Alcorn Gordon D. Birds and Their Young. Courtship, Nestling, Hatching, Fledging - the Reproductive Cycle

Harrisburg, PA: Stackpole Books, 1991. — 214 p. — ISBN: 0-8117-1016-5.The reproductive cycle in birds and the associated sciences of oology (eggs) and nidology (nests) are complex. From the initiation of the cycle and the enlargement of the gonads, each internal event parallels changes in the behavior of the parent birds and eventually the young as well, first when they leave the egg and later when they fledge. In most birds, the cycle follows the same general pattern with specific adaptations due to environmental forces, meteorological changes, and genetic influences. Birds must in a comparatively short time seize upon a habitat within a selected environment, called territory, and get all the preliminaries for a successful nesting cycle (courtship, mating, nest construction) out of the way. Once these preliminaries have been accomplished the parent birds can move into incubation, which is a more or less monotonous period of greatly reduced activity. After the eggs hatch the pace picks up a bit with caring for the young, but not to the same level as the frantic lifestyle necessary before egg laying.
To bring to print the details of the reproductive cycle from beginning to end for all bird species would be a monumental task. While the general cycle follows a fairly common pattern in all birds at all stages, there are modifications in almost every one of the world's approximately 8,500 species. These adaptations can be seen as attempts to overcome the difficulties or take advantage of the assets of an environment, thereby making the fledgling stage more successful.
The following pages outline the general steps that parent birds go through to succeed in the fledging of their young. I have tried to use sufficient examples to point out the overall similarities among different species. At the same time, I have tried to show how the behaviors of some birds change in unusual conditions such as extreme heat or cold. Such extremes make reproductive processes more difficult, and certain species of birds must adapt in one way or another to avoid disastrous results.
For most species of birds, a significant part of their year — up to ten or eleven months in the megapodes — is devoted to reproductive activity. Instincts for reproduction are highly developed in the thousands of species of birds, and because of these special instincts birds show a marvelous and colorful series of behavioral, structural, and physiological patterns to establish the reproductive cycle and raise their young.
A few birds, such as brood parasites, modify their behavior to exclude some of the normal steps, such as incubation and feeding, instead assigning those tasks to host parents. Consequently, for expediency, certain behavioral activities must be substituted for others. Parasitic females must, for example, instinctively know how to select a suitable host nest and when to lay their eggs there.
In the discussion here, repeated references are made to various historical items. References to old egg records that are scattered throughout the text are taken from original data blanks for egg sets found in the Slater Museum at the University of Puget Sound Museum of Natural History. These are referred to in the text as UPS Museum. Many of these sets with accompanying records date from the late 1800s and the early 1900s.
Oology as a science reached its peak at about the turn of the century. At this time egg collecting was extremely popular among scientists, amateurs, and curious bird lovers of all ages. But with the coming of state and federal laws prohibiting the indiscriminate collecting of bird eggs, the number of collectors declined. For a time, states issued collecting permits for interested private collectors. But today most collecting permits are issued only to scientists associated with institutions. Not surprisingly, the rise of protectionism was paralleled by a sharp decline in oology and nidology; the general population today has little interest in these fields. Most large collections are managed by government agencies or colleges and universities in their museums.