Every year, rippling pink streamers descend from the sky and settle on Lake Natron in Tanzania, materializing into thousands of mating flamingo pairs. East Africa is home to 75 percent of the world?s population of lesser flamingos, and Lake Natron offers the most important breeding ground for these otherwise nomadic birds.
Up to 2.5 million can settle there at breeding time when conditions are right, and this year is one of the most significant breeding events in recent time. Large groups were spotted flying toward the lake this month, and several hundred thousand are already gathered there. The expected population boom could strengthen the position of conservation groups intent on halting construction of an industrial plant that will lay pipes across the lake?s surface to extract soda ash from its watery shallows.
Flamingos are famously mobile, says Dr. Felicity Arengo, a flamingo specialist and associate director of the Center for Biodiversity and Conservation at the American Museum of Natural History in New York. ?They?re not considered to be properly migratory in that they don?t have a directional seasonal movement,? she said, ?but what they?re doing is tracking resource availability in a whole complex of wetlands.?
By moving from one place to another, the pink-stockinged birds are able to explore several feeding grounds. The lesser flamingo, which is the smallest and most common species, feeds predominantly on the blue-green algae that proliferates in numerous salty lakes.
Yet breeding requires more stability, which explains why the birds flock to larger bodies of water like Lake Natron to take part in the lengthy annual ritual of pairing up, mating, and laying their eggs.
For such itinerant creatures, these dependable breeding sites play a surprisingly vital role. Habitat fragmentation means that fewer true wetland areas exist. ?Some have gone,? Dr. Arengo said, ?so some breeding sites have been consistently important.?
These larger areas work like ?satellite sites? that offer a kind of refuge that is increasingly sought after ? especially for the lesser flamingo, described as ?near-threatened? on the International Union for Conservation of Nature?s Red List.
The birds are somewhat delicate breeders: by building their nests at the lake?s center, they depend on a perfect balance of water to keep them safe. Too much rainfall into the lake will flood their nests; too little water leaves them high and dry, and vulnerable to opportunistic predators that will venture in. But on Lake Natron, which is a Ramsar site ? a measure that recognizes ecologically valuable wetland habitats ? the lesser flamingos face another potential threat.
Since 2006, there have been plans to build a soda-ash extracting facility on the lake. Soda ash is the commercial name given to sodium carbonate, a product that occurs naturally in alkali lakes like Lake Natron, and is mined for its widespread industrial uses in items like detergents and dyes, ramen noodles and sherbet.
Plans for development lay fallow until Tanzania?s president, Jakaya Kikwete, announced a decision to proceed with the plant last year. There are concerns that the plans could seriously disrupt the flamingo activities there. ?A breeding colony is very nervous and prone to deserting nests and young if there is any disturbance,? said Sarah Ward,?a geographer from the University of Southampton who specializes in East African lake research.
For the several hundred thousand eggs laid during a robust breeding event, home is a brown mound. On their return to Lake Natron each year, the nesting flamingos ?can reuse mounds, but they?ll always repair and build on an existing mound,? Dr. Arengo said. That additive material comes from the lake, because unlike other birds, flamingos source their nesting products locally. Mining soda ash could change that dynamic by excavating the lake, which creates a greater influx of water, and so dilutes the dense mud that helps solidify the nests.
And then there are the inevitable disruptions of an industrial site?? ?movement and the presence of people, the coming and going of heavy machinery,? said Dr. Arengo ? and how they might affect a skittish bird.
But the problems at Lake Natron represent what is happening elsewhere. Unprotected lake and wetland habitats are increasingly subject to developments that threaten their waters. Effluent from agriculture and deforestation on the shore can silt up the water, and the encroachment of industry causes contamination. Harder to control or predict are the effects of climate change.
Seeing it like a flamingo does, from several hundred meters up in the sky, ?you have to look at this on a landscape level,? Dr. Arengo said. Even though they are so mobile, the birds still need many habitat options in order to exist, so it?s not about protecting just one lake for this year?s population boom.
?They need to be able to move,? Dr. Arengo said. ?While they?re adapted to this behavior, they are eventually going to run out of options.?
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