Day 55:
Moluccan masked owl – Tyto sororcula
A rainforest spectre
In almost
every habitat in the world there is an owl who owns the night. Whilst the
Accipitriformes and Falconiformes have dominated the diurnal predatory niches,
the Strigiformes have taken the equivalent nocturnal positions. The
Strigiformes comprise just two families, the Tytonidae (barn owls) and the more
speciose Strigidae (true owls). The Molccan masked owl is a member of the
former which are known for their heart shaped faces and sometimes ghostly
appearance.
There isn’t a
huge amount known about this owl species but it is part of a complex of similar
species which inhabit the islands of Indonesia and Papua New Guinea. None are
well described but one species, the Seram masked owl (Tyto almae), has proven especially elusive. It was first noticed
from a photograph taken in 1987. It wasn’t until 2012 that a team from the
Natural History Museum of Denmark and the Indonesian Institute of Sciences
caught a masked owl in a mist net in Seram (an island in Indonesia) and later
described it as a new species. It is still known only from these two records.
The predatory
nature of owls might suggest close relatedness to other birds of prey but
ornithologists may be quick to point out that owls are distantly related. However,
recent research suggests that the predatory hawks, falcons and owls all share a
raptorial ancestor but each lineage contains more closely related bird bird
groups who have independently evolved almost every other form of dietary
ecology. WARNING: below comes a taxonomic blur, not for the faint-hearted.
Traditionally,
and matching the order of my work and this blog, the owls are amidst the ‘near-passerines’,
the serious of groups that take us closer and closer to the passerines. This
started with the soundgrouse followed by the pigeons, parrots, turacos and
cuckoos and after the owls come the nightjars, swifts and hummingbirds,
mousebirds, trogons, hornbills, kingfishers and woodpeckers.
Recent
genomic analysis upsets this tradition remarkably. Soundgrouse and pigeons are
shoved to the edge of the Neoaves (i.e. all bird but ratites and fowl) with the
mesites, flamingos and grebes in the clade Columbea. The much larger clade
Passerea contains, at the edge, the cuckoos, turacos, bustards, nightjars and
swifts. Next comes the hoatzin, paired with the shorebirds, followed by the remaining
seabirds in the rough order we covered them. The rest of the orders are land
birds containing the Afroaves (raptors, owls, mousebirds, trogons, hornbills,
kingfishers and woodpeckers). Finally, the nearest birds to the passerines are
the two seriemas, the falcons and the parrots. Congratulations if you have followed
this, I certainly find it very confusing. For a superior explanation see Jarvis
et al (2014).
Day 56: Snowy
owl – Bubo scandiacus
Call me Hedwig one more time!
This gorgeous
white owl may be famous for being Harry Potter’s companion but reality is far
more interesting. As one might predict, the snowy plumage indicates the owl’s
circumpolar distribution where it breeds in the northerly reaches of the Arctic
tundra. The snowy owl might look cute and cuddly but it is a proficient hunter
of a variety of Arctic wildlife. Although the diminutive lemming is its main
food source, the snowy owl can hunt large rodents, rabbits and hares as well as
ducks, geese, waders and gulls. The females have even been known to take other
owls and raptors. Like other owls, snowy owls have very large gapes enabling
them to swallow prey whole. All the non-digestible parts of the prey are
coughed up as pellets of hair, bone and teeth. Pellets are useful for
biologists who wish to characterise the diet of owls. As for the raptors,
female owls are the larger of the two sexes.
As well as being smaller, male
snowy owls are more uniformly white and thus a better choice for the Harry
Potter films despite playing a female owl!
The snowy owl
is a more unusual character in the genus Bubo
which comprises the horned owls and eagle-owls. The Eurasian eagle-owl is one
of the largest, with a wingspan over 6 ft. By comparison, the elf owl (Micrathene whitneyi ) would easily fit
in your pocket. The Strigidae are a large family of owls which include most of
the owl species you might be familiar with.
Day 57:
Short-eared owl – Asio flammeus
Silent but
deadly
Two owls down
and yet I haven’t discussed some of the fantastic adaptations that unite the
owls. Well, what better way to do it than with one of my favourite British
birds, the stunning short-eared owl. As we know, owls evolved for the night. As
it happens the shorties are observable during the day, as I have seen them over
the grassy fields of Portland Bill, however the majority of their hunting
occurs at night when a battery of adaptations come into effect.
In the
blackness of night, owls must be able to navigate effectively and hunt small
prey which may skulk, unseen, in the undergrowth. To accomplish this, owls have
fantastic night vision. They have very large eyes with wide pupils which
maximise the amount of light passing to their sensitive rod cells. Furthermore,
an advanced neural mechanism extracts a superior amount of information from the
retina. Owl’s eyes face forward enabling excellent binocular vision so that
they can judge distance and depth efficiently (this eye placement gives them
their anthropomorphous, ‘wise’ face). Fitting such large eyes into a relatively
small head results in their tubular shape. ‘Eyetubes’ cannot be swivelled as
eyeballs can, so owls must rotate their heads. They famously do this rather
well, being able to rotate the head through up to 270°.
The other
sense which owls have mastered is hearing. Don’t be fooled by their ‘short ears’.
The ears of the ‘eared owls’ (Asio)
are simply tufts of feathers, thought to break up the outline of a roosting
bird. The real ears are set on either side of the head, beneath the feathers.
Here, we encounter another case of asymmetry as owls’ ears are placed at slightly
different heights. This allows owls to pinpoint sounds in three dimensions. We
(and many other animals) are good at locating sound horizontally but vertical
pinpointing is quite difficult (hence why I sometimes put my head on my side to
find singing skylarks). The ears are aided by a ruff of stiff feathers that
form a facial disk which collects sound waves and directs them to the ears.
Even the beak is designed to minimise sound loss. What was striking when measuring
the owls was how small the skeleton was beneath the feathers and how
structurally different the facial feathers were to achieve their function.
Owls are excellent
at detecting prey but they also need not to be detected. Thus, owls are literally
deathly silent. Large, broad feathers allow owls to float around with minimal
flapping. Along the leading edge of the wing feathers, serrations disrupt the turbulence
that would cause sound in a normal bird whilst velvety down absorbs some of the
sound that is still produced. As this silent spectre descends, with talons
spread, an unsuspecting vole stands little chance.
Day 58:
Papuan frogmouth – Podargus papuensis
Why the wide face?
The frogmouth
is a bizarre looking bird - that is, if you were able to spot it as they
exhibit impressive cryptic plumage and behaviour. They roost motionless with
their necks outstretched which, coupled with their mottled-brown plumage, makes
them resemble a branch, complete with a stick-like head tuft. All frogmouths
have extremely wide gapes (hence the name) and the Papuan frogmouth has the
largest of them all. Like the owls before them, the frogmouths are nocturnal
foragers however their foraging mode is slightly more ungainly. They hunt
around the ground for insects but will take prey as large as rodents, lizards
and frogs. A huge mouth helps the frogmouth to grab prey in the dark without needing the finesse of an owl.
The frogmouths
(Podargidae) are part of the nightjar order Caprimulgiformes. The species of
this order are characterised by their nocturnal, insectivorous habits and their
cryptic plumage. A morphological perspective placed the Caprimulgiformes
between the owls and the swifts and it is easy to see why. Since then
they have been affiliated with various ‘near-passerine’ groups and genetic
evidence has confused matters although there was strong support for a
monophyletic clade uniting the nightjars, owlet-nightjars (Aegotheliformes) and
the swifts (Apodiformes). This is corroborated in the most recent whole-genome
analysis however this clade (the Cypselomorphae or Caprimulgimorphae), is
placed nowhere near the owls. Instead, they are located with cuckoos, bustards
and turacos on the periphery of the Neoaves. I’m still trying to get my head
around this new, counter-intuitive world order of bird.
