Taiwan J For Sci 26(3): 255-66, 2011 255 Research paper Dominance Rank and Interference Competition in Foraging among Six Species of Birds in a Park in Kaohsiung City, Taiwan Chao-Chieh Chen,") Hui-Yu Wu,2'3) Tzu-Tsen Liu,')Bao-Sen Shieh') [ Summary 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 Kaohsi- ung 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. Concern- ing foraging behavior, feral pigeons (Columba livia) and Spotted-necked Doves (Streptopelia chi- nensis) 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 gradu- ally consumed, and smaller species accordingly increased their foraging in the food area. Never- theless, 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 oc- cupied 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. Key words: David's score, dominance hierarchy, dove, foraging behavior, Tree Sparrow. Chen CC, Wu 11Y, Liu TT, Shieh BS. 2011. Dominance rank and interference competition in for- aging among six species of birds in a park in Kaohsiung City, Taiwan. Taiwan J For Sci 26(3):255-66. °Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, 100 Shiquan 1st Rd., Kaohsiung 80708, Taiwan. ANINV'V' t_41)4NV%fniAtA.1)4V*. 2)Department of Oral Hygiene, Kaohsiung Medical University, 100 Shiquan 1st Rd., Kaohsiung 80708, Taiwan. ANINV'V' EuriRit_V*. 3) Institute of Biodiversity, National Cheng Kung University, 1 University Rd., Tainan 70101, Taiwan. ' 70101tAir'l--,4M19R. ° 4) Corresponding author, e-mail: [email protected] Received March 2011, Accepted June 2011. 2011*3)1')A, 2011*6)1-AA 256 Chen et al.Dominance rank and foraging behavior of birds in a park MA-tACR-allUtl*fit,-4Hi-A 1,4) 1.4 23) VI] -1);AIWA" 2431 ")-ni120096/A 19)A rnlYfAtiglitEXT.LOITJ--AMMMffiEMIT11. fflRAMIU*WRWARgEDAMM4MaffiRAANI-411U.MfflfflTiR pgra-WAnDavidinirmArfu4,0-t-ofs A-A-Mj-Py± vrgavcolumba tiviamWjApa (Streptopeliachinensis)JEAUFFAftirTZPAiKV.E,IVAII/jat(Passer montanus)trini]Mh MMAM°ElltbAtAMAE01,0M19MMR4MMMAMAUNOMIMMMOM°fiU AWARRTR,MR4MMM**MM14,1MR/PVAMAMAUNAAnthRTEZMU° (Acridotheres javanicus)RnEU(Pycnonotus sinensis)n+ 1444 2.11..MIntAntr412A At2J--*CCMMITEAU 24TPAIOTTAMIMA4114-PAIVJ rgaig ELd/J\MLit'ffiP.AfEMPFIAO-fi MITJRiratrak:TDavidiA2. MAT7 /J\ J-',1.1tYMNPEM.firi`Jf4MaliMig ° 3J p :Davidaf4MaliMI r I AMJ-Py Ait ° IAM'?, 5q7C/fVi10--44 Ewa2011AtiffriAfrOMIR2f4MaliMRAA-4144i1Py ° tiR t441.3M26(3):255-66 INTRODUCTION In addition to intraspecific competition, body size to be the major factor determining competition for resources among different dominance rank among birds, exceptions do animal species may also result in dominance occur. For example, the larger Black-backed hierarchies (Fisler 1977, Millikan et al. 1985, Woodpeckers (Pico ides arcticus) often stop Wallace and Temple 1987). Larger species foraging and move away when the smaller usually have a higher dominance rank and ac- Hairy Woodpeckers (P. villosus) approach cess resources earlier or take more food than within 10 m (Villard and Beninger 1993). Ap- smaller species (Hogstad 1989, Jablonski and parently, other factors such as aggressiveness Lee 1999, French and Smith 2005). Once or group size may also affect the dominance dominant species appear, they often occupy a rank (Burger and Gochfeld 1984, Chapman better position and make subordinate species and Kramer 1996, Basset 1997, Sandlin 2000, shift to other foraging sites (Alatalo 1981, Creel 2001). For example, the Grey-headed Alatalo and Moreno 1987, Jablonski and Lee Junco (Junco caniceps) won social encoun- 2002). Morse (1980, 1989) stated that an un- ters at a higher rate in larger groups (Millikan even partitioning of resources usually stems et al. 1985). On the other hand, gender, age, from different social dominance ranks among experience, and residence time at feeding birds. sites were proven to influence the dominance Although Basset (1995) considered rank among conspecific individuals (Davies Taiwan J For Sci 26(3): 255-66, 2011 257 1992, Stanback 1994, Emlem 1997, Martin et been feeding birds in the park every day for al. 1997, Pusey and Packer 1997). a long period of time, hundreds of birds, in- The study of urban ecosystems has be- cluding feral pigeons, Spotted-necked Doves, come quite popular in recent decades (Savard Tree Sparrows, etc, are attracted to the feed- et al. 2000, Fontana et al. 2011). Although ur- ing site almost every day. ban parks, especially forest parks, are consid- The food area was defined as the area of ered habitat islands in an ocean of buildings, ground covered by food, and it was circular they are actually important habitats for bird with a radius of about 1 m. Bread crumbs and communities living in big cities (Fernandez- bean sprouts were provided in the food area Juricic and Jokimaki 2001, Sandstrom et al. twice a day, once in the morning and once 2006). Furthermore, people may put out food in the afternoon. The quantity of food was at feeding areas of parks to provide birds with recorded whenever we began an observa- additional food (Orams 2002). According tion. The quantity of food in the food area to the US Fish and Wildlife Service (1989), was divided into 3 levels: 1) abundant, when about 82 million Americans use many dif- food had just been spread in the food area to ferent ways to feed birds, and Cowie and about 75% of food remaining; 2) medium, the Hinsley (1988) found that 75% of households remaining food covering > 50% of the food put out food during winter in Cardiff, UK. In area, and soil was clearly exposed in certain contrast, people in Taiwan seldom feed wild areas; 3) little, < 50% of the food area was birds. A feeding site in a park in Kaohsiung covered by food, and dark brown soil was ex- City provided us the opportunity to study posed in most parts of the circle. interspecific competition among some park bird species. Among them, the Tree Spar- Field methods row (Passer montanus), Chinese Bulbul From 25 June to 30 September 2009, (Pycnonotus sinensis), Spotted-necked Dove we recorded social interactions and foraging (Streptopelia chinensis), feral pigeon (Colum- behaviors of these bird species at the feeding ba livia), Grey Treepie (Dendrocitta formo- site. Concerning social interactions, we made sae), and White-vented Myna (Acridotheres note of the time, species involved, aggressive javanicus) are common bird species in city behavior, and outcome of the interaction. We parks of Kaohsiung (Chen et al. 2005) and scored a 'win' for birds that initiated aggres- frequently occur at the feeding site examined sive behavior, and a 'loss' for the bird that in this study. We investigated the dominance displayed submissive behavior. Aggressive rank and interference competition in foraging behavior included attacking others with the among these 6 bird species. beak, chasing others, and threat displays with posture or sound. Birds which displayed MATERIALS AND METHODS submissive behavior usually retreated or yielded to the bird that initiated the aggres- Study area sive behavior. For foraging behaviors, we The study site is located within the San- recorded foraging techniques applied by each Min Park (18.4 ha, 22°64'N, 120°31'E) in bird species at the feeding site. Foraging tech- Kaohsiung City, southern Taiwan. It is a well- niques included foraging within the food area, maintained park, full of trees and meadows. carrying food out of the food area, carrying Owing to an enthusiastic resident who has food up to trees, or snatching food from other 258 Chen et al.Dominance rank and foraging behavior of birds in a park individuals within the food area. defeated by species i (David 1987, de Vries To estimate the abundance of each bird 1998). Because our data had many interacting species at the feeding site, we used scan sam- pairs with reversals, application of David's pling at 10-min intervals (Martin and Bateson score was considered appropriate (Gammell 1993) to count the number of each species et al. 2003, Bang et al. 2010). We then used in the feeding site. If birds had flown away the Spearman rank correlation coefficient to because of a disturbance before the scanning test if the dominance index was positively time, we waited for another 10 min to repeat correlated with the body size of each bird the scanning. In between the sampling points, species (SAS 1999). Body size indices were we recorded social interactions among species derived from PRIN1 through a principal com- and the foraging behaviors of each species. ponent analysis (PCA), that integrated body We made additional observations to length and weight of the 6 bird species (Table examine the distribution of Tree Sparrows 2; SAS 1999), because body length and mass inside and outside the food area and the abun- may both play a role in dominance displays dances of large-sized bird species in the food (Robinson-Wolrath and Owens 2003).