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November 2019 Natural Mystery Answered

posted Dec 3, 2019, 4:50 PM by Jonathan Poppele   [ updated Dec 4, 2019, 12:25 PM ]
Everyone who sent in an answer correctly identified these as woodpecker tracks. Congratulations to Mike Watling, Kim Cabrera, Terry Hunefeld, Kirsten Welge and one anonymous contributor who all identified these tracks to the species. A further congratulations to Kirsten Welge, René Nauta and our anonymous contributor who worked out what direction the bird was facing—a very difficult task with these nearly symmetrical zygodactyl tracks.

These are the tracks of a Northern Flicker, which was facing toward the bottom of the frame when it left these tracks. To break this down, I'll first turn things over to our anonymous contributor for a quick primer on zygodactyl feet:

"Zygodactyl feet only occur in some species of birds. Zygodactyly refers to the fact that the 1st ("thumb") and 4th toes are or can be reflexed rearward. In Minnesota, the species likely to display this trait are woodpeckers (including the Northern flicker), some swifts, ospreys, and owls. Roadrunners (and cuckoos), parrots (psitticines), and other birds also display this trait. There's another version of a reflexed toe (toe 2 pointed rearward) but it only occurs in species that reside in tropical forests. (Not that some swifts can move 1st and 4th toes either forward or rearward, which is a different type of foot structure.)"

Kirsten shared many of these points as well, while also noting that "the zygodactyl foot is the second most common toe arrangement in birds."

Our anonymous contributor continued with a few words about why this is a Flicker:

"It's not an owl because the straightest part of the track is on the outside of the foot. These feet belong to a bird probably just under crow-sized. You mentioned that this bird is seen here in both spring and fall. Northern flickers are common in MN year round, and a flicker seems to be the closest fit for size and pattern."

Mike echoed this, stating simply that “the size fits well with a Northern Flicker.” Terry noted that “Pileated woodpecker and other zygodactyls have much more robust toes and/or wider 'Ks' than Northern Flickers." Kim added some behavioral clues, pointing out that “Flickers usually hop when on the ground, so their tracks are usually paired like this. They are often seen on the ground, so this is a fairly common bird track to find.” Kirsten similarly reasoned that, in addition to the difference in size, "Downy, Hairy, Red-Bellied, and Pileated Woodpeckers regularly feed along trunks and branches, not on the ground like Flickers"

As for what direction the bird was facing, our anonymous contributor offered this very simple and accurate analysis:

"This bird seems to be facing downward, since the discrepancy in toe length is greater between 1 & 4 than 2 & 3, and the largest length discrepancy is in the two toes in each track oriented toward the top of the image."

Kirsten arrived at the same conclusion after taking a deep dive into woodpecker foot morphology. In her research, she found the terrific photo shown here (as well as this one and this one), and came up with these notes about woodpecker feet:

1) The hallux (Toe 1) is consistently the shortest toe. It’s also the most delicate looking of the toes.
2) Toe 4 consistently looks like the longest toe. Interesting, it also looks like the most robust of the toes.
3) The difference in length between hallux and toe 4 is greater than the difference between toes 2 & 3.
4) It also looks like the splay between toes 1 & 4 may be greater than that between toes 2 & 3.
Based on this, the hallux & toe 4 are pointing to the top of the photo: this bird is heading towards the bottom of the picture."

This is exactly correct. Toe 4 looks the longest and Toes 2 & 3 are closer in length than Toes 1 & 4. Several people noted in their answers that Toe 3 is the longest in Flickers. Which is true. Sort of. In woodpeckers, Toes 2 & 3 are partially fused at their bases, so only part of the shaft of Toe 3 is visible beyond where it joins Toe 2. This makes Toe 3 appear slightly shorter in the track than Toe 4. Check out the photos Kirsten turned up and this month's Featured Track Illustration for a close look at flicker track morphology.

Thanks again to everyone who submitted answers to this month's Natural Mystery, and congratulations again to Kirsten, Mike, Kim, Terry, René and our anonymous contributor.

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