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present (Grimm etal. 2008; Patra etal. 2018). These mosaics are diffuse with patches of
native vegetation interspersed by areas with different levels of human occupation (Marzluff
etal. 2001; Yi etal. 2016).
Biodiversity can be directly or indirectly affected by urbanization (McDonald et al.
2019; Turrini etal. 2016). Direct effects are observed when a natural area is replaced by
an urban area with the construction of buildings, houses, or other human modifications
(Pejchar etal. 2015). All the changes that occur to biotic and abiotic conditions in a newly
urbanized environment, such as modifications to temperature, light, and wind (Beninde
etal. 2015; McDonald etal. 2013), as well as reductions in connectivity among vegetation
fragments and increased edge effects, are also considered direct effects of urbanization on
biodiversity (Concepción etal. 2015; Schneider etal. 2015; Veselkin etal. 2018). Pollu-
tion produced by urban areas and the resources needed for the correct functioning of the
city, like energy and food, are considered indirect impacts of urbanization on biodiversity
(McDonald etal. 2019; Turrini etal. 2016).
The effects of urbanization can be evaluated by the impacts on local biodiversity, such
as birds (Ikin etal. 2012; Ortega-Álvarez and MacGregor-Fors 2009). Birds are commonly
dependent on local environmental characteristics and are often used to measure the degree
of urbanization (Fontana etal. 2011; Møller etal. 2015; Ortega-Álvarez and MacGregor-
Fors 2009; Rodrigues etal. 2018). Birds are excellent models for studying the impacts of
urbanization and fragmentation because they are easily observed in cities, their taxonomy
is well defined and they present high species and functional richness and thus are consid-
ered good bioindicators for habitat quality (Anjos etal. 2015; Li Yong etal. 2011; Powell
etal. 2015). In this way, it is possible to use characteristics of species, such as food prefer-
ences, and characteristics of the urban landscape, such as the degree of urbanization and
the presence of vegetated areas, to assess how an urban center acts as a filter for bird spe-
cies (Ikin etal. 2012; Silva etal. 2016).
Different trophic guilds of birds can respond differently to urbanization (Cristaldi etal.
2017; Evans etal. 2011; Sol etal. 2014). Granivorous and omnivorous species are more
common in urban areas because they feed on food items that are abundant there (e.g., grass
seeds are common in cities) or have a more generalist diet and consume a wide range of the
available food items, including human-industrialized food wastes (Croci etal. 2008). More
specialized bird guilds, like frugivores and insectivores, are rarer in urban environments
because they normally occur in larger green areas that provide more food and specific habi-
tats (Cristaldi etal. 2017; Silva etal. 2016).
Urbanization can increase the abundance of several species, but it usually reduces total
richness (Chace and Walsh 2006). Due to the changes in conditions that urbanization of
environments brings, many species become extinct, which leads to biotic homogenization
(Blair 2008). On the other hand, there are indications that the maintenance of green areas
in cities, such as parks, squares and trees on public roads, favors the occurrence of bird
species in urban areas (Barth etal. 2015; Castro Pena etal. 2017). Even though they are
small, birds use these green areas as habitat or as stepping stones (small green areas used
as a resting place when traveling to larger green areas; Boscolo etal. 2008; Metzger 2001).
These small fragments can allow greater permeability of species into urban landscapes
(Baum etal. 2004; Bhakti etal. 2018; Fischer and Lindenmayer 2002), by making con-
nections with other fragments of vegetation located in peri-urban areas (Ikin etal. 2013;
Manhães and Loures-Ribeiro 2005).
Landscapes of cites are continuously changing, with new urban areas being added as cit-
ies grow (Farrell 2017). Green areas within cities also change, often being excluded from
the matrix after renovations (Mensah 2014). However, there are cities that are considered