I am just going to guess at the cause. You say that usually there are not that many yotes in the area however now there are. Might it be that the animals have reproduced beyond their carrying capacity. There may now be more coyotes than their food chain can support. Causing disease, and reduced growth because there is no longer a plentiful food source for all. Also mange is a bad one, can make a coyote look like it was run over with a truck. Sounds like they will probably starve themselves out then reduce in numbers again.