Something that happens only rarely occurs ‘once in a blue moon’. ARC's Pool Frog Recovery Project Manager details why this celestial phenomenon is so crucial to the UK's rarest amphibian.

Astronomically, there are two definitions of blue moon, but the most commonly used refer to the second of two full moons occurring in the same month. The next "seasonal" blue moon falls on the 19 August this year (2024). Traditionally some cultures have named full moons marking different times of the year.  A quick Google search reveals that the full moon in August has been named sturgeon moon in North America. Closer to home there is a less well-known herpetological link to this time of year. 

John Morton, in one of the earliest county-based accounts of natural history (1712) wrote about a poddock moon. This was a term used by rural people to describe the warmest part of the year, about four weeks in August. Poddock (sometimes paddock or puddock) is an old English word for a frog or toad. According to Morton’s local folklore, poddock moon described the time of year when the frogs stop calling. To distinguish a period of time on the basis that frogs have gone quiet is odd. The common frog calls sporadically over only a few weeks of breeding activity much earlier in the year.   Its call is relatively quiet - barely audible at any distance from a breeding pond and hardly loud enough to create a subsequently notable silence.  Morton, however, was writing about Northamptonshire where proximity to the former Fens, may have meant that the calling frogs in this case were northern pool frogs.  The northern pool frog was probably never widespread in England but its historic range is understood to have spanned the East Anglian Fens and Brecks. 

References to frogs fitting the description of northern pool frogs in historic literature was one of several lines of evidence that demonstrated the native status of the northern pool frog.  Individually such references are rarely definitive and sometimes unreliable evidence.  And indeed, Morton went on to write about the lack of calling being due to frogs holding their breath over the warmest part of the year, and perhaps even resuming calling as it cools.  None of which makes much sense now.  Nevertheless, a broad review of historic literature can provide useful leads. 

The review carried out by Geoffrey Kelly for the northern pool frog is available online as a report to English Nature.