3. Breeding biology
Rhys E. Green
3.1 Introduction
Collecting information on breeding biology and performance is an important
part of many studies of the population ecology of birds and is often essential in
identifying effective conservation measures for threatened and declining species.
As with all scientific research, care is needed in designing an appropriate program
of fieldwork on breeding birds. It is important to think through in detail the ques-
tions you wish to answer. For example, do you want to estimate the mean number
of young reared per female or pair in the breeding season or is it also important to
know about the success of individual breeding attempts and the causes of failure?
Make a preliminary model of the population you are studying or the sequences of
events in the breeding cycle of the individuals within it. This might be a simple
flowchart describing how you think the events in the breeding season of an
individual female relate to one another and to her environment. What determines
whether or not she attempts to breed, when she begins her first breeding attempt,
and how many eggs she lays? What influences the chance that her nest fails?
Does she renest after failure? How long does that take? What influences whether
she re-nests or not? It may seem strange to do this before you begin your study.
Many people think you should collect a lot of information first and only then
use it to construct a model. However, building a preliminary model based upon
whatever is already known about the birds you are studying or, failing that, what
is known about other species in the scientific literature, will help you to organize
existing knowledge for many bird species. There is much useful information on
basic aspects of breeding biology, especially clutch size, duration of incubation,
and nestling period, and time of breeding, and this is well summarized in ornitho-
logical handbooks. Most importantly, constructing a preliminary model will
force you to make explicit the assumptions you are making about how the things
you can observe and measure relate to the reality you want to know about.