The hooded hawk mystery, by Franklin W. Dixon.

Enhanced descriptions from Syndetics:

The young detectives receive a trained peregrine falcon as a gift that involves them in an exciting mystery. Imagine their astonishment when the swift-flying falcon brings down a homing pigeon carrying two precious rubies! Startling events that ensue indicate the gems are a ransom that has been paid for the release of a kidnapped student from India, who had come to the United States to complete his education. But Tava, the son of a wealthy industrialist, is still being held captive. Hoping to find a clue to Tava's whereabouts, the Hardys try to track down the owner of the ruby-bearing pigeon. Their every move, however, is thwarted by the dangerous criminals not only involved in the kidnapping, but also in the large-scale smuggling of aliens from India to the United States. How Frank and Joe eventually outwit their adversaries climaxes this thrill-packed mystery adventure.