One Swallow Doesn't Make a Spring (Or Any Other Season)?

Swallows generally fly into the UK in Spring, feed up on flying insects and raise several broods of young. in September, they normally gather and migrate back to South Africa to over-winter. The migration is arduous and the birds have to feed on flies etc as they fly. There are many casualties en route. Changing weather patterens have caused these birds to arrive much earlier than 50 years ago. It has also been noted that some 'stragglers' are now starting their migrations much later in October. There is now a report of a Swallow that has remained in the UK in November (https://www.theguardian.com/environment/2020/nov/22/one-little-straggler-the-swallow-that-didnt-fly-south-for-the-winter). I don't think that that this represents a trend towards ceasing the migration and staying in the UK. The chances of any Swallow surviving a winter here, without flying insects on which to feed, is extremely remote. Single birds, starting a very late exodus, would also be doomed. Swallow populations are declining and the currently very variable weather patterns appear to be one potential cause.