Is dispersal distance of birds proportional to territory size?

Abstract

Recent research has demonstrated that dispersal distance and the square root of home-range size covary proportionately across mammal species. I tested whether these findings could be generalized to another taxon. Breeding territories of some bird species are analogous to mammalian home ranges, so I tested whether dispersal distance and territory size in these birds covaried and were proportional. Variables were log10-transformed before analysis. When considered independently of body mass, median natal dispersal distance and breeding territory size were positively related (F[1,29] = 8.91, R2 = 0.23, P = 0.005). Median dispersal distance was proportionally related to the square root of territory size by a multiple of 12. This relationship was especially strong for non-migrants (F[1,15] = 49.84, R2 = 0.77, P = 3.87 × 10–6). Maximum natal dispersal distance and breeding territory size also covaried when body size effects were removed, but this relationship was only significant when migrants were removed from the sample (F[1,24] = 5.66, R2 = 0.19, P = 0.025). Maximum dispersal distance did not have a proportional relationship with territory size. This could result from sampling error or from real processes (e.g., relatively shorter dispersals by birds with large territories). The proportional relationship between median dispersal distance and territory size can be used as a cross-species scaling rule.