Snakes declining at alarming rate, say scientists
Study suspects sharp reduction in snake numbers in a variety of habitats in five countries is caused by habitat loss and prey.
The widespread disappearance of snakes will be one impact of climate change that some people may find it hard to regret. But as vital predators in sensitive habitats such as rice fields, their decline will have wider ecological consequence, say scientists.
The first major study of the problem, published today, will also be seen as another powerful sign of the worldwide destruction of the natural world, which is causing growing concern about the loss of vital services from rainfall to medicines.
Scientists in five countries across three continents report they found "alarming" declines in snake numbers after monitoring 17 populations in a variety of habitats – something they believe could be part of a global phenomenon.
The paper reports 11 of the population groups "declined sharply", while five remained stable, and one showed a very weak sign of increase. Many of the researchers in the UK, France, Italy, Nigeria and Australia also found evidence of "population crashes" – a sudden decline followed by no sign of recovery – a trend which would make the survivors more vulnerable to being wiped out by further pressures.
"All the declines occurred during the same relatively short period of time and over a wide geographical area that included temperate, Mediterranean and tropical climates," write the authors. "We suggest that, for these reasons alone, there is likely to be a common cause at the root of the declines and that this indicates a more widespread phenomenon."
Although the paper stresses there is no proof of the cause of the losses, the researchers say they "suspect" loss or deterioration of habitats and declining prey are among the main problems faced by snake populations. They believe that all the immediate threats have climate change as a common cause.
"The main importance of these findings is that snakes are top predator within the habitats they are found in and as such play a potentially important role in the functioning of many ecosystems," said Chris Reading of the UK's Centre for Ecology and Hydrology, who led the research. "For example they play an important role in pest control – small rodents [like] rats and mice - in areas such as paddies and sugar cane plantations."
The snake study, published in the Royal Society journal Biology Letters, is the latest in growing number of research papers warning of widespread biodiversity loss in the UK and around the world. The International Union for the Conservation of Nature has said that one third of amphibians and fish, one fifth of mammals and more than one in ten birds is threatened with extinction, and described the rate of loss as one of the great extinctions – the last being the events that wiped out dinosaurs 65m years ago. Natural England, the government's countryside agency, reported in March that on average more than two species are becoming extinct in England every year.
The IUCN said it had not done an analysis of snakes, but based on assessments of nearly one in five reptile species it estimates that 28% are threatened. This figure could reduce in future as vulnerable species are often assessed as a priority.
Researchers tracked the snake populations between 1987 and 2009 by carrying out regular surveys, a method not designed to measure absolute population sizes but relative abundance. The surveys varied in method between sites – from daily reports over several months of the year to monitoring roadkill – but were always the same in each location.
Herpetologists have "suspected" for some time that global populations were in decline, but the paper was the first reliable evidence of the problem, said Reading.
"The problem is that snakes are very difficult to work on and there are very few long-term individual based population studies of them," he added. "If, as a result of our paper we can get herpetologists around the world to analyse their data again then we may start to build a clearer picture of what may be happening to snakes and what the causes of any declines may be. The hope is that through better understanding we might then be able to reverse any declines."
The authors note that six of the eight species showing which "crashed" had small home ranges, sedentary habits and relied on ambushing prey rather than actively seeking it out. "These patterns fit the prediction that 'sit-and-wait foragers may be vulnerable because they rely on sites with specific types of ground cover, and anthropogenic activities disrupt these habitat features, and ambush foraging is associated with a suite of life-history traits that involve low rates of feeding, growth and reproduction'," they add.