[aeshna5]

Blackbirds can certainly dominate Song Thrushes, but I've never seen any literature implicating them in the fortunes of latter. However there is suspicion as temperaures have risen that Blackbirds have occurrred at higher altitudes + may be a factor in the decline of Ring Ouzels as they dominate.

Back to Song Thrushes + the good news is that there has been a small turnaround in their numbers, which is good news.

I suspect the thrush you read about defending a bush of berries was the larger Mistle thrush which frequently guards such a bush against others- sometimes a lost cause if a whole flock of Redwing or Fieldfare descends.

Where I worked recently we had a Yew tree which every autumn was noisily defended against other thrush species, including Blackbirds, by a pair of Mistle Thrushes.