Experts believe that storms and severe weather in North America and Asia have disrupted bird flight paths across the world and swept huge numbers of bird species towards the British Isles. Birds flying to the other side of the Atlantic or to the Pacific to lay their eggs have been trapped in Britain and Ireland, adding their numbers to native species, and causing great excitement in the bird-watching community. Local birdwatchers have already observed a total of 442 species in the British Isles this year. The highest number ever seen in one year is 445, in 2008. "We only need four more to break our record," said Lee Evans, who runs the British Birding Association. "With three months to go I'm sure we'll do it." Last month an extremely rare Siberian Rubythroat bird was seen in Scotland, sending hundreds of birdwatchers north in the hope of catching a glimpse of this colourful Asian beauty. Another very uncommon bird, the bufflehead duck was cited in Cornwell and caused similar excitement. "I couldn't believe it," said Evans. "The poor thing was completely  _ . It must have been blown to England by the storms while trying to fly from Canada to the southern United States for the winter. That's 3000 miles!" Evans said that global warming over the past decade was playing a key role in transforming bird movements across the world. In addition, melting Arctic sea ice may also be opening up bird flight paths over the North Pole, making it easier for birds from the Pacific -- such as the slaty-backed gull and tufted puffin, both of which appeared in London earlier this year -- to reach Britain. Bird-watching is becoming an increasingly popular hobby among all age groups, added Evans. "A fifth of our members are under 18. This is a round-the-year hobby that you can enjoy from the kitchen window or from a car. More and more people are bird-watching, and as a result more and more unexpected species are being spotted in the British Isles." Which of the following is NOT mentioned as a possible reason for seeing more bird species in Britain?
An increase in the number of birdwatchers. A growth in the number of native species. Storms due to global warming. The melting Arctic ice cap.