Abstract
BackgroundUrban 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.MethodsWe 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.ResultsGround-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.ConclusionsOur 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.
Highlights
Urban expansion has been identified as one of the leading drivers of biodiversity change or loss
These sites were selected because they are exposed to a gradient of anthropogenic disturbance from the highly urbanized to the non-urbanized site, which positively correlates with urban surface (Blair 1996; Warren et al 2006)
Based on our 500 m radius circle, our urbanization analysis supports the classification of the study sites from more to less urban sites: urban surface comprised 66% of the highly urbanized site, 57% of the medium–high urbanized site, 52% of the medium–low urbanized site, 22% of the low urbanized site, and only 1% of the nonurbanized site
Summary
Urban expansion has been identified as one of the leading drivers of biodiversity change or loss. Birds may establish territories during the breeding season (Brown 1963), or year-round (Woltmann and Sherry 2011; Duca and Marini 2014; Holland et al 2017). Territories may provide places for mate attraction, food, and nesting (Nice 1941; Osborne and Bourne 1977; Woltmann and Sherry 2011). Territories may provide food and roosting places (Nice 1941; Salomonson and Balda 1977; Kraaijeveld and Dickinson 2001). In Western Bluebird (Sialia mexicana), outside the breeding season, groups of up to 12 individuals defend territories against other individuals to protect food resources (Kraaijeveld and Dickinson 2001)
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