Although sized for small birds such as finches and sparrows, it attracts larger ones as well. A cardinal is perhaps the largest that will comfortably fit under the roof. A blue jay can fit uncomfortably or dangle from a cup’s front edge and feed by poking its head under the roof. Birds as large as a red-bellied woodpecker have used that latter method. And therein lies a design flaw.
When the cup is sufficiently empty, the weight of the dangling bird will tip it out of the feeder to drop to the ground below. For us, there are several inconveniences to retrieving the cup: leaving a cozy bed, descending the stairs to the main floor, exiting the house, and walking along to where the cup fell. At its worst this involves a pajama-clad trek through deep snow or in hard rain.
Our solution was to glue a plastic tab to the rear of the protruding bottom of each cup. Should a bird be in danger of tipping the cup out, the tab will press against the underside of the feeder’s floor and prevent it. As a consequence the cup can no longer be dropped directly into the hole in the feeder, but must be tipped slightly so the tab goes underneath, and slid along until it drops and seats itself. Not an inconvenience since that is how we were installing the cups anyway.
While casting about for some scrap plastic to cut to size, we discovered some unused drawer dividers for a small parts organizer. We were fortunate that these dividers had perfect dimensions or near enough to require no cutting. Almost as wide as the protruding bottom, when placed a little short of the drainage holes, the tab extended as far as the edge of the cup itself.
The glue was, of course, a cyanoacrylate. We used a version that comes in a bottle with a brush built into its cap. Whether it stays reusable as is claimed we shall see but it was certainly our least messy ever application of such a glue. No inadvertant gluing of fingers. In addition the glue has a very pale purple tint when applied and then hardens clear. It is not “easy to see” as the advertising claims (not to our old eyes anyway) but is a visible improvement over the usual lack of any color at all.
At this writing, our modified cups have been in place for nearly a month and we have several times seen a tab rescue a tipping cup from falling. Not once since our bodging have we had to retrieve one. We are pleased with ourselves.
2016-Mar-01 : We must report that in the two years since we published this post we have indeed had to retrieve a cup once but not due to any action by birds so we still regard the original problem completely solved. Our single fall was due to letting the cups go empty during a very high wind. An unfortunate gust simply lifted and tilted a cup to remove it much as we do for filling. We have been more careful since to not let the feeder go empty.