Tuesday, 16 July 2013

Brood Parasitis.

Avian interspecific brood parasitism is a reproductive strategy whereby the parasitic bird lays all its eggs in the nests of other species, sparing themselves the expense of rearing their own offspring. (Intraspecific is where they are laid in other nests of the parasite's own species).

For the parasite the benefits are greater allocation of their resources towards mating and egg production without the need to defend nests, incubation and subsequent feeding of their young. For the host species the issues range from diminished nestling growth rate due to competition by the parasitic offspring (e.g. Cowbirds) to total loss of their own eggs and nestlings through eviction by the early-hatching parasites (Cuckoos). As far as I am aware the most commonly studied avian brood parasites are Cowbirds and Cuckoos but I only have limited experience of witnessing the outcome of the latter species' breeding success and subsequent rearing by a host species.

Females of the Common Cuckoo (Cuculus canorus) generally lay their eggs in the nest of the species which raised them and Dunnock, Reed Warbler and Meadow Pipit are their current favoured 'hosts'. The males will fertilize females of all lines thereby ensuring adequate gene flow among the different maternal lines. A single female may visit up to 50 nests each breeding year and in order to prevent rejection she is able to mimic the colouration of the host species own eggs, albeit they are often larger in size.

The hosts: Reed Warbler, Meadow Pipit and Dunnock.

Some years ago I was alerted to the fact that a juvenile (Common) Cuckoo had taken up residence in a specific area of a garden where I was working. It didn't take me long to locate the begging 'sree, sree, sree' calls, much like other small birds but very penetrating, and there it was perched for a photo call. So here are the results taken with my trusty old Olympus OM1, a little rough, as they were scanned from the original photos.

What I didn't expect to see was the juvenile Cuckoo being fed by its host parent, a Dunnock (Prunella modularis) which made constant forays into the undergrowth to locate suitable titbits to satisfy the constant begging and voracious appetite of its fast growing charge. 

Although I didn't get an image I also watched a Robin join the Dunnock and it also presented food to the Cuckoo but was that just a case of mistaken identity or the result of another inter-relationship!

After an extensive feeding session it quietly hunkered down to presumably await the next feeding session. It remained in this location for several days and then disappeared so I always wondered if it ever made the long, hazardous journey to its wintering grounds in Africa and did it ever return as an adult to add to the gene pool of this parasitic species.    FAB.

Linking to Wild Bird Wednesday where you can view all manner of species from around the globe.


  1. wow! huge size differential! and the baby is marked so neat - like our nighthawks, here.

    i like how cuckoos - no matter what continent they're in - sit with their wings hanging below their tail feathers. :)

  2. Great post and images Frank. I can't imagine what the 'parent' bird thinks when 'their offspring' just keeps on getting bigger and bigger!...[;o)

  3. Brilliant photos Frank and the story.

  4. Great juvvie Cuckoo shots Frank you must be real pleased with them.
    Again lovely set.

  5. what a wonderful image of the Dunnock feeding the juvenile, a wonderful twist on nature.

    Great post

  6. you certainly were the early birder today Frank; looks like you are first on the EBW list? Great post and I see this happening here between the Koel (cuckoo) and it's foster Mum, the Little Wattlebird. Your Dunnock though is quite a bit tinier than the wattlebird it seems. I can't help but feel quite anxious for the foster Mum and all her duties to keep up with the feeding routines for these bigger drop-ins

  7. Great story, Frank! The juvie Cuckoo and the Dunnock are cool looking birds. Wonderful shots!

  8. Great photo documentation of this phenomenon. Here, I've seen Song Sparrows and Cardinals feeding Cowbird babies.

  9. Beautifully illustrated, and highly interesting post, Frank. Thank you!

  10. That Dunnock is glorious! I know that we have the Brown Headed Cowbirds here that work it the same way and while that is nature, they are pretty, it does bug me! We had Carolina Wrens create a nest at our front door a few weeks ago, and eventually raised 5 young. However, as the days were of egg laying, the Cowbirds tried to get to the door and basket to lay an egg and we did not allow them the opportunity this season~

  11. Very interesting post and great photos!

  12. Wonderful to see Frank... and such a coincidence as I have just seen my first Cuckoo for a couple of years.

  13. Oh fantastic post Frank! The images of the Cuckoo being fed by the tiny Dunnock are very special.

  14. I am amazed by your photo of the tiny dunnock feeding the cuckoo - and on the ground! Intriguing macros of the dappled patterns on the cuckoo's feathers!

  15. The tiny host 'parents' must spend all daylight hours feeding such a large youngster.

  16. o dear, the young cuckoo is really big compared to the other adult bird feeding it.

  17. I really enjoyed your post and great photographs! Very interesting subject.

  18. Wow.. I love this post of yours, the robin feeding the Cuckoo chick is excellent. :)

    Angad Achappa

  19. Watching a bird (I dont know what sort!) feeding a cuckoo as a kid in the field across from my house is a dealy clear memory.

    Shame that the cuckoo seems to have declined so much.

    Cheers and thanks for linking to WBW

    Stewart M - Melbourne

  20. Hi Everyone.

    Many thanks for all your comments. I have no idea when I might witness this event again but the memory of the incompatible size between the Dunnock and the Cuckoo will stay with me for a long, long time.


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