４月に孵化した雛も５ヶ月になった。身体の大きさは親鳥とほぼ同じ、オス鳥のとさかが少し小さいぐらいか。

。、。

The chick that hatched in April is now five months old. It's about the same size as its parents — if anything, the male's crest is a little smaller.

Literal

April [locative-に] hatched chick [also-も] 5-months became. Body [possessive-の] size [topic-は] parent-bird [with-と] nearly same, male-bird [possessive-の] comb [subject-が] a-bit smaller [wondering-ぐらいか].

A diary/observation-style sentence, probably about a chicken or similar bird. Note the relative clause 4月に孵化した雛 ('the chick that hatched in April') modifying 雛 — Japanese places the full modifying clause before the noun, without any relativizer word. ~ぐらいか at the end expresses self-directed musing ('maybe about that much?'), as if the observer is still deciding. The particle も after 雛 ('even the chick has become 5 months') carries a sense of 'already this much time has passed'.