Prince William holds first talks with President Obama, The Duke of Cambridge has met US President Barack Obama at the White House as part of a three-day visit.
Prince William held talks with President Obama in the Oval Office, in advance of the prince's speech to the World Bank on wildlife crime.
President Obama said work to protect endangered species was "very important".
The prince also joked with the president about the "chaos" surrounding the birth of Prince George.
Prince William and his wife, the Duchess of Cambridge, arrived in New York on Sunday night. He travelled to Washington alone while Catherine remained in New York.
At the White House, the prince told the president about his son's arrival, saying: "The excitement of the event and everything else was just chaos."
He also predicted a "busy year" in 2015, when Catherine is due to give birth to the royal couple's second child.
BBC royal correspondent Nicholas Witchell said the prince had enjoyed access "most politicians can only dream about".Later, speaking at the World Bank, the prince said: "In my view, one of the most insidious forms of corruption and criminality in the world today is the illegal wildlife trade."
He attacked those who "loot our planet to feed mankind's ignorant craving for exotic pets, trinkets, cures and ornaments derived from the world's vanishing and irreplaceable species."
Paying tribute to his father, the Prince of Wales, and his grandfather, the Duke of Edinburgh, he said: "They helped to bring about a revolution in attitudes towards our natural environment."
'Loss to humanity'
He added: "From them, I learned that our relation to nature and wildlife goes to the heart of our identity as human beings. From our sheer survival, to our appreciation of beauty and our connection to all other living things.
"Seen in this light, the extinction of any of the world's species of animals is a loss to all humanity."
He said wildlife crime "goes to the heart of our security", "distorts economic development" and "fuels sources of conflict".
Ahead of his speech, the prince wrote a blog for the Huffington Post saying that the response to illegal wildlife trading must evolve "rapidly".Meanwhile, Catherine has visited a development centre in Harlem, and the couple will attend an NBA basketball match later.
Ahead of the visit, Danny Lopez, the British consul general in New York, said there had been "incredible interest" in the royal couple.
He said there was "huge excitement" from people in the city.
