Weighing and Observing Birds: Automatic Data Recording and Processing
Psztor Erzsbet, Cristopher M. Perrins*, Tth Zoltn
ELTE Genetikai Tanszk, *Edward Grey Institute of Field Ornithology, Deptartment
of Zoology, University of Oxford
We discussed techniques for the automated observation of (free living) birds
that allow behavioural and ecological parameters to be measured. The method in
focus was observation by weighing. We were also interested to see the special
potentials of the combination of different observation techniques.
In the last decades there were a few dozens of studies that involved weighing
individuals at nests or on perches to collect data on body weight changes and
visiting activities of a number of different bird species. The weighed object,
which is the place visited regularly by the observed animals, may be a
nest(box), an artificial perch or feeder. Consequently researchers can use the
method to investigate bird species that nest in boxes (Great Tit Parus major,
Crimson Rosella Platycercus elegans), on platforms (e.g. on buildings; Blackbird
Turdus merula, Black Redstart Phoenicurus ochruros), in burrows (Sand Martin
Riparia riparia), or on the ground (Lapwing Vanellus, Antarctic Petrel
Thalassoica antarctica); or those frequenting a perch (Red-backed Shrike Lanius
collurio); or those accepting food provided by a feeder (European Starling
Sturnus vulgaris). Moreover, it was possible to measure birds that are visiting
on foot: penguins at the "gate" to their colony or kiwis at the entrance to
their nest burrow. The activity during which weights are measured may be nest
building, egg laying, incubation, courtship feeding, brooding, nestling feeding,
fledging; or singing, foraging, resting at a perch; or the feeding intensity
and the dominance relations at a feeder.
Computers and electronic balances offered a higher level of automation for these
measurements. Data may be recorded by a local computer (e.g. palmtop) beside
each balance, or by one central computer connected to the balances by long
cables or by radio transmission. The central computer provides effective
supervisory control over the observations.
However, a relatively complete software package has been developed only
recently, aiming to support not only automated, non-stop, long-run data
collection but also to reduce the tremendous work required by the processing of
the resulting floods of data which is needed to extract variables for
statistical analyses. Zoltn Tth developed "The Wisitor" software for weighing
nests and he collected data on breeding attempts in ten bird species, including
tits, sparrows, starlings and blackbirds. Parts of the software were used in
Oxford (Richard Woodburn, Robin McCleery), Canberra (Elsie Krebs) and
Nyregyhza (Tibor Szp).
Data recording in "The Wisitor" weighing system is done on the basis of event
recognition. Two series of weighing results are stored (pre-event and post-event
series) at each arrival and departure. Data processing modules estimate the
weight levels and their measurement error from the recorded raw data and build
the visit records. The high-level support of data processing includes automated
calculations with adjustable parameters, interactive graphs, automated
identification of the two parents from the body weights of the visitors, and
several output files with different data structures. Visit records contain
identification (male/female), time of arrival and of departure, length of in and
out bouts, body weight, load weight, delta parent weight.
A crucial feature of this measuring system is the potential of estimating the
measurement error from the recorded weight series. This addresses a generally
overlooked problem: Weighing moving objects under field conditions imposes a
significant error on the measurements of small quantities. In order to detect
differences between those (e.g. the average load sizes of individuals, nests,
territories) it is essential to find and exclude the bad measurements and in
turn reduce the average measurement error of the remaining data set. Tth and
Psztor, with the help of Evert Meelis (Leiden), created a numeric method to
estimate a major component of the measurement error for each weighing series.
Filtering the data with an error limit yields more reliable estimations of both
load weights and body-weight changes between consecutive visits.
These weight variables can be used to define rough behavioural acts as foraging
trip with or without self-feeding, which form the basis of an analysis of
parental foraging behaviour. For instance, the minimum amount of the collected
food and its allocation between nestling- and self-feeding can be assessed. The
time budgets of the observed birds can be reconstructed from the acts for entire
nesting periods. However, without additional measurements, the energy budgets of
the parent birds cannot be reconstructed from continuous weighing, as it was
pointed out by Sally Ward (Aberdeen).
Ruedi Nager (Glasgow) warned that body composition of birds may change with
environmental conditions without being reflected in changes in body mass. Gulls
which were experimentally manipulated to lay one additional egg lost a small,
but significant amount of protein from their flight muscles. This effect is
small compared to the natural variation in mass, but it had very important
consequences on the bird's ability to raise young.
Visual observation - the most traditional direct observation method - can
provide information on the behaviour of visitors beyond visiting activity, and
what's more also on the behaviour of resident individuals, like nestlings,
including interactions. When some load is involved in the observed activity
(e.g. feeding) it can give information on the volume (length, width) and the
identity of the cargo (e.g. classification of prey). Direct observation,
however, may be too time-consuming or practically unrealizable, especially when
it's used long term, for example supplementing some automated observation.
Taking pictures in an automated fashion can overcome not only these problems but
it can increase the reliability and the resolution of the visually obtained
data. Pictures may allow subtle identification of individuals and items (e.g.
prey) and measuring the exact size of those. The drawback is that pictures are
restricted in many ways (angle, focus) compared to direct observation.
Robin McCleery told about the Oxford study on Great and Blue Tits (Parus
caeruleus) that included monitoring nests both by automated weighing ("The
Wisitor") and by automated photography, simultaneously. The head and beak load
of the entering parent was photographed at each visit, using a Super-8 mm cine
camera with single-frame film-advance and flash synchronization, triggered by a
micro-switch at the entrance hole. The sex of parent, the number and type of
prey delivered (often to species level) and the time were determined. The
records allowed detailed analyses of the diets of nestlings between day 4 and
fledging. Sample size for feeding activity data was increased by nest visit
counters that were triggered by the depression of a micro-switch wire each time
a bird passed through the entrance hole of the nest box.
Marcel Lambrechts (Montpellier) used video cameras and metal detectors to obtain
information about the feeding frequencies of tit parents. The time of the visit,
the volume and length of the prey, and its type (caterpillars, spiders,
grasshoppers) were determined from the video, and information was obtained on
the behaviour of the parents and the young in the nest.
A disadvantage of picturing systems is that coding and quantifying the available
information into data from the records remains "manual" and extremely time-
consuming. Using modern digital techniques it would be possible to record
pictures directly in electronic formats. Digital picture processing on a
computer with a specialized software can make extracting the data more efficient
by automatic selection of relevant frames, and by providing tools for measuring
the size of (prey) items and maybe even for their identification.
The combination of the automatic recording of brood and parent weights with
radio-tracking of the parents' range use offers some attractive opportunities.
Balances weighing artificial nests made of non-moistening material quantify
brood growth as well as changes in parent condition with high temporal
resolution. Simultaneous records of the parents' range use therefore allow the
amount of food obtained from different habitat types to be quantified. In a
pilot study of the Swiss Ornithological Institute, reported by Beat Naef-
Daenzer, the simultaneous application of both techniques was tested successfully
on the Barn Swallow (Hirundo rustica). Initial data on four pairs have
demonstrated that e.g. adverse weather greatly reduces the amount of food given
to the nestlings, but this is not due to a reduction in searching effort of the
parents. Since swallows forage in distinct areas for about 0.5-3 hours foraging
success and the amount of food taken to the nest can be quantified with a
resolution of a few hours.
Elisabeth A. Schreiber (Washington, D.C.) talked about observations on the time
and energy budgets of breeding boobies and tropicbirds. Presence and absence of
radio transmittered birds was recorded by a computer to track adults' presence
at the nest in order to determine feeding rates and resting times at nest. Watch
activity recorders fixed on their leg were used to determine time on the water
(resting) when away from the nest. Results did not support the energy limitation
hypothesis, as adults spent most of their time resting and could increase
feeding activity significantly when manipulated.
A multisensor telemetry system for studying flight biology and energetics of
free-flying Eurasian Griffons (Gyps fulvus) were presented by Ralf Boegel
(Berchtesgaden). The method is suitable for long-term monitoring of heart rate,
body temperature, plumage temperature and air pressure (flight altitude) of
large birds. For establishing good correlations between measured parameters a
calibration in two ways is essential: 1) correlating energy turnover rate versus
heart rate and body temperature in a metabolic chamber (laboratory), and 2)
later on in the field making visual observations to identify certain patterns of
measured parameters, which correlate with a certain ethological context (e.g. a
fast decrease in plumage temperature is associated with flight activities, even
if the air pressure sensor indicates no changes in altitude, i.e. constant level
flight). After these calibrations, most of the data can be interpreted without
having visual observations.
While automated measurements can produce high-resolution and accurate data -
otherwise unavailable, the equipments are often expensive and without good
software support data processing may become overwhelming. Constraints on sample
size (of individuals) call for efficient experimental designs and a combination
of direct observations with joint application of complementary automated
techniques.
|
|
|
