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Is lead shot killing wild grey chicks?

Research has found that because they mistake lead shot for essential grit, grey partridges are dying of lead poisoning, says Conor O’Gorman.

Wild grey partridge chicks face many challenges from the moment they hatch. They start out the size of bumblebees and, with lemming-like tendencies, the parents have their hands full getting their offspring through the critical first few weeks. 

We all know the story of the English partridge and how their numbers have plummeted in Britain since the 1950s, largely due to the loss of key invertebrates in farmland habitats for the chicks to eat. It seems obvious now that the ubiquitous postwar use of herbicides and insecticides was having a detrimental impact on a range of bird species, including the grey partridge. 

From the 1960s onwards the Game Research Association and subsequently the Game Conservancy — now GWCT — started investigating the environmental impact of herbicides and insecticides, with a sustainable harvest of quarry species in mind. Such research results were controversial for the farming community and agro-chemical companies. Denial was, understandably, the first line of defence. 

We now know from many decades of research that there are three key ingredients we can provide for wild greys to thrive: nesting cover, brood-rearing cover and predator control — the “three-legged stool”. 

There are two things that we cannot control, which can make or break the local wild grey population despite all our conservation efforts. They are excessive rainfall and below-average temperatures during the peak chick hatching period — typically June in England. However, there has long been an elephant in the room, and that is the impact of lead shot. 

Unfortunately, grey partridges are among a range of bird species susceptible to lead shot poisoning. The evidence has been growing since the 1870s and it is now conclusive: partridges, young and old, need to eat grit to aid digestion and they will eat shot, mistaking it for grit. The lead shot grinds in their acidic gizzards, toxic lead salts are absorbed into the bloodstream and find their way into the tissues of vital organs. Death for many birds occurs in a few days or weeks, and for those that survive their behaviour, resistance to diseases, mobility and ability to breed are affected. 

Detailed data on every aspect of partridge biology and ecology has been gathered by generations of British game biologists, with more than 1,300 postmortems on record for wild grey partridge adults and chicks found dead on shooting estates in the UK. 

The evidence on lead shot was hidden away in the archives until 2005 when the late Dr Dick Potts — director-general of the Game Conservancy from 1993 to 2001 — published a paper on the incidence of lead shot in wild grey partridges. The findings were stark. 

Dead chicks with up to 26 pieces of lead shot in their gizzard were among the data sets, and it was typical to find that the lead shot found had been eroded in half. Most of these chicks were in the first few weeks of life. That is a massive lead dose. 

Dying chicks 

Based on all this postmortem data, the incidence of lead shot ingestion in grey partridge chicks was 6.9% +/- 4.7%. That’s on average one or two chicks per brood ingesting lead shot and probably dying as a result. 

The chick survival rate is, of course, critical to partridge population growth or decline. GWCT research in the British Isles has shown that the knife edge is 32% — above that the population increases, below that figure and the population decreases. So if lead shot is reducing the chick survival rate by even 2%, let alone 10%, that is a significant controllable risk. 

I am not saying that chicks eating lead shot is a primary reason for the decline of wild greys in the UK. Without shooting interests keeping the remaining pockets of wild grey populations going, they would be long extinct as a British breeding bird. 

What I’m suggesting is that lead shot is likely stifling our conservation efforts. Perhaps we need to consider a fourth leg for that three-legged stool by moving away from lead shot where we can?