Habitat influences on urban avian assemblages

Abstract

Urbanization is increasing across the globe and there is growing interest in urban ecology and a recognition that developed areas may be important for conservation. We review the factors influencing urban avian assemblages, focusing on habitat type and anthropogenic resource provision, and analyse data from a common bird monitoring scheme to assess some of these issues. The review suggests that (1) local factors are more important than regional ones in determining the species richness of urban avian assemblages, raising the potential for the management of urban sites to deliver conservation; (2) habitat fragmentation frequently influences urban avian assemblages, with the effects of patch size being greater than those of isolation, and (3) urban bird assemblages appear to respond positively to increasing the structural complexity, species richness of woody vegetation and supplementary feeding, and negatively to human disturbance. Data from Britain's Breeding Bird Survey, combined with habitat data obtained from aerial photographs, were used to assess a number of these issues at the resolution of 1‐km squares. Green‐space constituted 45% of these squares, and domestic gardens contributed 50% of this green‐space, though their contribution to large continuous patches of green‐space was negligible. There was no significant positive correlation between the densities of individual species in urban areas and surrounding rural areas. Rural species richness declined with increasing latitude, but urban species richness was not correlated with latitude. This contrast contributes to slightly higher avian species richness in rural squares in Southern England than urban ones. Occupancy and abundance were strongly positively correlated in urban avian assemblages, and some indicator species of conservation concern occurred in few urban areas and at low densities. Such species will require conservation action to be precisely targeted within urban areas. Of the urban indicators of conservation concern, only the House Sparrow Passer domesticus and Common Starling Sturnus vulgaris were more abundant in urban than rural areas. Moreover, the densities of these two species were strongly and positively correlated, indicating that they may be limited by shared resources, such as nest‐sites or supplementary food. There was little evidence that high densities of nest‐predating corvids were associated with reduced densities of their prey species. Species richness and the densities of individual species frequently declined with an increasing number of buildings. Current trends for the densification of many British urban areas are thus likely to be detrimental for many bird species.

Variability of bumblebee communities (Apidae, Bombini) in urban green areas

“…The theory states that the bigger the area of habitat, the more bumblebee species can be expected there. Analogical conclusions were drawn in relation to birds (Evans et al 2009), amphibians (Parris 2006), mammals (Magle et al 2009), and ground beetles ) living in urban habitats, and bumblebees living in meadow habitats of the rural landscape (Diaz-Ferero et al 2012).…”

Space invaders: House Sparrow densities along three urban-agricultural landscapes

“…In order to assess which environmental variables were related to House Sparrow numbers in the three surveyed cities, we reviewed previous studies relating the presence and abundances of urbanexploiter species to environmental variables (e.g., Kark et al 2007, Evans et al 2009, Murgui and Macías 2010, Ortega-Álvarez and MacGregor-Fors 2009, 2011. We identified 12 specific variables that describe vegetation structure, urban infrastructure, and human activity, which we sampled within the 50-m radius area at which we surveyed the sparrows: (1) tree cover, (2) tree abundance, (3) maximum tree diameter at breast height (DBH), (4) maximum tree height, (5) shrub cover, (6) maximum herbaceous plant height, (7) number of lamp poles, (8) number of telephone and electric power poles, (9) number of telephone and electric power cables, (10) maximum building height, (11) number of passing pedestrians in five min, and (12) number of passing cars in five min.…”

“…This can importantly affect the ecology of an entire geographic region, and, as a result, threaten native species (Emlen 1974, Beissinger and Osborne 1982, Czech et al 2000, Van Rensburg et al 2009, Maxwell et al 2016. As urbanization poses novel pressures to biodiversity, some species are able to adapt, and even thrive, within urban centers, while those unable to do so decline in number (Chace and Walsh 2006, Evans et al 2009, Fischer et al 2015. In particular, several bird species have been shown to successfully exploit areas of human development, to the degree that they have established populations beyond their native geographic ranges (Blair 1996, Shochat 2004, Kark et al 2007, Blackburn et al 2009).…”

Supplementary feeding restructures urban bird communities

“…avian ecology | community composition | garden birds | human interactions | wildlife feeding N umerous factors influence the structure of urban bird assemblages, including habitat fragmentation, competition, and predation (1,2). One of the most critical factors in the regulation of all animal populations is food resource availability (3)(4)(5).…”