This is a question that has been exhaustively debated by human psychologists for decades, but for birds it’s definitely both nature and nurture. In two studies, scientists asked the question, “Do alien plants harm birds?”
In the first study, one habitat was almost entirely native grasses and forbs, whereas the second was dominated by two invasive alien grasses: Lehmann lovegrass (Eragrostis lehmanniana) and buffelgrass (Cenchrus ciliaris). Both of these alien species were introduced in the late 1940s to “restore” overgrazed rangeland. Their introduction was such a “success” that they have now replaced millions of acres of native prairie vegetation throughout the southwest.
The results are in and the study showed that restructuring the grassland plant community with alien plants has, in turn, restructured the insect community and the birds that depend upon the insects within the study area. On the native prairie, there were 60% more insects and spiders which supported 32% more insectivorous birds compared to the grasslands invaded by the alien plants.
In the second study conducted at Medicine Lake National Wildlife Refuge in Montana researchers found that longspur nestlings reared in areas dominated by alien crested wheatgrass grew more slowly and were smaller than nestlings reared in native prairie vegetation. This is an obvious sign that food was in short supply. Being small is dangerous in nature, and nestlings in the wheatgrass were 17% more likely to die on any given day than the nestlings reared in the native prairie grasses.
The results were conclusive. When you remove the food (native plants) of the food (insects) that birds need to rear their young, it will result in fewer birds. So you see, it really does take nature to nurture. And, native plants do it best in a sustainable landscape design.
Alien vursus native, can it really be that harmful...
Wednesday, February 15, 2011