A copy of this has recently been published! Love the Wood Duck.
Holden, B.R. 2016. Harlequin Duck - Great Lakes Population . The Wood Duck 69(6):128-129.
Do you get the feeling that Harlequin Ducks have become more of a regular occurrence on Lake Ontario in recent years? In my early days of birding the Hamilton area the discovery of a Harlequin Duck was a big event, and the thought of seeing a stunning adult male hovered somewhere between a hope and a prayer. The Birds of Hamilton (Curry, 2006) details records from ~1850-2005, and notes that the Harlequin Duck was increasing as a winter resident through the second half of the 20th century. At the time of publication, the high count for Harlequin Duck was 3 individuals, from 1958 and 1980. Since publication, that count of three birds has been matched in 2005, 2009, 2012 and 2013 with a new high count of 4 in 2010 (eBird 2015). Clearly, Harlequin Ducks are on the rise in Hamilton - and, although I'm not willing to do an equally detailed search for other regions around the Great Lakes, you can be sure that high counts from Prince Edward Point, the Niagara River and the incredible eight (with five adult males!!) from Whitby this fall all mirror the upswing of occurrences on the Great Lakes. Check out the Harlequin Duck occurrence map from eBird, 2010-2015:
The reason I'm putting pen to paper on this topic is due to a recent discussion I had on this increase in Harlequin Ducks in our area in contrast to my disappointment in having not recorded one from my home in Stoney Creek since moving here in 2012. Now, I may be greedy for suggesting I should have seen a Harlequin Duck by now, as they are rare birds... But my place is a bonafide duck bonanza on a normal day (Holden 2014), not to mention that I have the ability to watch active migration throughout the seasons whenever conditions are good. For context, I've seen at least 20 different individual King Eiders in the same timeframe. So where are the Harlies?
To try and explain, I'm going to move from the realm of stats and facts into something theoretical. Is it possible that we are on the brink of having a genuine wintering population of Harlequin Ducks, sustaining itself from year to year with augmentation from wandering/vagrant individuals? The eastern Canadian breeding population of Harlequin Ducks was assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1990, and was subsequently down-listed to Special Concern in 2001. Recent assessments suggest a population of roughly 4600 mature individuals (COSEWIC 2013). Dramatic increases to the wintering populations of Long-tailed Ducks, White-winged Scoters, and other duck species are well documented since the arrival of Zebra Mussels (Curry 2006). The Harlequin Ducks small source population could be masking a shift in the species wintering biology from vagrant individuals to a true wintering population.
Historically any Harlequin Ducks that reached our shores would not have encountered beds of the invasive Zebra Mussels to sustain them, whereas now, in the 21st century, they find this new and abundant food source and are able to successfully winter. After initial success, the same individuals are encouraged to return year after year, increasing the odds of encountering other individuals of their species. Chance encounters in the fall and winter could theoretically lead to courtship rituals prior to migrating back to their breeding grounds further increasing the benefits of wintering in the Great Lakes. This hypothetical scenario would lead to a gradual increase in numbers, which mirrors the patterns the birding community has been documenting through eBird and other databases. It is also unlike the dramatic swings in occurrence and number for other vagrant species where meteorological events set the stage for irruptions or invasions - leading to wild swings in year to year occurrence and numbers (see Holden 2015). Many Harlequin Duck records over the past ten years in the Hamilton Study Area and beyond have involved one or more individuals wintering at the same site for multiple years - which helps explain why numbers are on the rise, but why the odds of getting that first record for my place in Stoney Creek has not risen correspondingly. If one or more of these theories proves true, we should continue to see a steady increase in numbers and occurrences of the species - an exciting prospect for all local birders regardless of their home address!
COSEWIC 2013. COSEWIC assessment and status report on the Harlequin Duck Histrionicus histrionicus Eastern population in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. ix + 38 pp. Available online at www.registrelep-sararegistry.gc.ca/default_e.cfm
Curry, R. 2006. Birds of Hamilton and Surrounding Areas. Hamilton Naturalists’ Club. 647pp.
eBird. 2015. eBird data accessed December 2015. Harlequin Duck for southern Ontario from 2010 to 2015. http://ebird.org/ebird/map/harduc?neg=true&env.minX=-84.41170419375004&env.minY=39.93719814144728&env.maxX=-71.44783700625004&env.maxY=47.2662540267814&zh=true&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=range&byr=2010&eyr=2015
Holden, B.R. and K.G.D. Burrell. 2015. The Cave Swallow, Petrochelidon fulva, in Ontario, 1989-2014. Ontario Birds, 33(1): pp 44-48
Holden, B.R. 2014. eBird checklist for aaa_Condo, Hamilton County, Ontario, CA. 2 November 2014. Available online at http://ebird.org/ebird/view/checklist?subID=S20416921