Having 3 Belugas does not guarantee at least one male and one female whereas pidgeons multiply just by hanging out on my neighbor's roof.
indeed, but then it would depend on what armor the belugas have equipped. Perhaps a Pidgeon Deflector, which protects from beak attacks? It also depends on the pidgeons magic defense, since we all know belugas are heavy magic users. Which brings up the question- do the belugas have any Royal Syrup, Ethers, Elixirs, or other MP/FP recovering items? You gotta look at all sides. Also, let's not forget their level. Obviously, the pidgeons are lower then level 36, otherwise they will have evolved into gibbons. The same holds true for Belugas, at level 42, they evolve into white walruses while losing all magical abilities in favour of physical attacks with their "tusk" weapon.
Let's not forget that three belugas can perform the powerful "triple beluga slam" attack, as well as a "Delta Belugite" attack. On the other hand, if the pidgeons can multiply to 6 members before the belugas fill up their battle meter, they could perform their "triple shooter" fece attack, which will reduce the belugas magic attack just enough to allow the pidgeons to grow some grain.