Quite a complicated topic, but thats why they call it a challenge.
I hope my stab fits the criteria

This was taken at a little known mission named Santa Ysabel in

San Diego County. The swallows are legendary for the fact that

they return year after year from a long journey from Argentina

Because of the massive urban sprawl, some of the more well known

missions in densely populated areas see less and less swallows every

year.