Data from: Facultative migration in two thrush species (Fieldfare and Redwing): rowanberry abundance more important than winter weather.

Description of data table on fieldfare and redwing

Columns included are:

Time period/Year: E.g. 80 = 1980-81 = December 1980-February 1981

Fieldfare (Turdus pilaris) individuals/redwing (T. iliacus) individuals: number of individuals reported to the National Biodiversity Information Centre in Norway (www.artsobservasjoner.no) for each time period (December-February) and for each region of Norway (eastern Norway and western Norway; see paper for detailed explanation of each region).

Bird records: Total number of records of all bird species reported to artsobservasjoner.no for each time period and for each region. One record contains an observation of one or more individuals of one species at one site at one date. Total number of records was considered to reflect observation effort.

Fieldfare index/redwing index: The ratio of number of individuals of fieldfare or redwing to total number of bird records.

Fieldfare index/redwing index (log): Log (x) for fieldfare and log (x + 0.0001) for redwing.

Rowanberry index: Annual index of rowanberry flowers based on the "Varsling innen PlanteSkadegjørere" project (VIPS, see www.vips-landbruk.no/applefruitmoth/) run by the Norwegian Institute of Bioeconomy Research (NIBIO) and Norsk Landbruksrådgivning (the Norwegian Agricultural Extension Office). See paper for details of calculations.

NAO indices: monthly values for November-January and mean of November-January based on data from the National Weather Service in the US (www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml).

Temp (Temperature) indices: monthly values for November-January and mean of November-January based on data from the Norwegian Meteorological Institute (www.yr.no).

Snow: Total number of days with snowcover (≥ 1 cm) for each month during November-January and the sum across the three months based on data from the Norwegian Meteorological Institute (www.yr.no).