Assortative mating can, at times, arise as a consequence of social competition. Traits in certain individuals may indicate competitive ability which allows them to occupy the best territories. Individuals with similar traits that occupy similar territories are more likely to mate with one another. In this scenario, assortative mating does not necessarily arise from choice, but rather by proximity. This was noted in western bluebirds although there is no definite evidence that this is the major factor resulting in color dependent assortative mating in this species. Different factors may apply simultaneously to result in assortative mating in any given species.