From that photo I'd be inclined to say Wilkin's. It would make sense on locality too, so long as they were obtained relatively locally. From photos I've been looking at, the two species are really quite separable on appearance.
However, I definitely want to say that I'm 100% sure. You'd need to be sure of origin for that, I think.
From the photos I've seen (with locality so I can be sure of what they are), brachyotis does seem very grey without prominent markings, while wilkinsi is much richer in colour with very strong striping.
