Laudator Temporis Acti

Michael A. Steele and John L. Koprowski, North American Tree Squirrels (Washington: Smithsonian Books, 2001), p. 67:

Perhaps best known for their mastery of food-hoarding are the territorial pine squirrels (i.e., red and Douglas' squirrels). Common denizens of the conifer forests of Canada and the western and northern United States (Steele 1998, 1999), these small but highly aggressive and vocal squirrels store huge quantities of conifer cones that they vigorously defend against competitors (Gurnell 1987; Steele 1998, 1999). Such extensive hoards (or middens as they are sometimes called), easily recognized by their conspicuous piles of cone cores and bracts under which new cones are placed, provide a cool moist environment that is ideal for the storage of cones (C.Smith 1965, 1968). Most middens contain enough food to last one to two seasons, and they are often passed on through several generations of squirrels (Gurnell 1984; Lair 1985).

This is a somewhat unusual use of the word midden. I would have expected it to apply only to the pile of discarded cone fragments above, not to the hoarded whole cones beneath. The primary meaning of a midden is a dunghill or a refuse heap. I don't know how widespread the meaning hoard is among biologists, and I haven't seen this meaning in the few dictionaries I consulted. But there may be some justification for the meaning hoard concealed in the history of the word midden.

At first glance, the two roots that make up the two halves of the word midden seem to be synonyms. The Oxford English Dictionary (OED) gives the following derivation:

< an early Scandinavian compound (cf. Norwegian (Bokmål) mødding, Danish mødding (earlier møgdynge), Swedish regional mödding) < the Scandinavian base of Old Icelandic myki (see MUCK n.¹) + the Scandinavian base of Icelandic dyngja (see DUNG n.). The expected Old Icelandic form would be *myki-dyngja (cf. Norwegian regional mykjadunge, mykjardunge).

Muck and dung mean the same thing to us. But see the OED's etymology of dung, which reveals that some cognates of dung can also mean hoard or heap:

OE. dung = OFris. dung, OHG. tunga manuring, mod.G. dung and dünger manure. Cf. also Sw. dynga dung, muck, Da. dynge heap, hoard, mass, pile, mod.Icel. dyngja heap, dung. The original sense is uncertain: see Kluge s.v.

In Friedrich Kluge, Etymologisches Wörterbuch der deutschen Sprache (Strassburg: Trübner, 1882), p. 57, s.v. Dung, I find an interesting reference to Tacitus, Germania 16. Here is Tacitus in the translation of Church and Brodribb:

They are wont also to dig out subterranean caves, and pile on them great heaps of dung, as a shelter from winter and as a receptacle for the year's produce, for by such places they mitigate the rigour of the cold. And should an enemy approach, he lays waste the open country, while what is hidden and buried is either not known to exist, or else escapes him from the very fact that it has to be searched for.

solent et subterraneos specus aperire eosque multo insuper fimo onerant, suffugium hiemis et receptaculum frugibus, quia rigorem frigorum eius modi loci molliunt, et si quando hostis advenit, aperta populatur, abdita autem et defossa aut ignorantur aut eo ipso fallunt, quod quaerenda sunt.

So it appears that hoarding food beneath a pile of refuse is a custom of both ancient Germans and modern squirrels.