Never seen this before. A group of house sparrows in Reston, VA, USA are chomping on the brick siding of a local condominium complex. My guess is that some calcium carbonate is leaching out from the mortar holding the bricks together, and the sparrows are lapping it up.
Does make you wonder about the quality of the masonry work on the condos, though.
Does make you wonder about the quality of the masonry work on the condos, though.