Background
The serin, in the words of Kinzelbach, is a bird that "was a topic of particular interest to ornithologists of the 19th and 20th century," due to "the rapid expansion of its range in historical times."

What was done
In the words of the author, "all the sources of records of the serin in 16th century Europe are (re)-examined, both those already known and some that have been newly discovered."

What was learned
Kinzelbach reports that this exercise confirms the findingss of Mayr (1926), i.e., that "north of 48°N there were no free-living populations of Serinus serinus in the 16th century."  During that period, the serin may have attempted to expand its range, but Kinzelbach says it "was halted by colder periods of the Little Ice Age after 1585, only resuming a rapid expansion at the beginning of the 19th century," after which it was "able to expand its range from the Mediterranean region throughout large areas of Central Europe within a mere 200 years."

What it means
The migratory history of the serin provides an important reality check on the Mann et al. (1998, 1999) hockeystick temperature record of the past millennium, which it fails miserably, since it does not depict any Northern Hemispheric warming until at least 1910, a full century after the serin began its dramatic northward expansion.  The temperature history of Esper et al. (2002), however, passes with flying colors, as it depicts post-Little Ice Age Northern Hemispheric warming beginning at about the same time the serin began its northward migration.

References
Esper, J., Cook, E.R. and Schweingruber, F.H.  2002.  Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability.  Science 295: 2250-2253.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Mayr, E.  1926.  Die Ausbreitung des Girlitz (Serinus canaria serinus L.). Ein BEitrag Zur Tiergeographie.  Journal of Ornithology 74: 571-671.