Measurement of plumage badges: an evaluation of methods used in the Great Tit Parus major




Дата канвертавання25.04.2016
Памер165.21 Kb.




Measurement of plumage badges: an evaluation of methods used in the Great Tit Parus major

JORDI FIGUEROLA* & JUAN C. SENAR2

Department of Applied Biology, Estacion Biologica tie Donana, CSIC, Avda. Maria Luisa s/n, E-41013 Sevilla, Spain, 2Museu

de Zoologia, Ap. Correus 593, E-08080, Barcalona, Spain



There is an increasing interest in the variation in plumage coloration and a number of theories have been proposed to explain its evolution (Butcher & Rohwer 1989, Savalli

1995). Birds have been considered to signal through

plumage their dominance status, ability to evade preda­ tors, parasite resistance or for example their parental care abilities (reviewed in Butcher & Rohwer 1989, Andersson

1994, Savalli 1995, Johnstone 1997). However, the mea­

surement of plumage badges and its accuracy have received little attention (Savalli 1995). In the case of the

Great Tit Pants major, for instance, several studies have analysed the importance of the breast stripe size as an indicator of dominance status in winter flocks (Jarvi & Bakken 1984, Pöysä 1988, Lemel 1989, Wilson 1992) and its importance in mate choice (Norris 1990, 1993), but the badge has been estimated using very different indices, even in studies performed by the same authors (Norris

1990, 1993). We compare the performance of different indices in estimating Great Tit stripe size, by comparing them with badge surface area obtained from image analysis of digital photographs. We propose that digital photography provides a reliable and inexpensive method to measure plumage badges in birds and we demonstrate its performance in the Great Tit.


METHODS
Birds were captured in feeder funnel traps in two areas near Barcelona (northeast Spain). Individuals were ringed, measured and photographed. Birds were positioned over a millimetric grid and held fully extended, with the crown and legs in contact with the background (Fig. I). In each individual we indicated the position of the upper and lower part of the stemum, to enable its recognition in the photograph. Photographs were taken with a Sony Digital Mavica MVC-FD7 from a variable distance. A subsample of six birds was returned to cloth bags before taking a
Correaponding author.

Email jordi@ebd.csic.es



Figure 1. Photography of Great Tit ready for analysis. The tip of the scissors marks the position of the clavicle, and number eight indicates the position of the posterior end of the sternum.
second photograph in the same position and being liber­ ated. Photographs were saved by the camera on a floppy disc and transferred to a computer.

Images were analysed with the public domain program



NIH (developed by the US National Institutes of Health and available via FTP from zippy.nimh.nih.gov). For each

photograph we calculated the different indices used in the papers dealing with breast stripe size in the Great Tit (see

Table 1). Additionally, we calculated stripe surface as the

area of the black band between the point of inflexion, where the ventral stripe widens to a throat patch, and the posterior end of the stripe. All measurements were taken by the same author for all individuals. Parametric statistics were used in the analyses because all the variables were normally distributed. To compare measurement reliability we calculated measurement repeatability and the correla­ tion of the different stripe size indices with breast stripe surface as obtained from image analysis. Repeatability was calculated according to Lessells and Boag (1987). Breast area was chosen as the standard to which the other methods are compared because it corresponds to the measurement of the complete badge and not to the measurement of geometrical simplifications, as is the case for the other methods. Measurements are provided in mm or, in the case of surface measurements, as mm’.




Table 1. Measurements used to study the significance of Great Tit badge size. Repeatability is reported for both sexes and for each sex separately. Pearson correlation between the values obtained with each method and the estimated stripe surface are reported.


Reference

Method Range


A This study

B Järvi & Bakken (1984), Poysa (1988) C Lemel (1989)

D Norris (1993) E Norris (1993) F Norris (1990)

G Poysä (1988) H POysa (1988) Wilson (1992)

Stripe surface (see Methods) Width at the level of the clavicle

The product of the two shortest distances between the white cheeks and the yellow breast feathers

Estimated as the sum of stripe width measured at four standard points along its length

Estimated as the width at the mid-point between the base of the sternum and the anterior end of the stripe

Area between the posterior end of the sternum and an imaginary parallel line running 20 mm anteriorly

Minimum width

Maximum width

The sum of stripe width measured at



8 equidistant lines running across the breast
Repeatability

304.5—1235.1

4.7—21.6

207.0—659.8

16.4—74.8

2.8—15.9


107.1—428.5

1.8—11.9


13.7—25.9

40.8—138.3






Both sexes
F1112



P




Males
F56



P




Females
F

Correlation coefficieni
P rp P

A

0.98

112.6



<0.001

0.86

12.75



<0.005

0.79



8.48


<0.05







B

0.83

10.5

<0.001

0.08

1.18

ns

0.50

2.98

ns

0.81

<0.001

C

0.91

22.1

<0.001

0.85

12.10

<0.005

0.39

2.27

ris

0.73

<0.001

D

0.80

9.1

<0.001

0.68

5.21

<0.05

0.20

1.49

ns

0.90

<0.001

E

0.89

17.6

<0.001

0.91

21.31

0.001

0.54

3.33

ns

0.70

<0.001

F

0.89

18.2

<0.001

<0

0.80

ns

0.61

4.14

ns

0.95

<0.001

G

0.91

20.6

<0.001

0.41

2.40

ns

0.60

3.94

ns

0.87

<0.001

H

0.66

4.9

0.005

0.84

11.57

0.005

<0

0.43

ns

0.77

<0.001




0.86

13.7

<0.001

0.39

2.30

ns

0.11

1.26

ns

0.98

<0.001



RESULTS DISCUSSION
A total of 49 individuals was included in the analyses. We These results show that it is possible to measure plumage took a second photograph of 12 of these individuals (six badges with a precision equal or superior to other charac­ males and six females). Repeated photographs for six of ters traditionally used in ornithological research, such as these individuals were obtained on the same day and for wing-, bill- or tarsus-length (e.g. 0.97, 0.78 and 0.97 another six individuals one or two weeks after first respectively; Senar & Pascual 1997). Although the magni­ capture. Stripe surface was the most repeatable measure tude of the possible errors in measuring plumage badges (r1112 = 0.98), whereas lower estimates were obtained could be high, due to small changes in the distribution of with the other indices (r1112 between 0.66 and 0.91, see the feathers, it is true that the range of variation in these Table 1). characters is higher than that found in other morpho­ A similar picture appeared when repeatabilities were logical characters of birds. In the case of the Great Tit, calculated for each sex separately, but in this case non- stripe surface provides a highly repeatable estimate of repeatable estimates were obtained for females with most badge size. Alternatively, other direct measurements of the methods. could be used. However, none of the other methods Correlation of the different measurements with esti- proved reliable for measuring female badge size. For sexes mated stripe areas was also highly variable, the variation combined, the highest repeatabilities and correlations in stripe size explained by these other indices varied from with stripe size were obtained with measurements that just 49% to as much as 96% (Table 1). should be taken from photographs (like Wilson 1992




index). Norris area measurement (Norris 1990) proved highly repeatable when data from both sexes were combined, but its performance was greatly reduced when each• sex was analysed separately. The measurement of stripe width at four standard points (Norris 1993) provided repeatable estimates with good correlations with stripe surface, and probably constitutes the best index if photography could not be used. Minimum stripe width and width at the level of the sternum proved less reliable but still explained 66—75% of the variation in stripe surface. Three other measures are not recommended. Maximum width, Lemel index (Lemel 1989) and the measurement provided by Norris (1993) for females, showed the lowest (and in some cases only marginally significant) repeatability and/or explained less than 60% of the variation in stripe surface. The selection of badge size index should be made much more carefully for studies dealing with intrasexual variation, since most of the indices showed low repeatabilities in these cases. Nevertheless, badge area remained highly repeatable for both sexes when data from males and females were analysed separately.

Digital photography now provides an inexpensive method to measure plumage badges since the economic costs are reduced to that required for the camera, com­ puter and medium used to save the images (1.44 Mb allows storage of more than 30 images). In addition, because the images can be stored, different measurements can be taken long after the bird is released.


We are grateful to M.L. Arroyo, D. Bone, J. Domenech and E. Vilamajor for field assistance. This is a contribution to the DGICYT research project PB95-0l02-C02-02.

REFERENCES
Andersson, M. 1994. Sexual Selection. Princeton, NJ; Princeton

University Press.

Butcher, G.S. & Rohwer, S.A. 1989. The evolution of conspicuous and distinctive coloration for communication in birds. Curr. Ornithol. 6: 51—108.

Järvi, T. & Bakken, M. 1984. The function of the variation in the

breast stripe of the Great Tit (Parus majo,). Anim. Behav. 32:

590—596.

Johnstone, R.A. 1997. The evolution of animal signals. In Krebs, J.R. & Davies, N.B. (eds) Behavioural Ecology: 155—178. Oxford: Blackwell Science.

Lemel, J. 1989. Habitat distribution in the Great Tit Parus major in

relation to reproductive success, dominance, and biometry.



Ornis Scand. 20: 226—233.

Lessells, C.M. & Boag, P.T. 1987. Unrepeatable repeatabilities: a common mistake. Auk 104: 116—121.

Norris, K.J. 1990. Female choice and the evolution of the conspic­

uous plumage coloration of monogamous male great tits. Behav. Ecol. Sociobiol. 26: 129—138.

Norris, K.J. 1993. Heritable variation in a plumage indicator of via­

bility in male great tits Parus major. Nature 362: 537—539. Poysa, H. 1988. Feeding consequences of the dominance status in



Great Tit Parus major groups. Ornis Fenn. 65: 69—75.

Savalli, U.M. 1995. The evolution of bird coloration and plumage elaboration. A review of hypotheses. Curr. OrnithoL 12:

141—190.

Senar, J.C. & Pascual, J. 1997. Keel and tarsus length may provide a good predictor of avian body size. Ardea 85: 269—274.



Wilson, J.D. 1992. A re-assessment of the significance of status

signalling in populations of wild great tits, Parus major. Anim. Behav. 43: 999—1009.





© 2000 British Ornithologists’ Union, Ibis, 142, 482—484


База данных защищена авторским правом ©shkola.of.by 2016
звярнуцца да адміністрацыі

    Галоўная старонка