Olkowicz, et al. (2016) Birds have primate-like numbers of neurons in the forebrain

https://www.pnas.org/doi/full/10.1073/pnas.1517131113

Sorry, nothing specific. A while ago I read 'Bird Sense' by Tim Birkhead but this is about their sensory systems rather than their intelligence as such, and is a bit discursive. There are a couple of useful starting points on Wikipedia, such as [0] and [1].

In general, birds are sometimes surprisingly different to mammals. Their eyes are quite different. For example, raptor vision has a much higher acuity and framerate than ours, and many birds do different things with their left and right eyes. Their respiration is also different (including lungs that have 'in' and 'out' pipes), which allows something like a falcon to eat the moment it has finished hunting, unlike say a cheetah, which has to get its breath back before eating after a successful chase.

[0] https://en.wikipedia.org/wiki/Avian_brain

[1] https://en.wikipedia.org/wiki/Bird_intelligence

Jennifer Ackerman's "The Bird Way"

Instagram. There's a bottomless supply of videos showing birds being clever