Breed-specific companions—Inter-individual distances reflect isolating mechanisms within domesticated chickens (Gallus gallus f.d.)

White Crested Polish (WCP) chickens are an interesting breed because of skull anatomy (crest), brain size and composition. This makes them attractive to investigate processes of selection that could parallel a step towards speciation in terms of ethological isolation. Lohmann Brown Classic (BL) and Red Leghorn (RL) were selected as comparative breeds to detect whether WCPs flock together as shown by shorter inter-individual distances within WCP than across breeds. WCP and BL were observed in the first year whereas RL served as comparative breed to WCP in the second year. Eggs of both breeds of each year were incubated at the same time, and chicks hatched and were raised together. Three young hens of each breed were randomly chosen and observed weekly in an open field situation for 20 min between the first and 31st week of life. Intra-breed distances differed significantly from those distances measured across breeds. Results demonstrate breed-specific flocking within observed breeds. This flocking behaviour may reflect breed-specific social and sexual preferences. Our observations indicate that domestic breeds may represent an ethological entity. Selective processes controlled by human intervention as given in domestication may therefore to be set in parallel to evolutionary processes.