by Dan Gleason

So many of us know the joy of seeing our dogs run free and enjoy the wide open spaces--even in the city. But, how often have you seen dogs running off-leash in a public park and wondered whether they have any impact on the local wildlife? Is this just harmless fun? Maybe not.

Unfortunately, birds, squirrels and other wildlife are not happy to have a visit from your dog. From their viewpoint, dogs constitute a threat.

All local parks have ground-nesting birds from early March until the end of July. Even if our dogs may not be catching or killing birds outright or even stepping on the nest, they may be driving the parent bird off the nest with dire results. Birds, of course, must incubate their eggs for successful hatching, and frequent disruption may impair that success. After hatching, young altricial birds are very dependent on their parents’ body heat and protection for survival. When the parents are driven away and cannot brood, the nestlings quickly lose heat and are put at risk. Young precocial birds, like Killdeer, are better able to regulate heat but they still need the security of protective parents. Dogs running loose can separate parents from young. No matter how well-trained, some dogs simply cannot resist the temptation to chase a baby Killdeer or duckling that is fleeing.

Off-leash dogs at inappropriate sites may also impact the vegetation is such a way as to create new tracks and trails. What was once a safe haven for the birds is suddenly now more vulnerable. These "trails" allow other predators such as skunks and raccoons to more easily discover nests, eggs or hatchlings. So even if the dog does not cause the direct threat, its actions may still put the nesting birds at greater risk. If a dog startles a parent bird, the ensuing commotion may signal the nest location to other predators, especially avian predators that are always on the alert for any unusual activity. Normally, nesting birds are very secretive when coming and going to and from the nest. Repeated disruptions throughout the day from many dogs can lead to nest failure for the impacted birds.

Sudden fright can take a toll on birds in other ways. When suddenly frightened, a bird can undergo fright molt, in effect, suddenly dropping a large number of feathers, a potentially fatal condition in cold weather. Also, birds have a very rapid heart beat, so fast that it is possible for sudden fright or trauma to increase the rate to 1000 beats per minute, causing the aorta to rupture. I once saw this happen to a Hermit Thrush that was startled and became entangled in old fishing line hanging in the brush. As we tried to untangle the line, the bird suddenly died. Out of curiosity, we examined the bird and discovered that the entire chest cavity was filled with blood. Fright molt and aortic rupture are not common events but can occur and we have a responsibility to not take actions that expose birds to these or other potential risks.

Instead of assuming that any park is OK for an off-leash run, we should use our local off-leash parks for free run of our canine friends. These provide friendly places for dogs to run, and they help to minimize the harmful interaction of dogs and wildlife.

Most pet owners are responsible and do clean up after their pets and many dogs do not chase wildlife. However, please consider the other impacts of your dog and the fact that this happens over and over again throughout the day. Combine this with the fact the there are a significant number of pet owners who are not responsible and some who even encourage their dog to chase the geese and ducks. This all totals to a large impact on wildlife that is already stressed from the multitude of other pressures to be found in a public park.