Surfbirds News

Starling © Major Gilbert, from the surfbirds galleries

Why should urban populations of a particular species arrive later after dawn than their rural counterparts? Interestingly, there are a number of factors which may operate differently between the two habitats. Urban areas are well known for the degree of light pollution associated with them, in the form of street and security lighting. If this light pollution was influencing the urban populations then you would expect to see earlier emergence in urban areas rather than later emergence. Another factor operating in urban areas is heat pollution, with waste heat escaping from factories, residential properties and other buildings. This waste heat can increase the temperature in urban areas by as much as 8°C, particularly in our larger cities, creating what is known as an ‘urban heat island effect’. With higher overnight temperatures in urban areas, it seems likely that small birds roosting in these areas would need to use a smaller amount of their fat reserves than would be the case for birds roosting within the wider countryside. With fewer reserves lost overnight, urban populations could afford to be more leisurely come the morning, the need to replenish reserves less urgent than for birds that had spent a colder night elsewhere.