Anything with David Attenborough's name on is sure to be informative, but I did spend most of this series asking "how do they know?". The second series is better at explaining some of the current thinking. Mostly I relied on other wildlife programmes of modern animals to draw parallels. Some of the stories made me laugh out loud, showing it's not all bad. There is too much emphasis on contrived stories (this seems to be the way of Natural History shows these days) which made me wince when there is a potential danger but phew! emergency over.
I'm not sure what I was expecting, but clearly I was a little disappointed in this, due to the lack of explanation which usually accompanies Attenborough's programmes. The imagery is very impressive, holding up my score to three stars.