Bovino vs bovo
I noticed in the course that "bovino" is used for "cow". While that's technically correct, since cows are female cattle, from an Esperanto point of view I believe it to be better to use "bovo" in the course...
Ne sole bovinoj estas mamuloj, virbovoj ankaŭ estas mamuloj! ;)
In Esperanto, the neutral terms such as bovo, koko, hundo, etc. are either masculine or undetermined. To specify female, you add -ino, to specify male, you add vir-.
koko: chicken (or cock)
hundo: dog (or stud)
ĉevalo: horse (or stallion)
ŝafo: sheep (or ram)
I've always found the lack of "masculine suffix" a big issue in Esperanto. Of course the language was created in times when things were just assumed to be masculine unless specified otherwise, but times have changed... Maybe if Duolingo popularises Esperanto enough, there could be a language reform? For example, to introduce -iĥo as masculine suffix, so that unspecified actually means unspecified? You could then also get rid of ge-
but how do you say "parent"? You can't. Gepatro is not correct because ge- only works with plurals.
patro: parent (unspecified gender)
patroj: parents (unspecified gender)
gepatroj: parents (specifically both fathers and mothers)
Oh well... One can always dream, I guess! :D
If one sees a herd of cows, they're usually female. I mean occasionally you'll see a bull on its own or maybe a group of bullocks, but if you're talking about individual animals, 'cow' generally means either it's of indeterminate sex or it's female. Bovino seems much more appropriate.
Following that logic, chickens should be "kokinoj" and sheep should be "ŝafinoj", since the domesticated animals of those kinds that one sees are predominantly female as well.
It seems that the choice for "bovino" instead of "bovo" for "cow" is mostly based on the fact that the English word "cow" is also actually the female animal, while "chicken" and "sheep" are gender-unspecified, even though in Esperanto there's no need or even logic to go for that choice.
I think the animals lesson is one I skipped in the placement test, so I don't have an opinion as regards the Duolingo course, but if I saw a group of chickens or sheep I'd call them kokinoj or ŝafinoj. Though I am only a relative beginner.
(Far from the only language where some animals are commonly referred to by one gender or the other, and the standard isn't always male.)