Bird courtship
For the next few months, the behaviour of birds will prove to be a visual delight for the birdwatcher
Courtship, mating and the raising of young birds is a boom time for birders
F ROM EARLY FEBRUARY to the end of summer, birds have only one thing on their minds – the propagation of the species. For some, only part of that period will need to be used, for others, virtually every waking moment, but for birdwatchers, it’s a win-win-win situation, because at almost every stage of it – courtship, mating, and especially the feeding and raising of young birds – will be more active, more visible and will eventually be present in greater numbers than at any other time of year. So, if you’ve set out on your #My200birdyear quest, now’s the time to get your list growing. If all you want to do is observe birds and bird behaviour well, now’s also a great time. Bird courtship For some species, this will have started back at the end of last year. Some birds build nests (or renovate old ones) in late autumn and winter, with the nest acting as an advert to females. The best-known, globally, are the bowerbirds of Australasia, which adorn their abodes with a mass of colour co-ordinated items. But closer to home, the tiny but ubiquitous Wren does exactly the same – each male builds several nests on his territory, ready for inspection by prospective partners. To get the females there, the male generally needs to grab their attention. This can involve a display, and singing (the Wren’s preferred strategy – it has an astonishingly loud song). Both have the twin aims of capturing the attention and admiration of unpaired females, and of warning off rival males. At their extremes, displays can be truly extraordinary, and can involve both the bird’s specialised breeding plumage, and some sort of ritual or performance. A Black Grouse lek, for example, at its peak in February and March, is astonishing, as the males show off their white undertail coverts, and inflate the bright red ‘combs’ above each eye. Perhaps the most remarkable display of all, though, is the Ruff’s. It breeds in the UK in very small numbers, but males passing through on the way to Arctic breeding grounds sometimes perform here, as their display is primarily directed at the other males. The leks involve three ‘types’ of males. Most (84% of males) erect their black or chestnut ruffs, then leap, run, lunge, flutter and posture at other males present. A second type, satellite males (about 15%), are smaller and have white ruffs, and do not have their own territories but attempt to ‘steal’ females, while a third (just 1%), look like females and use this ‘disguise’ to get close to actual females. Here are three more displays to look for – none of these species are rare, but all become much
A Black Grouse lek, for example, at its peak in February and March, is astonishing, as the males show off their white undertail coverts, and inflate the bright red ‘combs’ above each eye
more visible at this time of year. Great Crested Grebe: In spring, their ornate ruffs make them very obvious, while their ‘weed dance’, in which male and female mirror each other’s movements and even present each other with pieces of vegetation, is elegantly beautiful and unmistakable. Lapwing: Feeding on ploughed fields or huddled on marshes, they appear little more than dark blobs. In the breeding season, though, the males perform energetic, tumbling aerobatics, accompanied by their ‘peewit’ call, plus a variety of other squeaks and whistles. Sky Lark: Often the first indication spring is in the air is that the Sky Lark is in the air, too. Their song flight, a step-by-step ascent followed by a parachuting descent, accompanied by a loud warbling, can be seen in open country, now. Mating
Once a bird has successfully paired off, the actual process of mating is brief, so it’s pretty rare to see it taking place, although pigeons and doves seem remarkably unabashed about coupling in full public view. In most bird species, males and females have a single opening – the cloaca – that is the exit for their digestive, urinary and reproductive systems. During the breeding season, it swells and protrudes slightly, while most of the year it is much less prominent. When birds are ready to breed, their reproductive organs – the testes and ovaries – swell and produce the sperm and ova. Male birds store sperm in their cloaca until a mating opportunity arises, and females receive it into their cloaca before it fertilizes their ova – the transfer between them is very quick, and you might not see much more than one bird briefly hopping on and off the other amidst a flurry of wing-fluttering. The complicated bit, though, is how often what appears to be a solid pair of two birds actually turns out to be anything but. The humble and unobtrusive Dunnock is the best-known example. Chicks within a brood often have multiple fathers, as a result of the females breeding with two or more males at once. But the males, aware of this, try to ensure their own breeding success by pecking at the cloaca of a female with which they’re about to mate, to stimulate ejection of any rival males’ sperm. This polyandrous system is the most common mating system among Dunnocks. But depending on the ratio of male to female Dunnocks, and the availability of food (abundant food means smaller territories), things get even more complex. If a male and a female territory overlap, a monogamous system is used, but if multiple female territories overlap a single male’s, that male might mate with several females (polygyny). And multiple males might defend a territory containing several females, with all the males potentially then mating with multiple females, and providing food to multiple nests. Life as a Dunnock can seldom be dull, or anything other than exhausting! In fact, polyandrous and polygynous mating takes place in a wide variety of species, with strictly monogamous pair bonds rarer than you might think. In the UK, corvids are the most visible
example of the latter – although you’ll see many of them in flocks at one time or another, they’ll eventually separate back into pairs. Incubation This is the process of keeping the eggs warm until the young inside are ready to hatch. In doing so, the parent birds are also obviously on hand to protect the eggs from predators, which can include other birds, such as, for example, corvids and Great Spotted Woodpeckers. In most birds, the parent loses breast and belly feathers, forming a ‘brood patch’, which enables their body heat to be transferred to the eggs and keep them at the optimum temperature. Length of incubation varies, but broadly speaking, the larger the bird, the longer it is. Both the laying and incubation can be timed to coincide with the availability of particular food (Blue Tits, for example, try to take advantage of the emergence of certain caterpillars). Some species (and most garden birds) start incubation towards the end of the laying sequence (most lay one egg a day), but others start earlier, meaning that the eggs hatch at different times. This is usually deliberate, so that the last chick or chicks to hatch can be left to die if feeding conditions are bad. It’s a seemingly cruel strategy but one carried out by Jackdaws, for example, as well as Barn and Tawny Owls. Finally, incubation can be shared by both sexes – Starlings, House Sparrows and Woodpigeons are among familiar species in which this is the case,
In most birds, the parent loses breast and belly feathers, forming a ‘brood patch’, which enables their body heat to be transferred to the eggs and keep them at the optimum temperature
with the birds alternating between incubation and feeding themselves. In many others, such as Blackbirds and Robins, the female does the incubation, and is usually kept supplied with food by the male. Feeding and raising young
Once the eggs hatch, things get really busy for the parent birds, as they work round the clock to find enough food for their family. Well, not quite all parents. Some species have precocial chicks, which is to say that they can walk as soon as they hatch, to evade predators, and to find food. Even in these cases, though, which include waders, many ducks and geese, and rails, the parents often supply some of the food, or help the chicks find their own. During the breeding season, EVERY bird becomes a predator, because the youngsters need protein to develop, so whether it’s a Golden Eagle catching a Mountain Hare, or a Goldcrest snaffling aphids, they’re all hunters. That’s why encouraging insects in your garden is so important, because even seed-eating species need them as food for their young for at least a few weeks each year. So, the humble House Sparrow, for example, starts grabbing insects to feed its young, while the adults continue eating their usual diet of weed seeds or, if they’re lucky enough to live in a garden with feeders, a commercially produced seed mix. So, don’t stop topping up the feeders just because the spring weather has arrived. But let’s take our cover bird, the Barn Owl, as an example of how young birds develop. Each adult bird needs three or four prey items a night, typically Field Voles (45% of a British Barn Owl’s diet), Common Shrews (20%), or Wood Mice (15%). But during the breeding season, each owlet, and there can be up to seven, needs the same amount, too, for at least eight and usually nine weeks. A large brood, then, could require over 1,750 prey items in the course of the season. You can see at a glance that even a short spell of bad weather (Barn Owls can’t hunt in the wet) can upset that equation badly, and also why Barn Owls often hunt in daylight, because the short spring and summer nights don’t leave them enough time to meet their targets. You can understand why such a huge amount of food is required if you look at just how fast a young Barn Owl grows. At two weeks old, an owlet will weigh about 165g, while its wings will be 55mm long; a week later, it’s an average 239g, with a wing length of 92mm, and at the five-week mark, 385g and 171mm. After that, things level out a little, until by the time the birds are fully fledged at nine weeks, the weight is down to 346g, and wing length is 275mm. This rapid growth happens in most species – an extended childhood is a luxury that birds can’t afford, so everything is geared to the youngsters becoming able to feed themselves and evade predators as quickly as possible. But while some chicks, like Barn Owls, actually weigh a little more than their parents by the time they leave the nest (as a sort of insurance policy, in case they initially struggle to find food), others leave when they are still below adult weight. In the following pages (from page 30), we look in depth at the development of young owls, while over the next few issues, we’ll look at other key aspects of the breeding season, such as song, diet in detail, and what happens to young birds after they’ve left the nest. But whatever you do, take full advantage of this time of year to see more birds, and a greater variety. Turn to page 38 to find out how to send us your photos of birds and their young (taken without disturbing them of course) – you could win yourself a pair of Minox binoculars!