Dominance Rank and Interference Competition in Foraging among Six Species of Birds in a Park in Kaohsiung City, Taiwan

Through body size, social interaction, and foraging behavior, we investigated the dominance rank and interference competition among 6 bird species foraging at a park feeding site in Kaohsiung City, Taiwan. Social interactions and foraging behaviors of these birds were recorded in June to September 2009. David's scores were calculated from an interspecific interaction matrix, and the score roughly increased with the body size of birds, but some exceptions were noted. Concerning foraging behavior, feral pigeons (Columba livia) and Spotted-necked Doves (Streptopelia chinensis) took over the food area once they appeared even though Tree Sparrows (Passer montanus) usually arrived first. A linear regression model indicated that the number of Tree Sparrows outside the food area was positively correlated with the number of feral pigeons and Spotted-necked Doves inside the food area. Feral pigeons and Spotted-necked Doves moved away as the food was gradually consumed, and smaller species accordingly increased their foraging in the food area. Nevertheless, the Tree Sparrow was also suppressed by other medium-sized birds, like the White-vented Myna (Acridotheres javanicus) and Chinese Bulbul (Pycnonotus sinensis), and they eventually occupied the food area in large numbers at a later stage. This study revealed that body size did matter and the Tree Sparrow was clearly the least dominant species among the 6. However, a discrepancy between the dominance status and interference competition in foraging was apparent. In addition to David's score, we suggest incorporating body size, group size, and interference competition to reach a more-comprehensive dominance hierarchy in bird communities.