We've enjoyed watching birds in our yard this past summer. We're in a suburb, fairly forested, inland northeastern USA hardiness zone 5. As we scaled up the amount of diversity and net primary production around the house, and added a bird feeder, we notice an uptick in various kinds of wildlife. However, we're surprised to see a stark decline in the amount of birds starting around late summer/early autumn.
What could cause the sudden decline in birds in late summer? Is there a migratory trend starting up around this time; it seems early to me for birds to be flying south?
The birds in question include a family of cardinals, occasional blue jay, downy and hairy woodpeckers mid-summer (some are still around), many various sparrows, yellow finches, chickadees, et al.
We continue to fill the bird feeder as usual. We haven't changed anything about our yard routine. We have a rescued feral cat which goes outside and hunts despite our efforts to stop it, and it has killed many mice and a few chipmunks mid-summer, so perhaps the birds have become wary of him and the dead bodies of small mammals left in forested edges around the yard.