If you live near wooded areas or have seen coyotes or tracks in your yard lately, this might be why. 

I live out in Westport with a decent amount of woods around our yard. Since I have three big dogs, who always let us know when somethings walking around the yard, we've been keeping an eye out for tracks in the snow the last month or so. Recently, we've seen some huge tracks (we have a dog who weighs well over a hundred pounds, and these tracks are as big as his) coming through the yard and in some instances, right up to the fence around the house and pool.

I have no problem sharing my yard with the coyotes, as long as they don't mess with my fur kids. But I found some info on why coyote activity may ramp up in the next month or so and why they might be a bit more aggressive than normal. According to a Team Indiana post, it's coyote mating season:

TIP: The next 4-6 weeks is mating season for coyotes. Please do not let your dogs out alone. The coyote gets your dog to chase him and then somewhere in the distance the pack waits for your dog. Then the outcome is tragic as they can & will attack/kill your pets. Just be aware it can happen to your beloved pet. {Coyote breeding typically peaks in late February and early March, the gestation period averages 58 to 63 days. Male coyotes can become more aggressive during this time of year, the long and short of it all is that coyotes always pose a risk to your dog (and other small pets). That risk increases during mating season.}

A general rule of thumb: if you have tiny pets, don't let them out unsupervised at night. And don't feed the coyotes if you know they come through your yard - even if you kind of really want to, like me.