The chart about the increase in crows' urban population gave me an "aha" moment: I don't recall ever seeing crows in the various cities I've lived in, but now in the last couple of years I've notice that I see them regularly. In particular a flock of them seems to be regularly hanging out around/over a shopping plaza in a semi-urban/semi-suburban area near me in the small city where I live (New Haven, CT). They fly into and over the area in swirls, perch on telephone wires or on top of light poles singly or in groups, and sometimes one or two or more swoop down to get a piece of pizza or other scrap in a parking lot. As a result of this class I'm getting even more enjoyment out of peering at them. I certainly notice their shapes, from the first lesson. Great course.
Inbreeding, just as with humans, could increase the likelihood of harmful mutations becoming expressed as disabled offspring or death before reaching breeding age.
I didn't know birds paired up so much, so extra-pair fertilization is not so surprising to me. It could be beneficial in widening the gene pool.