Myth. They DO recognize the eggs, but their only strategy is to build a new floor for the nest, burying their own eggs too. Warbler and most sparrow bills are too small to grasp the egg to toss it out.
New research has also led to the discovery that when parent birds do throw out a cowbird egg, cowbirds return and wreck the nest a lot. Margaret Morse Nice found that with Song Sparrows, at least some young tend to survive with a cowbird "foster sibling." The main birds that actually suffer population losses tend to be Neotropic migrants that usually nest just once a season--cowbirds can represent serious issues for them. One of the really bad cases is the Black-capped Vireo, which has a longer incubation period than most vireos, so the baby cowbird is already a big bruiser when the vireo eggs hatch, IF they hatch--the cowbird can trample the eggs and babies into the nest material. They're not at all aggressive (unlike European cuckoos), but they're very big compared to the tiny vireos. Best, Laura Duluth On Fri, Apr 23, 2021 at 11:11 AM Halle O'Falvey <halleofal...@gmail.com> wrote: > This discussion has be so enlightening and fun! As we feel some relief > from Covid-19 I appreciate all who have contributed. I learned a lot and > am a little bit less hostile as I see the brown heads > > Myth or truth? > > Yellow warblers have figured out the difference of the BHC eggs and don’t > have to rear them??? > > Halle > > On Fri, Apr 23, 2021 at 10:46 AM Laura Erickson < > chickadee.erick...@gmail.com> wrote: > >> The point is, I didn't say the parasitism habit EVOLVED for the bison. I >> just said it was darned beneficial to have it for one particular species >> that did hang around the bison. NOW we know female cowbirds can be >> sedentary as long as possible, but this article, not a scientific >> paper, offers no evidence that they did this pre-settlement. >> >> None of us see and understand the whole elephant. >> >> Best, Laura >> >> On Thu, Apr 22, 2021 at 11:06 PM Anthony Hertzel <axhert...@gmail.com> >> wrote: >> >> > For a different perspective, I recommend Dennis Paulson’s essay on the >> > topic. < >> > >> https://www.birdnote.org/explore/field-notes/2015/05/cowbird-story-revisited >> > > >> > >> > I can also recommend a few more scientific papers that say essentially >> the >> > same thing. >> > >> > > On Apr 22, 2021, at 10:49 P.M., Laura Erickson < >> > chickadee.erick...@gmail.com> wrote: >> > > >> > > Brood parasitism is indeed found in cowbirds from South America, where >> > the >> > > genus *Molothrus* probably originated, and so although it follows that >> > > brood parasitism almost certainly evolved in that genus in the first >> > place >> > > for reasons other than because they needed to follow a wandering >> mammal, >> > > the Brown-headed Cowbird's well-documented dependence on nomadic bison >> > > certainly made brood parasitism uniquely valuable for it, at least >> until >> > we >> > > decimated the bison while introducing cattle. >> > > >> > > It's virtually impossible to know the full story about any >> species--we're >> > > always finding out more. Learning new information doesn't mean we >> throw >> > out >> > > a whole body of old but accurate observations--it means we work out >> how >> > all >> > > the pieces of information, including both DNA/evolutionary biology and >> > > natural history fit together. Otherwise, we're just like the >> blindfolded >> > > people each describing one part of the elephant, with nobody getting >> the >> > > full picture. >> > > >> > > Best, Laura Erickson >> > > Duluth >> > >> > Anthony Hertzel >> > axhert...@gmail.com >> > >> > >> > >> > >> > ---- >> > Join or Leave mou-net: http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net >> > Archives: http://lists.umn.edu/archives/mou-net.html >> > >> > During the pandemic, the MOU encourages you to stay safe, practice >> social >> > distancing, and continue to bird responsibly. >> > >> >> >> -- >> Laura Erickson >> Duluth, MN >> she/her/hers >> >> For the love, understanding, and protection of birds >> www.lauraerickson.com >> www.patreon.com/lauraerickson >> >> You were made and set here to give voice to this, your own astonishment. >> —Annie Dillard >> >> Please consider the environment before printing this e-mail. >> >> ---- >> Join or Leave mou-net: http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net >> Archives: http://lists.umn.edu/archives/mou-net.html >> >> During the pandemic, the MOU encourages you to stay safe, practice social >> distancing, and continue to bird responsibly. >> > -- > Sent from Gmail Mobile > -- Laura Erickson Duluth, MN she/her/hers For the love, understanding, and protection of birds www.lauraerickson.com www.patreon.com/lauraerickson You were made and set here to give voice to this, your own astonishment. —Annie Dillard Please consider the environment before printing this e-mail. ---- Join or Leave mou-net: http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net Archives: http://lists.umn.edu/archives/mou-net.html During the pandemic, the MOU encourages you to stay safe, practice social distancing, and continue to bird responsibly.
