Abstract
The southern giant petrel (Macronectes giganteus) (Gmelin 1789), also known as the giant fulmar, or even ‘stinker’, is a member of the family Procellariiformes. These large scavengers of the ocean are classified as Least Concern by the IUCN. Population trends are variable, and identified threats are mortalities seen in longline fishing, as well as disturbance on breeding sites.
The bird was admitted to the SAAMBR marine bird rehabilitation facility, where it presented with paresis of the hind legs and drooping wings. A radio-dense object in the proventriculus could be seen on radiographs. Attempts to remove the object surgically were unsuccessful, and it was treated with a chelating agent. A barium study was also performed but did not indicate any significant pathology. Due to the paresis progressing in severity and the deteriorating condition of the plumage, it was decided to euthanise the bird.
The foreign object, which was found in the gizzard during the post-mortem, was analysed by a forensic specialist, who confirmed that it was a high-speed projectile, possibly a .22-calibre lead bullet/core or a 4.5-mm pellet.
Heavy metal analysis of the blood, bone, feathers, and liver showed a significant increase in lead, as well as mercury.
Lead is a well-known heavy metal toxin with clinical symptoms such as paralysis of the digestive tract, and progressive paralysis of the wing and feet muscles described at levels of 200 ng/g. Levels above 500 ng/g are considered toxic.1 The blood lead levels increased significantly (from 519 ng/g to 18,152 ng/g) between the two blood samples collected at the beginning and end of treatment. It is thought that manipulation of the gut and the lead object during surgery caused it to dislodge, which resulted in this spike. The lead levels detected in the bone tissue were as high as 10,735 ng/g.
The high mercury levels identified (liver tissue: 36,532 ng/g) are consistent with those already identified in giant petrels.2 High levels of mercury in the tissue are reported to influence health, physiology, behaviour, and reproduction. The lowest documented effects in birds were observed at concentrations of 200 ng/g.3 It is unclear how the high levels observed in this bird contributed to the clinical symptoms observed.
Histopathology identified a proventricular and gizzard candidiasis. It is possible that the heavy metal intoxication could have caused significant immunosuppression, predisposing the bird to secondary infections like candidiasis.
Plumbism (lead toxicity) is often reported in terrestrial birds of prey and scavengers.4 It is assumed that this bird managed to ingest the bullet when it scavenged on an animal that was killed using a pellet gun. The amount of mobility observed by this patient was surprising, given the high lead levels found in the tissue. While these are known scavengers of the ocean that have been reported to regularly consume plastic and other foreign bodies,5 this will be the first report of plumbism observed in a marine bird. Because of their widespread distribution, and the fact that they are long-lived and top predators, marine birds are useful as bioindicators of environmental pollution.6 However, this case also highlights that the extent of anthropogenic lead exposure4 is no longer limited to the terrestrial environment but is also reaching marine areas not previously recorded.
Acknowledgements
The authors would like to thank SAAMBR, the KZN Stranding network and the marine bird rescue team for their continued contributions and commitment towards marine bird conservation. The marine bird rescue and rehabilitation activities were conducted under the DFFE TOPS marine standing permit #S03174.
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