Salvadori, in vol. xxi of the British Museum * Catalogue of Birds,' divides the Pigeons into five families, of which the two most easily separated, the Gouridae and Didunculidae, are not represented in our regions.
The three remaining families are the Treronidae or Green Pigeons, which frequent and roost in trees; the Columbidae or True Pigeons, which frequent trees principally hut are also found about buildings or cliffs and can run and walk well on the ground; the Peristoridae or Doves, which are much given to walking on the ground. Following Blanford, I unite these three families in one, the Columbidae, in which we find the structural features of the order Columbae, in so far as that refers to the countries with which we are dealing.
In the Pigeons the palate is schizognathous, nostrils schizorhinal; basipterygoid processes present; dorsal vertebrae heterocoelous, cervical vertebrae fifteen in number; sternum with four deep posterior notches, the inner pair of which may be converted into foramina; the external lateral processes are much shorter than the internal; furcula U-shaped. The deep plantar tendons are united with a vinculum, the hallux connected with the flexor longus hallucis and the three front toes with flexor perforans digitorum. The ambiens muscle is sometimes present; the femoro-caudal, semitendinosus, accessory semitendinosus and accessory femoro-caudal present in all Indian species; oil-gland nude or wanting; caeca and gall-bladder sometimes present, sometimes absent; both carotids always present. The external characters are: upper mandible having the most slender portion posterior to the tip; the basal portion, which contains the nostrils, is covered with a cere or soft skin; the tip is swollen, hard and convex, giving the appearance of having a small knot. The four toes are on the same level, webless, with the hallux or hind-toe well developed; the soles are broad but differ in this respect in the different subfamilies, being most greatly expanded in the Treronidce or Green Pigeons. Wings acquincubital, long and pointed, with close-set coverts, eleven primaries and the fifth secondary wanting. Spinal feather-tract well developed and forked on the interscapulary region; after-shaft rudimentary or entirely wanting.
In dividing the Family Columbidae into subfamilies, it is difficult to find structural characters of any great value. The broad soft-soled feet of the entirely arboreal Green Pigeons divide them definitely from the Doves with their slender hard-soled feet, whilst others are intermediate. Again, in so far as our Indian birds go, the number of tail-feathers, 12 or 14, divide Pigeons and Doves into two groups. At the same time with so great a number of specie's a division into groups is an assistance both to the Museum student and to the field-naturalist, so I therefore retain Blanford's six subfamilies, to which the following are alternative keys.
Key to Subfamilies (1).
A. Tail of fourteen feathers *.
A.No ambiens muscle present.
a1. Oil-gland absent...............Treroninae, p. 179.
b1. Oil-gland present...............Geopeliinae, p. 257.
B.Ambiens muscle present ...............Duculinae, p. 202.
B. Tail of twelve feathers.
c.Ambiens and oil-gland present; no caeca.
c1. Tarsus longer than middle toe........................ Caloenadinae, p. 212.
d1. Tarsus moderate, not as long as middle toe........................Phabinae, p. 214.
d.Ambiens, oil-gland and caeca present...................Columbinae, p. 218.
A. Tail of fourteen feathers.
A.Plumage generally with much green.
Wings always over 125 mm., always under 200 mm.; soles of feet broad and fleshy...............Treronidae, p. 179.
B.Plumage dull, no green; wings always under 125 mm.; soles of feet not broad or fleshy............... Geopeliinae, p. 257.
c.Plumage various; size large, the wing always over 215 mm.; soles of feet not broad or fleshy............... Duculinae, p. 202.
B. Tail of twelve feathers.
d.Neck-hackles long and green .......... Caloenadinae, p. 212.
c. No hackles on neck.
a1. Plumage above dark, metallic green; bill red; wing under 150 mm.....Phabinae, p. 214.
b1. Plumage not glossy or, if glossed, to some extent, the wing is over 200 mm………………..Columbines, p. 218.