Are wader chicks a potential victim of tick attack?

A new study by the Game & Wildlife Conservation Trust and published in the latest edition of the BTO science journal Bird Study has been investigating whether threatened populations of moorland wader bird chicks are victims of ticks and tick-borne diseases.

This one-year pilot study confirmed fears that curlew chicks are indeed vulnerable to tick infestation with more than 90 per cent of broods carrying ticks. The study particularly highlights the need to carry out more detailed research in other moorland areas to identify whether these rapidly declining wader species are susceptible to life-threatening tick-borne diseases.

Recent studies have shown that tick populations have increased dramatically in recent years and this is creating problems for not just humans but many wildlife species too.  Wildlife in particular are either succumbing to diseases transmitted by these blood-sucking parasites or they are simply dying through the impact of ‘tick worry’ caused by the sheer number of ticks feeding upon one host.

The study was carried out on upland heather moorland in the North York Moors, which has internationally important numbers of several declining species, including golden plover, curlew and lapwing.  It is therefore important to identify whether these vulnerable species could be under further threat from ticks and the diseases that they carry.

Of particular concern in this study was whether sheep ticks were infecting the wader birds with diseases such as the louping ill virus.  Louping ill has been recorded for more than 200 years in Britain and is traditionally considered a disease of sheep, although other domestic and wild animals such as cattle, horses, pigs, goats, dogs and red grouse can be infected too with dire consequences. In humans the bite of an infected tick can transmit  a protozoan (a single cell organism)  causing Lyme disease, which is an extremely debilitating illness that can last for many years.

Since the early 1980s the Game & Wildlife Conservation Trust has been studying the impact of sheep ticks and the disease louping ill on red grouse in Scotland.  Research has shown that this serious viral disease can kill up to 80% of red grouse chicks infected.  Worryingly, the Trust’s research has identified that ticks are on the increase due to the growth in host numbers such as red deer and it is thought that warmer winters could also trigger increased tick activity, for example in 1985 around four per cent of grouse chicks encountered by Trust researchers had ticks, but by 2003 the figure had risen to 92 per cent in Scotland.

Although it is evident that red grouse are seriously affected by louping ill virus infections it is not known whether other ground-nesting birds and their chicks are affected by high tick numbers or if they are susceptible to tick-borne diseases. 

The study found curlew chicks had the highest tick infestations, with more than 90 per cent of broods carrying ticks. The lowest incidence of ticks among waders was in lapwing with 6 per cent of broods carrying ticks, while the study identified that 47 per cent of golden plover broods had tick infestations.

Dave Newborn, a senior scientist with the Game & Wildlife Conservation Trust said, “The North York Moors National Park provides essential breeding habitats for nationally important numbers of wader birds.  Previous research shows that tick-borne diseases such as louping ill can reduce the breeding success of red grouse, so it is possible that nesting wader birds sharing the same habitat might also be susceptible to ticks and their diseases.  Historically, we have found louping ill in wader chicks, but do not know how wide-spread this might be.”

This study was conducted on estates where a successful scheme of treating sheep with tick-killing pesticides (acaricides) plus the use of vaccines against louping ill has been undertaken by graziers to reduce tick abundance and the diseases they transmit.  The tick problem would have been far worse if estates had not treated the sheep to protect the grouse populations.

Dave Newborn explains, “We found wader chicks as young as three weeks old with heavy tick burdens, indeed some chicks had in excess of 60 ticks, which caused blindness and thus reduced body condition.  However, the body condition of the majority of chicks in this study did not appear to be affected.  We suspect that this is because active acaricide treatment of the sheep to kill ticks was occurring to benefit the grouse population and thus benefiting the wader chicks. 

“However, it was recently reported that no wader chicks have fledged on a moor in the Bowland fells this year and this could be a result of tick attack.  As waders also breed on upland moorland areas with less or no tick management, we feel that it is vital to repeat this study in areas with higher tick densities in order to identify the severity of the problem, particularly as this study demonstrates that wader chicks are used as hosts by sheep ticks.”

END

Photo-caption: A new study by the Game & Wildlife Conservation Trust and published in the latest edition of the BTO science journal Bird Study has been investigating whether threatened populations of moorland wader bird chicks are victims of ticks and tick-borne diseases.

Notes to editors

This work was part of a project funded by North York Moors National Park Authority and local moor owners.

The Game & Wildlife Conservation Trust is an independent wildlife conservation charity which carries out scientific research into Britain’s game and wildlife. We advise farmers and landowners on improving wildlife habitats and we lobby for agricultural and conservation policies based on science. We employ 14 post-doctoral scientists and 50 other research staff with expertise in areas such as birds, insects, mammals, farming and statistics.  We undertake our own research as well as projects funded by contract and grant-aid from Government and private bodies.   The Trust is also responsible for a number of Government Biodiversity Action Plan species and is lead partner for grey partridge and joint lead partner for brown hare and black grouse.

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