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Why do gull nests get flooded on the Yukon River in Whitehorse at this time of year?
Every year around this time, people notice a few unfortunate Mew Gull nests getting threatened by rising water in the Yukon River in downtown Whitehorse.
Typically these at-risk nests are located on very low and often small gravel islands, for example in the Quartz Road/Shipyards Park area. I just got an email from a concerned resident who noticed this very thing (see photos). Why do these gull nests get flooded? Is Yukon Energy responsible for this?
Well, as it happens, the rising water at this time of year is a natural phenomenon. Natural runoff from snow melt causes this rising water. Yukon Energy operates water control structures (dams) in Whitehorse and at Marsh Lake, but from May through July they just let the River flow without any restriction. They do regulate the flow of water beginning in August and throughout the winter months to make optimal use of all the storage capacity they are allowed to use upstream of the Marsh Lake dam on Marsh, Tagish, and Bennett Lakes.
If you look at the chart above you will see that the water level on the river in Whitehorse is at a minimum in May, after which it rises rapidly through June, July, and into August due to snow melt and glacial runoff. At Marsh Lake, which is located upstream of both the Whitehorse Rapids and Marsh Lake dams, the annual minimum water level is also in May and rises in much the same fashion during June and July (see chart below).
The differences between these two locations show up during August though April, when Yukon Energy is manipulating flows through both dams to provide electricity generation when it is needed most — during the cold months of winter.
Mew Gulls begin nesting in May when water is at a yearly low pretty much everywhere in Yukon. They nest on the ground, so they are smart enough to choose islands in order to prevent terrestrial predators such as foxes, coyotes, and the like from eating their eggs and young. Successful nests are the ones that are placed high enough on these islands to survive the rising water until the eggs hatch. Once hatched, young gulls are very soon able to swim and can safely leave the nest and move to higher ground where their parents continue to look after and feed them. Some gulls, perhaps the younger, less experienced ones, gamble by nesting very close to the low water. In some years this might work – they are safe from predators and win the race against the rising water; in others they get flooded. Maybe it is a mistake they only make once — we don’t really know.
Should we rescue these nests? We probably could scoop up some of these nests and place them on the adjacent islands, but would the parents accept this or simply abandon the nests? Would other gulls nesting nearby take offence and attack the newcomers?
In fact this type of thing (nests getting flooded) happens all the time in nature….birds take risks. If they are lucky they will live to learn from them. As long as we are not causing this problem, I don’t really see a reason to intervene in the few instances that are right in front of our noses. What do you think?