Wild birds dying from vitamin deficiency
A Swedish study has shown that large numbers of wild birds in the Baltic Sea area are dying from a paralytic disease caused by deficiency of thiamine, commonly known as vitamin B1. The findings, published in the Proceedings of the National Academy of Sciences (PNAS), demonstrate that the B1 deficiency is causing breeding failure as well as many other altered behaviour patterns in a number of species.
Thiamine is essential for birds and other vertebrates. Lack of thiamine can lead to neurodegenerative diseases, loss of sensation, paralysis and death. It is particularly important for the proper functioning of the nerves.
The researchers examined wild birds around the Baltic Sea and in Iceland and demonstrated that there is a connection between the paralysis observed in many of the wild birds in these areas and thiamine deficiency. They analysed the geographical spread of the deficiency and the number of species affected, and found that advanced thiamine deficiency was occurring in birds around the Baltic Sea, and that incipient thiamine deficiency was threatening bird populations in Iceland.
The research team, led by Professor Lennart Balk of Stockholm University, noted that thiamine deficiency in the birds showed in their eggs, liver and brains. They also found higher numbers of relevant enzymes than usual in the birds' liver and brains, but observed a lack of thiamine cofactor, a compound essential for these enzymes to function properly.
The effects of thiamine deficiency are manifested in different ways, the authors explained. Paralysis was observed in 78% of the wild birds, and in some species, such as herring gulls, it is causing a reduction in egg production. Females of some species are not producing eggs at all, and some are producing eggs that have no thiamine in them. These variations suggest that the birds are suffering from differing levels of thiamine deficiency.
The team also observed altered behaviour: less aggressive behaviour than normal was seen in wild birds, reduced noise in herring-gull colonies and incomplete nest building in several species. The research also suggests a link with avian influenza, as it is possible that this disease may spread more quickly among wild birds with low thiamine levels.
The researchers believe that the higher mortality rates and breeding failures of wild birds in the Baltic area are part of a widespread thiamine deficiency syndrome that has probably contributed to an overall decline in wild bird populations in the past decades.
Previous observations of paralysis, high premature death levels and breeding failure in recent decades have been attributed to lack of food. But the new study shows that thiamine deficiency may be the more specific cause, as it leads to starvation by suppressing appetite. The authors suggest that in fact lack of food alone does not cause thiamine deficiency in birds; rather, the deficiency may be caused by a direct agent affecting levels of thiamine in the birds or by insufficient thiamine levels being transmitted to the birds through the food chain.
The researchers stress that further research is needed to pinpoint the causes of thiamine deficiency in wild birds, and also to ascertain whether other forms of wildlife are being affected in the same way.
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Data Source Provider: Stockholm University; Swedish Research Council; Proceedings of the National Academy of Sciences
Document Reference: Balk L., et al. (2009) Wild birds of declining European species are dying from a thiamine deficiency syndrome. Proceedings of the National Academy of Sciences, USA (in press). Published online 13 July; DOI: 10.1073/pnas.0902903106.
Subject Index: Life Sciences; Scientific Research; Veterinary and animal sciences