Surface Tension In Animal Habitat

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Aquatic habitats pose unique challenges to the species to capture food. Some animals and birds who feed on small sized preys cannot have sophisticated feeding structures like most other species of animals.
Moving such structures in water will displace their preys along with the displaced water.
For shorebirds like Phalaropes , swallowing the prey and transporting it to their mouth is yet another challenge, apart from capturing. With their long thin beaks, facing vertically down, they must capture their food along with water droplets by pecking at water, and move it all the way long up to their pharynx ,defying gravity.
Phalaropes use their beaks like a pair of chopsticks , rapidly closing and opening them in tweezing motion to push
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If the liquid maintains an angle ‘a’ with the surface, it is said to completely wet the surface if a → 0 . For any non-zero finite value of a , the liquid is said to partially wet the surface.
Surface Tension :Formally, Surface tension is the energy required to raise the surface area of some liquid by 1 unit.
The molecules at the surface of the liquid experience a net downward force of cohesion. Thus the energy of surface molecules is higher, and the surface of liquid behaves like a stretched membrane exhibiting the property of surface tension, by virtue of which it tries to aquire the minimum surface area to attain lowest possible energy.
Contact Angle Hysteresis: A liquid climbing up along some surface always has the leading angle of contact ( aL ) greater than or equal to the preceding angle of contact ( aP ). This difference in the angle of contacts aL-aP is called the Contact Angle Hysteresis. This difference in the angle of contact generates a net upward force opposite to gravity, allowing the liquid to move upwards.This is the principle behind why raindrops resist falling down a glass
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This action of individual pecking is an attempt to reduce the movement of much body parts to prevent displacing water in the act of catching prey , since their preys are majorly copepods,which are small.
Phalaropes do not have tongue or suction mechanism,size of their prey is so small (=(weight of droplet + weight of the prey).
Also , since Phalaropes rely on surface tension of water to catch their prey, any pollutants in water that modify the surface tension of water can hamper their abilities to catch their prey.

Future Perspective:
This capillary feeding mechanism in Phalaropes can be further studied and the same principle can be applied to design of systems for directed transport of droplets in a micro-fluid system.
It can also be used to design valve-less pumps.
Fine tuning of the surface wettability, the thinness of the capillary tube designed, and its tapering angle can make this process very efficient.
Since the transport of food via surface tension is also an important taxonomic trait, further study can be carried out to find out other shorebirds which employ the same technique to eat their

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