Just what I was thinking. At this time of the year the nesting birds like robins will makes short work of any maggots they find in the open. And it is astonishing how they find them: I had some grass seed in a cardboard pack that had been sealed for a number of years. When I opened it some moths flew out, and when I tipped the contents on to the lawn, robins appeared and kept back and forth picking out all the maggots, which I could scarcely distinguish from the seeds. Very sharp eyes they have.
Also use this method with sardine tins - having made sure to buy in brine not oil: let the cats lick the tin out to save on smelly sink or bin.
S