Bio mass-living weights of birds.

How productive is your garden? A pigeon can weigh upto 400grams which is equivalent to 40 blue tits or 80 goldcrest. Normally the number of birds are counted and number of species. The higher the bio mass of birds, the better your garden is. I would like you to take one hour to count the maximum number of any species you see in your garden. So if you see one pigeon that is the equivalent of seeing forty blue tits for the bio-mass.