“Junk” dumped in the terrestrial environment is often mistaken for bone fragments and swallowed by scavenging raptors to cause choking, poisoning, intestinal obstruction, malnutrition and death. Junk-induced nestling mortality is seriously threatening the re-establishment of Critically Endangered California Condor in the wild.
Vultures and condors seek out and swallow bone fragments and indigestible items in order to acquire calcium and help in food pellet regurgitation. Although this is a natural behaviour, the presence of toxic or sharp debris dumped in the terrestrial environment by humans means that these raptors now frequently swallow objects that can poison them or lodge in and penetrate their gut. Raptor nestlings are particularly at risk from choking, poisoning, intestinal obstruction and malnutrition because they cannot regurgitate indigestible items (Ferro 2000). The low breeding success of Griffon Vultures Gyps fulvus in Israel and Armenia is a result of nestlings dying after eating metal objects, and nests of Critically Endangered White-rumped Vulture G. bengalensis in Pakistan are often found strewn with glass, china fragments, plastic and metal which could easily be swallowed by nestlings (Ferro 2000, Houston et al. 2007, BirdLife International 2008).
The re-establishment of a wild breeding population of Critically Endangered California Condor Gymnogyps californianus is particularly threatened by junk-induced nestling mortality. California Condor became extinct in the wild in 1987 following precipitous population declines as a result of lead poisoning (Cade 2007). A small free-flying population of 164 individuals now exists (as of March 2008) thanks to the California Condor Recovery Program. However, of the 13 breeding attempts in the wild since 2001, only one has resulted in successful fledging. Since 2002 eight nestlings have died in the nest or were removed from the wild, and six of these had swallowed substantial quantities of glass shards, metal bottle-tops, ammunition cartridges, electrical wiring, plastic piping, pieces of rubber and cloth (see figure a). The ingestion of this junk was the direct cause of mortality in two cases and contributed strongly to others. Two nestlings were found to have ingested their own body weight in junk and one nestling suffered from zinc poisoning as a result of metal ingestion. Most nestlings also showed retarded feather development as a result of malnutrition stemming from distended and blocked digestive systems (Mee et al. 2007).
The amount of junk in the environment has increased since the last California Condor was removed from the wild in 1987, with significantly more junk being held in modern-day nests (see figure b). Although efforts have been made to clean up sites frequented by condors, the scale and diversity of sites likely to hold junk is huge. Unfortunately the most-frequented sites are also the most polluted, being the closest to major centres of human habitation (Mee et al. 2007).
Related Case Studies in other sections
BirdLife International (2008) Anthropogenic junk ingestion leads to high nestling mortality in vultures and condors. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/180. Checked: 13/02/2016