Day 5: Caucasian grouse - Lyrurus mlokosiewiczi
Lord of the lek
We are now firmly in amongst
the wild fowl in the family Phasianidae. Many of these species we know as
game-birds and they have fed people around the world for thousands of years. As
such they are well represented in the museum collection. This group of birds is
typified by its dimorphism as gaudy males strut and compete for female
attention. The Caucasian grouse is no exception. Closely related to the British
black grouse (Tetrao tetrix), this bird leaps and twists in the air, flashing white feathers
and a fantastic tail. As a result, they provide ample interest for behavioural
ecologists.
The lek is a paradigm of behavioural
ecology and evolution. Males must compete for mating opportunities with females
and this usually involves flashy displays. How does this all come about?
Firstly, females already invest a lot of energy in their eggs which means they
are the limiting factor on reproductive output. Females could just mate
randomly with males but they (or their offspring) stand to gain from choosing
which males to mate with. Males could provide direct benefits to a female
(protection, territory full of resources) or indirect benefits to her offspring
by making them fitter (more likely to survive) or sexier (more likely to
reproduce).
On what does a female base
her choice? Males can prove their fitness in battles of aggression as in
rutting deer. Such conflicts are rare in birds, however, with displays being more
aesthetic. Investing time and energy into strutting around can only be afforded
by a healthy individual. Energy investment is a trade-off and only the fittest
individuals can sustain themselves and perform for the ladies. Ornaments are
also a costly adaptation, inhibiting movement and attracting predators. By
definition, a male who survives to have glossy bright plumage is a survivor
which bodes well for his offspring.
Finally, and especially relevant to the
game birds, is immune health. The ability to create large and beautiful
ornaments is hampered by disease so only the males with the best immune systems can manage it.
The blazing red skin patches of grouse and pheasants is indicative of the
parasite load as only males free from infection can metabolise the carotenoids
needed to make such colouration. A good immune system is hereditary. But what
about all those monogamous birds? They will come later.
Day 6: Grey partridge - Perdix perdix
Partridge in pear tree
Oft called the English
partridge, the grey partridge actually has a range that stretches all the way
to china. No doubt the national epithet was used to distinguish it from the
red-legged ‘French’ partridge (Alectoris
rufa) which was introduced to England from France (this species is
similarly not confined to its geonym). A partridge takes pride of place in The
Twelve Days of Christmas amongst the fruit of the Pyrus tree.
The song originated in England in the 1780s soon after
the introduction of the red-legged partridge but was adapted from similar French
carols. Thus the partridge is probably, ironically, French! The pear tree is
unique to the English carol however it probably derives from the old French for
partridge: pertriz. So should it be a
partridge in a partridge?!
The Twelve Days of Christmas celebrates the time of merriment and gift giving between Christmas and the Feast of Epiphany and it teems with birds. If you were lucky enough to receive all of the gifts in the song you would be the proud owner of no less than 184 birds. The second bird on the list is the turtle dove (Streptopelia turtur) which, like the grey partridge, is red listed in the UK. Agricultural intensification has greatly diminished suitable habitat for these agricultural associates causing their populations to crash. Elsewhere on the list we see the hens and geese which would have provided eggs and meat during the cold months whilst calling birds and beautiful swans may have provided some winter joy. Other than that, I’m not sure what these species have in common or why they make the list!
Day 7: African blue quail - Excalfactoria adansonii
Good things, small packages
Weighing as little as 30 g and just 5 inches in length this tiny quail is the smallest of the galliforms. By contrast the aforementioned wild turkey weighs as much as 14 kg, 500 times heavier than this quail. This order, therefore, has one of the largest size ranges of any bird order. Size is obviously very important for any organism and is an important form of niche partitioning.
Different orders represent the first level of niche partitioning in birds (and other animals). There are wild fowl and water fowl, shore birds and birds of prey. Thus, simply put, the order defines the mode of living. Within that, a large part of niche partitioning is based on size. Take raptors as an example, once predatory adaptations evolved, some groups specialised in small prey, some in large prey and the size of their prey defined their own size. Within the Galliformes, size ranges from turkeys to pheasants to partridges to quail, each group occupying relatively discrete size ranges. An ecosystem can only support species which are sufficiently different from each other so rather than have an ecosystem full of quail species, there tend only to be one or two representatives of each group. When we are measuring birds we certainly notice this. We might have a genus with a species in each Asian country which rarely overlap. Then moving to the next genus we start to go over the same countries again. Thus, every island in Indonesia appears to have a magapode, a pheasant and a partridge. Size is only one way that niche space can be partitioned as we will discover later.
Day 8: Golden pheasant - Chrysolophus pictus
King of the pheasants
The golden pheasant was the last galliform that I measured and what a way to finish, in a crescendo of colour across the pheasant species. The birds stand out as an especially colourful bunch in comparison to the more muted colours of the mammals. As in mammals, plainer colours are produced by pigments, particularly melanins with pheomelanins producing the browns and eumelanins producing the greys and blacks. Carotenoids create the fiery colours found in the combs and wattles of the galliforms.
The truly dazzling feather colours are not produced by pigments but are structural features of the feathers which determine how light is refracted. The iridescent blues and greens are a product of diffraction gratings, regular, parallel lines scored in the nano-structure of the feather. Changes in the angle of the observer cause the colour to shift slightly. Structural colouration can be used in concert with pigmentation to mix and merge colours. It seems that the hairs of mammals are not able to support such adaptation or else highly colourful males would surely have evolved. I wish I understood the physics more!
To maintain these feathers and to avoid the damage accrued over time, feathers are moulted and replaced. This usually happens after the breeding season when birds are at their most disheveled and it causes them to become more reclusive as they get themselves back in order.
