There's a robin outside our window that's building a nest in one of the trees outside. It's fun to watch it bring each piece - first some paper, then some grass, and then some bits of string - and arrange it all to make a little nest. The paper is still flapping and in danger of blowing away! The cats next door will be very pleased if baby robins are born in the nest. They're indoor cats but I don't think that matters when it comes to cats chasing birds :)
I love watching the leaves come out, the flowers bloom, and now the bird making its nest. Even the colour of the light is different throughout the day as it's filtered through the budding trees (and very little pollution). Spring brings new life and renewal and that's why it's just about the best time of year for this reason, I think.
BTW I want to reassure you that while I do get sad about my dad sometimes, I'm not sad all the time. I've been pretty happy overall, in fact - but it is important for me to share the feelings I have about my dad and his passing.