Northern leopard frogs breed in the spring from March to June. Men use a snoring rumble to attract women. Once the female selects the male, the pair is paired once. After mating, the female produces up to 6,500 eggs in the water. Eggs are gelatinous, round and deep in the center. The eggs hatch into a pale brown sputum with black spots. The rate of incubation and development depends on temperature and other conditions, but it usually takes 70 to 110 days to develop from egg to adult. At this time, the cockroach will grow bigger, develop the lungs, long legs, and eventually lose the tail. The World Conservation Union classifies the protection of northern leopard frogs as “the least concerned.” Researchers estimate that hundreds of thousands or millions of frogs live in North America. However, the population has been declining rapidly since the early 1970s, especially in the Rocky Mountains. Laboratory studies have shown that the possible explanation for regional recession is related to the effects of higher than normal temperatures on crowding and bacterial infections. Other threats include habitat loss, competition and predation of introduced species (especially bullfrogs), hormonal effects of agricultural chemicals (such as atrazine), hunting, trapping research and pet trade, pollution, bad weather and climate change.