Each morning, blackcaps and thrushes sing in Malahide’s Robswall Park. The star performers, however, are skylarks. Like the other songsters, they are ‘passerines’; three toes point forward and a fourth projects backwards.
A passerine’s feet lock automatically when it lands on a branch. The bird can sleep comfortably when perched. However, with no trees on the open grassland where skylarks nest, this ability is of little use to them.
Nor are there song-posts from which to proclaim territories. Shelly’s ‘blithe Spirit’ cannot defend a territory in the usual songbird fashion, so he proclaims a ‘virtual’ one. Rising about 50m into the air, while singing constantly, he claims ownership of the ground beneath him. His territory will be the base of a notional cone extending downwards. The higher he ascends, the larger the area claimed and the more favourable the impression he makes on prospective females. Rival skylarks, with three-dimensional mathematical skills, can estimate the extent of his territory and avoid it.
Most songbirds broadcast from perches. Silent intervals in their songs are important; the singer listens out for rival challengers. A skylark, however, produces hundreds of notes in a continuous two-minute-long cadence with no silent intervals.
Alternatively, he can just close his wings and fall in a ‘sky-dive’, like a parachutist plummeting towards the ground and pulling the rip-cord just in time to avoid impact. The performance may not be in the peregrine-stoop league, but it is still one of the ‘sights’ of Irish nature. The Robswall skylarks opt for free-fall after most of their performances.
A high-flying tenor with strong lungs is just what a female skylark seeks to father her chicks, so you might get the impression that the elaborate song-flight is just a stunt to impress females, the skylark equivalent of a peacock’s tail. But it is not. Show-offs, such as peacocks, are generally promiscuous. Their harvest of conquests depends on the quality of the displays. Skylarks, however, are monogamous, at least seasonally. Their spouses do not need high-flying musical recitals to keep them faithful.
Pulling out at the end of his dive, the singer will not alight close to the nest. To do so might disclose its location to an enemy. Instead, he plunges into the long grass some distance away and creeps unseen to home-sweet-home.
Like people during the Covid-19 threat, skylark pairs remain ‘locked-down’ on their patches for the summer. The territory is self-sufficient, offering places to nest, insect food for chicks, and long grass to hide them from predators. But there is a downside. Ground nests are particularly vulnerable to accidents, weather, and predation. Such is the attrition rate of eggs and young, that pairs must raise three or four broods, each with three to five chicks, in order to compensate for the high mortality.
Lockdown ceases at the end of the breeding season. Irish skylarks do not appear to migrate. Although it has not been proven, many pairs remain intact throughout the winter. Migrant skylarks, from northern Europe, pass through Ireland on migration, temporally increasing the local population.