Walden Ponds white heron

[Steven Mlodinow]

Greetings. 

I hate to say this, but I believe the Walden Ponds "Little Blue Heron" to be an odd young Snowy Egret

It is common for young Snowies to have entire yellow-green/green legs for months after fledging. Additionally, a great number of young Snowies have bicolored bills if you look hard. Admittedly, usually it is dark gray shading into black, however the following photos from the Macauley Library show young Snowy Egrets with bill patterns that are reasonably similar to the Walden bird. I've seen birds like this myself.

https://macaulaylibrary.org/asset/66332971 (this shows green legs as well)

https://macaulaylibrary.org/asset/61891821 

https://macaulaylibrary.org/asset/31794221

In one set of photos I looked at, the heron-in-question was near several Snowies. The bill gave the impression of being thicker, but also seemed a bit shorter than that of the obvious Snowies. I wonder if the apparent thickness is due to the bill being fully thick, but not fully long, still growing out (as happens in young herons, ibis, shorebirds...) 

Finally, young Little Blues should still have some dusky primary tips. This can be hard to see, but given the number of people who have watched the bird, no one has commented on this and I can't see dusky on the primaries in any of the photos.

I think this is probably a late-hatching (or slow-to-mature) Snowy Egret

Alas

Steve Mlodinow