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 delivering a speech to the World Bank on wildlife crime.
During the speech, he described the illegal wildlife trade as "one of the most insidious forms of corruption and criminality in the world today".
His wife, the Duchess of Cambridge, visited a New York children's centre.
The couple arrived in New York on Sunday night, with the prince travelling to Washington alone on Monday.
At the White House, the prince joked with Mr Obama about the birth of Prince George, saying: "The excitement of the event and everything else was just chaos."
He added that he expects a "busy year" in 2015, when Catherine is due to give birth to the royal couple's second child.
President Obama said the prince's work to protect endangered wildlife was "very important".
BBC royal correspondent Nicholas Witchell
It seems fair to assume that America's first family would happily have received William and his wife to the White House.
As it was, only Prince William got to sit by the presidential fireplace in the Oval Office and chat to President Obama, reminiscing about the birth of Prince George and presumably - after the media had been ushered out - discussing his campaign against the illegal trade in wildlife parts.
Catherine had stayed in New York to pursue her very deliberately separate programme.
Both the tour planners and the couple are anxious to give both of them a chance to be seen pursuing their separate objectives without either overshadowing the other.
And so Prince William was given a clear run to pay his visit to the White House and deliver his speech at the World Bank without any risk of being upstaged by Catherine's presence.
There is certainly not the envy or sense of competition that existed between Prince William's father and mother when they were fulfilling engagements.
Instead there is a realistic awareness of each other's ability to command column inches and a desire to work together to achieve the maximum impact.
Later, in his speech 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."
Prince's passion for wildlife
Prince William founded the umbrella organisation United for Wildlife to try to preserve the planet's most endangered animals and habitats.
The prince has been the royal patron of Tusk since 2005. The charity supports projects in 17 African countries, aimed at protecting wildlife and alleviating poverty.
Before starting at St Andrews University, the prince went on a gap year, some of which was spent in Africa learning about its wildlife and game conservation.
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".
- One of biggest threats to survival of world's most threatened species, including rhinos, elephants and tigers
- Rhinos poached for body parts - powdered horn used in traditional Asian medicine as supposed cure for illnesses, from hangovers to fevers and even cancer
- Rhino horn now worth more than gold and platinum
- Elephants killed for meat and ivory - often carved into ornaments and jewellery
- Ivory can sell for more than £1,200 per kilogramme
- Tiger skin, bones, meat and other body parts highly valued - mainly for use in traditional Asian medicine
The duchess, meanwhile, visited Harlem's Northside Centre for Child Development.
She was greeted with cheers from well-wishers when she arrived at the centre, which provides educational and mental health services to children and families.
Some of the youngsters believed Catherine was Princess Elsa from the hit animated movie Frozen.
Rose Ann Harris, director of early childhood services, said: "When they heard she was coming they thought it was Elsa - we said a princess and they got a princess."
Later, the Duke and Duchess of Cambridge met former US Secretary of State Hillary Clinton and her daughter Chelsea at a reception held at the British Consul General's residence to highlight conservation efforts.
They then attended a NBA basketball game between the Brooklyn Nets and the Cleveland Cavaliers.
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.
On Tuesday, the duke and duchess will visit the 9/11 Memorial Museum and a New York youth organisation.
The visit will end with a University of St Andrews 600th anniversary dinner at the Metropolitan Museum of Art.