Study shows some cuckoo birds may actually help their hosts

Mar 21, 2014 by Bob Yirka report
A carrion crow brood parasitized by a great spotted cuckoo. Credit: Vittorio Baglione

(Phys.org) —A team of researchers in Spain has found that at least one species of cuckoo bird may actually help its nest-mates survive. In their paper published in the journal Science, the team describes how in studying the great spotted cuckoo, they found that crow hatchlings were actually more successful due to the presence of an uninvited bird.

Most everyone knows that cuckoo birds are the ultimate free-loaders. Mothers lay their eggs in the nests of birds of different species, leaving them to raise their young for them. What many may not realize however, is that different kinds of cuckoo birds behave differently when they hatch. Some famously push all the other eggs out of the nest, leaving themselves as the sole survivor and beneficiary. Other's however, don't do that, instead, they leave the other chicks alone and share in food the mother brings, acting as an adopted sibling, of sorts. At first glance it would appear that the host birds gain no benefit from this arrangement, but upon closer inspection, that assumption has been proved wrong.

The researchers in Spain were studying the relationship between cuckoos and host carrion crows. In so doing, they were surprised to find that survival rates for chicks in nests shared by a cuckoo, were actually higher than for cuckoo-less nests. Looking even closer they discovered that the cuckoos had a survival mechanism that crows did not—they gave off a stink when threatened that caused predators such as feral cats to stay away. The stink, the researchers found, was caused by a chemical mix of repulsive compounds that included indoles, acids, sulfur and phenols. Taken together it proved too much for cats and birds of prey which typically find chicks in a nest easy pickings when the mother is away gathering food.

The discovery by the team came as part of a 16 year study of carrion crows that included observations of birds in 741 nests. After noting the advantage to crow chicks when a cuckoo chick was present, the team actually moved chicks around between crow nests, to find out whether it increased their chance of survival—it did, on average by 40 percent, even when there were fewer crow chicks.

The team's research shows that parasitic relationships among are more complicated than originally thought. Prior research has also shown that carrion crow mothers appear to understand the benefit of a chick—upon discovery of the interloper, they treat it as their own, rather than push it out of the nest.

Explore further: Feline fame in cyberspace gives species a boost

More information: From Parasitism to Mutualism: Unexpected Interactions Between a Cuckoo and Its Host, Science 21 March 2014: Vol. 343 no. 6177 pp. 1350-1352 DOI: 10.1126/science.1249008

ABSTRACT
Avian brood parasites lay eggs in the nests of other birds, which raise the unrelated chicks and typically suffer partial or complete loss of their own brood. However, carrion crows Corvus corone corone can benefit from parasitism by the great spotted cuckoo Clamator glandarius. Parasitized nests have lower rates of predation-induced failure due to production of a repellent secretion by cuckoo chicks, but among nests that are successful, those with cuckoo chicks fledge fewer crows. The outcome of these counterbalancing effects fluctuates between parasitism and mutualism each season, depending on the intensity of predation pressure.

add to favorites email to friend print save as pdf

Related Stories

Magpie parents know a baby cuckoo when they see one

Dec 11, 2013

Cuckoos that lay their eggs in the nest of a magpie so that their chicks can be raised by the latter better hope that their young are not raised together with other magpies. The chances of cuckoo fledglings raised in mixed ...

Birds find ways to avoid raising cuckoos' young

Apr 08, 2013

Some species of birds reproduce not by rearing their own young, but by handing that task on to adults of other species. Known as brood parasitism, this habit has been most thoroughly researched in the cuckoo. ...

Chickless birds guard nests of relatives

Dec 20, 2013

(Phys.org) —New research has solved a mystery as to why some birds choose not to reproduce, and instead help to guard the nests of their close relatives. This occurs in about nine percent of all bird species.

Cuckoos impersonate hawks by matching their 'outfits'

Oct 16, 2013

New research shows that cuckoos have striped or "barred" feathers that resemble local birds of prey, such as sparrowhawks, that may be used to frighten birds into briefly fleeing their nest in order to lay ...

Recommended for you

The ants that conquered the world

Dec 24, 2014

About one tenth of the world's ants are close relatives; they all belong to just one genus out of 323, called Pheidole. "If you go into any tropical forest and take a stroll, you will step on one of these ...

Ants show left bias when exploring new spaces

Dec 23, 2014

Unlike Derek Zoolander, ants don't have any difficulty turning left. New research from the University of Bristol, UK published today in Biology Letters, has found that the majority of rock ants instinctively go lef ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.