Mafia Cowbirds

There is recent research from the Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ce. Which may cause more questions then it answers. The following is from World Science "Mafia" behavior noted in birds

Many spe­cies, no­ta­bly cuck­oos, are brood par­a­sites that lay their eggs among un­wit­ting hosts.

Some of the free­load­ers lay eggs that look like the hosts’ eggs, ex­plain­ing why the hosts ac­cept them. But in oth­er cases, the in­t­rud­ers’ eggs look dra­ma­t­i­cal­ly dif­fer­ent from those of the hosts; this is the case with the par­a­sit­ic brown-headed cow­bird.

That raises the ques­tion of why the vic­tim pa­rents ac­cept the eggs. Al­though some of them toss the al­ien eggs from their nest, it hap­pens sel­dom enough that the par­a­site strat­e­gy works as a whole.

One ex­pla­na­tion could be that the free­loaders en­force ac­ceptance by de­stroy­ing the eggs or nests of hosts that re­ject their eggs. While such be­hav­ior has been re­ported in a cuck­oo spe­cies, con­trolled stud­ies haven’t been per­formed, ac­cord­ing to the in­ves­ti­ga­tors in a new study, which sought to rem­e­dy this.

They con­trolled cow­birds’ ac­cess to the nest of a host, the war­bler. They then ma­nip­u­lat­ed war­blers’ re­jection of cow­bird eggs to see the con­se­quenc­es. The re­ported re­sults: cow­birds ran­sacked 56 per­cent of re­jecter nests, com­pared to just 6 per­cent of ac­cepter nests.

Ran­sack­ing was­n’t lim­it­ed to re­tal­i­a­tory sit­u­a­tions, though. Cow­birds al­lowed ac­cess to host nests al­so were found to ran­sack one in five non-par­a­si­tized nests. This sug­gests cow­birds “farm” for hosts, de­stroy­ing war­bler nests so they can lay their eggs af­ter the hosts re­build, the sci­en­tists ar­gued. Sup­port­ing this no­tion, they added, cow­birds par­a­si­tized 85 per­cent of re­built nests.

Over­all, re­jecter war­blers pro­duced few­er off­spring than ac­cepters, sug­gest­ing hosts may be bet­ter off in ev­o­lu­tion­ary terms ac­cepting cow­bird eggs, the in­ves­ti­ga­tors said.

The re­search, by Jeff Hoo­ver Il­li­nois Nat­u­ral His­to­ry Sur­vey in Cham­paign, Ill., and Scott K. Rob­in­son of the Flor­i­da Mu­se­um of Nat­u­ral His­to­ry in Gaines­ville, Fla., is to ap­pear this week in the ear­ly on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

The question that comes to my mind is how does the warbler for instance know that the cowbird may possibly destroy her nest? We learn about such mafia behavior by seeing the results or reading about it etc. but how does a bird of a couple years of life learn about the mafia behavior? Though this may be explained by the destruction of nests even if no parasitic eggs have been placed there. Sort of like burning down the neighbor buisnesss to make it known that the mafia has moved into the area. Interesting area of investigation.