Variation in colour within a population of northern flickers: a new perspective on an old hybrid zone

Abstract

We used a digital camera to quantify the colour of the tail feathers of 245 northern flickers (Colaptes auratus) in central British Columbia and investigate the frequency of colour morphs in the population of hybrids. The colour values generated by the camera corresponded well to the conventional method of ranking colours by eye, but was advantageous because it provided finer discrimination and a continuous colour variable. Rectrix colour varied in a continuum from the yellow of C. a. auratus to the red of C. a. cafer. By experimentally exposing red and yellow feathers to sunlight we showed that the intermediate orange colours were not a result of secondary fading of the carotenoid pigments. The distribution of colours in the population was bimodal. A paucity of intermediate phenotypes (orange birds) could not be explained by their mortality because return rates of birds to our study area was not associated with colour. New immigrants into the population tended to resemble parental types more often than hybrids. Assortative mating by colour in this population may tend to keep the subspecies separate, contrary to the situation in more southerly areas of the hybrid zone.