Blue-tailed monitor

The blue-tailed monitor, blue-tailed tree monitor or Kalabeck's monitor (Varanus doreanus), is a monitor lizard of the Varanidae family. It belongs to the V. doreanus group of the subgenus Euprepiosaurus.

Taxonomy
Two subspecies have been described:
 * V. d. doreanus (Meyer, 1874)
 * V. d. finschi (Bohme, Horn & Zeigler, 1994)

The latter has since been elevated to full-species status as Varanus finschi.

Once considered a member of the V. indicus species complex, it now forms its own species complex with V. finschi, V. semotus, and V. yuwonoi, having diverged from the V. indicus species complex 5.8 million years ago. The V. doreanus species complex formed at most 4.1 million years ago. V. doreanus is the most basal and widespread member of this species complex.

Distribution
This species can be found throughout New Guinea, New Britain, the Bismarck Archipelago, Biak, Salawati, and Waigeo. The blue-tailed monitor is also found on mainland Australia on the tip of the Cape York Peninsula. It inhabits rainforest areas, dry streambeds, and riparian zones.

Description
The blue-tailed monitor can reach a total length (including the tail) up to 135 cm (53.15 in). The maximum size record of this species belongs to a male specimen collected from Cape York in 1948, with a total length of 173.5 cm despite missing its tail tip.

The body is greyish-blue in colour and covered with round ocelli. The throat is whitish and strongly marbled. The tail shows clearly a double keel. The tail is light blue (hence the common name of this species), which is interrupted by black cross bands. In adults this color partially fades away. Scales on its neck are smooth and oval. It has a yellow tongue, which is a shared characteristic of the V. doreanus species complex.

Ecology
Like other monitors of the V. doreanus species complex, the blue-tailed monitor feeds on a relatively high amount of vertebrate prey such as birds, especially when compared to other monitors of the subgenus Euprepriosaurus. It will also feed on invertebrates such as beetles.

Like many monitor lizards, males fight over females and territory by standing on their hindlegs and grappling with each other.

In Australia, they are predated on by black-headed pythons.

It is sympatric with the mangrove monitor and the peach-throated monitor in many parts of its range.