Our guide, Michael Taylor, puts his fingers to his mouth and makes a fantail call. My 6-year-old son Henry is particularly wide-eyed at the noise produced and mimics Michael mimicking a fantail, who is chasing insects being stirred up by our footsteps.
Taylor is from the Auckland branch of the Ornithological Society of New Zealand and leads guided birdwatching walks through Cornwall Park twice a year.
As my children say hello to the fantails, two doves land nearby. Michael and Peter Woods, a retired head teacher from Britain, are quite excited about the doves, more often seen in residential gardens and already I'm surprised to see so many different birds in a city park.
"There are always a few swallows where the sheep are because they stir up insects and always skylarks near the summit," says Taylor.
As we pass the barbecue area, we see red-billed gulls, who come into the park at lunchtime to pinch the food. A man is chopping wood with an enormous axe next to one of the barbecues and I hope he doesn't mind too much about having his lunch taken.
Birdwatching as a hobby may lead to an interest in nature photography or even sound recording and I'm told rosellas are as beautiful to listen to as they are to look at.
Woods says there are fewer songbirds back in England so to see the thrush and blackbird here is a welcome reminder for him of his homeland.
"Cornwall Park is a good place to practise bird photography because the birds here are used to having people around," says Woods. "It's used to teach people skills for more remote nature reserves."
As we pass through a kind of "walk six paces and plant a tree" mini-forest, Taylor talks about "endemics" found only in this country, about native birds we share with other countries (usually Australia), and about introduced bird species. There are also birds that were thought beneficial to agriculture, such as the starling and the minah, and "caged-escaped" species, such as the rosella and spotted dove.
"Homesick early settlers wanted to bring blackbirds, thrushes and finches to New Zealand, and later, introduced game birds like pheasant, as well as other birds they could shoot and eat," explains Taylor as we watch a pheasant in a field nearby.
"It's a very mobile hobby," says Woods, whose birdwatching and photography has taken him from Cape Reinga to Stewart Island, ticking off birds as he sees them.
We stop to notice a nest at the base of a tree. Not only do birds look, sound and fly differently from each other, their nests are even different. Like a detective, Taylor takes it in his hands for an examination.
"It's the simplest of nests, so, is probably that of the silvereye," explains Taylor.
As we continue, I notice it's very peaceful tuning into senses you normally take for granted - like intently listening for the different bird sounds - though it must get easier with practise, and later, on our deck, we chop an orange in half, as suggested, and hope for some birds to stop to eat it.
"Birds in New Zealand are usually well-fed so instead of food, a bird bath close to the ground is the best option," advises Taylor, who says a metal bird bath will scare birds away as they think their reflection is another bird.
Birdwatching is also a good excuse to stay for longer in the park and the highlight for my children was the tricks Taylor showed them about how to play conkers with nuts from a horse chestnut tree and later, a lesson about "plantain shooters", which he says is a "fairly harmless form of warfare."
And, even though it will take a while for Henry to master the art of whistling to a fantail, with beautiful parks like this in the middle of Auckland, there will be plenty of opportunity for him to try.
* Cornwall Park guided bird walks
Sunday May 20 or Wednesday June 6, 10am-12pm. Information centre.
Join guide Michael Taylor of the Ornithological Society. Bookings essential. Ph (09) 630 8485, or email firstname.lastname@example.org. cornwallpark.co.nz
Also at the park, join the guided tree walks (Wednesday May 23 or June 23) with botanists Mike Wilson or Graeme Platt or the guided archeological walk with Gary Law (Wednesday May 30).
* Shakespear Regional Park is now pest-free and has many birds to watch, including bellbirds from Tiritiri Matangi, so is a good next step in your birdwatching hobby.
One of many websites and online communities dedicated to birdwatching.
A great source for beginners with beautiful photos of common New Zealand birds, articles about bird photography and where to spot them.