Bird courtship

For the next few months, the be­hav­iour of birds will prove to be a visual de­light for the bird­watcher

Bird Watching (UK) - - Contents - WORDS: MATT MERRITT

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!

ELAB­O­RATE DIS­PLAY

Great Crested Grebe Great Crested Grebes per­form their ‘weed dance’ 

Golden Eagle

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