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Index of Subjects James, Thanks for the link to the paper. Fascinating subject with lots of ways to analyze the data. -- Gerald On 9/9/14 11:59, James Churchill wrote: > hi folks, > > Here is a recent paper summarizing host defense against cowbird > parisitism in North America: > > HOST DEFENSES AGAINST COWBIRD (MOLOTHRUS SPP.) > PARASITISM: IMPLICATIONS FOR COWBIRD MANAGEMENT > > Ornithological Monographs, 2005 > http://www.biosci.missouri.edu/avianecology/courses/avianecology/readings/Peer_BD_2005.pdf > > Note, this opens a pdf. > > cheers, > > > > > On Tue, Sep 9, 2014 at 12:38 AM, Stephen Shaw <srshaw@dal.ca > <mailto:srshaw@dal.ca>> wrote: > > An interesting question is why host species at least in some cases > do not take countermeasures to turf out the egg(s) of the parasite. > At least in one case, it is not a problem of clever cryptic > coloration having been used to evade detection. The single cuckoo > species we used to see in UK often lays an egg in the nest of the > hedge sparrow (dunnock). The single cuckoo egg is much larger than > those of the dunnock, is often white with brown spots versus always > plain bright blue for the dunnock. Some birds, perhaps most, have > good colour vision so there should be no problem in detecting an > alien egg that is also twice the size. The newly hatched cuckoo > throws out all the dunnock's eggs, so the dunnock ends up not > rearing any offspring of its own for that breeding cycle. This > should be a strong evolutionary incentive to develop a defense. > > Presumably there must be some disadvantage attached to developing a > simple defense of detecting then removing an alien egg? I could see > it if the parasite's eggs looked very similar to those of the host > -- the defending host bird then might remove some of its own eggs by > mistake, a disadvantage. At least for the UK cuckoo this is not the > case: the eggs are easily distinguished from those of most host > species'. > > Is there a plausible explanation for this, and is it a general > phenomenon? If parasitism of the dunnock by the cuckoo were a very > recent development, it could be argued that the dunnock has not yet > had time to evolve countermeasures, but this sounds a bit lame. > Have any N. American brood parasites (cowbirds?) developed eggs > that mimic those of their hosts -- is there a general rule for > this, where the UK cuckoo is an exception? My guess is that 97% of > the folk on NatureNS are birders of some ilk, so someone out there > must have an answer. > > As a related afterthought, bird books in the UK in the 50s-60s used > to describe the nests, eggs and nesting habits of birds, not just > their plumage. I haven't seen this here in the Sibley, Petersen etc > recent era in Canada/USA or I could probably have answered the > cowbird question myself. I presume the main (and valid) reasons > are now to discourage any interest in egg-collecting or > nest-disturbing, by simply not giving out any useful information? > Steve (Hfx) > ________________________________________ > From: naturens-owner@chebucto.ns.ca > <mailto:naturens-owner@chebucto.ns.ca> > [naturens-owner@chebucto.ns.ca > <mailto:naturens-owner@chebucto.ns.ca>] on behalf of Randy Lauff > [randy.lauff@gmail.com <mailto:randy.lauff@gmail.com>] > Sent: Monday, September 8, 2014 2:03 PM > To: NatureNS > Subject: Re: [NatureNS] Brood parasites > > Our own Black-billed Cuckoo normally builds its own nest, but will > sometimes brood parasitize other species. > > They avoid wiping themselves out in the same way carnivores do...too > many carnivores, not enough prey, many carnivores starve, prey > rebounds, carnivores increase. This is a basic explanation...there's > a lot to this. > > Randy > > _________________________________ > RF Lauff > Way in the boonies of > Antigonish County, NS. > > On 8 September 2014 13:49, Gerald <naturens@zdoit.airpost.net > <mailto:naturens@zdoit.airpost.net><mailto:naturens@zdoit.airpost.net <mailto:naturens@zdoit.airpost.net>>> > wrote: > I hope brood parasites is the correct term for birds that lay their eggs > in the nest of a different species. > > Are there such parasitic bird species who can also build their own > nests? How do they avoid becoming so successful that they wipe out the > hosts and thereby themselves? > > -- > Gerald > > > > > -- > James Churchill > Kentville, Nova Scotia > jameslchurchill@gmail.com <mailto:jameslchurchill@gmail.com> > (902) 681-2374 <tel:%28902%29%20681-2374> > > >
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