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.