since 1966, Red-headed Woodpecker populations have been tracked across North America by the Breeding Bird Survey (BBS). Analysis of BBS trends suggests that Red-headed Woodpeckers have been undergoing significant declines across North America since the beginning of the survey, at a rate of about -2.7% per year. This suggests that the number of Red-headed Woodpeckers in North America may have declined by about 65% since 1966! The primary reason for population declines is thought to be loss of breeding habitat, due to removal of large dead trees.
In 2000, Red-headed Woodpeckers had a Canada rank of Sensitive. This has been changed to May Be At Risk in 2005, due to a combination of new information about population size, and the high rate of population decline. Red-headed Woodpecker was first assessed by COSEWIC in 1996 (Special Concern); COSEWIC plans to re-assess the status of this species in 2007.
Results of assessmentFooetnote1
More detailed information is available about bird populations than for any other groups of species covered in this report. In particular, the Breeding Bird Survey (BBS) makes large-scale, long-term data on population trends widely available for a variety of bird species. BBS data is most useful for studying the relative population trends of songbirds that are widely distributed in southern Canada. In some cases, BBS data shows that bird species are undergoing population declines, despite having a large, wide-spread population. For example, the Canada Warbler (Wilsonia canadensis) has an estimated total population size of 1.4 million individuals, of which at least 80% breed in Canada. However, BBS data for this species show a significant, long-term population decline, which has led the Partners in Flight (PIF) program to put this species on their 'watch list'. Such species receive regional and Canada General Status ranks of Secure, to maintain consistency with other groups, for which detailed, long-term information on population trends is simply not available. The comments field in the general status search tool provides additional information on long-term trends population trends, where applicable.
The majority of Canada's bird species are migratory and use different habitats and different regions of Canada throughout the year, exposing them to different threats in different periods of their life cycle.. When Canada ranks were created for migratory birds, particular attention was paid to each species' status on its breeding grounds. For example, within Canada, the Ruddy Turnstone (Arenaria interpres) breeds primarily on the tundra in northern Nunavut. Here it is ranked Sensitive due to population declines. However, the Ruddy Turnstone is a common migrant in suitable habitat throughout much of southern Canada, and is ranked Secure in every province except Saskatchewan where it is ranked Accidental. Nevertheless, Ruddy Turnstone received a Canada rank of Sensitive, due to concerns within its breeding range. This kind of exception was applied to approximately 16 bird species, and is documented in the comments section of the general status search tool.
The majority of bird species have Canada ranks of Secure (55%, 358 species, Figure 2-9-i and 2- 9-ii, Table 2-9-i). However, nearly a third of bird species have Canada ranks of Accidental (30%, 195 species), the highest percentage of Accidental species of any group covered in this report. In addition, 6% of bird species have Canada ranks of Sensitive (41 species), 4% have Canada ranks of At Risk (27 species), 2% have Canada ranks of May Be At Risk (12 species) and less than 1% have ranks of Extinct (three species) or Extirpated (one species). Finally, 2% of bird species have Canada ranks of Exotic (11 species) and 1% have Canada ranks of Undetermined (five species).
|May be at risk||12||29||7||1||22||3||17||10||10||9||12||1||12||7|
aIn Wild species 2000, species assessment results were presented as the proportion of resident species ('resident species' excludes species with Canada ranks of Extirpated, Extinct and Accidental). In this report, we have used the more straightforward method of presenting results as a proportion of total species richness. Therefore, proportions given in the 'Results of assessment' sub-sections cannot be directly compared to results given in the text of Wild Species 2000. To compare results for birds directly between the text of Wild Species 2000 and this report please use the following figures, which represent the 2000 results as a proportion of total species richness: Total species richness: 639 species Extinct/Extirpated: 1%, At Risk: 3%, May Be At Risk: 2%, Sensitive: 8%, Secure: 54%, Undetermined: 3%, Not Assessed: 0%, Exotic: 2%, Accidental: 27%.
Comparison with Wild Species 2000
The total number of bird species ranked in Canada has changed from 639 in 2000 to 653 in 2005. Since 2000, 17 new bird species have been added to the national list. All of these species have Canada ranks of Accidental, and most have been recorded from only one province or territory. Two bird species, Crested Myna (Acridotheres cristatellus) and Mountain Quail (Oreortyx pictus, both previously ranked Exotic), have been removed from the national list, since they are no longer found in Canada. In addition, there have been several taxonomic changes. Black-backed Wagtail is no longer considered a separate sub-species from White Wagtail (Motacilla alba), due to new information about the extent of hybridization between these taxa. Following genetic studies, Cackling Goose (Branta hutchinsii) is now ranked as a full species, separate from Canada Goose (Branta canadensis). Finally, although the taxonomy of snipe (genus Gallinago) remains unclear, two separate species are now ranked in Canada; Wilson's Snipe (Gallinago delicata, found across the country), and Common Snipe (Galinago galinago, breeds in Europe, a rare visitor to Canada's east coast). In addition, the taxonomic treatment of two sets of species has been altered since 2000. In 2000, two sub-species of Anas crecca; American Green-Winged Teal and Eurasian Green-winged Teal, were ranked separately. In 2005, both sub-species are now ranked together as a single species; Green-winged Teal. Similarly, two sub-species of Numenius phaeopus, Whimbrel and Eurasian Whimbrel were ranked separately in 2000, but are now ranked together as a single species; Whimbrel. Once species which have undergone taxonomic changes are excluded, a total of 629 species were ranked in Canada in both 2000 and 2005.
Changes to Canada ranks have been made for 9% of the species that were ranked in both 2000 and 2005 (55 species, Table 2-9-ii). 38% of the changes moved species into a category with a higher level of risk (21 changes), 36% of the changes moved species into a category with a lower level of risk (20 changes), and 25% of the changes moved species out of the Undetermined (12 changes) or Not Assessed categories (two changes). Changes in Canada ranks had no major impact on the overall percentage of species in each general status category (Table 2-9-iii). The majority of changes were due to changes in process (62%, 34 species). Other changes were due to new or updated COSEWIC assessments (16%, nine species), improved information (11%, six species), and a combination of improved information and biological change (11%, six species).
|2005 Canada rank||2000 Canada rank||English name||Scientific name||Reason for changea|
|At Risk||May be at risk||Ivory Gull||Pagophila eburnea||C|
|At Risk||May be at risk||Pink-footed
|At Risk||May be at risk||Ross's Gull||Rhodostethia rosea||C|
|At Risk||Sensitive||Least Bittern||Ixobrychus exilis||C|
|May be at
|Sensitive||Clark's Grebe||Aechmophorus clarkii||P|
|May be at
|Sensitive||Snowy Egret||Egretta thula||I|
|May be at
|Sensitive||Cerulean Warbler||Dendroica cerulea||B/I|
|May be at
|May be at
|Secure||Red Knot||Calidris canutus||P|
|Sensitive||May be at risk||Great Egret||Ardea alba||P|
|Sensitive||Secure||Ruddy Turnstone||Arenaria interpres||P|
|Sensitive||Secure||Black-bellied Plover||Pluvialis squatarola||P|
|Sensitive||Secure||Harris's Sparrow||Zonotrichia querula||P|
|Sensitive||Secure||Wandering Tattler||Heteroscelus incanus||I|
|Sensitive||Secure||Rusty Blackbird||Euphagus carolinus||C|
|Sensitive||Undetermined||Little Gull||Larus minutus||P|
|Secure||Sensitive||Buller's Shearwater||Puffinus bulleri||P|
|Secure||Sensitive||Tufted Titmouse||Baeolophus bicolor||P|
|Secure||Sensitive||Upland Sandpiper||Bartramia longicauda||P|
|Secure||Sensitive||Black Tern||Chlidonias niger||P|
|Secure||Sensitive||Common Nighthawk||Chordeiles minor||P|
|Secure||Sensitive||Black-headed Gull||Larus ridibundus||P|
|Secure||Sensitive||White-winged Scoter||Melanitta fusca||P|
|Secure||Sensitive||Surf Scoter||Melanitta perspicillata||P|
|Secure||Sensitive||Brewer's Sparrow||Spizella breweri||P|
|Secure||Sensitive||Swainson's Hawk||Buteo swainsoni||I|
|Secure||Sensitive||White-throated Swift||Aeronautes saxatalis||B/I|
|Secure||Sensitive||Peregrine Falcon||Falco peregrinus||B/I|
|Secure||Sensitive||Laughing Gull||Larus atricilla||B/I|
|Secure||Undetermined||Black Swift||Cypseloides niger||P|
|Secure||Undetermined||Northern Wheatear||Oenanthe oenanthe||P|
|Secure||Undetermined||Manx Shearwater||Puffinus puffinus||P|
|Secure||Undetermined||Cassin's Vireo||Vireo cassinii||P|
|Accidental||Undetermined||Parakeet Auklet||Aethia psittacula||I|
|Accidental||Undetermined||Red-throated Pipit||Anthus cervinus||I|
|Accidental||Not Assessed||Fea's Petrel||Pterodroma feae||P|
|Accidental||Not Assessed||Mottled Petrel||Pterodroma
a C: change due to new COSEWIC assessment. P: change due to procedural change. I: change due to improved knowledge of the species. B: change due to biological change in species' population size, distribution or threats.
|Number||Canada rank||Number and
of species in each in Wild Species 2000
of species in each rank
in Wild Species 2005
|Summary of change||Reason(s) for change(s)|
|0||Extirpated/Extinct||4 (1%)||- a||-||-|
|0.2||Extinct||- a||3 (<1%)||-||-|
|0.1||Extirpated||- a||1 (<1%)||-||-|
|1||At Risk||21 (3%)||27 (4%)||↑||COSEWIC assessment b|
|2||May be at risk||11 (2%)||12 (2%)||↔||COSEWIC assessment b,
Combination of improved
knowledge and biological
change c, Process d,
Improved knowledge e
|3||Sensitive||53 (8%)||41 (6%)||↓||COSEWIC assessment b,
Combination of improved
knowledge and biological
change c, Process d,
Improved knowledge e,
|4||Secure||345 (54%)||358 (55%)||↑||COSEWIC assessment b,
Combination of improved
knowledge and biological
change c, Process d,
Improved knowledge e,
|5||Undetermined||17 (3%)||5 (1%)||↑||Process d, Improved
|6||Not Assessed||2 (<1%)||0||↓||Process d, Improved
|7||Exotic||13 (2%)||11 (2%)||↓||Biological change h|
|8||Accidental||173 (27%)||195 (30%)||↑||Process d, Improved
knowledge f, Taxonomy e,
New Species g
a The single category of Extinct/Extirpated in Wild Species 2000, was replaced with two separate categories in 2005; Extinct and Extirpated. See the Background section for details.
b A formal COSEWIC assessment has been conducted, and used as evidence for a change in rank. A biological change (i.e. a change in species population, distribution or threats) since 2000 is not suggested.
c A combination of improved knowledge and biological change was used as evidence for a change in rank.
d A different process has been used for assigning ranks, leading to a change in the Canada rank.
e New information has been collected or brought to light, and used as evidence for a change in rank. A biological change (i.e. a change in species population, distribution or threats) since 2000 is not suggested.
f A taxonomic change has lead to the addition or removal of a species from the national list.
g A new species has been added to the national list.
h A biological change in species’ population size, distribution, threats or trends has lead to species being removed from the national list.
Key to symbols: ↑Number of species in this category has increased. ↓Number of species in this category has decreased. ↔ An equal number of species have been added and removed from this category; no net change. = No species have been added or removed from this category.
Threats to Canadian birds
The major threats to Canadian birds are fairly well known, and include habitat loss and fragmentation, pollution and contamination, changes in rates of predation and brood parasitism, disease, overexploitation, competition from invasive or Exotic species, anthropogenic mortality (e.g. building strikes, road mortality) and natural and anthropogenic climate variation. However, the situation is complicated by the fact that threats can occur in migratory stopovers and in wintering habitat as well as in breeding habitat. Therefore, many research programs involve international co-operation to study the same species in different locations and at different points in the life cycle.
Canada provides important breeding habitat for many species of North American birds, and many Canadians appreciate the diversity and abundance of birds that spend all, or part of the year here. For these reasons, and many others, it is important to update general status ranks for birds regularly. Although the proportions of bird species in each general status rank have not changed significantly since 2000, this update has allowed Canada ranks to be adjusted to ensure that ranks are comparable within and among species groups, as well as allowing the national list to be updated with species new to Canada. Although birds are generally better studied that other groups covered in this report, it is still important to improve our knowledge of bird populations, particularly for species breeding in northern Canada and other remote locations, and for species not adequately covered by current surveys.
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