Resident species
Resident birds are those that spend all year in Wales, such as Robins, Blackbirds, Song Thrushes and Wrens, although their numbers are boosted by European and Scandinavian birds during the winter months.
Generally the season which brings most mortality is winter. Cold temperatures, long periods of frost and a lack of food, all have a major effect on survival rates.
Climate change, bringing warmer winters and shorter periods of frost, should in theory, mean reduced winter mortality and an increase in the breeding population.
The BTO runs several surveys, one of which is the Breeding Bird Survey (BBS). This survey uses standard techniques throughout the country and can therefore let scientists compare populations across the UK and produce indices on population changes in the UK and for smaller geographical areas – such as Wales and even individual counties.
