| Description |
Habitats around the world, especially in the tropics, are being fragmented at a rapid rate, causing a tremendous loss of biodiversity[1]. For example, 12% of the approximately 10,000 bird species are threatened with extinction in the next 10 to 100 years, and another 8% are near-threatened[2]. This loss of species is likely to result in the collapse of significant ecosystem processes and free ecosystem services to people[3], such as pest control by insectivorous birds. Tropical forest insectivorous birds, such as antbirds, woodcreepers, and wrens, present a good example of an important, species-rich group of small, noncharismatic organisms who do not get much public attention, but whose demise may have significant negative ecological and financial consequences. They are among the species most likely to go extinct as a result of forest fragmentation[4] and their loss may result in insect pest outbreaks in tropical forests and surrounding agricultural areas. Finding out the causes of the disappearance of understory insectivores may help explain the disappearance of the other small, short-lived, and specialized bird species that comprise the majority (65%) of threatened bird species in the world[5]. In a recent study of the factors behind the disappearance of insectivorous birds in Costa Rican forest fragments reported in the Proceedings of the National Academy of Sciences[6], we provide evidence that interfragment dispersal, rather than food limitation, may be the most critical factor for the persistence of understory insectivorous birds in forest fragments. As in previous studies[4,7], small forest fragments had significantly lower insectivore species diversity and abundance than more extensive forest. However, our initial hypothesis - that the decline of insectivorous birds in forest fragments is caused by an impoverished invertebrate prey base - was not supported by invertebrate counts and examination of bird diet samples. Instead, the inability of understory insectivores to use the nonforest matrix surrounding the fragments seemed to be the main reason for their decline. |
