A year in the life of Choughs
Where do Choughs nests?
Most Choughs build their nests on ledges in crevices and caves of coastal cliffs, although some pairs use inland crags and cliffs. A small proportion of the Irish population nest in ruined buildings, with the watch towers dotted along the coast often supporting a pair.
Choughs are monogamous usually pairing for life, although if the pair fail to breed successfully
over a number years one of the pair may be replaced.
A Chough’s nest consists of a sprawling and bulky cup fashioned from twigs, usually stems of heather,
which is then lined with sheep’s wool, moss and grass.
On hatching the chicks are bold, blind and helpless and the female broods them for a short period.
Threat of predation
Unattended chicks are at risk from nest site predators such as Ravens and adults must remain vigilant to attacks at all times. With dramatic effect the outsized Choughs are often observed bravely fending off Ravens with their plummeting aerial assaults and piercing calls.
The chicks remain in the nest for about 6 weeks and moving into June the nestlings start to fledge. Pairs usually manage to successfully fledge between 1 and 3 chicks. Once fledged the young and their parents form a family group. Initially, the family group remains within their breeding season home range while the youngsters develop their powers of flight. At this stage the fledgings are still reliant on their parents and beg for food incessantly.
Young Choughs only take on the bright red colour of beak and legs about month after fledging.
Juveniles are easily recognisable from a distance by their begging calls, submissive behaviour and clumsy flight.
Post fledging flocks
Over July family groups start coming together to form ‘nursery’ flocks that are often observed travelling to feeding sites away from breeding areas. Initially, family groups will return to their nest site to roost; but towards the end of the summer ‘nursery’ flocks begin to converge at communal roost sites. These roosts tend to be close to good foraging habitat like grazed dune systems. By October there are large numbers of Choughs in dune systems. The bond between recent fledge birds and their parents is severed over the autumn and youngsters are left to fend for themselves. Juveniles join flocks of non-breeding birds, while the adults gradually drift back to breeding areas.
A flock of more than 20 Choughs is a noteworthy occurrence. The largest flocks are observed after the breeding season when adults and their recently fledged young congregate during the late summer and occasionally flocks numbering 100 birds are recorded. Note the square shape of the wings in flight and marginated flight feathers giving the wingtips finger like projections.
During the winter pairs generally maintain a loose association with their breeding season home ranges but tend to forage over a wider area. Some pairs may centre their winter foraging activities on dune systems and may join the non-breeding flocks.
Choughs take up to three years to reach breeding age and over this sub-adult stage they join a flock of non-breeding birds. In these flocks young birds learn how and where to forage and will find a mate. Sub-adult birds are important in replacing pairs that are reaching the end of their reproductive lives and declines in this component of the population are often a precursor to crashes in the number breeding pairs. During the breeding season non-breeding flocks usually range in size from 4 to 20 birds, although larger flocks are occasionally recorded.
Pitfalls to avoid when counting non-breeding flocks
Breeding pairs will sometimes join non-breeding flocks for short periods and care is taken to exclude pairs from the count of non-breeding birds. Nevertheless, this behaviour can make estimating the size of non-breeding flocks complicated. In addition non-breeding flocks are extremely mobile, often ranging beyond the areas surveyed and therefore they can easily be over looked during the census. Alternatively, there is always the risk of double counting these mobile flocks.
Egg laying and incubation
In early to mid April between 1 and 6 eggs are laid in the wool lined nest cup. The female is solely responsible for incubating the eggs and during this time the male forages alone returning to the nest periodically to feed the female and allowing her time to feed close to the nest. Once female has feed the male is often seen ushering her back to the nest to resume incubating duties.
The eggs hatch after about a 21 days incubation period and female broods the chicks until they are able to thermo-regulate for themselves. Over the month of May there are hungry mouths to feed and both the male and female share the provisioning duties. They leave the nestlings for periods of up to half an hour or more to forage. Generally, pairs stay within a few hundred meters of the nest although sometimes they may travel over a kilometre to forage.
The build up to the breeding season
Most Pairs start displaying their ownership of breeding territories in March when they become highly vocal and pairs are often observed flying in together, swooping and bouncing in the vicinity of nest sites. Occasionally, you may see birds carrying a twig or wool back to their nest sites that they add to nest material from previous years.
Choughs usually breed in pairs, although very occasionally a third bird may be employed as a helper. Generally the bond forming between pairs endures over the reproductive life of a pair, which can be as long as 10 years. Pairs of Choughs tend to be site faithful meaning that once a pair has established a breeding territory they return year after year to breed at the same location. There are even records of the same nest site being occupied over generations.