Donald Trump has slammed renewable energy, saying wind power is expensive and is “killing all the Golden Eagles” in California.

Speaking at a press conference on the same day he clinched the magic number of 1,237 delegates to become the Republican nominee, Mr Trump said solar power and wind power are both costly and only work with government subsidies.

He added that people are “put in jail” in California for shooting a Golden Eagle, yet windmills are reportedly killing “hundreds and hundreds” of the world’s “most precious birds”.

“Having said that I support all forms of energy,” he told the crowd in North Dakota.

The Bald and Golden Eagle Protection Act is a federal law, and does not just apply in California.

According to a 2014 study by environmental consulting firm West Inc and two federal scientists, between 214,000 and 368,000 birds are killed annually when they collide with wind turbines, but the study found the birds face much bigger threats from collisions with mobile phone and radio towers (6.8 million fatalities) and cats (between 1.4 and 3.7 billion fatalities).

In August 2015 Mr Trump did not seem so keen on these rare and "precious" birds when he was posing for a cover of TIME Magazine in Trump Tower with a Bald Eagle.

The beady-eyed bird appeared to give the Republican quite a fright when it lunged for his hand and the eagle handler had to smooth down Mr Trump's hair after it got ruffled.

The GOP frontrunner has engaged in a long battle against wind turbines.

Just six months ago, Mr Trump lost a court battle to stop the construction of 11 offshore wind turbines in sight of his golf resort in Aberdeenshire, Scotland.

At the same press conference on Thursday, Mr Trump endorsed fracking, saying his rival Hillary Clinton would “ban” the practice.

He also said he would approve the controversial Keystone XL oil pipeline from Canadian energy firm TransCanada, but only as long as the US takes its share of the profits.

“I want the Keystone pipeline, but the people of the United States should be given a significant piece of the profits,” said Mr Trump.

“That’s how we’re going to make our country rich again, and it’s how we’re going to make America great again.”