Frogs can be found throughout the United States and Canada. They live in many habitats although their usual habitat is near water among damp vegetation and can often be found in gardens.
Frogs start mating with the male calling for the female by croaking. The male will attach himself to the back of the female in a position called amplexus. The female releases eggs into the water which the male then fertilizes externally.
Frogs can be found from sea level to high mountainous regions but they are so well camouflaged that they are not the easiest animal to spot as they sit among vegetation. Normally the first you know you have happened upon a frog is when it leaps off nearby or when you hear it croak.
There are many species of frogs in North America and many have shades that distinguish themselves from one another. There are species that are bright yellow, while others are the more usual olive-colored brown or greenish-gray.
The markings on each species of frog can also be very different from each other. Some have speckles while others have spots or marbling. Most species of frog have streaks around the eyes and dark cross bars on the limbs. These bars help the frog camouflage when crouching as they come together to form dark streaks on the body. These bars help it to merge into its surroundings by breaking up the outline of the frog.
Frogs have another excellent way not only of camouflaging themselves but also making them more attractive to a mate. They can change their color, lightening, or darkening their skin. They change their color by moving the pigment cells around the body, which they do by contracting or spreading the pigment cells.
Although they can change their color the patterns on the frog remains the same, their color can fully change within an hour. The shade a frog changes to is determined by the environmental conditions. In colder, damper weather frogs generally turn darker, but in drier, warmer environments frogs will generally turn a lighter shade.
A frog’s skin has small bumps on the flanks but is generally smooth. However, the skin of the female becomes rougher during the spawning season. This allows the male to distinguish sex during this period.
Frogs have mucous glands in the skin which keeps it moist, allowing the frog to breathe through its skin, which helps the respiration of its lungs.
The skin can also absorb water so the frog doesn’t need to take in water. Frogs shed skin as they grow. The transparent layer of dead skin is shed once the mucous glands have lubricated the fresh skin underneath. The old skin is taken off by the feet before it eats it.
Frogs are generally first seen in the year around February or March. At this time the adults emerge from their winter homes of ponds or ditches.
In February or March, frogs can be found congregating at different breeding sites, with flowing water ponds and canals seeming to be a favorite. Frogs travel for up to half a mile to get to their breeding sites and can be seen together on rainy nights.
Males arrive at the breeding site before the females and start croaking to attract females. The mating call sounds like a ‘grook-grook-grook.’
The sound is made by the frogs by closing their mouth and nostrils, moving air backward and forwards over the vocal cords. The sound can be amplified by moving more air in and puffing out their throat pouch with the vocal sac.
Female frogs are generally quiet and much quieter than male frogs. They may make the odd grunt but can never be heard as much as the male frogs.
Unlike many mammals and birds, frogs do not go through a series of flamboyant and elaborate mating rituals. There are no huge displays of preening or prancing, males just grab the closest female as they arrive at the site.
The male jumps on the females back before wrapping their forelimbs around her body. They then grip the nuptial pads in a position called amplexus.
Males externally fertilize the eggs released by the female into the water. Females can lay over 2000 eggs at this time. The female presses her forelimbs on her abdomen while the male fertilizes them with his sperm. Amplexus can take several seconds or even as long as a month. This usually takes place on the water.
The eggs are fertilized as soon as they are laid, and before they absorb water.
Each egg is small (2-3mm) in diameter. The eggs are held in a gelatinous capsule which swells soon after up to 10mm. The eggs fall to the bottom of the water before floating once again, joining up with the other spawn.
The next stage for the eggs is when they develop into a tadpole which can take 10-21 days, depending on the location and temperature. Tadpoles survive by using the jelly around them which they digest using a special gland. At this point, they have no mouths and get their nourishment from the egg yolk.
They then start to eat plants and breathe through three pairs of gills. The gills are external but they are covered by a flap of skin.
Inside, a gill cavity is used for breathing, connected by a spiracle to the outside. After seven weeks the hindlegs have finished forming and a week later the lungs have developed.
By May or June, the frog is fully formed and about 15mm long. In colder conditions, tadpoles may grow slower. Frogs reach sexual maturity when they are in their third year.
Once the female has laid her eggs, the female usually leaves the spawning ground. However, the male will stay there to find another female. Both the male and female will return to the same breeding site every year after.
Although there are close to 2000 eggs laid by the female, many of them do not survive for long. Predators such as gulls ducks, herons, snakes, shrews, and badgers will feed on them.
Another reason for the low survival rate is the dredging of rivers leading to fewer ponds. Pollution is also another peril that can cause damage to masses of frogspawn along with insecticides used by farmers.