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CHIRPY CHIRPY CHEEP CHEEP: Geochemistry for birds
In this age of bird flu and global change, pinpointing bird migration routes and monitoring any changes in them
has become of considerable interest. In the past, all sorts of methods have been used as tools in this type of
research, but Laura Font may have found a new and better way.
In Durham, Laura’s research involved measuring Sr and Pb isotopes in plagioclase from volcanic samples. It was
at Durham where Laura started developing her method to use Sr and Pb isotopes in bird feathers to track bird
migration routes.
SEM image of a bird feather (x 55.6), showing shaft and dust specks (bird species is Myiopsitta monachus)
Previously, other isotopes (H, C and O) as well as certain trace elements have been used to infer migration routes.
Sulfur isotopes in combination with hydrogen isotopes were also tried, in an attempt to distinguish between birds
foraging in the marine realm and terrestrial feeders. The problem with such methods is that their discriminatory
power is relatively limited, and fractionation mechanisms in birds complicate matters in some cases.
Other methods such as the use of tags or leg bands and the counting of birds at specific locations are labor-intensive
and do not carry an overwhelming success rate. In addition, censuses do not provide any data on origin.
Using feathers to obtain information about bird migration is relatively easy and does not or hardly impact birds.
While many bird feathers do have a blood supply while still on the bird, these veins do not run along the entire
shaft. A large part of a feather could therefore be clipped off and this would not impact a bird’s flight at all.
However, that is often not even necessary as birds naturally lose enough feathers that can simply be collected on-site.
Previous studies involving bones, claws and shells had already shown that Sr isotopes do not appear to fractionate
in birds and reflect a bird’s natural environment. There are geological situations involving preferential release
of Sr during weathering that require special care, but for most sites, the relationship is quite straightforward.
However, what is seen most notably in bones tends to reflect the bird's environment during its lifetime and birds
are relatively long-lived. Bird migration research wants to acquire data on the bird's environment at specific
points in time, for example prior to and after migration (i.e., a much shorter time-scale). Feathers represent
such specific points or shorter periods.
In contrast, birds periodically renew their feathers, and feathers tend to represent the environment at the
time of growth, for example specifically prior to migration. To use the composition of bird feathers as a
much less invasive and less labor-intensive method is therefore a great idea. Bird feathers consist largely
of keratin, like human hair and finger nails, and reflect what the organism has consumed. The analysis of
bird feathers is therefore not a new idea in itself. Dr. Font’s method is a different story, however.
First of all, a method had to be devised to remove all dust from the feathers as this dust would constitute
serious sample contamination. Tests were carried out in which a bird’s dust bath was simulated by sweeping
feathers through a sandy soil, followed by various cleaning methods and SEM imaging to inspect the feathers’
cleanliness. Using several blasts of nitrogen gas turned out to be the best way to remove both dust and wax deposits.
The next problem is that feather samples contain very little Sr. Multicollector inductively coupled plasma
mass
spectrometry (MC-ICP-MS) is not able to measure quantities as low as < 12 ng Sr because of Kr interferences
(Kr is present in the Ar plasma). Dr. Font’s new method uses ultra-low blank ion-exchange chemistry followed
by thermal ionization mass spectrometry (TIMS). Sample preparation is necessary to preconcentrate the Sr and
to remove as much organic material as possible from the sample. The organics would interfere with the column
chemistry and if you load a “dirty” sample on a TIMS Re filament, you are not going to get good results
(if any at all).
To optimize ionisation, the feather-derived samples are loaded onto a very small area of the filament
by running a 1-A current through it and melting two strips of parafilm onto the filament to define the
loading area. After loading a mix of sample and TaF5 activator, the parafilm is burned off with a 2-A current.
At the end, more activator is loaded on top of the sample to seal the sample onto the filament and prevent any sample loss.
Dr. Font is developing a new method for the analysis of Pb isotopes in bird feathers that will use
the same fraction as used for the Sr analysis (collected from the columns after the Sr fraction).
In 2007, feathers had already been collected at various sites in Europe and Africa for the new project.
In 2008, Dr. Font collected feathers from Pied Flycatchers and Collared Flycatchers in Gotland in Sweden
as well as soil, water, bird prey and feces samples.
SEM image of a bird feather (x 104), with some dust (bird species is Myiopsitta monachus)
It’s nice to see work that radiates such elegance and thoroughness in all its details, and reflects
an innovative and exploring spirit.
A slightly different version of this article was also published in the newsletter of the Geochemical Society in 2008.
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