Two male song thrushes are fighting for supremacy. There’s no physical violence involved: their weapons of choice are their phenomenal voices. The two antagonists have taken up positions in trees about 20 metres apart. Surrounded by twigs and branches, they’re barely visible – but their breathtakingly beautiful songs fill the morning air.

It may enchant the human ear, but this singing contest is deadly serious: males sing to proclaim their territory, scare off rivals and demonstrate their prowess to attract or keep a mate. It’s a sure sign that the breeding season is rapidly approaching.

Song thrushes began their tuneful competitions at Potteric Carr in the cold and dark days of late January. Some of the reserve’s most familiar residents – robins – sing all year round but ramp up their efforts as spring approaches. Robins are among the most territorial of our native birds and will aggressively defend their patch against rivals (while invariably welcoming anyone with a pair of binoculars or a camera).

As spring gets closer, male blackbirds produce a melodious song from a vantage point to mark their territory. But if that fails to deter a challenger, they’re not above a bit of brawling on the ground.

Many smaller birds – including great, blue, and coal tits - will have joined together in the winter to form mixed flocks to help protect them from predators and find scarce food. As the days lengthen, the instinct to band together for safety is ousted by a more competitive urge to find a partner and breed, meaning you’re more likely to see them in pairs, rather than groups. According to folklore, birds choose their mates on Valentine’s Day – certainly not entirely accurate, but with a grain of truth in it.

One song that’ll be listened out for especially keenly in the coming few weeks at Potteric Carr is the piercing “tiu, tiu, tiu” of the willow tit – Britain’s fastest-declining resident bird. The reserve had a population of seven pairs in 2011, but that’s dropped to just two pairs over the last few years, meaning a successful breeding season is crucial.

Another rare species is already making itself heard elsewhere in South Yorkshire…but not yet at Potteric Carr. Bitterns – secretive members of the heron family – are perfectly camouflaged in the reed beds where they live. It’s their deep, booming call that usually gives their presence away. Potteric Carr has two females and one male, and the suspicion is that the lack of masculine competition means he hasn’t got as much incentive to show off his vocal prowess.

Elsewhere at Potteric Carr, the mating game is well underway. Mallard, shoveler and other species of duck have already paired off. Visitors can watch great crested grebe couples perform their elegant courtship dance, while aggressive male coots get to grips with their rivals in a frenzy of tangled legs and splashing wings. Tawny and barn owls started the breeding season even earlier: they lay eggs from late January onwards.

Over the next couple of months, things will hot up even more. Buzzards and sparrowhawks will perform their “rollercoaster” display flights. Meanwhile thousands of singers will be flying in to add their voices to the Potteric Carr choir. Warblers and other migrants will make the long journey from Africa to breed in South Yorkshire – and they too will need to sing to attract a mate and proclaim their territory.

While our resident birds are already performing a tuneful prelude as winter turns to spring, the music will reach a crescendo in the long, light days of early May, when their numbers are swelled by these new arrivals. That’s the best time to set your alarm, get up at stupid o’clock and immerse yourself in the magic of a dawn chorus.

*Potteric Carr is organising a dawn chorus walk on Sunday, May 7. Tickets need to be booked in advance at:

https://www.eventbrite.co.uk/e/dawn-chorus-walk-tickets-543217687727