From water to land
Icekissers and cormocranes
While anatids and sheathbills maintain their monopoly over the antarctic land, other bizarre birds clade are slowly making their appearance, progressively losing their marine habits and becoming more linked to continental wetlands.
On the edge of the underworld
Icekissers are a penguins' radiation that can be found in the internal waters of Antarctica. Eating any invertebrates on the riverbed, this bird underwent to a progressive miniaturization, often becoming endemic to single large rivers. The most abundant species is the desman icekisser (Idritalpornis temperatus), which lives in the cold waters of the Kalt and Froid rivers, in the D.D. It's a very small penguin, not exceeding 300 grams (10 oz) with semi-fossorial adaptation: while their swimming abilities are discrete, this icekisser also creates long and complex tunnels on the riverbank, that is used as a nest, but also for feeding. Lots of insects in fact can be found in the first substrate, a valuable supplementary food when aquatic invertebrates are scarce or are hiding under the detritus.
Icekissers have a different digging method compared to ground tyrants: while semifossorial tyrants use mostly their legs (and secondarily their beak) to dig their den, icekissers move away the detritus thanks to the complementary use of beak and wings, the latter being shorter but wider in order to better move away the soil. Legs are weak and are used only to push its body in tunnels or to stand up on land while basking.
Like other species of penguins, they are colonial, living in small groups of up to 30 individuals.
An aberrant cormorant
In the course of bird evolution, similar body plans independently evolved many times. Ardeids, ciconiids, gruids and ibises for example have evolved various common features like stilted legs, a long neck and a conical beak, giving them a very elongated structure. And recently, another group of birds convergently achieved a similar form: a likely descendant of the land shag has given birth to a group of heron-like birds, endemic to the Antarctic continent: the cormocranes (Pseudoardea sp.). Despite the seasonal presence of storks and some heron species, there's a strong niche partitioning and little interspecific competition, especially due to size differentiation. The antarctic cormocrane (Pseudoardea ddensis) for example are more bound to the immense bogs of Antarctica, where they hunt invertebrates, small aquatic birds and carrion. Fish are very rare in their daily diet. During winter, southern populations migrate to wintering areas, mostly being the D.D. and the upper part of the Antarctic peninsula, including the northern small archipelagos.
Some millennia ago, one lineage of antarctic cormocranes has diverged, losing its semiaquatic habit and becoming exclusively terrestrial. It's the ground cormocrane (Pseudoardae aptera), a flightless species endemic to South Georgia, one of the northernmost islands of the Antarctic plate. With a cool oceanic climate, this island maintains a very balanced temperature, not frosty nor hot.
No more than 10.000 ground cormocranes are thought to be present in South Georgia. Despite being a low number, they're not in danger: overall species fitness is high, due to the absence of any large predator on the island and lack of competition.
