Evolving a pokemon will almost always give it more CP. So, when you evolve your pidgey to pidgeotto, it will have more than 61 CP and be stronger than your current pidgeotto. If you're looking to have a pidgeot as strong as possible, evolve the pidgey twice rather than the pidgeotto once.
As you level up, you will come up with pidgeys much stronger than 61 CP, so you may still want to replace that pidgeot later by evolving a stronger pidgey or pidgeotto.
ETA: Looking at this CP table, your pidgey is probably on level 4-4.5 and will have 184-250 CP when evolved all the way to pidgeot. Your pidgeotto is only on level 1, and would only have 24-29 CP if evolved to pidgeot.
ETA2: There are a few species of pokemon that lose CP when evolved. These are mostly bug pokemons evolved from caterpillar form to cocoon form.