Trends in bird species richness, abundance and biomass along a tropical urbanization gradient

Abstract

AcknowledgementsWe thank Lilian Twanza and Osman Mwebe, who also took part in some of the bird counts in Kampala, and to NatureUganda for data from the rural sites. We are also grateful to L. Bennun, J. Roberts, P. Robinson and J. Pierini for providing personal observations on scavenger populations in African cities, and to an anonymous referee whose constructive comments improved the manuscript. 3Abstract Impacts of urbanization on biodiversity are commonly studied using urbanization gradients which provide a space-for-time substitution in estimating consequences of urban expansion. Rates of urbanization and human population growth are high in tropical countries of the developing world, which also hold most of the world's biodiversity hot-spots, yet few studies have considered biodiversity trends along urban gradients in these regions. Bird communities across a gradient of nine sites in Uganda, from the city centre of Kampala to outlying rural locations, were studied over a six year period. These sites were ordered along an urbanization gradient using Principle Components Analysis based on habitat variables estimated at each site. Bird species richness showed a decrease from rural to urban sites, a trend especially evident in forest birds. There was no clear pattern in total abundance, total biomass or biomass per individual along the gradient. However, this latter result was heavily influenced by a colony of Marabou Storks at one site.When this species was omitted, there was evidence of a positive trend with urbanization, showing that as species richness decreased, the bird community was increasingly dominated by larger species with increasing urbanization, which were mainly scavengers able to exploit human refuse. These results provide further support for the negative impacts of urbanization on species richness, but also demonstrate trends in abundance and biomass are variable across different regions. In particular, the increasing dominance of larger species in urban areas may be relevant to certain geographic and/or socioeconomic contexts.

Environmental filtering of avian communities along a rural‐to‐urban gradient in Greater Washington, D.C., USA

“…We observed a decline in species richness across the rural‐to‐urban gradient, a relationship that has been observed across numerous biogeographic regions (reviewed in Marzluff , Chamberlain et al. ). Several studies have documented a peak in species richness at intermediate portions of the rural‐to‐urban gradient, a pattern expected under the intermediate disturbance hypothesis (e.g., Blair , Blair and Johnson , reviewed in Marzluff ).…”

The Greener the Better! Avian Communities Across a Neotropical Gradient of Urbanization Density

“…We retrieved a total of 114 publications after filtering out those outside our research focus. It was evident that the most frequent response to urbanization was negative (84% of publications; e.g., Clergeau et al, 1998;Palomino and Carrascal, 2005;Lepczyk et al, 2008;MacGregor-Fors and Schondube, 2012;Chamberlain et al, 2017;Sol et al, 2017), few studies reported no clear relationships (8% of studies; e.g., Merenlender et al, 1998;Fraterrigo and Wiens, 2005;Sorace and Gustin, 2008;Suhonen et al, 2009;Meffert and Dziock, 2013), as well as higher species richness at intermediate levels of urbanization (6%; i.e., Jokimäki and Suhonen, 1993;Blair, 1996Blair, , 1999Blair, , 2004Clucas and Marzluff, 2015;Battisti and Fanelli, 2016;Guetté et al, 2017), and even positive responses to urbanization (2%; i.e., Leveau and Leveau, 2005;Coetzee and Chown, 2016).…”

Non‐linearities in bird responses across urbanization gradients: A meta‐analysis

“…Researchers have commonly observed lower species richness in urban areas relative to that of the surrounding rural landscapes (Clergeau, Croci, Jokim€ aki, Kaisanlahti-Jokim€ aki, & Dinetti, 2006;Sandstr€ om, Angelstam, & Mikusinski, 2006). However, these patterns are by no means universal, and other studies have found a non-linear response, in which areas with intermediate levels of urbanization exhibit the highest richness (Blair, 1996;Marzluff, 2001;McKinney, 2002;Tratalos et al, 2007), whilst overall bird abundance often increases from rural to urban areas (Chace & Walsh, 2006;Faeth, Bang, & Saari, 2011;Njorge, NdaNg'ang'a, & Natuhara, 2014) although other studies have found no trend (Chamberlain, Kibuule, Skeen, & Pomeroy, 2017) or inconsistent responses across different cities (Garaffa, Filloy, & Bellocq, 2009;Jokim€ aki, Clergeau, & Kaisanlahti-Jokim€ aki, 2002).…”