Symbiotic nesting of birds with formidable animals: a review with applications to biodiversity conservation

Increased predation and parasitism of bird nests has become a major problem in many biological communities altered by human activities, often causing declines in bird populations. To help solve this threat to biodiversity, I propose restoring the abundance of symbiotic nest-protecting animals in hab itats where birds face an increased risk from predators and parasites, so t hat birds there can increase their chances of reproductive success by nesti ng close to these protectors. The re-establishment of such protective nesti ng associations to increase avian reproductive success differs from other p roposed solutions to this problem in that it involves point defense of bird nests themselves. Rather than diminishing the number of nest predators and brood parasites in the whole habitat or community, as proposed with other approaches, the presence, activity and success of these enemies are reduced only within the microhabitat defended by the protector. The animal protect ing the nest need not be larger in size than the predators or brood parasit es, and is often many times smaller. In addition, it need not be from a hig her trophic position, and in many cases comes from the same or a lower trop hic level. Research suggests that an informed and careful use of nest prote cting animals by wildlife managers can help reverse or prevent the decline of many bird populations, especially when used in combination with other ap proaches such as restoration of top predator populations and habitats. Alth ough wildlife biologists have long recognized the important role that plant s play in concealing and protecting bird nests from enemies, and regularly recommend manipulation of vegetation to enhance nest survival, they have ge nerally ignored the important role that formidable animals play in protecti ng bird nests, and failed to incorporate animal protectors into management strategies. Because of this neglect, a host of new studies and experiments are urgently needed to provide managers with the critical information neede d to use protective nesting associations effectively in integrated strategi es to preserve avian biodiversity.