Breeding failure in Great Tits and Blue Tits following unprecedented torrential rainfall

The breeding success of Great Tits and Blue Tits using nest boxes at a 12.5-ha site in southwest Scotland has been monitored for 11 years (2014–24). Data collected includes date of first egg laying, clutch size, brood size and brood mass at 11 days old, and fledging success. A short burst of exceedingly heavy rain on a single afternoon in May 2024 resulted in extensive breeding failure: in 2024 there was 49% survival to fledging in Great Tits (n = 7), compared to 74% over the preceding 10 years (n = 40), and 34% in Blue Tits (n = 9) compared to 73% over the preceding 10 years (n = 38), with surviving broods having very low biomass.