According to the internet, ‘one swallow does not a summer make’ is a quote that can be attributed to Aristotle. The connection between summer and swallows is clearly a longstanding one. British swallows winter in South Africa. Or, arguably, South African swallows come to the UK to breed. There are many other birds whose migration to the UK at this time of year is part of the coming of summer.
Swifts, swallows and house martins aren’t always easy to tell apart in flight, and at twilight when they hunt for insects, telling them apart from bats can also be tricky. It’s the way the hunter is obliged to follow their prey through the air that means insect eating birds and bats are similar. There’s a rather (accidentally) amusing poem by D.H. Lawrence in which the poet is rather upset that his birds turn out to be bats. You can read that here - https://www.poetryfoundation.org/poems/44574/bat
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