As they stab up and down at the bird food in her palm I'm paralysed by memories of the Hitchcock classic but Newkirk is in Dr Doolittle heaven, even luring a squirrel and a few fat crows down to join the seething mass of pigeons. "Those pigeons are vermin," warns the photographer, which is rich since he provided the bird food. "Oh rubbish," replies a beaming Newkirk. "Pigeons are lovely. They just get a bad press."
There is little that Newkirk, the British-born founder of the world's largest animal rights group - the US-based People for the Ethical Treatment of Animals (Peta) - would not endure to highlight animal abuse, or to put animal rights issues right up there alongside those of humans.
She is currently protesting at the South African embassy in London about the export to the US and Europe of baby elephants. She likens their enforced separation - "while they weep" - from their mothers to the barbarities of the slave trade. Earlier this year Newkirk made international headlines when she locked herself in a cage in Taipei to draw attention to the plight of millions of stray dogs currently roaming Taiwan or, worse, languishing "skeletal and caked in filth" in the country's dog pounds.
In the past she has walked naked down Oxford Street, and streaked her way through a host of other European capitals, in order to denounce the fur trade. She has been arrested numerous times, once after she rushed the General Motors float in a charity parade to protest at the company's use of baboons and pigs in car-crash tests and another time when she stormed the catwalk during a New York fur show to throw blood-stained money at the startled audience. After all that, being suffocated by pigeons for the cause must be a doddle. She even gets to keep her clothes on.
Think of all the most high-profile animal rights stunts of recent years and Peta was probably responsible. It was Peta which dreamed up the anti-fur campaign which persuaded a gaggle of supermodels, including Christy Turlington and Naomi Campbell, to pose naked (although Campbell now models fur again). Newkirk and her followers also stormed the Paris offices of French Vogue wearing steel leg traps and fur coats splashed with red paint.
In the past 18 years Peta has conducted several successful, gutsy undercover operations to expose the cruelty endured by animals in laboratory experiments. But it also understands the value of glamour. Seldom has a campaign group recruited so successfully in Hollywood, counting actress Kim Basinger, her actor husband Alec Baldwin, actors Richard Gere, Dustin Hoffman and Ali McGraw and singer Belinda Carlisle among its devotees. Even our own Sir John Gielgud has appeared in a Peta video denouncing the force-feeding of geese to make pate de foie gras.
Standing in Hyde Park, surrounded by the fluffy and feathered, Newkirk, a youthful 49, seems all sweetness and soft focus. But those at the receiving end of her crusade will tell you that behind the girlish smile, quirky humour and gentle (and still very English), voice, there lurks a zealot whose extremist views fuel an endless campaign of "terror" and intimidation.
While Peta's admirers focus on its clever and amusing stunts - it once printed four million flyers reading "Avon killing" instead of "Avon calling" - it is clear that Peta is not all laughs. There is also menace. Ask Anna Wintour, editor of American Vogue who last year wrote a rather un-PC piece on her enduring affection for fur. She was lunching in a plush Manhattan restaurant when a Peta supporter walked up, screamed, "Shame on you, fur hag, this is for the animals," and dropped a dead raccoon on her plate.
Or ask actress Cybill Shepherd, whose home was besieged by Peta supporters chanting "blood and death" as part of a campaign against the cosmetics giant L'Oreal for whom Shepherd modelled. L'Oreal eventually stopped all animal testing of its products but Shepherd was scathingly critical of what she described as the "publicity terrorism".
Does Newkirk think these tactics over-zealous? A slither of steel suddenly surfaces. "I think we could be more vigorous rather than less," says the woman who compares animal abuse to Nazi concentration camps. So one raccoon was not enough for Wintour? "You would have to bury her under a truck load of raccoons to get her attention. She is a hard woman."
And of Shepherd's complaints - echoed by an array of scientists whose homes have also been Peta targets? Newkirk says people should not be allowed to simply melt back into their neighbourhoods each night when they have spent all day "committing atrocities".
In the US, government officials have accused Peta of being no better than terrorists. Interestingly, though she insists Peta sticks to non-violent protest, Newkirk refuses to condemn the tactics of the extremist Animal Liberation Front. Why should she condemn ALF violence when so much pain is being inflicted on animals all over the world?
Newkirk has always sided with the animals. The only child of a British engineer and his social worker wife, she spent her first seven years in England, with Sean her faithful setter as both surrogate sibling and best friend. "We did everything together," she says, reminiscing about their 1950s trips in the back of her parents' Austin Princess.
Sean was put down when her parents moved to India, though she was told he had died during a visit to the vet. She did not find out the truth until later. "I was very angry at my parents," she says. She now admits that Sean was too old to make the journey but still adds they "would never have done that to a child".
In India she was surrounded by human suffering on an epic scale. But while her mother busied herself with Mother Theresa's charities, the young Ingrid was "always out the back feeding the dogs". Why, I ask, do animal rights people so often seem more moved by the suffering of animals than people? Because, says Newkirk, no matter how awful conditions are for human beings, those for animals are always more terrible.
In her late teens Newkirk moved to the US. A chance visit to the local animal pound appalled her and nudged her a little further towards the philosophical leap from animal welfare to animal rights. Determined to improve conditions in the pound she got a job there. Later she trained as a deputy sheriff so she could hunt down those who inflicted injuries on animals. Eventually she managed to jettison all the human law-enforcement work and achieved the highest animal-cruelty arrest rate in Montgomery County, Pennsylvania.
It was the late 1970s and the animal rights movement was beginning to blossom. Newkirk was poised to become one of its early heroes. When she became pound master in Washington DC she took on the universities who visited regularly to collect animals for laboratory tests. She insisted on her right to visit their labs. Soon they were seeking animals elsewhere.
In 1980 she co-founded Peta with student Alex Pacheco. They pooled their skills - she had the knowledge of the law and he was versed in direct action, having worked with British hunt saboteurs and crewed an anti-whaling ship. Since then Peta has mushroomed in the US. Its membership now stands at more than 325,000. Its annual budget is over $13m and it employs more than 90 staff, mainly at its Maryland headquarters.
At the beginning of the 1990s Peta set up a branch in the UK. But the organisation has failed to make a comparable impact in this country. While British groups claim to admire Newkirk's commitment and Peta's creative campaigns, privately they complain that the group is "hit and run", raising issues but seldom building on them. The tactics are also a little un-British. Philip Lymbery, campaigns officer with Compassion in World Farming, says that his group would not dump a raccoon on someone's lunch plate or harass a scientist at home. Perhaps it is also just not the British way to polarise debates beyond any hope of middle ground.
Still rather subdued in Britain, Peta continues making noise in the US. Its latest stunt is a ground-breaking advertising campaign aimed at a consumer boycott of Procter and Gamble's Tide washing powder. In the Peta adverts, which will run from December, a drag queen called Lady Bunny brandishes a box of detergent called "Died" under the slogan "Sometimes Big Bright Packages Contain Dirty Little Secrets".
In the past Peta has successfully targeted cosmetics giants such as Revlon, Avon and Gillette. But this is its first attack on a top brand, rather than a company, and it has earned it a special mention last month in the Wall Street Journal. The Peta campaign, said the newspaper, marked "the opening of a nasty new frontier in consumer - boycott battles".
P&G is exasperated. It claims to have reduced animal testing by more than 80 per cent and to be investing heavily in alternative safety measures which will make all animal tests unnecessary. Peta must feel P&G could still do with encouragement. Earlier this year an activist slammed a Tofu cream pie into the face of P&G chief executive John Pepper at an awards ceremony and Peta supporters have also leafleted Pepper's neighbours.
It's in-your-face tactics such as this which have some American corporate voices demanding that targeted firms fight back. Some scientists say that the public should look beyond Peta's legitimate concern for animals to what the group's idealistic vision would ultimately mean - a world in which no animals would be raised for food or clothing and experiments on them would never be justified even if they brought a cure for Aids. Even some animal rights activists warn Peta that it will alienate the public with its uncompromising and simplistic tenets.
Newkirk may still be too extreme - in philosophy and tactics - for many, particularly back in the land of her birth, but she remains undaunted. She is fond of a quotation from the Texan politician Jim Hightower, which harbours an unintended animal rights twist: "There's nothing in the middle of the road but yellow lines and dead armadillos. So who wants to be there?"