How many birds are there in a city of half a million people?

Aim Urban environments are often characterized as supporting a few abundant, generalist species best adapted to living alongside humans, and as such, cities are seen as agents of biotic homogenization. However, there are surprisingly few descriptions of biological populations found in cities. Here, we provide the first complete citywide population estimates of birds for any UK city, and examine the conservation status of the assemblage in comparison with the country’s avifauna at large. Location Sheffield city, central UK Methods We surveyed birds in every 500 m × 500 m square across the 160 km 2 of the city. Using a Distance sampling protocol, we estimated bird population sizes for the city and compared these with the size of the human population. We also compared the conservation status of the city’s avian population with that of birds across the UK as a whole. Results Aggregation of population estimates for the 77 species observed during the surveys produced a total estimate of 602,995 (95% confidence interval (CI): 404,565‐942,573) breeding birds, equating to 1.18 birds per person. The size of the non-breeding population was similar at 578,603 (464,396‐728,574) individuals, or 1.13 birds per person. Surveys revealed only three non-native species, but relatively few species of national conservation concern. However, some species of conservation concern achieved very high population densities within the city, and the overall density of birds was more than six times that of the nation at large. Main conclusions If declines in some species are to be arrested or reversed, conservation effort will need to focus much more strongly on understanding and managing urban populations, because these might buffer some species against wholesale regional population depletion, particularly where intensive agriculture in the surrounding hinterland has led to declines in bird populations at large. Such a focus will require a significant increase in the priority and resources devoted to conservation activities in urban areas.

[1]  S. Baillie,et al.  Large-scale habitat use of some declining British birds , 1998 .

[2]  Joseph A. Teramino,et al.  Bat community structure in an urban park , 1992 .

[3]  A. Huckauf.  Biodiversity conservation and the extinction of experience , 2008 .

[4]  J. Kirkpatrick,et al.  Does variation in garden characteristics influence the conservation of birds in suburbia , 2006 .

[5]  John M. Marzluff,et al.  Importance of Reserve Size and Landscape Context to Urban Bird Conservation , 2004 .

[6]  Stephen R. Baillie,et al.  Evaluating the Breeding Bird Survey for producing national population size and density estimates , 2005 .

[7]  J. Chamie,et al.  World Urbanization Prospects: The 2003 Revision , 2004 .

[8]  D. Norman.  BIRDS IN EUROPEAN CITIES , 2007 .

[9]  J. Marzluff.  Worldwide urbanization and its effects on birds , 2001 .

[10]  G. Siriwardena,et al.  Size and trends of the House Sparrow Passer domesticus population in Great Britain , 2005 .

[11]  S. Ribeiro,et al.  Effects of urbanization on Neotropical wasp and bee assemblages in a Brazilian metropolis , 2005 .

[12]  J. Tanacredi,et al.  Rare and endangered plants at Gateway National Recreation Area: a case for protection of urban natural areas , 1996 .

[13]  I. Kühn,et al.  Urbanization and homogenization – Comparing the floras of urban and rural areas in Germany , 2006 .

[14]  K. Gaston,et al.  Commonness, population depletion and conservation biology. , 2008, Trends in ecology & evolution.

[15]  Kevin J. Gaston,et al.  The lognormal distribution is not an appropriate null hypothesis for the species–abundance distribution , 2005 .

[16]  J. Sauer,et al.  A citywide breeding bird survey for Washington, D.C. , 1997, Urban Ecosystems.

[17]  J. Marzluff,et al.  Relative importance of habitat quantity, structure, and spatial pattern to birds in urbanizing environments , 2006, Urban Ecosystems.

[18]  Birds breeding in British gardens: an underestimated population? , 2004 .

[19]  Jeremy T. Kerr,et al.  Effects of Human Activity on Global Extinction Risk , 1995 .

[20]  M. Vennetier,et al.  Gardens in urbanizing rural areas reveal an unexpected floral diversity related to housing density. , 2008, Comptes rendus biologies.

[21]  R. Johnston.  Synanthropic birds of North America , 2001 .

[22]  C. Mason.  Thrushes now largely restricted to the built environment in eastern England , 2000 .

[23]  J. Greenwood,et al.  Bird densities are associated with household densities , 2007 .

[24]  J. Niemelä,et al.  Carabid beetle assemblages (Coleoptera, Carabidae) across urban-rural gradients: an international comparison , 2002, Landscape Ecology.

[25]  H. Mooney,et al.  Human Domination of Earth’s Ecosystems , 1997, Renewable Energy.

[26]  K. Gaston,et al.  Garden bird feeding predicts the structure of urban avian assemblages , 2008 .

[27]  I. Vähä-Piikkiö,et al.  Species number, historical elements and protection of threatened species in the flora of Helsinki, Finland , 2004 .

[28]  Birds in European Cities , 2007 .

[29]  R. Parker,et al.  Communities and Local Government , 2008 .

[30]  C. Harrison.  An Atlas of the Birds of the Western Palaearctic , 1982 .

[31]  William B. Meyer,et al.  HUMAN POPULATION GROWTH AND GLOBAL LAND-USE/COVER CHANGE , 1992 .

[32]  F. W. Preston.  The Commonness, And Rarity, of Species , 1948 .

[33]  I. Kühn,et al.  The flora of German cities is naturally species rich , 2004 .

[34]  James R. Miller.  Biodiversity conservation and the extinction of experience. , 2005, Trends in ecology & evolution.

[35]  G. Matlack.  Sociological edge effects: Spatial distribution of human impact in suburban forest fragments , 1993 .

[36]  Per Angelstam,et al.  Ecological diversity of birds in relation to the structure of urban green space , 2006 .

[37]  K. Gaston,et al.  Urban Domestic Gardens (IV): The Extent of the Resource and its Associated Features , 2004, Biodiversity & Conservation.

[38]  M. Fasola,et al.  Recent declines in urban Italian Sparrow Passer (domesticus) italiae populations in northern Italy , 2007 .

[39]  M. Schwartz,et al.  Conservation's Disenfranchised Urban Poor , 2002 .

[40]  G. Luck,et al.  A review of the relationships between human population density and biodiversity , 2007, Biological reviews of the Cambridge Philosophical Society.

[41]  K. Gaston,et al.  Biodiversity and extinction , 2007 .

[42]  P. Clergeau,et al.  Are urban bird communities influenced by the bird diversity of adjacent landscapes , 2001 .

[43]  R. Gregory.  Species abundance patterns of British birds , 1994, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[44]  F. Adriaensen,et al.  Population dynamics and partial migration of the european robin (Erithacus rubecula) in different habitats , 1990 .

[45]  S. Croci,et al.  Avifauna homogenisation by urbanisation: Analysis at different European latitudes , 2006 .

[46]  E. Shochat.  Credit or debit? Resource input changes population dynamics of city‐slicker birds , 2004 .

[47]  B. Freedman,et al.  Plant communities of selected urbanized areas of Halifax, Nova Scotia, Canada , 2004 .

[48]  Örjan Hallberg,et al.  The Urban Decline of the House Sparrow (Passer domesticus): A Possible Link with Electromagnetic Radiation , 2007, Electromagnetic biology and medicine.

[49]  S. Juliano,et al.  POPULATION DYNAMICS , 2007, Journal of the American Mosquito Control Association.

[50]  I. Kühn,et al.  Plant richness patterns in agricultural and urban landscapes in Central Germany—spatial gradients of species richness , 2006 .

[51]  P. Clergeau,et al.  Bird abundance and diversity along an urban-rural gradient : A comparative study between two cities on different continents , 1998 .

[52]  Richard J. Hobbs,et al.  Conservation Where People Live and Work , 2002 .

[53]  W. Turner,et al.  Global Urbanization and the Separation of Humans from Nature , 2004 .

[54]  B. Wakeling,et al.  Lizard species distributions and habitat occupation along an urban gradient in Tucson, Arizona, USA , 2001 .

[55]  C. Wernham.  The migration atlas : movements of the birds of Britain and Ireland , 2002 .

[56]  D. Green,et al.  Urbanization impacts on habitat and bird communities in a Sonoran desert ecosystem , 2003 .

[57]  J. Lockwood,et al.  Biotic homogenization: a few winners replacing many losers in the next mass extinction. , 1999, Trends in ecology & evolution.

[58]  D. Chamberlain,et al.  Effects of the winter beechmast crop on bird occurrence in British gardens , 2007 .

[59]  R. Blair.  Creating a homogeneous avifauna: Local extinction and invasion along urban gradients in California and Ohio , 2001 .

[60]  S. Buckland.  Introduction to distance sampling : estimating abundance of biological populations , 2001 .

[61]  Madhusudan Katti,et al.  Linking Optimal Foraging Behavior to Bird Community Structure in an Urban‐Desert Landscape: Field Experiments with Artificial Food Patches , 2004, The American Naturalist.

[62]  Clairie Papazoglou,et al.  Birds in the European Union : a status assessment , 2004 .

[63]  M. McKinney,et al.  Effects of urbanization on species richness: A review of plants and animals , 2008, Urban Ecosystems.

[64]  R. Dennis,et al.  The impact of urban development on butterflies within a city region , 1999, Biodiversity & Conservation.

[65]  M. McKinney,et al.  Urbanization as a major cause of biotic homogenization , 2006 .

[66]  C. E. Adams.  Urban Wildlife Management , 2005 .

[67]  J. Simon,et al.  Extinction rates. , 1996, Science.

[68]  Kevin J. Gaston,et al.  Biodiversity and extinction: species and people , 2005 .

[69]  J. Marzluff,et al.  Avian Ecology and Conservation in an Urbanizing World , 2002, Springer US.

[70]  K. Gaston,et al.  Psychological benefits of greenspace increase with biodiversity , 2007, Biology Letters.

[71]  N. Dempsey,et al.  Urban domestic gardens (XI): variation in urban wildlife gardening in the United Kingdom , 2007, Biodiversity and Conservation.

[72]  J. Niemelä,et al.  Carabid beetle assemblages along urban to rural gradients: a review. , 2009 .

[73]  Kevin J. Gaston,et al.  Trends in the use of private gardens by wild birds in Great Britain 1995–2002 , 2005 .

[74]  J. P. Collins,et al.  A New Urban Ecology , 2000, American Scientist.