On the Park - June 2005
The
tasks that our 'flying' staff undertake are many and varied. Here Jane
Robertson gives us an insight into one facet of her job - the incubation
and rearing of raptor chicks.
As an extra goody, Jane has provided us with video
footage where she explains, in words and pictures, some of the things
she is talking about. The videos are broken down into chunks of one
minute in duration, and the files are each about 1MB. The candling video
is short (21 secs) and less than 400KB
INCUBATION BY JANE ROBERTSON
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| The first egg in the incubator |
When I first got involved with the Hawk Conservancy Trust eleven years
ago, I assumed in my naivety that you just put a male and female bird
of prey together and, hey presto, you got eggs then chicks, as a matter
of course. I now know that it’s far from that simple. Firstly
in most raptor species, if the male and female do not get on, the male
can end up as lunch for the bigger, more powerful female. Who says that
the Spice Girls invented “Girl Power”? If they do actually
bond with each other you are still not guaranteed fertile eggs. Out
of the breeding season the reproductive organs of males and females
deactivate - no point putting energy into lugging around something you
are not using.
The courtship behaviour that you see at the start of the breeding season
is the trigger for the organs to come back on line. However, in a new
pairing, the timing may be off and some, or all the eggs in a clutch may
be infertile. Even if they manage to get the first two things right, they
may still fail to raise young. The pair may not sit tight on the eggs,
or they may incubate them perfectly but then not know what to do with
the resulting chick. Imagine being presented with a baby that you have
no idea how to care for. There are no chick care books that they can read,
no friendly district nurse to pop around with advice. The maternal instinct
is usually very strong, but in the wild they might lose several clutches
before they get it right.
When you are captive breeding a rare species
you do not want to take any chances, so this is where we step in and take
the egg for manual incubation. If possible we will substitute a chick
of a similar species when the egg is removed; this way they get to practice
their parenting skills on a more robust chick. There are other reasons
for removing an egg for manual incubation. You may want the birds to produce
a second clutch. Most birds will recycle if the eggs are removed in the
first fourteen days. This gives you two for the price of one - especially
important in critically endangered species like the Oriental White-Backed
Vulture. They may lay at the wrong time of the year. Some species will
lay during their native spring/summer, which can fall in the middle of
our winter. The chick would not survive the cold. Lastly you may want
a hand-reared bird for training, or to use in artificial insemination.
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| The first hatchling |
So you have made the decision to remove the egg, now how do you hatch
it? You could give the egg to another pair of established breeding birds.
For example, we know that our pair of buzzards will hatch and care for
Red Kite chicks, but they may not breed at the same time, so this might
not be an option. Up until this year we would use chicken power to hatch
the eggs. Visitors to the park will have noticed the free-range chickens
that wander around the grounds. We have hens of all sizes and our CEO
Ashley Smith is second to none when it comes to sizing up the potential
of a broody chicken. Whilst this method may not seem very scientific,
it has been very successful over the years. The only drawbacks are that
you may not have a suitable broody chicken ready when the eggs are laid,
and if you have a very large, or very small egg, we may not have the correct
sized chicken. So at the end of last season we decided to join the 21st
Century and get a high spec. incubator. Fortunately we also got the assistance
of someone who knew how to use it, in the person of Simon Brough, who
for many years has been responsible for hatching and rearing baby raptors
at the National Birds of Prey Centre in Newent. He stayed with us long
enough to explain all the scary knobs and dials and to impart some of
the knowledge that he has gathered over the years; and although he has
now left, he remains in touch for long distance hand holding.
So how do you become a substitute parent? Well the main incubator is
about as close as you can get to the real thing. It has a plastic membrane,
which folds down over the eggs, and is heated by warm air. This simulates
the brood patch of the parent bird. Then, every half hour, the membrane
lifts and the eggs are turned 180 degrees. This ensures that the egg
is evenly warmed. The parents will do this in the nest, changing direction
so that the egg does not always turn in the same way. If the egg was
always turned the same way, the membrane which attaches the chick to
the shell would twist and strangle the chick. The incubator can be set
up to turn a variety of directions and for variable lengths of time.
The bigger the egg, the longer it takes to turn a full 180 degrees.
It gets really tricky when you are incubating several different sized
eggs at once. Then the roller that holds the eggs in place can be set
at varying distances to slow the roll of the smaller eggs down. After
the turner has been set up correctly it can be left alone, although
we monitor it daily to make sure that the eggs are still turning correctly.
The other settings on the incubator are also checked every day. The
falconers take it in turn to do this.
First thing in the morning we will go in and check the temperature
in the incubation room. The room itself is part of the incubation process
and the temperature and humidity are controlled and monitored. Access
to the room is limited to assist this, and to prevent the possibility
of passing infections to the eggs. The shell is a porous membrane, which
passes fluids and gases in and out of the egg. This makes it very easy
to pass infections, such as salmonella, to the developing chick. Therefore,
every one who comes into contact with the eggs or the incubators always
wash their hands first. After the room conditions are checked and adjusted,
the incubator itself is checked and the settings noted down. Next the
eggs are removed one by one and weighed and candled.
Over the incubation period the egg should lose an average of 15% of the
initial lay weight. This is monitored daily, and if it is losing too much
or too little the conditions can be adjusted to bring it back into line.
If it loses too much weight the chick will be small and weak; not enough
and the chick will not develop properly. If it is losing too much the
humidity is raised. The chick will then absorb the moisture through the
shell. If it is not losing enough you would lower the humidity, which
would draw moisture out of the egg. If you get this right after an incubation
period of anything from 28 days for many owls, to 55 days for a large
vulture, the egg will start to hatch. The first sign of this is the air
sac at the top of the egg becomes larger as the fluid around the chick
is absorbed/expelled. At this stage the egg is moved to a very humid incubator
and is no longer turned. Then the chick will internally pip into the air
sac. At this stage the chick may start to call. The next stage is to break
the shell. This first appears as a small crack. After this the chick can
rest up to 12 hours before it goes for the final push. When it is ready
the chick will break open the shell, using the egg tooth. This is a special
adaptation of the beak, a small hard lump at the top of the beak, which
it uses to knock against the shell. At this stage the chick is checked
at regular intervals to make sure that it is breaking free. It is very
tempting to help the chick break the shell, but you could very easily
kill it, if you are not careful. The chick remains connected to the shell
by a membrane and blood vessels, and this connection is not broken until
quite late in the hatch process. The chick also has to absorb the yolk
sac into its abdomen. This provides the chick with nutrition for its first
hours/days of life. If the chick hatches too soon the yolk will not have
been absorbed.
Once the chick has hatched it will be moved across to a warm dry incubator
and the rearing begins. We have had a few disappointments so far. The
first few eggs proved infertile and the first Milky Eagle Owl chick
did not survive the hatching process, although its sibling, which was
left with the parents until it was 11 days old, is doing well, as you
can see from the pictures. However we have just had our first incubating
success. Three Great Grey Owl chicks hatched out on the 12th, 13th &
15th May, and are all doing well. We all feel like proud parents, about
to pick out the paint colour for the nursery! This has now given us
the confidence to manually incubate rarer eggs in the incubator, such
as Red Kites and the Oriental White-Backed Vultures. This time next
year we hope to be telling you all about our new vultures and Red Kites.
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