Friday, February 17, 2012

Spitting Cobra Naja Nigricollis Habitat

Spitting Cobra (Naja Nigricollis)

The Spitting Cobra is part of the family Elapidae, which consists of several other species such as mambas, coral snakes, tipands, and kraits. They are characterized to be venomous snakes possessing erect fangs that are in front of each maxillary bone. They lack left lungs, a coronoid bone in the mandible, and external and internal girdle and limb features. “Cranially, they have only a left carotid artery, endentulous premaxillaries, longitudinally oriented, shortened maxillaries with anterior teeth that are large and tubular, and optic foramina that usually perforate the frontalparietal paraphenoid sutures”.

 The most diverse and widespread genus of Spitting Cobra . They are medium-sized, less than two meters, and black in coloration. Other species of this genus such as Mozambique spitting cobra is red in coloration. Spitting cobras are categorized as generalist predators. They are well equipped to prey on a wide variety of small vertebrates. They also tend to feed on fairly larger species that are relative to their own body size. In all, they have an adaptive capability in which they could prey on several different species when they’re exposed to different microhabitats. When the spitting cobra feels threatened it exhibits a defensive behavior. N. nigricollis defend themselves by spitting their venom in the face of their harassers and/or predators, thus given the common name “spitting cobra”. The venom of the spitting cobra is non-toxic to the skin, but is harmful to the eyes of their aggressor.

Spitting Cobra Habitat
The venomous Elapid species occupy much of the Australian, African, and Asian continents. Cobras classified under the genus Naja are widely distributed in the desert and tropical regions of Asia and Africa. Specifically, N. nigricollis are found in the south eastern Nigeria where its habitat has been altered from a tropical rainforest to man-made farmlands, plantations, suburban areas, and a few fragmented forests.

Aside from the spitting cobra residing in this region another species called the black forest cobra, N. melanoleuca, occupy this once forested area of south eastern Nigeria. Nigeria was once a continuous rainforest with a tropical climate. It still is a region that exhibits two seasons; a wet season during the months of May to September and dry season from October to April. According to Luiselli’s studies, the spitting cobra has taken an advantage to the deforestation of Nigeria. It is suggested from the study that the spitting cobra forages in much drier microhabitats. N. nigricollis has been currently extending its range from the south eastern regions of Nigeria to the arid savannas of central Nigeria.

Spitting Cobra Diet
Species of the Elapid family have very generalized diets. Therefore, N. nigricollis is a generalist predator and is adapted to feed on different prey items from a number of small to a number of medium sized vertebrates. In the study that Luiselli et. have conducted in the comparative feeding strategies and dietary plasticity of N. nigricollis in three diverging Afrotopical habitats (suburbia, plantation-forest mosaic, and mature forest) significantly different prey items of adult and juvenile spitting cobras were observed. For the food habits of N. nigricollis in a suburbia setting, adults preyed on commensal rodents, poultry, semiaquatic frogs, and agamid lizards.

While the juvenile spitting cobra preyed most on agamids. In the plantation-forest mosaic habitat, the adult hunted for rodents especially striped rats, Lemniscomys striatus, and lizards that belong in the Scincidae and Agamidae families. The juveniles’ diet consisted of agamids and skinks. In the third habitat, mature forests, the adult spitting cobras preyed on rodents and the young fed on lizards and fish. Overall, this study had concluded that spitting cobras is adaptive to prey on both endotherms and ectooterms and organisms that are terrestrial, aquatic, and even arboreal.

Most snake species usually stop feeding during certain conditions. Spitting cobras reduce their food consumption during the peaks of dry season, which are the months from October to April. Males of the species N. nigricollis exhibit this practice during mating season. Females withdraw from feeding when they are carrying eggs and are just a few weeks from giving birth.

Spitting Cobra Behavior
When snakes feel threatened then and there do they only demonstrate defensive behaviors. Some snakes have visual or acoustal displays toward their predaors and/or harassers. In situations where visual displays fail, snakes resort to biting. The Elapid family is characterized for their venomous defense mechanisms. Another species of the same family that also spit their venom is the species N. pallida. One other cobra that had developed this element of spitting is the African rinkhals, Hemachatus haemachatus. 

Spitting cobras only spit venom when they feel they’re in danger. The N. pallida spit their venom by ejecting either of the two jets they retain. The N. nigricollis releases their venom in a fine spray or propelled mist-like fashion. The spitting cobra first opens its hood as a visual cue or warning against it’s predators. The spitting act of the N. nigricollis occurs through fast undulating head movements. These head movements allows for a larger distribution of the venom. Specialized muscles contracting the venom gland forces the venom out through its fangs when the spitting cobra opens it’s mouth. 

“The teeth of spitting cobras are hallow with a round exitorifice for the venom leading the venom jet perpendicular to the axis of the teeth”. With this unique feature the spitting cobra forces the venom out in a spin increasing accuracy and precision. Spitting cobras can spit their venom to a distance of at least three meters. In such studies, the spitting cobra’s maximum capacity is fifty-seven consecutive spits.

The venom exhausted through the fangs and toward its aggressor eyes causes harmful effects such as pain and could result in necrosis on mucous membranes which can cause blindness from the destruction of the cornea in the eye. According to Westhoff studies, a spitting cobra had developed a feature to visually differentiate between their aggressor’s hands and faces. They’ve adapted this skill because the venom has its greatest impact on eyes.


Post a Comment

Twitter Delicious Facebook Digg Stumbleupon Favorites More

Design by PlanetAnimalZone | Bloggerized by PlanetAnimalZone - PlanetAnimalZone | Animal and Pets Review