Field sampling
To document the morphology and diet of black wheatears we carried out
captures throughout the study area, during the entire breeding season
from April to August of 2014 to 2016, using spring traps baited with
mealworms (Tenebrio molitor ). Birds were removed from the traps
immediately after being captured, placed in a cotton bag, and afterwards
ringed and measured. Birds were retained for less than 15 minutes and
all procedures were made with the required permits from national
authorities. We made a total of 143 captures, but for this study we only
considered the first capture of adult individuals, i.e.
2nd calendar year or more identified following
Svensson (1992), totalling 110 adult black wheatears, 79 males and 31
females. For each individual, a number of morphometric measures were
taken following Svensson (1992): maximum cord wing length;
3rd primary length; tail length; tarsus length; bill
length, depth and width at the distal edge of the nostril; and body
mass. Wing, 3rd primary and tail were measured using a
ruler to the nearest 0.5 mm, tarsus and bill measurements were made with
a calliper to the nearest 0.1 mm, and body mass with a digital balance
to the nearest 0.1g. All measures were taken by LPS and when feathers
were not fully developed (i.e. moulting birds) the measurements affected
were not recorded (Table S1).
Droppings for molecular analysis were collected from bird handling bags,
or directly from small rocks used to disguise the bottom of the spring
traps (McInnes et al., 2017; Oehm, Juen, Nagiller, Neuhauser, &
Traugott, 2011). Bags were soaked in 10% bleach for 1 hour and then
washed between each use to minimize contamination. From the 93 droppings
thus collected, 62 from males and 31 from females, three were obtained
from birds that defecated inside the traps but were not captured.
Droppings were stored in 2ml tubes with 98% ethanol at 4ÂșC until
laboratory analysis (da Silva et al., 2019a).