Urbanization has opposite effects on the territory size of two passerine birds

Abstract

Background Urban expansion has been identified as one of the leading drivers of biodiversity change or loss. For birds, urbanization is specifically related to survival, breeding success, and territory size. Understanding how different birds adjust territory size in response to urbanization is essential for their conservation in urban environments and to better understand why some species are lost and others persist under this condition. We evaluated the effect of urbanization on the territory size of an urban avoider species, White-eared Ground-Sparrow (Melozone leucotis), and an urban adapter species, House Wren (Troglodytes aedon), at five Costa Rican sites. Methods We measured the size of 30 ground-sparrow and 28 wren territories using a total of 296 h of observation. We followed each individual for at least 1 h per day for at least 2 days of two consecutive years, and geo-referenced their locations. Territory size was estimated using the minimum convex polygon method. We measured the urban surfaces (roads, buildings, any other paved area, soccer fields, lawns, and gardens with short grass) within territories. Results Ground-sparrow territories were larger at the highly urbanized site than at the non-urbanized site. Wren territories were larger at the low urbanized site than at the highly urbanized site. We found a positive relationship between urban surface and territory size for the ground-sparrow, but not for the wren. Conclusions Our results showed that not all birds adjust territory size in the same way in response to urbanization. We showed that urban avoiders probably need to defend larger territories in urban environments to find all the resources required to survive because urban environments may provide insufficient resources such as food or shelter. Urban adapters on the other hand defend smaller territories in urban environments because even small territories may provide sufficient resources. These results suggest specific behavioral adaptations developed by Neotropical birds inhabiting urban environments.

Bertalanffy-Pütter models for avian growth

“…However, one bird was exceptional (K7V3278), as the best-fit BP-model did not achieve RL-squared above 95% (namely RL 2 = 94.2%). For this nestling, asymptotic mass was excessive (1.4�10 13 ). This was also insofar exceptional, as generally asymptotic mass was close to the maximal observed mass: The median of the quotient of the asymptotic mass over the maximal observed mass was 1.006 with the 95% confidence interval between 0.998 and 1.016 (computed from one-sided sign tests [79] with p = 0.0224 for both limits).…”

“…However, we did not aim at pinpointing exact causations for the observed effects. Thus, the finding for ISA was biologically plausible, as impervious area around the nest could inhibit the success of provisioning [ 13 ] and this clearly would affect the growth of the nestlings. Light pollution, on the other hand, is known to affect the behavior of birds [ 14 , 15 ], but from the data we could not discern a mechanism explaining its possible impact on the growth of nestlings.…”

“…It was used to relate growth to predation [ 6 , 7 ], to environmental variation [ 8 – 10 ], to annual adult mortality rates, and to incubation period duration [ 11 ]. Literature has considered various environmental factors that may affect growth, such as: tree cover [ 12 ], impervious surface [ 4 , 13 ], pollution by light [ 14 , 15 ] and sound [ 16 – 18 ], or nest interference by humans and pets [ 1 , 2 , 19 ]. All these factors are also known to affect the breeding success.…”

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“…However, we did not aim at pinpointing exact causations for the observed effects. Thus, the finding for ISA was biologically plausible, as impervious area around the nest could inhibit the success of provisioning [13] and this clearly would affect the growth of the nestlings. Light pollution, on the other hand, is known to affect the behavior of birds [14,15], but from the data we could not discern a mechanism explaining its possible impact on the growth of nestlings.…”

“…It was used to relate growth to predation [6,7], to environmental variation [8][9][10], to annual adult mortality rates, and to incubation period duration [11]. Literature has considered various environmental factors that may affect growth, such as: tree cover [12], impervious surface [4,13], pollution by light [14,15] and sound [16][17][18], or nest interference by humans and pets [1,2,19]. All these factors are also known to affect the breeding success.…”