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THE RING 34 (2012) DOI 10.2478/v10050-012-0004-1
COMPARABILITY OF WING LENGTH MEASUREMENTS
BASED ON DATA COLLECTED
AT TWO TWIN STATIONS DURING MIGRATION
Grzegorz Zaniewicz
ABSTRACT
Zaniewicz G. 2012. Comparability of wing length measurements based on data collected at
two twin stations during migration. Ring 34: 37-43.
Data collected during bird migration include measurements taken during ringing. The va-
riety and quality of information, which these measurements can potentially provide, de-
pend strongly on their accuracy and comparability.
The analysis of the comparability was made based on the measurements of wing length
taken by different ringers during autumn migratory seasons at the southern Baltic coast. An
experiment was run with the measurements taken from six passerine species during several
(from 8 to 10, depending on the species) migratory seasons at two twin sites belonging to
Mierzeja Wiœlana station. Pearson’s correlation coefficient was used to evaluate how
strongly the habits of different measurers influence the measurements taken. The results of
this experiment show that correlations between the measurements collected at these two
sites are strong and statistically significant for the Blackcap (Sylvia atricapilla), Garden
Warbler (Sylvia borin), Robin (Erithacus rubecula) and Song Thrush (Turdus philomelos).
However, for the Goldcrest (Regulus regulus) and Willow Warbler (Phylloscopus trochilus)
the relations were not significant. The last species allow to consider other causes, independ-
ent from human factor, which are possibly responsible for the average wing length local
variability. In such species, we still need to look closer at the potential sources of their differ-
entiation, such as the preferences of habitat selection between sexes, populations, etc.
Key words: wing length measurement, personal bias, migration
INTRODUCTION
The length of the wing is the most common measurement taken during ornitho-
logical studies. Three different techniques of the wing length measurement are used
(Svensson 1992, Gosler et al. 1995), which unfortunately precludes a direct compari-
G. Zaniewicz, Bird Migration Research Foundation, Przebendowo, PL-84-210 Choczewo,
Poland; Bird Migration Research Station, Wita Stwosza 59, PL-80-308 Gdañsk, Poland,
E-mail: zidia@wp.pl
Publication appointed to the SE European Bird Migration Network papers
son between data collected at some stations. Relatively simple techniques of measur-
ing the wing length compared to the tail length or wing formula, allow to collect data
useful for various studies concerning long-term changes, climate changes, popula-
tions, sex and age differentiation, adaptation for migration, timing of migration (e.g.
Busse 1968, 1988, 1997, 1999; Busse and Maksalon 1986; Lo Valvo et al. 1988;
Tellería and Carbonell 1999; Nowakowski 2000, 2002; Pèrez-Tris and Tellería 2001,
2002; Yom-Tov et al. 2006; Zaniewicz and Busse 2008; Salewski et al. 2010; Van
Buskirk et al. 2010; Kovács et al. 2010, 2012; Arizaga et al. 2012). However, clear de-
pendencies are usually hidden, as the variation in wing length depends on several fac-
tors, such as sex, age, population, status of the specimen (skin, live bird) (Svensson 1992,
Jenni and Winkler 1994, Fiedler 2005). Some additional variation is also caused by dif-
ferent habits of individual ringers who take measurements (Barrett et al. 1989, Morgan
2004). It is also confirmed, that the repeatability of wing length measurements between
two or more measurers is lower than it is in the case of an individual measurer (Harper
1994). This study is an attempt to establish the level of comparability for different
measurers who collected data independently on the same migration route.
STUDY AREA AND MATERIAL
Mierzeja Wiœlana (54°21’N, 19°19’E; Fig. 1). Migrants were captured in the mist-
nets and, in some years, additionally in the Heligoland-type trap. Two main capturing
sites (named here as MW and ML) were located on the Vistula Spit in young pine
stands and older stands mixed with oaks as well as in reedbeds surrounding the Vis-
tula Lagoon (for detailed description see Busse and Kania 1970). The numbers of
birds caught at both sites in particular seasons of study are given in Table 1.
METHODS
Fieldwork
A stable number of the mist-nets were used throughout the whole period of work
within a season. Captured individuals were ringed, sexed (when possible) and aged ac-
cording to plumage features and/or skull ossification (Busse 1984). A detailed descrip-
tion of the field methods was given by Busse and Kania (1970) and Busse (1984, 2000).
Wing length measurement
The maximum chord measurement was used – detailed description was given by
Busse (1974, 2000) – with the accuracy of 1 mm. The wing length measurements
were taken by different ringers during the analysed period of the study. The measure-
ments taken into the analysis included only first year individuals (immatures) repre-
senting six passerine species: Blackcap (Sylvia atricapilla), Garden Warbler (S.
borin), Robin (Erithacus rubecula), Song Thrush (Turdus philomelos), Goldcrest
(Regulus regulus) and Willow Warbler (Phylloscopus trochilus), for which the data
were sufficient enough to run statistical analysis (at least 20 individuals per season).
38 THE RING 34 (2012)
Table 1
Numbers of measured individuals
Site 1967 1968 1969 1971 1972 1973 1974 1981 1982 1983 Total
Sylvia
atricapilla
MW 60 70 72 74 48 35 43 39 32 30 503
ML 84 96 144 127 84 143 156 103 75 23 1035
Sylvia
borin
MW 40 38 29 42 90 30 21 60 28 - 378
ML 106 115 97 45 107 68 124 106 58 - 826
Erithacus
rubecula
MW 753 1002 960 898 774 1176 146 404 620 1094 7827
ML 808 1282 1281 969 805 1595 892 744 590 331 9297
Turdus
philomelos
MW 105 87 171 202 34 - - 241 98 275 1213
ML 381 277 239 81 108 - - 148 33 55 1322
Regulus
regulus
MW 1454 435 879 4387 3167 2409 69 420 522 4016 17758
ML 3932 1095 3504 3181 6105 8017 9633 3626 1071 2025 42189
Phylloscopus
trochilus
MW 100 208 65 566 214 169 99 248 267 157 2093
ML 302 813 354 383 173 259 407 103 53 22 2869
Total 8125 5518 7795 10955 11709 13901 11590 6242 3447 8028 87310
THE RING 34 (2012) 39
Fig. 1. Location of Mierzeja Wiœlana ringing station (above) and a map of two sub-stations – MW
and ML (below); after Busse and Kania 1970.
Evaluation of comparability of measurements
In order to present how the year-to-year variation in the average values of the
wing length reflects the actual changes of this trait in the nature, I analysed a relation
between the measurements taken simultaneously by different measurers in the same
area. The measurements were taken by different ringers at two places (sub-stations),
about 0.5 km apart, during each of the several autumn seasons when these two ring-
ing sites worked at the same time. On the basis of the average wing length calculated
for each season at both sub-stations (named as MW and ML) separately, I evaluated
the comparability of the measurements collected at these places with the use of Pear-
son’s correlation coefficient. A short distance between the analysed catching sites en-
sured that the migrants passing the sub-stations represented the same “migration
stream” as well as the same composition of populations. However, both sites were
a bit differentiated by their habitats (Busse and Kania 1970). A similar method based
on the analysis of the correlation coefficient was applied to examine repeatability of
the measurements taken at least two times from the same group of individuals (Mar-
tin and Bateson 1986, after Harper et al. 1994).
RESULTS
Comparability of measurements
The positive correlations between the average wing length of first-year Blackcaps,
Garden Warblers, Robins and Song Thrushes measured at two sites (MW and ML) of
Mierzeja Wiœlana station were generally very strong and highly significant (Fig. 2).
For Goldcrests, however, the positive correlation of the average wing length was not
significant and for Willow Warblers it was negative but not significant, either.
In the case of all the analysed species, the average wing length measured over the
studied periods at those two sub-stations showed no statistically significant differ-
ences (Table 2).
Table 2
Average wing lengths for species passing two sites (MW, ML) at Mierzeja Wiœlana.
Numbers of individuals – see Table 1.
Wing length SD t-test
MW ML MW ML tp
Sylvia atricapilla 75.89 75.64 0.64 0.76 0.75 0.47
Sylvia borin 78.06 78.44 0.86 0.71 1.03 0.32
Erithacus rubecula *71.59 71.98 0.70 0.62 1.29 0.21
Turdus philomelos 116.95 116.38 1.39 1.72 0.73 0.48
Phylloscopus trochilus *65.84 66.42 0.53 0.87 1.71 0.11
Regulus regulus *53.37 53.73 0.53 0.31 1.84 0.08
* some males have longer wings than females but this can also depend on population (Svensson
1992)
40 THE RING 34 (2012)
DISCUSSION
A strong and statistically significant correlation in the average measurements
taken independently by two ringers at two sites located very close during ten autumn
migration seasons indicates that the variation in the average wing length observed
over several years can reflect the actual biometric changes of the species/populations
passing the study site. The variability of the wing length assessment resulting from
the measurements taken by different ringers is generally considered to be low, par-
ticularly in birds similar in size to the Garden Warbler, for which a research con-
THE RING 34 (2012) 41
Fig. 2. Relations between the average wing lengths measured at two sub-stations (MW and ML)
of Mierzeja Wiœlana station. Regression equations, Pearson‘s correlation coefficients (r)
and statistical significance of correlations (p) are given.
ducted in Germany showed the variation of 0% (Salewski et al. 2010). However, in
the case of larger species the variation was as high as 29% of the total random error
variance (Salewski et al. 2010). Furthermore, the authors stated that the variation of
measurements caused by different habits of individual measurers had little and insig-
nificant influence on the recorded average annual wing length. In this paper we com-
pare the measurements not for the same group of individuals measured twice by dif-
ferent ringers, but for two independent groups of birds representing the same flying
stream. Significant correlations for the Blackcap, Garden Warbler, Robin and Song
Thrush give us at least two pieces of important information. The first one is general
also for other species and concerns the accuracy of measurements. Despite some po-
tential unknown variation between two compared samples of measurements, the
positive correlation for four species mentioned above tells us that data collected by
different ringers in the same area are comparable on long-term level and can provide
reliable information about the average size of wing. Another information, which can
be extracted from the results, is that the appearance of individuals belonging to those
species was quite random at compared sites, without any difference or particular
habitat preferences between sex groups or populations mixed in the study area. If
habitat preferences and/or non-random distribution of the individuals between sub-
stations existed, the result of the correlation would be largely affected. This scenario
fits the results of Pearson’s correlation for the average wing lengths of Goldcrests and
Willow Warblers. Especially for the Willow Warbler the negative correlation excludes
the influence of different measuring habits of the ringers. It is highly unlikely that this
pattern is caused by ringers’ customs while it does not occur in other measured spe-
cies. However, in order to be sure what exactly influences these results, we need some
more detailed investigation of segregation mechanism and habitat preferences of
these species.
REFERENCES
Arizaga J., Barba E., Cantó J.L., Cívico J.M., Cortés V., Greño J.L., Herranz J.M., Monrós J.S.,
Moreno P., Piculo R., Verdejo J. 2012. The usefulness of biometrics for the study of avian con-
nectivity within Europe a case study with Blackcaps Sylvia atricapilla in Spain. Ardeola 59, 1:
75-91.
Barrett R.T., Peterz M., Furness R.W., Durnick J. 1989. The variability of biometric measure-
ments. Ring. & Migr. 10: 13-16. DOI: 10.1080/03078698.1989.9676001
Busse P. 1968. Correlative topography – the method of analysis of the population differentiation.
Not. Orn. 9, 3: 1-9.
Busse P. 1974. Biometrical methods. Not. Orn. 15, 3-4: 115-126.
Busse P. 1984. Key to sexing and ageing of European Passerines. Beitr. Naturk. Niedersachsens
37, Suppl.
Busse P. 1988. New methods of interpretation of biometrical variability in migrating birds. Not.
Orn. 29: 151-192.
Busse P. 1997. Localization of breeding origin of migrants according to biometrical data: the meth-
odological problem. Ring 19, 1-2: 153-168.
Busse P. 1999. Correlative topography by Krigging – a useful method to study intra-group biometri-
cal differentiation. Ring 21, 2: 145-159.
Busse P. 2000. Bird Station Manual. SEEN, Univ. of Gdañsk, Gdañsk.
42 THE RING 34 (2012)
Busse P., Kania W. 1970. Operation Baltic 1961-1967. Working methods. Acta orn. 12, 7: 232-267.
Busse P., Maksalon L. 1986. Biometrical variability of Song Thrushes migrating through polish
Baltic Coast. Not. Orn. 27: 105-127.
Fiedler W. 2005. Ecomorphology of the external flight apparatus of blackcaps (Sylvia atricapilla)
with different migration behavior.Ann. NY Acad. Sci. 1046: 253-263.
Gosler A.G., Greenwood J.J.D., Baker J.K., King J.R. 1995. A comparison of wing length and pri-
mary length as size measures for small passerines: A report to the British Ringing Committee.
Ring & Migr. 16, 2: 65-78. DOI: 10.1080/03078698.1995.9674095
Harper D.G.C. 1994. Some comments on the repeatability of measurements. Ring & Migr. 15, 2:
84-90. DOI: 10.1080/03078698.1994.9674078
Jenni L., Winkler R. 1994. Moult and Ageing of European passerines. Acad. Press, London.
Kovács S., Csörgö T., Harnos A., Fehérvári P., Nagy K. 2010. Change in migration phenology and
biometrics of two conspecifis Sylvia species in Hungary. J. Ornithol. 152: 365-373. DOI:
10.1007/s10336-010-0596-7.
Kovács S., Fehérvári P., Nagy K., Harnos A., Csörgö T. 2012. Changes in migration phenology and
biometrical traits of Reed, Marsh and Sedge Warblers. Cent. Eur. J. Biol. 7, 1: 115-125. DOI:
10.2478/s11535-011-0101-1.
Lo Valvo F., Lo Verde G., Lo Valvo M. 1988. Relationships among wing length, wing shape and
migration in Blackcap Sylvia atricapilla populations. Ring. & Migr. 9, 1: 51-54. DOI:
10.1080/03078698.1988.9673923
Martin P., Bateson P. 1986. Measuring behaviour: An introductory guide. Cambridge Univ. Press,
Cambridge.
Morgan J.H. 2004. Remarks on the taking and recording of biometric measurements in bird ring-
ing. Ring 26, 1: 71-78. DOI: 10.2478/v10050-008-0058-2.
Nowakowski J.J. 2000. Long-term variability of wing length in population of Reed Warbler Acro-
cephalus scirpaceus. Acta orn. 35: 173-182.
Nowakowski J.J. 2002. Variation of morphometric parameters within the Savi’s Warbler (Locus-
tella luscinioides) population in eastern Poland. Ring 24, 2: 49-67.
Pèrez-Tris J., Tellería J.L. 2001. Age -related variation in wing shape of migratory and sedentary
Blackcaps Sylvia atricapilla. J. Avian Biol. 32, 3: 207-213.
Pèrez-Tris J., Tellería J.L. 2002. Migratory and sedentary blackcaps in sympatric non-breeding
grounds: implications for the evolution of avian migration. J. Anim. Ecol. 71: 211-224.
Salewski V., Hochachka W.M., Fiedler W. 2010. Global warming and Bergmann’s rule: do central
European passerines adjust their body size to rising temperatures? Oecologia 162: 247-260.
DOI: 10.1007/s00442-009-1446-2
Svensson L. 1992. Identification guide to European Passerines. Stockholm.
Tellería J.T., Carbonell R. 1999. Morphometric variation of five Iberian Blackcap Sylvia atricap-
illa populations. J. Avian Biol. 30: 63-71.
Van Buskirk J., Mulvihill R.S., Leberman R.C. 2010. Declining body sizes in North American
birds associated with climate change. Oikos 119, 6: 1047-1055. DOI: 10.1111/j.1600-0706.
2009.18349.x.
Yom-Tov Y., Yom-Tov S., Wright J., Thorne Ch.J.R., Du Feu R. 2006. Recent changes in body
weight and wing length among some British passerine birds. Oikos 112: 91-101.
Zaniewicz G., Busse P. 2008. Autumn migration dynamics and biometrical differentiation of the
Dunnock (Prunella modularis) passing the southern Baltic coast. Ring 30, 1-2: 31-54. DOI:
10.2478/v10050-008-0006-1.
THE RING 34 (2012) 43