I'm a birdwatcher, but now seriously into dragonflies and a bit into butterflies, though it is frustrating how many of the former (damselflies) are very small and striped blue and black and how many of the latter in Britain are basically brown and orange.
Birds are residents or migrants. Migrants can be passing through or coming to stay. Their arrival and leaving dates are affected by the weather, but for example, by the late April the first clear night with winds from the south should bring some Whitethroats and although the odd bird may arrive very early, in Southern England you listen for the first Cuckoo around 20th April. However, typically you get a few of any species, then some more, with the main arrival two or three weeks after the first pathfinders.
Butterflies and dragonflies also work to a timetable, but it can be much stricter. A few are migrants or vagrants, but for most, when they appear, they've just emerged from chrysalis (butterfly) or straight from the larva (dragonflies). I'm describing the situation in temperate climes, of course: near the equator dragonfly slecies can be around all year.
Two weeks ago as I walked Essex and Suffolk footpaths, suddenly there were lots of Gatekeeper butterflies, small, quite brightly-patterned red-orange and brown butterflies often found in numbers around bramble bushes. Yesterday, suddenly around marshes, there were lots of restless, red, small dragonflies called Common Darters. If I'd picked the right two days, I'd have drawn a blank on the first and seen numbers the next. The Common Darters will be around in declining numbers into late October or even November.
I love the seasons.