I have often wondered what is the difference between Swallows and Martins. I am sure there are plenty of knowlegeable birders out there who can explain
One of the problems that face people who take up birdwatching is that everyday names for birds may originate long before any attempt was made to classify them in some sort of orderly arrangement. A bird species' scientific name arises from such formal classification attempts since the 18th century.
Everyday names are described as common names, but these may, or may not, refer to the differences that formal scientific names have established as family, genus, species or subspecies. This irregularity is the reason that excellent questions like yours arise! The UK Sand Martin is the same species as the US Bank Swallow, which is an example the terms Martin and Swallow being used interchangeably, whereas they share not only the same species' scientific name
Riparia riparia, but are also the same subspecies
R.r. riparia!** (there are three other subspecies, two
taczanowskii, ijimae in E Asia and one,
shelleyi in Egypt).
All swallows and martins come under the scientific Family name of Hirundinidae. In general, just over half of the 90 or so species in that family have 'swallow' as part of their English name, but a few in the African genus
Psalidoprocne have neither 'swallow' or 'martin' in it, being termed 'Saw-wings'. If you thought that it is complicated so far, there is more! The main ornithological authorities that list the world's bird species don't necessarily agree the number of Hirundine species nor do they yet agree on common, or shared English names, but progress is being made in that direction. It is likely that a number of species will be split, but so far, not all authorities have yet got round to agreeing that either, but to be fair, the total number of bird species they have listed is around the 10,000 mark.
If you are mainly interested in European bird species, then you have five species that essentially occur north of the Mediterranean, and two that occur just south of it, and so you can remain securely with, for example, the Collins Bird Guide, for the English names of swallows and martins!
MJB
PS Another term for 'common name' in scientific circles is 'trivial name', but since to most people that usage seems a little insulting, it has largely fallen into disuse. However, to 19th-century researchers whose common ground with others whose first language was not English was a knowledge of Latin and Greek from which birds' scientific names were derived, the word 'trivial' meant that any common name in any language was inconsequential in correspondence and in formal publication of descriptions of species.
** It is quite unusual for a breeding species that occurs in North America and across Europe (and good bit further east) to belong to the same subspecies. Most species that share this pattern have subspecies that have evolved in noticeably different ways.