Red kite health surveillance in England-playing detective

Inez Januszczak

Spotting a pair of red kites circling above roads in England is no longer a rare sight. Once almost extinct in the UK, the red kite (Milvus milvus) is now flourishing, but only after some tumultuous times, before the population recovery. Their demise started as early as the 18th century. In 1903, the first Red Kite Committee was founded by concerned individuals who were worried about the dwindling red kite population . The rarity of the red kite at the time meant its eggs were a prime target for egg collectors and bounty hunters, who robbed up to a quarter of nests each year. By the 20th century, the breeding population was restricted to a handful of pairs in South Wales, thought to be as low as 2 pairs. 

Photograph of a red kite on the ground in a field, feeding

In 1989 a re-introduction programme was set up by the RSPB and the Nature Conservancy Council because of concerns about the slow rate of population expansion in Wales. Since then, red kites have been re-introduced to four areas in England: the Chilterns, East Midlands, Yorkshire and North-east England. The first birds were brought from Spain, but as the Chilterns population grew quickly it produced enough young birds to donate small numbers to establish populations in the other areas. Sophisticated nest protection initiatives introduced in the 1950s and 1960s succeeded in reducing the proportion of nests robbed, thus allowed the birds to continue breeding on their own. By 2010, the RSPB estimated that over 200 chicks had been reared from the initial release. This reintroduction has been so successful it is thought that there are now over 2000 breeding pairs in England. 

However, despite this success and extraordinary recovery of the population, the British red kite population still faces challenges, with anti-coagulant rodenticide poisoning and shooting representing threats to population recovery into the 21st century. The Disease Risk Analysis and Health Surveillance Programme (DRAHS) jointly run by Natural England and ZSL receives red kite carcasses, in collaboration with wildlife surveillance groups such as the RSPB and the Predatory Bird Monitoring Scheme (PBMS). The carcasses undergo a post-mortem examination, leading to discoveries about their lifestyle, as well as factors that may have been contributed to their death.

X-ray image of a bird showing a pellet lodged in the skull
A radiograph of a red kite examined in January 2019 - the shot pellet is clearly visible close to the eye socket.

Shooting

As of February 2019, 27 of 335 red kites that underwent post-mortem examination by DRAHS between 1994 and 2019, were found to have shotgun pellets when radiographed which illustrates the persecution red kites experience in the UK. The RSPB’s raptor persecution map shows that 258 raptor persecution cases were confirmed shooting incidences . Shot red kites have been found to have fractures, external trauma, and internal bleeding.

Parasite burdens

Nematodes are often found during post-mortem examination, commonly in the gastro-intestinal tract. However they might not always be associated with disease, many wild animals can cope with a small nematode burden. Judging what number of parasites is compatible with good health requires further research but it is likely that numbers of parasites will increase if the red kite’s immune system is compromised by other diseases. 

Anticoagulant rodenticide poisoning

The red kite is a scavenging species, opportunistic in their prey choice. This feeding behaviour, although valued in the mid-15th century in England and Wales as they kept the streets free of carcasses and rotting food, has become their detriment due to secondary poisoning. Red kites feed on the carcasses of rodents that have died from consuming anticoagulant rodenticide. This secondary poisoning causes internal bleeding; the effects are gradual, developing over several days . In the final phase of the intoxication, the poisoned animal dies from hemorrhagic shock, and the hemorrhage can be observed at gross post-mortem examination. Further testing of the tissues means the concentration and type of poison can also be determined. Once DRAHS receive the carcasses and they undergo a post-mortem examination, tissue samples are collected and sent to external collaborators for toxicology testing. A paper by Molenaar et al (2017), demonstrated that of 110 birds analysed for toxicological analysis, poisoning was diagnosed in 32 red kites, with 19 from second-generation anticoagulant rodenticides, 9 from other pesticides and 6 from lead poisoining . Combining the toxicology results and observations from the post-mortem examinations adds to the narrative on the possible circumstances surrounding their death. 

Close-up photograph of the contents of a red kite's intestines clearly showing a docking ring
A docking ring found in the gizzard of a red kite.

Objects found in the gastro-intestinal tract

The contents of the intestinal tract of red kites is interesting.  A docking ring (used by farmers on lambs) has been found in the intestinal tract of three red kites but in each case the bird was apparently able to survive.  Although docking rings are an effective method to remove the tail of lambs, the shed tails are attractive to scavengers like red kites and the rubber docking ring may be consumed too. Docking rings are small, rubber rings attached onto the tail of the lamb, constricting the blood vessels in the tail and the tail and ring falls off around 2 weeks after attachment.  Considering current concerns regarding waste, plastic and pollutants in the environment this finding is of interest.   Some other interesting findings in the intestine of kites included the foot of a teal, and pre-cut pieces of chicken, presumably provided by a sympathetic human. These discoveries do provide an insight into the prey of red kites. See here for more information on the appropriate way of feeding free-living red kites

Learn more about DRAHS

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