The British spring is a fickle season. We can experience floods and droughts, snow and rain, heatwaves and cold snaps. So, imagine how the range of different weather patterns in spring can affect migrant birds, many of which have made the epic journey from sub-Saharan Africa to be here.
Some years are worse than others. The spring of 1991 was one of the coldest on record, with a damp westerly or cold northerly airflows across the UK for almost all of April and much of May, and a cold, wet and dull June.
During adverse weather conditions, migrants such as swallows and warblers will often stay put on the other side of the Channel, waiting for the situation to change. But doing so has its risks: birds that arrive back later than usual may struggle to find a mate or nest site; and even if they do, then face a race against time to raise a family.
That year, however, they were right to be cautious. The start of April saw a run of deep depressions bringing high winds and torrential rain, followed by cold Arctic air from mid-April onwards.
Fortunately, a window of better weather at the end of April, with a run of easterly winds, allowed most migrants to cross the Channel, albeit two or three weeks later than normal.
• The picture on this piece was changed on 19 May 2023. The original picture showed a dusky warbler, which does not migrate from Africa to Britain.
