Page 70 - Hand rearing birds second

53

3

Incubation

Susie Kasielke

Introduction

Artificial incubation of bird eggs, like everything we do to care for animals, requires both art and
science. A large body of scientific work on avian embryonic development has been done to opti-
mize production in the commercial poultry industry. Fortunately for those working with nondo-
mestic birds, the process of development and hatching of avian embryos is highly conserved across
all species, so most of the knowledge derived from domestic species can be directly applied to other
taxa. Variation among species is seen in incubation periods (terms), temperature and humidity
requirements, and, to some extent, the hatching process. This is where the art, our collective avi-
cultural expertise, refines science‐based techniques to achieve optimal hatchability.
Artificial incubation may be used as a tool to increase production in rare and endangered spe-
cies, as many birds will lay replacement eggs if the first clutch of eggs is removed. In this case,
timing of removal of eggs may be carefully planned. Most often, however, artificially incubated
eggs have been rescued due to parental abandonment or other emergency situations. In some
cases, a combination of natural and artificial incubation may give the best results. Certain species,
such as raptors, have better hatchability if eggs are naturally incubated – either by actual or foster
parents – for one quarter to one third of the incubation term, before placing under artificial incu-
bation. With a new or contentious pair of birds who may squabble over incubation duties with
freshly‐laid eggs, replacing them with artificial or “dummy” eggs during most of the term will
protect valuable eggs from breakage. Once parents have settled in and proven themselves with
dummy eggs, the real eggs may be carefully returned to them, usually at internal pip, to allow
parental hatching and rearing.
In order to manage the process of artificial incubation, and to some extent natural incubation, it
is important to first have a thorough understanding of the structure of the egg, the functions of its
components, the development of the embryo and its extraembryonic membranes, and the hatch-
ing process. This chapter will provide a cursory review of these. The reader is strongly encouraged
to take advantage of more detailed references on the subject (Romanoff and Romanoff 1949, 1960;
Hamburger and Hamilton 1951; Anderson‐Brown 2002) and to practice incubation techniques
with chicken eggs or other domestic species.
When the egg is laid, the embryo, known as the blastoderm at this stage, is positioned over the
least dense area of yolk and so rises to the uppermost position regardless of the orientation of the
egg during early development. The yolk is surrounded by layers of albumen, including the chalazae,

Hand-Rearing Birds, Second Edition. Edited by Rebecca S. Duerr and Laurie J. Gage.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.