Some 200 intellectuals, scientists and artists from around the world urged the leaders of Mexico, the United States and Canada on Wednesday to save North America's endangered migratory Monarch butterfly.

US novelist Paul Auster, environmental activist Robert F. Kennedy Jr., Canadian poet Margaret Atwood, British writer Ali Smith and India's women's and children's minister Maneka Sanjay Gandhi were among the signatories of an open letter to the three leaders.

US President Barack Obama, Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto will hold a North American summit in Ottawa on June 29.

The letter by the so-called Group of 100 calls on the three leaders to "take swift and energetic actions to preserve the Monarch's migratory phenomenon" when they meet this month.

They urge the leaders to protect parcels of land containing milkweed, which is threatened by herbicides and feeds the butterflies on their 4,000-kilometer (2,500-mile) journey from Canada to Mexico's wintering grounds.

The letter also called on Mexico to prohibit mining and end all logging in the pine tree reserve where the butterflies live during the winter.

In 2014, Obama, Pena Nieto and then prime minister Stephen Harper agreed to take measures to protect the orange and black butterfly, whose population has drastically dwindled in the past two decades.

The butterfly's population rebounded this past winter season, but it is still far from its peak of 20 years ago.

In 1996-1997, the butterflies covered 18.2 hectares (45 acres) of land in Mexico's central mountains.

It fell to 0.67 hectares in 2013-2014 but rose to 4 hectares this year. Their population is measured by the territory they cover.

They usually arrive in Mexico between late October and early November and head back north in March.