Leg Modification in birds. By. Dr. Vidhin Kamble

                     

Leg / Feet Modifications in birds 

The birds are creatures, that adopted for true aerial flight.  In birds, the forelimbs are modified into the wing and hind limbs are for bipedal movement.  In the case of birds, there are several kinds of feet/leg modifications are according to the habits and habitat which are as follows.

1.   Perching feet

2.   Raptorial feet

3.   Scratching feet

4.   Climbing feet

5.   Climbing feet

6.   Clinging feet

7.   Wading feet

8.   Swimming feet

9.   Cursorial feet.

10. Thermoregulatory feet

1.     Perching feet. sparrow, crow, pigeon      

  

These modifications are observed in the majority of birds. The toes are slender and weak. In these birds, 4 toes are present. 1^st toe directed posterior/backward and three toes directed forward. The toes are opposable. Because of this, when birds seat on the branch, their body weight falls on toes, due to this, toes turn backward automatically because of tendons attached to it. This modification helps to perch the twig or branch very firmly.

2.     Raptorial feet:- Ex. Vulture, kites, owls, eagle.

In this type of feet modification, the legs are very strong used for grasping and holding the prey.  The toes are four in number. The toes are strong and powerful with sharply pointed claws.  A lower surface of the toe is rough due to the presence of a horny spine. Such type of feet is found in carnivorous birds. These toes are modified for firm grip around captured prey during flight.

3.     Scratching feet: ex. Fowl and peafowl

In this type, the feet are long and slender.  There is the presence of four toes. 1^st toe directed backward and 2^nd, 3^rd, and 4^th toes directed forward. The toes are long and slender with sharp claws. These types of feet are modified to scratch the ground to expose food grains, grubs, and tiny food particles. In the male there is the presence of sward like a tarsal spur, used for fighting. Hence, it is also called a fighting spur.  Spur is a sexually dimorphic character in these birds.

4.     Climbing feet : Ex. Parrots, woodpecker 

The feet modifications are adapted for climbing on the vertical surface. In parrot 4 toes are present. 1^st  and 4^th toes directed backward. Whereas, 2^nd and 3^rd toes directed forward.  In woodpeckers 1^st and2nd  toes directed backward and 3^rd and 4^th toes directed forward. Such type of feet modifications is called as heteroductylous or zygoductylous feet. The toes are with sharply pointed claws. Such type of feet are used to climb on the stiff vertical surface of the tree trunk or barks.

5.     Clinging feet – Ex. Swift, swallow

In these feet, toes are slender. All the four toes are directed forward. Such type of modifications are called homoductylous feet. Such type of feet is used to cling with vertical walls and ceiling.

6.     Wadding feet:- Heron, jackana, lapwing

Walking of aquatic vegetation is called wading. In this type the legs are long and slender. The toes are free, elongated and slender adopted for walking over aquatic vegetation.

7.     Swimming feet:-  e.g. Duck, Cormorants, Coot.

Swimming type of feet is found in waterside birds, adapted for swimming and floating. In these types of feet, the membranous skin fold is stretched between the toes forming a web. The web acts as a paddle for swimming. In the case of duck, the web is present between front toes. In the case of cormorant,  all the toes are included in the toes while in the coot web is lobe like.

8.     Running or Cursorial Feet: eg. Rhea, ostrich, bustard, etc.

In running birds, the feet are strong and powerful. In these birds, the number of toes is reduced. Poster toe is greatly reduced or absent. In the case of Rhea, Emu, bustards, etc. the toes are short and only forwardly directed 3 toes are present. in the case of ostrich, only two toes are present i.e. 3rd and 4th toes. All the toes terminated with the nail plate. These feet modification is used for fast running on the open ground.

Thermoregulatory feet.

Such type of feet is found in ptarmigan in the Antarctic region. In this bird, there are only forwardly directed three toes are present.  the toes are covered with soft feathers, which at as insulators to prevent loss of heat from the body. Hence, such type of feet is called thermoregulatory feet.