New York ? Wearing multicolored wings on the back of her sleeveless dress, 5-year-old Isabel DeLuca gingerly took a monarch butterfly in her hand and attached a tiny sticker to its wing.

“Bye!” she said as the butterfly flew off the landing at Belvedere Castle in Central Park.

Scientists say the insect was on its way to Mexico, like millions of others every year. As many as 500 million black-and-orange butterflies that summer east of the Rockies end up sleeping on top of each other during the winter in a mountainous area outside Mexico City, said butterfly expert Kurt Johnson.

Johnson, a lepidopterist at Florida State University, said that as many as 80 percent of the butterflies that migrate to Mexico die off during the winter. They reproduce enough to keep the species’ numbers steady, he said, but scientists fear the monarchs eventually will become endangered as illegal logging in Mexico thins forests and reduces their habitat.

Johnson said there was no scientific consensus on why the butterflies use Mexico as their winter home, although he believes forests there were originally thick enough to provide enough insulating foliage for the cold-blooded insects to maintain their body heat in the colder months.

Every autumn, researchers tag butterflies before their migration to study everything from how long it takes to fly 2,800 miles (most say about two months) to their body temperature during the winter.

Friday in Central Park, park rangers reached into a horseshoe-shaped plastic bubble filled with 100 butterflies, took out one at a time and helped schoolchildren attach tiny stickers to their wings.

The stickers identified the insects as part of a research project at Kansas University; the university’s researchers are in Mexico and pay a small fee to anyone who reports the tag numbers of butterflies they encounter.

Isabel, who dressed up in the butterfly costume she wore to her fourth birthday party, said she loved to watch the insects because “they’re pretty.”

She said she wished she could fly too, although she acknowledged her birthday-party wings wouldn’t get her far.

“I’m a different kind of butterfly,” she said, “a rainbow butterfly.”