I too am a believer in crows "farming" songbirds.

Crows are not the only ones who try to maximize their crop size, though.

Many years ago, in my Bald Eagle watching days (meaning spending countless hours each breeding season monitoring nests and observing behavior), I documented the first male eagle who took up residence in Lower Woodland Park near Green Lake (Seattle), "harvesting" the local crow nests contents just before fledging.

Lots of chunks of crow blood feathers around the base of the eagle nest tree that time each spring/summer (at least 2 years, then the eagles moved onto the Zoo grounds and I lost track of them). I twice watched the male eagle raid a crow nest, coming back four times within 3 hours at one nest and three times within 5 hours at the other nest, and taking one young crow each time. The adult crows and all the other crows within earshot would all respond to the emergency, but to no avail.

I don't have observations that the eagles scouted the crow nests before "harvest," but the fact that it happened two years in a row and that there were almost never crow feathers at the base of the eagle tree other times of year, makes me think this was a deliberate tactic.

And people wonder why crows hate eagles.

Martin Muller, Seattle
martinmuller at msn.com