Skip to main content

Arboreal birds do not avoid scattered trees in West Africa

  • LEO ZWARTS (a1), ROB G. BIJLSMA (a2) and JAN VAN DER KAMP (a1)

Arboreal birds tend to remain in woody vegetation and avoid crossing open areas. Therefore, few tree-dwelling birds are to be expected in scattered trees. We tested this expectation with field data collected in the deserts, savannas and open agricultural parklands of West Africa where woody cover in 1,327 stratified random study sites varied between 0.2 and 29%. We found no evidence that scattered trees were avoided. Instead, bird density in trees was independent of trees occurring clumped or singly. The presence of birds in an individual tree was related to tree species and tree-related variables, but not to woody cover or species composition of the surrounding woody vegetation. We hypothesise that scattered trees are not avoided because (1) travel time between trees is too short to have a negative impact on foraging time, (2) predation risk of arboreal passerines is very low (bird-hunting raptors are scarce in the deserts and savannas of West Africa and mostly prey on ground-feeding, not arboreal, birds), and (3) the probability of being chased away by other arboreal birds is less when trees are more scattered. Scattered trees are ecologically important since hundreds of millions of migratory woodland birds, of which several species are in decline, spend the northern winter in Africa in open, often human-modified, landscapes where trees are well spaced.

Corresponding author
*Author for correspondence; e-mail:
Hide All
Anadón, J. D., Sánchez, J. A., Carrete, J., Donázar, J. A. and Hiraldo, F. (2010) Large-scale human effects on an arid African raptor community. Anim. Conserv. 13: 494504.
Bélisle, M. and Desrochers, A. (2002) Gap-crossing decisions by forest birds: an empirical basis for parameterizing spatially-explicit, individual-based models. Landsc. Ecol. 17: 219231.
Blackburn, E. and Cresswell, W. (2016) High winter site fidelity in a long-distance migrant: implications for wintering ecology and survival estimates. J. Ornithol. 157: 93108.
Brown, L., Urban, E. K. and Newman, K. (1982) The birds of Africa, Vol. 1. London, UK: Academic Press.
Carrascal, L. M. and Alonso, C. S. L. (2006) Habitat use under latent predation risk. A case study with wintering forest birds. Oikos 112: 5162.
Cimprich, D. A., Woodrey, M. S. and Moore, F. R. (2005) Passerine migrants respond to variation in predation risk during stopover. Anim. Behav. 69: 11731179.
del Hoyo, J., Elliott, A., Sargatal, J., Christie, D. A. and de Juana, E. (eds.) (2017) Handbook of the birds of the world alive . Barcelona, Spain: Lynx Edicions. (Retrieved from on 23 July 2017).
Denslow, J. S. (1987) Fruit removal rates from aggregated and isolated bushes of the red elderberry, Sambucus pubens. Can. J. Bot. 65: 12291235.
Dolman, P. M. (2012) Mechanisms and processes underlying landscape structure effects on bird populations. Pp. 93124 in Fuller, R. J., ed. Birds and habitats: Relationships in changing landscapes. Cambridge, UK: Cambridge University Press.
Desrochers, A. and Hannon, S. J. (1997) Gap crossing decisions by forest songbirds during the post-fledging period. Conserv. Biol. 11: 12041210.
Fahrig, L. (2003) Effects of habitat fragmentation on biodiversity. Annu. Rev. Ecol. Evol. Syst. 34: 487515.
Gillies, C. S. and St Clair, C. C. (2010). Functional responses in habitat selection by tropical birds moving through fragmented forest. J. Appl. Ecol. 47: 182190.
Gonzalez, P. (2001) Desertification and a shift of forest species in the West African Sahel. Climate Res . 17: 217228.
Götmark, F. and Post, P. (1996) Prey selection by sparrowhawks, Accipiter nisus: relative predation risk for breeding passerine birds in relation to their size, ecology and behaviour. Phil. Trans. R. Soc. Lond. B 351: 15591577.
Harris, R. J. and Reed, J. M. (2002) Behavioral barriers to non-migratory movements of birds. Ann. Zool. Fenn. 39: 275290.
Hijmans, R. J., Cameron, S. E., Parra, J. L., Jones, P. G. and Jarvis, A. (2005) Very high resolution interpolated climate surfaces for global land areas. Int. J. Climatol. 25: 19651978
Hinsley, S. A. (2000) The costs of multiple patch use by birds. Landsc. Ecol. 15: 765775.
King, J. M., and Hutchinson, J. M. C. (2001). Site fidelity and recurrence of some migrant bird species in The Gambia. Ringing Migr. 20: 292302.
Lee, A. C. and Peres, C. A. (2009) Gap-crossing movements predict species occupancy in Amazonian forest fragments. Oikos 118: 280290.
Lima, S. L. (1993) Ecological and evolutionary perspectives on escape from predatory attack: a survey of North American birds. Wilson Bull. 105: 147.
Lindström, Å. (1989) Finch flock size and risk of hawk predation at a migratory stopover site. Auk 106: 225232.
Loveland, T. R., Reed, B. C., Brown, J. F., Ohlen, D. O., Zhu, Z., Yang, L. and Merchant, J. W. (2000) Development of a global land cover characteristics database and IGBP DISCover from 1 km AVHRR data. Int. J. Remote Sens. 21: 13031330.
Manning, A. D., Fischer, J., Lindenmayer, D. B. (2006) Scattered trees are keystone structures – Implications for conservation. Biol. Conserv. 132: 311321.
Mayaux, P., Bartholomé, E., Fritz, S., Belward, A. (2004) A new land-cover map of Africa for the year 2000. J. Biogeogr. 31: 861877
Myers, J. P. (1980a) Sanderlings Calidris alba at Bodega bay: facts, interferences and shameless speculations. Wader Study Group Bull. 30: 2631.
Myers, J. P. (1980b) Territoriality and flocking by buff-breasted sandpipers: variations in non-breeding dispersion. Condor 82: 241250.
Niethammer, G. (1959) Die Rolle der Auslese durch Feinde bei Wüstenvögeln. Bonn. Zool. Beitr. 10: 179197.
Norris, D. R., Stuchbury, B. J. M. and Thompson, I. F. (2002) Sexual differences in gap-crossing ability of a forest songbird in a fragmented landscape revealed through radiotracking. Auk 119: 528532.
Price, O. F., Woinarski, J. C. and Robinson, D. (1999) Very large area requirements for frugivorous birds in monsoon rainforests of the Northern Territory, Australia. Biol. Conserv. 91: 169180.
Pulido, F. and Díaz, M. (1997) Linking individual foraging behavior and population spatial distribution in patchy environments: a field example with Mediterranean blue tits. Oecologia 111: 434442.
Rabøl, J. (1987) Coexistence and competition between overwintering Willow Warblers Phylloscopus trochilus and local warblers at Lake Naivasha, Kenya. Ornis Scand. 18: 101121.
Robertson, O. J. and Radford, J. Q. (2009) Gap-crossing decisions of forest birds in a fragmented landscape. Austral Ecol. 34: 435446.
Robinson, S. K., Thompson, F. R., Donovan, T. M., Whitehead, D. R. and Faaborg, J. (1995) Regional forest fragmentation and the nesting success of migratory birds. Science 267: 19871990.
Rodríguez, A., Andrén, H. and Jansson, G. (2001) Habitat-mediated predation risk and decision making of small birds at forest edges. Oikos 95: 383396.
Salewski, V., Bairlein, F. and Leisler, B. (2002) Different wintering strategies of two Palearctic migrants in West Africa – a consequence of foraging strategies? Ibis 144: 8593.
Salewski, V., Almasi, B., Heuman, A., Thoma, M. and Schlageter, A. (2007) Agonistic behaviour of Palearctic passerine migrants at a stopover site suggests interference competition. Ostrich 78: 349355.
Sargent, S. (1990) Neighborhood effects on fruit removal by birds: a field experiment with Viburnum dentatum (Caprifoliaceae). Ecology 71: 12891298.
Sauvage, A., Rumsey, S. J. R. and Rodwell, S. P. (1998) Recurrence of Palearctic birds in the lower Senegal river valley. Malimbus 20: 3353.
Seymour, C. L. and Simmons, R. E. (2008) Can severely fragmented patches of riparian vegetation still be important for arid-land bird diversity? J. Arid Environ. 72: 22752281.
Shirley, S. M. (2006) Movement of forest birds across river and clearcut edges of varying riparian buffer strip widths. Forest Ecol. Manag. 223: 190199.
St Clair, C. C., Bélisle, M., Desrochers, A., and Hannon, S. (1998) Winter responses of forest birds to habitat corridors and gaps. Conserv. Ecol. [online] 2, 13.
Suhonen, J. (1993) Predation risk influences the use of foraging sites by tits. Ecology 74: 11971203.
Thiollay, J.-M. (1978) Les migrations de rapaces en Afrique occidentale: adaptations écologiques aux fluctuations saisonnières de production des écosystèmes. Terre Vie 32: 89133.
Thiollay, J.-M. (1999) Frequency of mixed species flocking in tropical forest birds and correlates of predation risk: an intertropical comparison. J. Avian Biol. 30: 282294.
Thiollay, J.-M. (2006) Severe decline of large birds in the Northern Sahel of West Africa: a long-term assessment. Bird Conserv. Int. 16: 353365.
Trichon, V., Hiernaux, P., Walcker, R. and Mougin, E. (2018) The persistent decline of patterned woody vegetation: The tiger bush in the context of the regional Sahel greening trend. Global Change Biol . 2018: 116.
Vickery, J. A., Ewing, S. R., Smith, K. W., Pain, D. J., Bairlein, F., Škorpilová, J. and Gregory, R. D. (2014) The decline of Afro-Palaearctic migrants and an assessment of potential causes. Ibis 156: 122.
Walther, B. and Gosler, A. (2001) The effects of food availability and distance to protective cover on the winter foraging behaviour of tits (Aves: Parus). Oecologia 129: 312320.
Willemoes, M., Tøttrup, A. P., Lerche-Jørgersen, M., Jacobsen, E. M., Reeve, A. H. and Thorup, K. (2017) Spatial behaviour and density of three species of long-distance migrants wintering in a disturbed and non-disturbed woodland in northern Ghana. Bird Conserv. Internatn. 114.
Zwarts, L. and Bijlsma, R. G. (2015) Detection probabilities and absolute densities of birds in trees. Ardea 103: 99122.
Zwarts, L. and Drent, R. H. (1981) Prey depletion and the regulation of predator density: oystercatchers (Haematopus ostralegus) feeding on mussels (Mytilus edulis). Pp. 193216 in Jones, N. V. and Wolff, W. J., eds. Feeding and survival strategies of estuarine organisms. New York: Plenum.
Zwarts, L., Bijlsma, R. G., van der Kamp, J. and Wymenga, E. (2009) Living on the edge: Wetlands and birds in a changing Sahel. Zeist, The Netherlands: KNNV Publishing.
Zwarts, L., Bijlsma, R. G., van der Kamp, J., Sikkema, M. and Wymenga, E. (2015) Moreau’s Paradox reversed, or why insectivorous birds reach high densities in savanna trees. Ardea 103: 123144.
Zwarts, L., Bijlsma, R. G. and van der Kamp, J. (2018) Large decline of birds in Sahelian rangelands due to loss of woody cover and soil seed bank. J. Arid Environ. 155: 115.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Bird Conservation International
  • ISSN: 0959-2709
  • EISSN: 1474-0001
  • URL: /core/journals/bird-conservation-international
Please enter your name
Please enter a valid email address
Who would you like to send this to? *
Type Description Title
Supplementary materials

Zwarts et al. supplementary material
Tables S1-S5

 Word (42 KB)
42 KB


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed