ORNITHOLOGICAL LITERATURE 
855 
landscapes in many regions may be due to edge 
effects of desiccation, wind and fire, generalist 
birds that outcompete forest birds, and increased 
predation. Linear forest at least 400 m in width 
may have a short-term chance of conserving some 
forest species. Many tropical birds of the forest 
understory in release experiments were reluctant 
nr incapable of crossing a water gap as wide as 
100m. Dispersal experimenLs and comparisons of 
bird species in nearby forest patches show 
continuous areas of forest may be necessary to 
allow dispersal and immigration ot birds between 
one site and another. 
Tropical birds facilitate ecosystem functions 
with their mobility and spatial link within forests 
and other habitats as they carry genetic material 
between plants or habitats (fruit and seed 
dispersal, pollination), nutrients (resource links 
include nutrient deposition from sea to land, and 
scavengers cleaning carcasses and reducing po¬ 
tential diseases), engineer their physical environ¬ 
ment (woodpeckers making nesting holes), or 
control insects. A few hirds are specialists that 
have closely coevolvcd with their food plants (as 
in mistletoe-feeding birds that disperse the seeds), 
but many seed dispersers are not so specialized, 
but are necessary dispersal agents for plants. 
Large frugivores have disappeared from many 
islands and forest fragments, and their dispersal 
and the regeneration and restoration oi forests is 
limited by the availability of these seed-dispersing 
birds to find plants with large seeds. Over a 
quarter of all frugivorous bird species ate 
threatened, near-threatened or extinct. Pollination 
of certain plant species in the Neotropics is largely 
effected by hummingbirds, and the chapter on 
ecological functions reviews the foraging behav¬ 
ior of hummingbirds in relation to their body size, 
bill size and shape, and habitat. 
An estimated 42% of bird species have been 
used by humans. Most wild birds (90% of total) 
•hat are caught and survive the international bird 
trade end up in the European Union; many others 
go to East and Southeast Asia. The capture and 
export of parrots in New World is a prime danger 
'o populations; half a million panels a year are 
taken from the wild. The wild bird trade also 
involves the local use of birds, as in Java and Bali 
where - 36% of households have pet birds with 
most of these caught within Indonesia or bred in 
captivity. Local use of birds may have decimating 
effects.' as in over-harvesting of eggs of an 
endangered Indonesian megapode. the Maleo 
(Macrocephalon maleo). Commercial exploitation 
in Indonesia of nests of swiflets Collocalia spp. 
for bird-nest soup is intense. The eggs of Edible- 
nest Swiftlet (Aerodramus fuciphaga) are some¬ 
times taken from their nests and cross-fostered in 
the nests of colonies of Uniform Swiftlet (A. 
vanikorensis). The edible nests are then exported 
to China, hut this cross-fostering in swiftlet 
farming in attempts to sustain the population 
may result in inter-species hybridization. Sustain¬ 
able harvests of birds with take rates ascertained 
from demographic models may allow local 
subsistence and recreational hunting, as for 
Magpie Goose {Anseranas semipalmata) in north¬ 
ern Australia. A few species are threatened with 
extinction due to human use (e.g., African 
vultures which arc killed for traditional medicine), 
but the threat is nothing like that due to loss of 
their habitats. 
Conservation concerns for migratory birds that 
winter in the tropics have focused on preserving 
their abundance. The decline of migratory song¬ 
bird populations in the temperate region may in 
part be due to a decrease in suitable wintering 
habitats, but the evidence is sparse. The migratory 
connectedness of breeding and wintering popula¬ 
tions across a wide geographic scale is being 
studied with new technologies of stable isotopes 
(plumages grown in the wintering region may 
have stable isotope ratios that are characteristic of 
the wintering sites), by molecular genetics for 
maps of populations in breeding areas and the 
tropics, and by radiotelemetry. Not considered in 
the migration chapter are other sources of 
information on connectedness, such as: (1) 
subspecific identification of birds in their sum¬ 
mer- and winter-use areas, and (2) banding 
recoveries. Some connectivity of migratory song¬ 
birds is known, for example in Indigo Buntings 
(Passerina cyanea) (R. B. Payne. 2006. Birds of 
North America. Number 4), where banding 
recoveries show the birds maintain their east-west 
spatial distribution in the New World between 
breeding areas, stopover sites in migration, and 
wintering areas. The recovery data in the U.S. 
Geological Survey. Bird Banding Laboratory, 
should be examined for geographic connectedness 
of summer- and winter-use areas of other 
migratory birds, as these data are certain and 
precise, and the recoveries can inform conserva¬ 
tion strategies. 
The term ‘bleak' characterizes the long-term 
prospect for birds in the tropics. Considering the 
