This being the Internet, however, it is uncertain as to how accurate this figure is, so I went digging for experimental detail. I was unable to find this particular one. However, there is a study by Matthew F. Gaffney and William Hodos in which they anesthetized a kestrel and poked stuff in its eyes. (More scientifically accurate detail here : http://www.sciencedirect.com/science/article/pii/S0042698903003043 ), in which they found that there is (potential) conspiracy behind avian vision acuity studies, and data does not always match the reality we live in. This (possibly) represents a scam in which bird scientists bilk the public out of hundreds of dollars to further promote their own research. It’s a travesty (maybe) and we should (perhaps) do something about it.
Alternatively, maybe different birds just have different eyes.