What is that weird loud trilly bird call that seems to only happen when it’s really humid this time of year? Well, it’s not a bird at all, but in fact, its Northern gray treefrogs calling looking for mates! With the warm humid weather settled into Warren County, the largest tree frog in the northern states, the Northern gray treefrog, can be heard frequently calling throughout the day and night. Its voice, a high-pitched trill, fluctuates in speed with the temperature and humidity — the higher the temperature and humidity, the faster the trill.
Adult Northern Gray Treefrog
There are two species of tree frog in New Jersey, the Southern gray and the Northern gray, which appear identical apart from their calls, and the calls themselves are very difficult to tell apart. However, in Warren County only the Northern species is present. The adult Northern gray tree frog adult skin is warty and typically gray in color; however, green or brown frogs may be seen, and individual frogs may show variations in color depending on conditions. There is usually a light spot under the eye. The inner surface of the hind legs is yellow or orange, sometimes with black marks. The frog has well developed, sticky adhesive rounded toe pads that enable them to climb rapidly. Juvenile frogs are often bright green, and tadpoles are easily
Juvenile Northern Gray Treefrog
recognizable, with reddish tails and olive bodies.
Gray treefrogs spend most of their time high in the trees, except during breeding season, late May through June, when they make their way to edges of waterbodies. Bare horizontal branches over water are the preferred calling sites during breeding season. They breed in vernal ponds, small ponds or swamps, and remain in mix forested uplands during the rest of the year.
Good places to hear and even see them at Merrill Creek Reservoir are: along the Orange Trail, especially by Richline Pond; along the shoreline at the Red Trail, and at the “bog” where the Blue and Yellow Trails intersect.