Capture, sampling, and measurements
All species except wheatears were caught using funnel traps. Wheatears
were caught using mealworm baited spring traps. Blood was collected from
the wing vein using Na- heparinized microcapillaries. All birds were
bled within 10 minutes of capture (range= 1-9.30 minutes, mean= 8.09
minutes), and hence before any expected impacts of handling stress on
immune parameters (Zylerberg et al. 2005). The plasma was separated from
the blood by centrifugation within 20 minutes of sampling for species
caught in funnel traps, and within 2 hours of sampling for the
wheatears. The plasma was stored at -20 °C during the field season and
at -50 °C later on.
The birds were ringed and measured after blood sampling. Body mass was
measured to nearest
0.1g. Fat score was estimated on a scale of 0 (no fat) to 8 (furcular
and abdomen bulging, and
breast covered with fat) based on methods described by Kaiser (1993).
Muscle score was estimated on a scale of 0 (sharp sternum, muscles
depressed) to 3 (sternum difficult to distinguish due to rounded
muscles) based on methods described by Bairlein (1994). All the
measurements were consistently carried out by a single person. The sex
of the birds was determined based on the plumage for Wheatears and
Chaffinch, and molecular sexing was performed for Song thrush and
Dunnock. All procedures were approved by the Ministry of Energy,
Agriculture, the Environment, Nature and Digitalization,
Schleswig-Holstein, Germany (permit number V 242-37068/2016).