For a bird that was once on the U.S. endangered-species list, the bald eagle has made a remarkable comeback. It is now so common in the Lower Mainland that even the most urban of city dwellers cannot fail to spot one.

With its striking white head and tail, dark body, massive bill and talons, and two-metre wingspan, the adult bald eagle is every inch a North American icon.

In the past few decades, the number of bald eagles wintering in the Fraser River delta has increased dramatically, with winter counts averaging between 600 to 1,300 birds.

This year, eagles are causing traffic jams and parking problems around Ladner–Boundary Bay farmland as photographers vie for the best views of these magnificent birds.

Eagle numbers down on Squamish River

In contrast, eagle counters at Brackendale—on the Squamish River, a famous wintering area—recorded much lower numbers than formerly in their annual January census this year.

In the Fraser delta, the eagles feed along the riverbanks, on tidal marshes, and in farm fields around Boundary Bay, preying on the tens of thousands of ducks and shorebirds that use the delta as a wintering area. Some eagles are more opportunistic, gathering in huge flocks around the Vancouver Landfill in Burns Bog and the composting facilities near Boundary Bay Airport.

Many of the eagles are visiting for the winter, some from as far away as Alaska, while others are local birds. By January, the residents are already paired up and working on repairing or building nests. Younger birds are distinguished from adults by their dark brown plumage streaked with white: the adult plumage, with its characteristic white head and tail, takes four to five years to develop.

There was once a time when there were very few bald eagles in the delta, but the number wintering and nesting there has steadily increased during the past four decades. A good source of information on their distribution is the annual Christmas bird-count data, coordinated by Audubon and Bird Studies Canada. This volunteer initiative began in North America in 1900 and has now expanded to 2,348 circle areas across the continent.

Eagle numbers up hugely since 1970s

In the Lower Mainland, Christmas bird counts are conducted around Vancouver, White Rock, and Ladner in Delta, among other areas. The count data (accessible on the Audubon.org website) reveal that, on average, between 1958 and 1974, fewer than three eagles were observed each year on the single-day midwinter count within a 24-kilometre radius of Ladner. Today it is a common occurrence to see a dozen or more adult and juvenile eagles perched in a single tree.

The local population change began in the 1980s, when average count numbers first rose to 76, then increased through the 1990s to 234, and soared to 936 after 2006. In 2015, the total eagle tally in the Ladner count circle was 1,360. Breeding numbers have also increased dramatically. David Hancock, a naturalist and writer with a special interest in eagles, estimates there are now 400 to 500 nesting pairs in the lower Fraser Valley.

The information gathered by thousands of volunteer bird watchers in Christmas bird counts is immensely valuable in learning about North American birds. Although a single year’s data can be misleading, because of changes in weather or observer efforts, collectively the surveys can demonstrate population trends, such as the recent increases in Lower Mainland bald eagles, Anna’s hummingbirds, and Eurasian collared doves. Some other bird populations, such as band-tailed pigeons and short-eared owls, can be seen to have declined in the same period.

The Ladner Christmas count is often ranked first in Canada for high numbers of birds, with, typically, 140 to 152 different species observed, but in 2015 only 134 species were seen, with the cold, wet weather being a factor. Eagles, however, do not seem to mind the cold.

Annual eagle counts at salmon-spawning sites

Besides the Christmas bird counts, eagle numbers are tallied annually at two famous salmon-spawning sites: Chehalis flats at Harrison Mills and Brackendale on the Squamish River.

During the Fraser Valley Bald Eagle Festival in November 2015, 1,400 bald eagles were counted at Chehalis. The eagles gather on the alluvial flats and in trees along the rivers in this scenic area, drawing visitors from far and wide.

Since the founding of the festival and annual monitoring 20 years ago, the area has seen fluctuating numbers of eagles gathering there for the fall salmon runs. In 2010, Hancock counted 7,362 eagles along three kilometres of the flats, with hundreds more flying overhead: a world-record gathering of eagles.

At Brackendale, eagle numbers have declined since a peak of 3,769 eagles in 1994 over a 40-kilometre stretch of the Squamish River during the annual January count. Typically, teams hike, raft, and kayak to count the birds. Cold, snowy weather, high water in the river, and fewer chum-salmon carcasses were blamed for a count of only 411 eagles on January 3, 2016, the lowest in the 30 years’ history of the count, which has averaged 1,385 birds annually since 1994.

Low numbers at Brackendale, however, have been offset by high numbers of eagles in Delta and the Comox Valley, both areas with sources of food other than salmon.

Salmon an important predictor in numbers

There are many complexities to the population dynamics of these majestic birds and a number of possible reasons for the changing eagle numbers in different areas. Salmon runs change in size annually and over the long term as habitat, climate, and fishing fluctuates.

Observers at Brackendale have commented on the loss of earlier coho, chinook, and steelhead populations in the river with habitat changes, yet there was an increase in chum populations in the 1990s. The high eagle count at Harrison in 2010 occurred in the same year as the largest Fraser sockeye run in 100 years.

This year, with a long drought in summer and heavy fishing pressure prior to fish entering the river, salmon numbers were low. Correspondingly fewer eagles were seen at Chehalis. Alternative food sources can also draw eagles, such as the vast waterfowl flocks on Boundary Bay or the presence of compost and landfill sites.

Hancock is concerned for the long-term viability of eagle populations because of their strong dependence on salmon. In modern times, the vast waters of the Pacific Ocean have become steadily more polluted, even as attempts are made to clean up the inland waters of the Salish Sea. The resident salmon-feeding orcas suffer greatly from toxic pollution.

Ocean pollution a concern for eagle health

Although western eagles were not so affected by the pesticide problems of the 1950s and ’60s, there is no escaping the global scope of ocean contamination, particularly for species that depend so heavily on fish in their diet. Hancock speculates that birds feeding on composting heaps and landfill sites could be less contaminated than northern eagles that are dependent on salmon for most of the year.

The large numbers of eagles gathering in the Fraser delta have impacts on the local environment. These are very large predatory birds, and their booming populations must have an effect on other species with which they compete for food and nesting areas. Besides more normal prey, such as salmon, ducks, and sandpipers, there are reports of them attacking young great horned owls, red-tailed hawks, small dogs, and other animals.

Even humans are at risk: it would be easy to get hit by a car while staring skywards and wandering absent-mindedly across one of the farm roads that are regular travel routes for local workers. Furthermore, the turf farm and composting facility, which attract hundreds of eagles daily, are located close to the end of the Boundary Bay Airport runway, creating a serious hazard for small planes using the airport.

Take care if you travel in eagle land!