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November 2020 Natural Mystery Answered

posted Dec 15, 2020, 10:09 AM by Jonathan Poppele   [ updated Dec 15, 2020, 10:36 AM ]
Everyone who sent in an answer to our November Natural Mystery recognized this as a webbed bird track, but there was some question about exactly which web-footed bird was responsible. Congratulations to Joe Conrad, Mike Holtz and Kirsten Welge who correctly identified the track maker.

These are the tracks of a mallard. Joe starts us off with this pithy explanation:

"Web footed—not big enough to be a Canada Goose."

Kirsten adds a few more details, noting:
  • Each print shows three clear toes, a hallux, and webbing.
  • Metatarsal pad looks to be circular. Goose metatarsal is typically teardrop-shaped.
  • Size of each track is about 2.75” long, which points to a large-footed duck and effectively rules out goose. Elbroch's goose track range starts at 3 7/8"" range.

Mike added that “Ring-billed gull would leave a smaller track.” This is true, but herring gulls leave similar size tracks and could be around this time of year. Kirsten pointed out the hallux in the tracks, and that is one clue that these are duck tracks rather than gull tracks. Ducks have a larger hallux than gulls, which registers more reliably in the tracks. Additionally, gulls nearly always splay their toes wider than we see here (ducks sometimes do as well), and their toes almost always appear more curved.

Mike also pointed out that goose and swan track would be larger "based on the time of the year." And, yes, gosling and cygnet tracks could overlap in size—though, as with gulls, geese and swans have a proportionally smaller hallux that is less likely to show in their tracks and, as Kirsten noted, their metatarsal pad looks different.

Finally, Mike notes that “mallards are a safe bet around town any time of year.” He suggests that “black duck is also a possibility, and looks similar.” And, indeed, black duck tracks are indistinguishable from mallard tracks. We can only say with 100% confidence that these tracks were made by a mallard rather than a black duck because Rob watched the duck leave the trail. However, given how much more common mallards are in the Twin Cities at this time of year compared to any other large duck, we could have greater than 99% confidence that these are mallard tracks based on the location.

Congratulations again to Joe, Mike & Kirsten, and thanks to everyone who submitted an answer to this mystery.

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