As well as being the smallest British bird, the goldcrest has the distinction of being one of the lightest birds anywhere in the world to make regular sea crossings as part of an annual migration. For a bird that weighs roughly the same as a twenty pence piece (about 5.3 grams) such movements are truly remarkable. In some years, bushes and hedgerows at east coast sites may be literally ‘dripping’ with exhausted goldcrests during autumn. These are birds that must operate very close to their physiological limits. Information generated from bird ringing schemes, operating across Europe, has revealed that goldcrests breeding in the northernmost boreal forests are almost completely migratory in their behaviour. Birds from breeding populations situated further south are more likely to remain where they are to overwinter. Some coastal populations on the edge of the Arctic Circle in Norway also remain close to their breeding grounds in winter. By doing so, they have to cope with severe cold and nights that are 18 hours long. It has been calculated that these birds may burn off a fifth of their body weight each night, just to maintain their body temperature at a safe operating level!
This autumn has seen very large numbers of these tiny birds arriving on our shores. Even though the main arrival took place in the second half of October, and was centred on the Yorkshire and Lincolnshire coast, there still appear to be good numbers within East Anglia. Most mornings, while exercising my overly energetic spaniels in Thetford Forest, I encounter goldcrests foraging among the conifers. As if to reinforce the origins of some of these birds, I received a report last week of one individual caught within a mile or so of Thetford which sported a Norwegian ring. One wonders where the individuals I had seen at Happisburgh were from.