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| What 97/98 |
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| What 97/98 |
The biologist Jeroen Creuwels
is spending his second season on Ardery Island during the summer of
1997/1998. Although Jeroen is often seen with his hands in his pockets when
he is in the colonies (according to him to warm up his hands), he seems to
collect much data on the breeding biology of fulmarine petrels. A
description of fulmarine petrels, his Ph.D project, the long-term project on
Ardery Island is given in Background of the Ardery
Island project. An overall idea of Jeroen's current research activities
will be given by describing some aspects of his work in more detail. Not all
this work could be done by himself alone, as he has only one pair of hands
and one pair of eyes. His two assistants on Ardery are a great help and
assist him with much field work.
Work-areas
The main work-areas are the two study areas
on the northern side of the island. In these study colonies all nest-sites
are numbered and marked. The Fulmar study colony is located near Robinson
Landing, just above the "Ardery wharf" where the inflatable rubber boats
(IRBs) from Casey land for resupply.
The Northern Plateau, a little plateau situated between steep slopes, is the
main study colony of the Antarctic petrels. The bird boffins at Ardery have
to climb 30m down on steep slopes to reach this plateau. Their safety is
ensured by two ropes to abseil down along the cliffs.
The location of the study colonies of the snowies and the capes are scattered all over the island. All study areas also have a reference area which is rarely visited. This way Jeroen is able to monitor how much impact his own research activities have on the breeding success in his study colonies. A similar number of chicks is expected in the much less disturbed reference areas, if the activities do not really affect the breeding birds.
The following aspects will be described:
- bird counts
- bird identification
- nest checks
- artificial nests
- diet studies
- satellite tracking
Bird counts
Counting birds is not always a very easy job, especially when your hands are
freezing off in the catabatic winds coming from the Antarctic continent.
Regular petrel counts in the study areas and reference areas on the island tell us how many birds are present in the colonies. For example during these counts we get estimates the number of breeding pairs, the total number of birds present, and the number of chicks.
Many birds and chicks cannot be seen during the counts. However the actual number of breeding pairs or chicks can be estimated in non-visited areas. If you assume that the proportion of birds not seen in the daily visited study-area is equal in the study-area and the non-visited areas, you can use the same ratio of seen/not-seen birds in the reference area to estimate the total of birds.
These counts could be compared between years to identify general trends
regarding food availability in the Southern ocean. For example, the number
of birds present in a colony could change due to differences in the fish or
krill stock in the Southern Ocean. Also the number of birds changes during
the season. These numbers are not stable during the summer, as numbers
fluctuate with different phases in the breeding cycle. During the "pre-egg
laying exodus" the colonies are sometimes almost abandoned as most of the
birds are out to sea to get fat reserves for the new season.
Bird identification
In this study it is very
important that individual birds can be distinguished from each other.
Therefore, the birds in the study colonies on Ardery Island are marked.
Individual recognition is achieved in three different ways.
In the first place the petrels in the study colonies get their life-long
PIN-code by giving them metal bands. Petrels rarely loose their metal bands
and the numbers on the bands don't fade away. Bands applied by American
biologists on Ardery in the early sixties are still readable in the late
nineties!
Furthermore, the birds are also marked visually by giving them a colour band
with a unique number. In this way birds can be identified from a distance,
which makes it possible to observe the birds without disturbing them.
In summer 1996/97 the Dutch have started to place "transponders" in petrels.
A transponder is a kind of microchip, which is also commonly used in cattle
and pets. These transponders are injected just below the skin of the bird's
leg. The antennas of the artificial nests are able to pick up this uniquely
programmed transponder number. During nestchecks a handheld reader can be
used to identify the bird by showing the transponder number on a screen.
Nearly all birds in the Fulmar- and Antarctic study colonies are banded
by now. Many of these birds were already banded in the first two field
seasons of Jan van Franeker, as these birds have a long life-span (up to 40
years and more) and are still breeding in the colony. By banding petrels we
now know that they are strongly attached to their nestsite, after 13 years
many of the retrapped birds were found back on the nestsite where they had
been banded before.
Regular nestchecks
During our daily visits to the study
colonies we note which birds are present on each nestsite. Also, if there is
still an egg and a chick present on the nest.
The data from the beginning of the season shows us how relationships are
formed and which bird is returning to their nest-site used the previous
year. Also, which birds are attempting to breed and which ones are not.
Later in the season when eggs are laid, we might be able to explain why
certain eggs are doomed to fail. For example when a partner doesn't return
in time to take over the incubation shift, the egg will be left behind.
Before it has cooled down too much, it will probably be taken by a Skua.
When the partner does return in time, but the breeding bird has been waiting
very long, their incubation-schedule might be too mixed up, so later in
season the egg could also fail.
Artificial
nest-system
The development of the artificial nest-system
started by the Technical Department of the Institute for Forestry and Nature
Research in The Netherlands (in Dutch: Instituut voor Bos- en
Natuuronderzoek, abbreviated to: IBN-DLO) in 1994. The main person behind
the development is Willem van der Veer, who designed the nests and the
software in close cooperation with Jan van Franeker. Willem is a technician
at the Technical Department of IBN-DLO. He gained experience with developing
artificial nests when he developed a weigh-system for an earlier project of
the IBN-DLO on geese in Siberia.
Willem was on Ardery Island in 1996, during the first half of the season, to
help to install the nests and to teach the birdos some basic knowledge of
electronic and technical equipment.
The artificial nest-system on Ardery Island consists of artificial
nest-units, energy systems to supply power in the field, and long data
cables from the study colonies to the datalogger-computer in one of the
apples. Each nest-unit has an artificial nest with a weigh- and an antenna
system inside. The antenna is able to pick up the transponder number from
the bird on the nest.
This
artificial nest is placed on the actual nest location, and petrels are so
strongly attached to their nest that they easily accept them as a new home.
Each nest-unit has a separate electronic box attached which controls the
power and the data generated by the nest.
This year approximately 25 artificial nests were placed in the Antarctic
petrel study colony at the Northern plateau and another 25 in the Robinson
Landing Fulmar study colony.
Every five minutes the weight of the nest and a possible transponder number appears on the screen on the datalogger inside the apple. This system runs for the whole breeding season and generates a big data-set for Jeroen's thesis, in addition to his nestchecks and other observations.
Much information can be obtained from the data on the weights and
presence of birds on the artificial nests, and a few examples are given
below.
While the bird is sitting on its egg it looses weight. A bird cannot keep on
loosing weight, so at a certain point all resources are depleted and it has
to go back to sea. The rate of weight loss differs from bird to bird, but
also the decision to go back to sea might differ between individuals. We are
also able to determine how much weight it gained while fishing at sea, as we
know the weight when it left and its weight on return. Without any effort we
get the exact times when the incubation shifts are taken over, even in the
dark or in blizzards when the colonies could not be visited. When we combine
the data on the nests on a certain time we are able to establish the times
of big events in the colony. For example when a Giant petrel visits the
colony all nests are suddenly empty!
In the chick-phase we are able to derive the meal-sizes for the chick, as
the antenna reads the transponder number and the chick will have sudden
weight increases. We can see if there are changes in food deliveries to the
chicks among both partners.
Diet studies
Comparative studies are needed to assess the changes in the food
availability in the Southern Ocean. Fisheries and petrels are both consumers
of the fish stock in the Antarctic waters. The breeding success or
indications of the general body condition in petrels could be used as a
measure for total food availability. Differences in fish and krill supplies
on a finer scale might be reflected in changes in their diet.
Therefore, every year a small sample of birds will be stomach-flushed to
see if there are any changes in their general fish and krill
consumption.
Data from the current study will be compared with data from earlier seasons
when Jan van Franeker had collected data on their diet, and with data from
other locations to see if there is any geographical variation in their
diet.
The next Ph.D will be working in greater detail on this subject.
Satellite tracking
Much biological research on animals takes place on locations where they can
be followed easily. For example, until recently it has been impossible to
follow a single bird cruising over the seas miles away from shore. But now
light weight satellite transmitters have become available which allow the
birds in flight over the ocean to be tracked.
This season a pilot study will be conducted with a small number of satellite
transmitters to gain information on where Fulmars and Antarctics go when
collecting food for their chicks, how far they go out and how long they stay
searching for prey at sea. All these factors influence the amount of food
they will return to their offspring.
The findings will be the starting point for more research by the next Ph.D
student on the foraging strategies of petrels.
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