In article , david
writes

"...Mind you, as many of the small birds caught by cats weigh less than an
ounce (Blue Tit - 10-15 grams = one-third to one-half of an ounce), their
output isn't going to reach half an ounce a day. 10-11 gram birds produce
about 0.7-0.9 grams dry weight per day(1)...."


But thy are more than made up for by Blackbirds, Magpies etc.

Even a Blackbird, weighing up to 3.5 ounces isn't going to produce half
an ounce a day! And not many cats catch Magpies otherwise the
anti-Magpie brigade would have their solution :-)

--
Malcolm