I was kinda worked up thinking that the background animals on page 2 might be referring to their zodiac animals, since the represented zodiacs are exactly 5 years apart each, consistent with their age differences.
However, after further calculation I was disappointed to find out that they are each off by 2 years, assuming Sakurako being 13 when Yuru Yuri first serialized in 2008.
So, the Sakurako chicken is probably a pajama reference after all.