In the US, tiny tree frogs called spring peepers begin to chirp. Pollen from ragweed and timothy grass cause people to sneeze. In the Midwest, spring is a time for tornadoes. Black bears and other animals end their winter hibernation. The Kentucky Derby is held on the first Saturday in May. If you live in Europe or the US, you can see the bright star Regulus in the south at night. In the US, monarch butterflies lay their eggs on milkweed plants. Hummingbirds court in the spring. Males swoop and dive to impress the females.