Day 43: Pin-tailed
sandgrouse – Pterocles alchata
Pterocles Queen of the Desert
This is one
of the most beautiful of the 16 species of sandgrouse which form their own order, the
Pteroclidiformes. The name sandgrouse refers both to the generally dry habitat
(and matching colour) of these birds as well as their superficial resemblance
to grouse. Sandgrouse are roughly grouse like in shape and sexes are dimorphic
with males bearing more ornate plumage. In the case of the pin-tailed
sandgrouse the male is handsome in ochre and burnished gold with a blue eye-ring
and a finely tapered tail.
One
difference between sandgrouse and grouse, however, becomes obvious in flight. Sandgrouse have
long, pointed wings which allow them to cover large distances at speed. This is
necessary for life in the plains when water can be patchily
distributed. This puts some constraint on parental provisioning, however sandgrouse have specially adapted belly feathers which enable parents
to absorb water and carry it back to their chicks. Drinking at watering-holes
must be brief as predators frequent such sites so sandgrouse maximise their chances
by congregating in large numbers, usually only visiting at dawn or dusk.
The resemblance
to grouse meant that sandgrouse were formerly considered members of the
Galliformes. Now they are placed next to the pigeons although they might be
more closely related to shorebirds.
Day 44: Crested
pigeon – Ocyphaps lophotes
Respect the pigeon
Here we enter
one of the largest non-passerine bird orders: the Columbiformes. This is the
order of the pigeons and doves, two terms which mean little biologically but, generally, pigeons tend to be larger species whilst doves are smaller. Some people
may have a derogatory opinion of pigeons but this is probably in part due to the most
familiar species, the feral pigeon (Columba
livia domestica) which derives from the cliff-living rock dove via
domesticated populations. With over 300 species there is , however, more to the pigeons
than the humble ‘flying-rat’!
The pigeons
vary in size from the goose-sized crowned pigeons (Goura spp.) to the sparrow-sized New World ground-doves (Columbina). Although there is only one
pigeon family (Columbidae) the pigeons and doves are split into around ten
subfamilies including the typical pigeons (Columbinae) and the arboreal doves
(Treroninae). Columbids are mostly granivorous however the latter subfamily
specialise in fruit.
The crested
pigeon is a small Australian pigeon of open habitats. It is notable for its
erect crest which is surprisingly rare in the Columbidae given the importance
of visual cues in courtship.
Day 45: Nicobar
pigeon – Caloenas nicobaricai
You should meet his cousin
The Nicobar
pigeon is a fantastic beast to behold. This large pigeon is covered in the most
exquisite pointed, metallic feathers from bronze to blue. As well as the
Nicobar islands the pigeon is found on small forested islands as far east as
Palau. It is generally gregarious, roaming the forest floor in search of seeds
and fruits. As well as their distinctive plumage the Nicobar pigeon has a
notable vulturine look which gives an air of the prehistoric.
This brings
me to its most important taxonomic relevance. The Nicobar pigeon is the closest
living relative of the dodo. Everyone knows about the dodo, that charismatic
species that met its demise at the hands of humans. The dodo was a large
flightless bird that evolved in isolation from predators on the island of Mauritius. Like
many flightless birds we have already come across, the dodo was at considerable
risk when humans came to the island at the end of the 16th Century. Although hunting would have placed pressure
on the birds the greater issue came from habitat destruction and nest predation
by introduced pigs and macaques. With its loss, as well as the extinction of
giant tortoises (Cylindraspis spp.),
Mauritius lost both charismatic species and important ecosystem engineers, responsible for shaping the vegetation of the island. On nearby Rodrigues the
swan-sized, flightless Rodrigues solitaire was another giant pigeon to become
extinct because of man.
Day 46: Mariana
fruit-dove – Ptilinopus roseicapilla
Jewel of the pigeons
The Mariana
fruit-dove is a member of the largest genus of columbids comprising around 50
species distributed around the islands of Southeast Asia and Oceana. Fruit-doves
generally occupy the same niche wherever they are, being arboreal frugivores.
This raises an interesting question about what causes some groups to be so
large. In some instances a clade will hit upon an adaptation which allows the
group to specialise into many different niches facilitated by the new
adaptation. Hummingbirds, for example, have capitalised on their hovering
flight and long bills to diversify and this is generally seen as an adaptive
radiation.
Examining the
fruits-doves, however, reveals little niche diversification within the genus.
One adaptation that precluded their diversity was the large gape which
facilitates frugivory yet there is little further specialisation. Instead the
clue is in thier short, rounded wings which are not evolved for strong, regular
flight. When this is coupled with the distribution of fruit-doves over the
islands of the Indo-Pacific it becomes apparent why there are so many species.
After the origin of the genus (probably in Southeast Asia), sporadic events
caused birds to hop islands and start populations in isolation. The lack of
regular dispersal meant that gene flow was soon cut short and the populations
diverged and speciated in allopatry. When this process is iterated across the
Indo-Pacific, the species richness of Ptilinopuus
becomes the result of a series of vicariant events.
It should be
noted that fruit-doves are not identical despite ecological similarity. In fact
they are the most colourful and aesthetically diverse group of pigeons, mostly green with patches of bright
orange, purple or magenta. The greater similarity in appearance of some species
to others tracks the evolutionary history of their divergence as they jumped from island to island. The Mariana
fruit-dove is a typical Ptilinopus
species endemic to the Northern Mariana Islands and Guam (both US territories).
I chose this species because it looks cool.
