That fiendish bird sneaks an egg into a much smaller bird’s nest and what hatches is a blind, naked murderer who immediately pushes overboard any “siblings”. A chick that runs its “parents” ragged and grows rapidly to monstrous proportions that could swallow a “parent” whole. It has such a mesmerising gape that even passing birds can’t help giving it food destined for their own. The long held belief that most birds are monogamous for life or a season is true; just turns out in the egg laying world it is also rife with egg dumpers, adulterers, bigamists and even divorces.
Left: reed warbler, often a victim of the cuckoo. Right: house sparrows in author’s garden.
The house sparrow is possibly the greatest practitioner of most of thse behaviours despite being a bird that pairs-up for life. The male even guards his female but she still finds opportunities to egg dump into other sparrow’s nests and mate with other males. Meantime, the male is a bigamist cavorting with multiple females. Up to 20% of their young are not full siblings. Basically, they are shameless property owners because being a pair ensures they retain their nest site.
Same species egg dumping females include wren, tree sparrow, several geese and ducks such as goldeneye, smaller/younger un-paired starlings, barn owl, moorhen who will also share nests and swift who eject an existing egg which suggests a count would give the game away. Other species egg dumpers include black grouse who drop eggs onto red grouse; oystercatcher and eider ducks put their eggs into gull nests.
A willow warbler sings to hold a territory, teach his young the tune and attract additional females.
The willow warbler is a polygynous bird; the male mates with multiple females but the female only has one partner. However, she tends to more choosy and is usually responsible for raising the young. One studied in Scotland had five mates over two consecutive years. Other examples are sedge warbler, starling, swallow, wren, pied flycatcher, dipper, pheasant, bittern, merlin, osprey, hen/marsh harriers and long-eared, tawny and barn owls.
Female adultery can produce nests where 10-70% of the occupants do not possess any genes from the supposed parents. Some male birds guard against this such as magpie, ducks, finches and swallows who, if they catch their partner cheating become less interested in their young. Female swallows are more attracted to males with tails longer than their mate. Female birds that arrive late and are left with the dregs (such as a stubby-tailed swallow) are more likely to divorce and blue tits with an unattractive male are more likely to be promiscuous. Both sexes of great tit play are adulterous. The female dunnock fools two males into thinking they are the father of at least some of the eggs and both help her raise the young.
A promiscuous sedge warbler?
And then there’s the male guillemot who watches for a nesting pair about to mate and literally runs at full pelt to push the ‘husband’ off his ‘wife’. The stunned bird takes several minutes to recover from being thrown off the cliff and returns, possibly none the wiser.
The cuckoo was probably originally an “egg dumper” and just got cleverer, even going to the extreme of mimicking another bird’s plumage; the european cuckoo resembles a sparrowhawk which may help scatter its target birds from their nests.
All these strategies increase genetic diversity, survival rates and produce stronger, fitter, longer-living young. But it does reveal that things not may be as they seem; is continued mating reinforcing a pair’s bond or is a shabby, smaller, one-eyed bird with a wonky head nearby, looking all forlorn?
Recent Sightings:
On the inner reedbed path; a strolling kestrel, which happened frequently last summer.
Around the visitor centre area: In the dragline compound the kestrels are coming along in leaps and bounds; their previously spacious accommodation is now cramped and they have begun to fledge. Little owl are becoming more frequent and has included two juveniles. Also seen green woodpecker, blackcap, whitethroat and linnet. Around Bowers lake the young sand martins are emerging from their small dark tunnels into what must seem a huge wide world.
Left: a little owl soaking up the sun. Right: What looks like an incredibly huge baby sand martin in comparison.
Along the hillside/pastures and opposite ditch: reed bunting, sedge warbler, meadow pipit, skylark, jay, long-tailed tit, stonechat, red kite, buzzard, peregrine, sparrowhawk, hobby and marsh harrier.
On the ridge and furrow and the adjacent Main lake: little egret, lapwing with young, curlew, redshank, black-tailed godwit, ruff, oystercatcher, common sandpiper, pochard with young, eclipse ducks such as teal, goldeneye, wigeon cormorant, jackdaw, starling, yellow wagtail, goldfinch and bittern from reeds near the cattle gate. Additionally loads of canada and greylag geese with young who take to the main lake en masse.
Around the reedbeds: bittern making feeding flights for three nests, reed/sedge warbler, lesser whitethroat, tree sparrow, linnet, wren plus families of great-crested grebe, pochard, gadwall, tufted duck, mute swan, occasionally black-necked grebe and fishing common terns.
Left: How do great-crested grebes get the young off their back? Without warning, they rear up and shake to fling them into the air. Right: Female pochard keeping her young close.
Getting all your tufted ducks in a row.
Astley lake and adjacent reservoir: black tern remains with two the other week, common tern with young, ringed plover, oystercatcher, curlew, swift, shelduck with young.
Lemonroyd lake: house martin and bullfinch
In summer, black terns eat insects and larvae. Skims water’s surface or twists/turns to catch in mid-air, even if it does mean contorting its head upside down (as per small not very good pic at right).
Acrobatic common tern searches bill pointed down, rises to hover and plunges in headfirst. A fish held crossways in the bill is for a partner or youngster.
Around Lowther lake and surrounding trees: willow warbler, chiffchaff, garden warbler, cetti’s warbler, blackcap, whitethroat, lesser whitethroat and cuckoo.
Around the site: Loads of insects including -
Dragon/Damsel flies: black/long-tailed skimmer, brown hawker, four-spotted/brown-bodied chaser and emperor, blue, azure, large red, red-eyed and banded demoiselle
Left: blue damsels depositing eggs with interfering interloper. Right: banded demoiselle eating lunch - a very small fly - with dessert ready near its right extended foot.
Butterflies/Moths: comma, green-veined white, small tortoiseshell, common blue, meadow brown, small/large skipper, six-spot burnet which contains cyanide. Best not lick one.
Left: six-spot burnet. Right: Meadow brown.
Recent more frequent visitors: spoonbill, juvenile starlings flocking in during evening to murmurate over reedbeds before sunset that usually appear nightly until August.
Left: Overhead spoonbill (taken at Lin Dyke, Fairburn). Right: Starlings rushing in during evening.
And finally:
Fight! Look at the size of that coot’s feet! Are they inflatable?
Yours, K Sp-8