Information of the variables in "egg_data.csv":

sample_ID: a unique ID for each sample
egg: egg ID
species: species name
subspecies: subspecies name
new_latin_name: updated scientific name for some species
name: common name
city: the city/municipality where the egg was collected
T4_yolk: yolk thyroxine concentration (pg/mg yolk)
T3_yolk: yolk triiodothyronine concentration (pg/mg yolk)
batch: an ID of the batch of extraction
T4_recovery: recovery (i.e. extraction efficiency) of yolk T4
T4_total: total amounts of thyroxine in the yolk (ng/yolk)
T3_total: total amounts of triiodothyronine in the yolk (ng/yolk)
notes: additional notes