We did not invent the concept of halos over bird feeders, and cannot guarantee that it is House Sparrow-proof given the myriad of designs and contexts that they are placed in. Though our survey data is largely favorable, it is also limited to just 15% of our customers who choose to participate. Some folks do report House Sparrows (HOSP) overcoming the Magic Halo and its hanging wires - particularly in times of poor weather and/or desperation. Factors may include nearby structures, the desirability of the food, visibility conditions that sharpen/blur perception of the hanging wires, availability of other food nearby, harshness of Winters, etc.
The original Paper from the University of Nebraska published in 1994 did confirm that Juvenile HOSP are Halo-tolerant, and it is poorly understood at what point they turn adult and how many there are at any given time. HOSP can have multiple broods through August. The study cited 2-11% of HOSP visiting feeders with Halos did manage to breach, leaving an approx 90% success rate. Juveniles are fewer than adults, but it further confuses the results that one might expect. They can be more abundant in some areas over others, and resemble adults as the season goes on. For this reason, it is best that new Halo users start out expecting a reduction in HOSP; if they are fully eliminated, so much the better.
Before deciding to purchase a Magic Halo, we strongly advise potential customers to read the following from FeederWatch and Sialis first. Attention should also be paid to recommended seed types that include husk-only (pure black oil sunflower, safflower). Avoid HOSP-friendly varieties such as millet, cracked corn, or hearts of any type, as these only increase temptation. In judging Halo efficacy, we ask that you examine your results with vs without, before vs after, and whether or not there's at least a net improvement in your bird feeding experience.
We appreciate your understanding.
In good conscience, we cannot guarantee "HOSP-proof" in using the Magic Halo over bird feeders. While many users do experience excellent results in HOSP elimination, others have observed some percentage overcoming the Halo's presence. In other words, the birds can be unpredictable, with variable behavior patterns from place to place. Then there is the issue of Juveniles. When it all comes down, the success of the product is too subjective to guarantee it as anything more than a deterrent.