Like Two Peas In A Pod

Hard to resist the bluebirds at the moment, they are so obliging in posing for me. Although I'm not in favour of supplying mealworms for them to eat, I would rather they forage for themselves, I understand the desire to encourage their numbers to grow (population, not size).

I wanted to call this one "Like Father, Like Son", but I'd already used that title.

Extra: Essence. With a focus on 'S'.