Post-hatching changes in brain mass were investigated in mallards and four
stocks of domesticated ducks, using growth curve analysis and allometry. Th
e birds varied in age between hatching and 154 days. Percentage brain size
at hatching in ducks varies between 22.5% and 28% which fits well into the
precocial category. Brain growth shows a sigmoid course. The point of infle
ction is very early when compared to other organs. However, growth is slow
after passing the growth rate maximum. Pekins show higher absolute brain ma
sses than mallards. However, the growth patterns with respect to time are v
ery similar among stocks. Strongly negative allometry is found with allomet
ric exponents between 0.31 and 0.37 with the highest value in mallards. All
ometrically, there is an increasing reduction of brain mass in Pekins when
compared to mallards to about 12.5% in adults. No differences were found be
tween mallards and either Muscovies or the Muscovy x Pekin cross. The reduc
tion in relative brain size in domesticated animals when compared to their
wild ancestors is generally attributed to a decrease in functional demands
resulting from the artificial environment. Because brain growth is more con
servative and less influenced by selection than body weight, we assume that
this reduction is, at least in part, a result of the constancy of brain gr
owth patterns.