There are just so many variables in the wild that finding the exact cause would be very difficult. With that in mind: to just throw up some ideas; Perhaps the area is more wooded than covered with dead grass and weeds or perhaps last fall produced an overabundance in dried leaves making the habitat more favorable to camoflauge the copperheads than the garters and predators are reducing the numbers, possibly there is a predator which prefers garters to copperheads and for whatever reason it's population is up for the year, since garters are found in and near water often, possibly there has been a water polutant, there might be a disease targeting the garters and not the copperheads, thee might be a disease affecting he food source such as frogs or fish and not mice and ground squirrels, or with all do respect perhaps the field outings have just turned up more copperheads as of late, it is impossible to know how may snakes are actually in the area when a great deal of there life is spent underground or in inaccessable locations. Like I said here are just too many variables in the wild, I'm sure i didn't even cover half of them.

I wish I could be more helpful,

Nathan

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