The Collaborative International Dictionary of English v.0.48:

Skylark \Sky"lark`\, n. (Zool.)
   A lark that mounts and sings as it files, especially the
   common species (Alauda arvensis) found in Europe and in
   some parts of Asia, and celebrated for its melodious song; --
   called also sky laverock. See under Lark.
   [1913 Webster]

   Note: The Australian skylark (Cincloramphus cantillans) is
         a pipit which has the habit of ascending
         perpendicularly like a skylark, but it lacks the song
         of a true lark. The Missouri skylark is a pipit
         (Anthus Spraguei) of the Western United States,
         resembling the skylark in habit and song.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lark \Lark\, n. [OE. larke, laverock, AS. l[=a]werce; akin to D.
   leeuwerik, LG. lewerke, OHG. l[=e]rahha, G. lerche, Sw.
   l[aum]rka, Dan. lerke, Icel. l[ae]virki.] (Zool.)
   Any one numerous species of singing birds of the genus
   Alauda and allied genera (family Alaudid[ae]). They
   mostly belong to Europe, Asia, and Northern Africa. In
   America they are represented by the shore larks, or horned
   larks, of the genus Otocoris. The true larks have
   holaspidean tarsi, very long hind claws, and, usually, dull,
   sandy brown colors.
   [1913 Webster]

   Note: The European skylark, or lark of the poets (Alauda
         arvensis), is of a brown mottled color, and is noted
         for its clear and sweet song, uttered as it rises and
         descends almost perpendicularly in the air. It is
         considered a table delicacy, and immense numbers are
         killed for the markets. Other well-known European
         species are the crested, or tufted, lark (Alauda
         cristata), and the wood lark (Alauda arborea). The
         pipits, or titlarks, of the genus Anthus (family
         Motacillid[ae]) are often called larks. See Pipit.
         The American meadow larks, of the genus Sturnella,
         are allied to the starlings. See Meadow Lark. The
         Australian bush lark is Mirafra Horsfieldii. See
         Shore lark.
         [1913 Webster]

   Lark bunting (Zool.), a fringilline bird (Calamospiza
      melanocorys) found on the plains of the Western United
      States.

   Lark sparrow (Zool.), a sparrow (Chondestes grammacus),
      found in the Mississippi Valley and the Western United
      States.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Alauda arvensis
    n 1: brown-speckled European lark noted for singing while
         hovering at a great height [syn: skylark, Alauda
         arvensis]