Cuckoos- Masters of mimicry
The cuckoo is renowned for two things, an iconic call and being the master of trickery, many a parental bird has unwittingly had their work load increased as the result of an extra and larger mouth to feed. However as research has shown, the ongoing battle between potential host and parasitic threat continues to develop with each having to constantly adapt to outwit the other.
Recent research would suggest that cuckoos consciously select host nests as a result of egg shell appearance, consequently resulting in selection pressures on recognising host eggs. The finding is the result of a comparison between cuckoo eggs in naturally parasitized nests and those randomly assigned to nests with a laying date close to nests which had been naturally parasitized. Eggs in naturally parasitized nests were found to show lower chromatic contrast to their hosts eggs, than eggs placed at random in nests which shared a similar laying date (1).
In a study on parasitism by common cuckoos on great reed warblers, nest visibility, reed density and timing of breeding all predicted parasitic behaviour by common cuckoos (2). As a result of breeding simultaneously in a large population for a prolonged period of time the percentage of nests not the victim of cuckoo parasitism increased. This was the result of nesting in less conspicuous locations further into dense vegetation and greater distances away from potential cuckoo perching places (2).
When simultaneous breeding took place in sparser numbers however, it was revealed that selecting denser nesting spots proved unsuccessful as cuckoos adjusted their nest searching strategy (2). This enabled them to spend greater time periods looking for a host. The findings of the study concluded that regardless of host abundance, cuckoos are always successful in finding a nest to parasitize (2).
Martins and swallows rarely experience parasitic behaviour from cuckoos and it was hypothesized this was a result of close proximity to humans and constructing nests in areas difficult for cuckoos to access. Findings of the subsequent research found the barn swallows in Europe were able to avoid parasitic behaviour by breeding indoors. As a result of barn swallows in China being unable to avoid parasitism when breeding outdoors, it is theorised instead egg rejection behaviour has been adapted (3).
Cuckoos however, have another trick up their feathers, last year research came to light to suggest cuckoos can mimic the plumage of raptor species .A link between cuckoos and sparrowhawk plumage had already been identified, however it has now been suggested this cunning adaption could also include the imitation of harrier hawks and bazas. By manipulating their physical appearance in this way, it is though this may scare adult birds of nests and consequently present an opportunity to lay their eggs in a host nest. (4)
Smart, adaptable and more than a little devious, there can be little doubt that cuckoos are the masters of the con. However it’s hard not to feel admiration for a bird which continually faces a battle to keep its way of life going smoothly while others continually strive to find ways to keep them at bay. The cuckoo is surely one of the most iconic members of the avian world.
1) Brood parasites lay eggs matching the appearance of host clutches
2) Common Cuckoos Cuculus canorus change their nest-searching strategy according to the number of available host nests
3)Avoiding parasitism by breeding indoors: cuckoo parasitism of hirundines and rejection of eggs
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