A team led by scientist Graham Ruxton at St. Andrews University in Scotland has performed a field study of Birdsbesafe cat collar covers. The results were published in the prestigious Journal of Zoology in October 2019.
The study showed a 78% reduction in birds caught, when cats wore Birdsbesafe collar covers.
From the Abstract: "The domestic cat (Felis catus) is one of the world’s most damaging invasive species, especially threatening to local bird populations. This study examined the efficacy of the Birdsbesafe® collar cover at reducing predation rates by household cats on avian populations. The vivid colours of the Birdsbesafe® collar cover are assumed to alert nearby birds to the cat’s presence, allowing them to escape safely. Overall, 19 cats were trialled over 8 weeks and the Birdsbesafe® collar cover resulted in a reduction of 78% in the number of birds killed."
In the media, a story describing the research was published in Germany's prestigious Biorama magazine, and another story in 24heures.ch.
