Threats to Birds
Destruction of the tropical humid montane forests to give way to a coffee plantations.
Threats to Birds
Birds are the most representative and ubiquitous group of animals. Birds have adapted and inhabit almost all habitats. It is likely that any habitat constitutes an essential part for a species or community of species to procure food, shelter, and place of reproduction.
Precisely because birds occupy almost all habitats on earth, any human activity that involves extraction or transformation of natural environments is likely to come in conflict with some type of bird or bird community. This makes birds a great indicator or barometer of environmental problems. Most threats to birds or conservation problems, for that matter, are related to human actions.
The main causes related to bird conservation include:
Loss of Habitat
The greatest threat to birds and the common denominator for the loss of biodiversity is the loss and degradation of habitats. This includes the fragmentation, destruction, and alteration of natural environments that birds need to complete their annual or seasonal biological cycle.
The most common human activities that result in bird conservation problems are mining and excessive extraction of natural resources, the transformation of natural habitats for agricultural activities, pollution resulting from industrial activities, or simply urban expansion.
In addition to the direct effect of extractive activities and habitat transformation, an indirect effect is the fragmentation of continuous habitats. Open spaces or with agricultural plantations constitute barriers to dispersal for many bird species.
Species with little habitat or fragmented habitats have difficulty completing biological cycles and maintaining genetic diversity resulting in a population decline followed by a local extinction.
The European Starling (Sturnus vulgaris) was introduced to North America where it competes with native species for nesting cavities.
An introduced species or also called an exotic species is one that is established as a population in regions outside its region of origin. Introduced species are generally transported by man. There is a list of more than 200 introduced bird species with populations established throughout the world.
The problem with introduced species is that they can compete for essential resources for native species such as food, shelter, spaces to protect themselves against predators, spaces or substrates for nesting, as well as direct aggression.
A problem with introduced species is also the loss of genetic integrity of native species through hybridization or interbreeding.
Another problem is the introduction of diseases and other pathogens to which the native species are not adapted.
The introduction of birds to new regions usually occurs in two ways:
- Intentional Introduction: An intentional introduction occurs when individuals of a species are released with the specific objective of establishing a population in the new place. The released of individuals go through a period of adaptation. If the introduction is not successful quickly, more individuals are introduced to help the initial population establish itself and begin to reproduce without food supplement or the release of additional individuals. Birds introduced intentionally are mainly species used for sports hunting.
- Accidental Introduction: the Accidental introduction is the most common type of bird introduction. This occurs when birds imported to a country or region as pets escape and establish new populations. The number of species in the market for ornamental birds and pets is large and perhaps most, at some point, escape. However, there are very few species that manage to establish populations in the places where they escape. Species that establish populations generally come from places where climatic conditions and habitat types are similar to the place of introduction. Groups of birds that more often establish introduced populations include parrots, sparrows, pigeons and allies, and ornamental ducks.
The illegal hunting of birds has reduced the number of certain species to critical population levels.
Birds are hunted for food be it commercial or subsistence, for sport, and for their feathers.
Historically, excessive hunting of certain species has caused their extinction. Subsistence hunting very rarely results in the extinction of bird species. Generally, when hunting becomes commercial and there is an economic incentive, hunting becomes an agent of extinction.
The best-known case in which excessive hunting by humans resulted in the extinction of a species of bird was that of the Passenger Pigeon (Ectopistes migratorius). Before being hunted, the Passenger Pigeon was the most abundant bird in the world. When hunting became a commercial activity the most abundant bird in the world was driven to extinction.
Hybridization occurs when individuals of an introduced species interbreed with individuals of a native species producing intermediate individuals with the characteristics of both parents.
Ornamental bird breeders usually perform hybridizations under captive conditions to obtain new varieties and colors of ornamental birds.
The problem occurs when ornamental birds escape or are released in regions where closely related species occur naturally. When the escaped species establishes itself in the new area, it breeds freely with the native species producing a progeny that is neither the native species nor the introduced species. The bigger problem occurs when the introduced species disperses over the geographic range of the native species, genetically contaminating the entire population and eventually causing the native species to disappear as such but to be composed of hybrid individuals.
Fishing with long lines is responsible for the death of thousands of albatrosses.
- Use of Pesticides: The use of DDT (Dichloro-diphenyl-trichloroethane), is a synthetic organic compound used as an insecticide that poisoned adult birds of prey and also made their eggshell of those that survived very thin to the point that eggshells would break only with the pressure of the incubating female. As a result, no new individuals were produced to replace the naturally dying adults and the populations were reduced, in some cases, to critical numbers. DDT was banned in 1972 and many raptor speceis began their dramatic population recovery.
- Fuel spills: Spills of oil and other fuels have devastating effects on birds, particularly on seabirds. The oil adheres to the feathers of the birds causing the feather to lose its waterproofing properties and exposes the sensitive skin of the bird to extreme temperatures. This can cause hypothermia. Also, instinctively, the bird tries to remove the oil from its feathers by grooming, which causes the bird to ingest the oil causing severe damage to its internal organs.
- Long-line Fishing: Mortality resulting from incidental long-line fishing represents a serious threat to many species of pelagic birds, particularly albatrosses. Fishing ships are important sources of food for many seabird populations which congregate around ships in search of discards after on board processing of fish. Seabirds try to get the bait set on hooks along a fishing line getting hooked and drowned. Most albatross species are now included in some category of threat or danger of extinction. It is estimated that the number of birds killed by incidental capture from long-line fishing reaches more than 300,000 birds per year. Collectively, the number of albatrosses caught by long-line fisheries is large. However, the total number of albatrosses killed by individual vessels is usually quite low. Such a low number per vessel is the reason why this sector of the fishing industry has resisted the notion that their industry causes bird populations to decline.
- Brothers NP. 1991. “Albatross mortality and associated bait loss in the Japanese longline fishery in the southern ocean.” Biological Conservation 55: 255-268.
- Gill, F. (1995). Ornithology. W.H Freeman and Company, New York.
- Moore, R., Robinson, W., Lovette, I., & Robinson, T. (2008). Experimental evidence for extreme dispersal limitation in tropical forest birds. Ecology Letters, 11(9):960-968.