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The colloquial British-English expression Cambridgeshire nightingale designates the edible frog, Rana esculenta.
This expression occurs, for example, in the following from Riveting bygones exhibition in Frog End, published in the Hertfordshire Mercury (Royston, Hertfordshire, England) of Friday 20th May 1994 [page 3, column 4]:
A chance to view exhibits from a bygone age is being offered by Shepreth resident Margaret Collins at her home in Frog End on Sunday.
[…]
[…] Mrs Collins, whose family has worked as farmers and farm labourers for several generations […,] has vivid memories of her childhood in Frog End, which is named after a species of edible frog, the Cambridgeshire nightingale, whose warble could be heard by residents across the village.
The expression Cambridgeshire nightingale refers:
– to Cambridgeshire, a county of eastern England;
– to the frog’s nocturnal croaking.
—Cf. also, the colloquial expression Dutch nightingale, designating any of various species of frog producing a call or song.
These are, in chronological order, the earliest occurrences of the expression Cambridgeshire nightingale that I have found:
—Note: Cambridgeshire nightingale often occurs in association with the synonymous expression Whaddon organ (in reference to a village in Cambridgeshire):
1-: From Note on the British specimens of the Edible Frog, dated Saturday 14th September 1844, by the British naturalist Thomas Bell (1792-1880), published in The Zoologist: A Popular Miscellany of Natural History (London, England) for 1844 [page 727]—the present-day name of the village in Cambridgeshire is Fowlmere:
I have received […] some specimens of frogs from Foulmire, in Cambridgeshire, which I am enabled to designate positively as the true Rana esculenta. […] The Rana esculenta may be at once distinguished from R. temporaria [the common frog of Britain], by the absence of the large, distinct black mark […]. There is a remarkable difference in the croaking of our two species—that of R. esculenta being so loud and shrill, as to have obtained for these frogs the name of “Cambridgeshire nightingales,” and “Whaddon organs!”
2-: From The Fens of England, published in the Friends’ Intelligencer (Philadelphia, Pennsylvania, USA) of Saturday 17th February 1855 [Vol, 11, No. 48, page 768, column 1]:
The edible frog, also, which is very seldom met with in England, was once common in Foulmire Fen Combs, and is still said to exist there. From the musical croak, these frogs were called by the natives ‘Cambridgeshire nightingales’ and ‘Whaddon organs’—the latter, from the name of a spot where they peculiarly abounded.
3-: From an account of a lecture on reptiles that “Mr. Miller, master of the boy’s British school, gave […] at the Public Hall, to the members of the Mechanic’s Institute”, published in the Cambridge Chronicle and University Journal, Isle of Ely Herald, and Huntingdonshire Gazette (Cambridge, Cambridgeshire, England) of Saturday 1st March 1856 [page 6, column 6]:
The edible frog so well known in France is also an inhabitant of this country and was first discovered here by Mr. C. Thurnall, of Duxford, in Foulmire Fen, in Cambridgeshire, in September, 1843, and is called the “Cambridgeshire Nightingale” from its peculiar croaking noise.
There have been synonymous British-English expressions, with reference to other place-names. The following, for example, is from The Vertebrate Fauna of Cheshire and Liverpool Bay (London: Witherby & Co., 1910), by the British naturalist Thomas Alfred Coward (1867-1933) [Vol. 2: The Reptiles and Amphibians of Cheshire: Natterjack Toad, page 13]:
The croak of the Natterjack is loud and continuous, sounding from a distance something like the “churr” of the Nightjar; on the Lancashire coast the Toads are known as “Bootle Organs” on the north side of Liverpool, and as “Southport Nightingales” in the neighbourhood of that town, but we have not heard any similar local name in Cheshire.
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