Warblers are dull greenish or brownish or yellow colored small birds. They are active fliers. They feed on insects. The Yellow warbler is most common in willows and mangroves. Warblers are known for their migrations. They abandon cold northern winter with little or no food and move south for moderate weather and food conditions.
Before taking to the skies, the Blackpoll warbler spends 10 to 20 days feeding and beefing up its weight from 1/3 ounce to ¾ ounce. The physically well- conditioned bird is now all set for an arduous journey.
The first lap of 1200mile journey involves the Blackpoll warblers flying over Bermuda, to Lesser Antilles. On reaching Florida, the warblers are helped by trade winds that sweep from the northeast. 86 hours after leaving their breeding grounds in the north eastern Unites States, the birds arrive in northern South America. Having neither rested nor eaten since the onset of their flight, they might be considered little more than living skeletons with feathers, their body reserves having been spent during the long journey. Yet these warblers could continue their journey farther. Those birds that are weak and ineffective for migration drop to death.
For a human being to match the metabolic exertion of the Blackpoll warbler, he needs to run a four minute a mile for eighty hours straight. Even the best sprinter in the world cannot dream of this mind- boggling feat.
The theory that birds use stars to navigate was first enunciated and demonstrated in 1957 with Garden Warblers. The birds were hand raised and were housed in circular cages in a planetarium. In the planetarium the night sky could be simulated to spring or fall. The researchers positioned themselves under the glass bottoms of the cage to watch the movements of the birds. When the time to migrate came, the warblers faced north in the ‘spring’ and south in the ‘fall’ of the simulated night sky of the planetarium. When the fake stars of the planetarium were dimmed the warblers became confused and disoriented. The researchers later rotated the planetarium sky by 18o degrees. The birds also reversed their internal compass to compensate for the shift. Migratory behavior is genetically controlled in birds.
Courtship in warblers involves singing. The male Sedge warbler will continue singing until he finds a mate. During courtship the song will become unusually long and sometimes more complicated. Belgian researchers found that the birds sang the songs of nearly one hundred European species as well as more than a hundred African species from localities where the bird spent its winters. The average male Marsh warbler has been found to mimic seventy- six species.
Warblers keep their nests clean and tidy. Immediately after the eggs are hatched, Yellow warblers eat the eggshells. It is good calcium food for the parent bird. Prairie warblers eat the fecal sacs of the chicks to keep the nest tidy. The warblers are tireless feeders of their brood. The female Arctic warbler has been observed feeding her chicks 18 hours a day.
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