Bird Bottles on the Brain

Hello friends -- we are back from another jaunt to Colonial Williamsburg, (hoping to get full value for those pricey annual passes.) and as you might expect I was fully focused on birds and even more so on bird bottles. The CW people make and sell a ceramic product they believe was used to attract martins in the 18th century. I have owned one since 2008 and it has yet to interest a single bird. So during my time in CW I endeavoured to find every bottle I could and determine its effectiveness. I eventually located 18 specimens (here are two side by side) although I didn't get into every back yard or alley, so perhaps twice or thrice that number is possible. And most of them were plainly used by very messy birds. In fact one bottle was even blocked off with a mesh! So effective, the users wanted the birds out! Nor did I get good cues on how high to affix one. Mine is fifteen feet up the wall. At CW they ranged from five to more than fifteen feet. Is it only starlings? house sparrows? I shall learn more this spring.