Marabou is a French word that means “ugly, misshapen old man”.
The Marabou stork ekes a living by scavenging food that vultures work free from carcasses, as it cannot cut meat with its straight bill. It also takes advantage of the abundance of catfish that become trapped in drying pools towards the end of the wet season.
The Marabou stork uses its feet to stir up the shallow muddy water to disturb the fish. It then locates the fish by sight or feel, and stabs viciously at it with its sharp beak. It swallows the fish head first so the scales and fins are aligned correctly and it doesn't choke.
The Marabou stork urinates on itself in order to cool its legs, which in turn cools the blood in the body via evaporative cooling. The urine also crystallises to a whitish colour and reflects the sun’s rays, thereby playing a role in thermoregulation. The correct term for this process is urohydrosis.
The Marabou stork will often rest on its tarsal joint or “knees”. Because it is closer to the ground, this may also be a way of warming the body in cool weather.
These storks will often been seen congregating on the ground, for the following reasons:
~ To exploit insect irruptions such as termites and caterpillars
~ Waiting to scavenge from vultures at a carcass
~ To get warmth from the ground in cool weather
Anatomy of a Marabou Stork:
Too much exposure of the bare facial and head skin to the sun can cause blistering, something which is minimised in heavily pigmented skin. These blisters often get infected when it delves around in carcasses.
It lacks any significant head feathering so that it can easily wash off fluids from carcasses that attach to the head and neck.
The pouch at the lower end of the throat is not a crop or gular pouch, as it is with pelicans. It is in fact a gular air sac, and is connected to the oral cavity where it is fed with air. It is a fleshy appendage that is richly supplied with blood capillaries. It functions as a thermo-regulator, which is when the air cools the blood that flows to the brain and throughout the body.
It is likely that it also serves as a dominance indicator (depending on size and possibly colour) in social interactions. This is particularly noticeable in posturing males, and in pairs during breeding.
The gular sac can be filled with air in hot weather in order to increase surface area for heat dissipation (with the capillaries dilated), as well as when the bird is stressed or threatened. Similarly, the capillaries are constricted and the sac inflated to be warmed by the sun on cold winter mornings.
Lacking the bright colours of other storks, the Marabou uses the gular sac, along with another much smaller air sac on the nape of its neck, for displaying.
These are generally used when threatened and during courtship, when the previously inconspicuous neck sac becomes bright red and bulges through the ruff of neck feathers.
Game Ranger in your Backpack
Chapter: Birds – Food and feeding Page 136
Chapter: Vultures Page 162
Beat about the Bush – Birds
Chapter: Waterbirds, waders and shorebirds Page 442, 450 – 452
Chapter: Did you know? Page 707