On the ecomorphology of migrants H A N S W I N K L E R * & B E R N D L E I S L E R ’

*Konrad Lorenz Institut fur Vergleichen~e Verhaltensforsckung der Osterrekhischen Aliademie der Wjssenschu~~en, A- 1 I 60 Wien, Austria; ‘Max Planch lnstitut fur Ver~altensp~ysiologie, Vogelwarte, D-7760 Radolfzell-Miiggingen, Germany

A multivariate analysis of data from a wide range of avian species revealed that migra- tory distance was related to a high aspect ratio, long and pointed wings and well-devel- oped distal wing segments. Migration also appeared to set limits on the development of the hind limb and on the wing muscles not involved in forward flight. Among Sylvia warblers it is shown that habitat use and migration may constrain each other.

Migratory behaviour is an important strategy for birds to cope with a changing environment. Yet, the ecomorphol- ogical consequences of migration are little understood and are apparently unimportant when broad ecomorphol- ogical patterns are discussed (e.g. Wiens 1989). Keast ( 1980) could not find any relationship between external wing morphology and migration distance in New World warblers. Likewise, Niemi ( I 985), in his analysis of morpho- logical variation among 39 passerines, could not detect an association between internal flight apparatus and migra- tory behaviour. Oehme (1990) stated that there is no clear-cut relationship between wing morphology and migration or habitat. Rayner ( 1 988) suggested that selec- tion favours adaptations for manoeuvrability and the ability to exploit “cluttered” habitats, whereas morpho- logical adaptations for low transport costs-which may be significant for migrants-were weak in smaller birds. Many other authors, however, have shown that migrants do show features which can be interpreted as adaptations for migration (e.g. Averill 1925, Niethammer 1937, Kipp 1942, Dilger 1956, Cox 1968, Caston 1974, Leisler & Winkler 1985, Winkler & Leisler 1985). Leisler ( 1990) summarized what has been claimed in the literature about the morphology of small migrant land birds: Migrants tend to be smaller than equivalent tropical residents, their bills are shorter and wider and they possess wings with relatively long distal elements. Moreover, the proportion of migrants in a group (family, subfamily) varies inversely with mean culmen-length and culmen variability (Cox 1968). I f migra- tion requires flight with low costs of transport, one can also predict from known functional relationships that migrants have high aspect ratios and average or low wing- loading (Rayner 1988). Yet low-cost transport over large distances may require various morphological adaptations which conflict with possible adaptations for foraging and habitat use; all aspects of flight performance cannot be favoured simultaneously (Eaton et al. 1963, Leisler & Winkler 1985, Winkler & Leisler 1985, Rayner 1988).

This study deals with those morphological characters which are associated with migration by testing the claims and predictions listed above within large multi-species data sets. Constraints will be discussed and analysed both in relation to the restricted variance of characters in different taxonomic groups and in the context of inter- actions between adaptations for habitat use and mig- ration.

M A T E R I A L S A N D M E T H O D S

The data for the present study come from various sources. In order to analyse some general patterns we drew on information collected and published by Hartman I 1961) and Austen ( 1988, pers. comm.) on New World birds. The main body of the analyses was based on our own data on sylviids, thrushes and European tits using 32 characters common to all groups (see Table 3 for a complete list). The respective measurements and methods are described in greater detail elsewhere (Leisler et al. 1983, Leisler & Winkler 1985, 1991, Winkler & Leisler 1985). Migration distances of sylviids were compiled from Berthold (1973, 19791 and Curry-Lindahl ( 1981 1. Rough estimates of migration distances of parulids and North American turdids were derived from distribution maps and other sources (Robbins et al. 1966, Robbins & Van Velzen 1969. Meyer de Schauensee 1970, Stiles & Skutch 1989). Measurements of vegetation height (means of several sample points in breeding habitats) for Sylvia were taken from Cody G Walter ( I976), Cody ( I978), and Zbinden E Blondel ( I98 I 1.

Univariate means were compared with two-sample 1 - tests. Welch’s approximate t was used when the F-ratio test indicated significant differences between variances (Zar 1984).

Multivariate analyses were done with respect to shape relative to body-mass. Hence, measures of length were divided by the cube root of body-mass, logarithms were taken and, for principal component analyses, correlation

21

22 H A N S W I N K L E R & BERND LEISLER IBIS 1 3 4 S U P P L . I

matrices were decomposed to weight characters equally. In one analysis across groups, the humerus was taken as the relevant measure of size because body masses were not available for all cases. The high correlation between humerus and body-mass (for sylviids r = 0.967, n = 25) justifies this procedure. In this study we concentrated on comparisons within genera, families and larger taxonomic units. The comparatively low intraspecific variation in the samples (see also Leisler & Winkler 1991) justified the use of species means in the analyses. Most characters were simple length measurements. The more derived charac- ters were Kipp's distance (the difference between longest primary and the first secondary). aspect ratio (the ratio between wing-span squared and wing area), wing-load (the ratio of body-mass to wing area). tail graduation (the difference in length between the outer tail feathers and central ones). and bill bending (largest deviation of maxilla-jugal arch from a straight line).

W e searched for possibly constrained characters with a new method based on the following considerations. To be a likely candidate for the action of constraints, a single character or a measure representing a suite of characters (e.g. a principal component score) must be of functional significance in at least two contexts. I f we assume a linear dependence, then the simplest possible form of a poten- tially constraining feature can be defined in operational terms as one which shows high simultaneous correlations with at least two ecological conditions, each contributing significantly to its total variation. Therefore, we regressed single morphological characters and PCA-scores on migra- tion distance and mean vegetation height in breeding habitats and considered them to be constrained if both predictor variables contributed significantly to their vari- ation in an trivariate analysis.

RESULTS

General attrlbutes of migrants Hartman's (1961) data set comprised 13 characters. W e initially divided it into four groups: non-passerine resi- dents, non-passerine migrants, passerine residents and passerine migrants. In a preliminary survey we found that certain groups (e.g. hummingbirds) distorted the data (see also Rayner 1988) so that further taxonomic stratifi- cation of the sample was advisable in order to normalize the data.

Among resident non-passerines the hummingbirds stood out for their relatively heavy flight apparatus, large Supracoracoideus and low wing loading. The latter, however, was an effect of body-size. When their small size is taken into account, hummingbirds have rather high wing loadings (Greenewalt 1962, 1975). Aspect ratios were also high, but lower than in Charadriiformes. It is noteworthy that pigeons and doves ( 14 species) have relatively larger Supracoracoideus muscles (mean 5.3 1 %); the difference

from I13 other non-passerine species (mean 1.65%. see Table I ) was highly significant ( P < 0.0001). Non-passerine migrants were characterized by high aspect ratios, although they were still lower than those of charadriiform residents. Migrant charadriiforms were lighter than resi- dents. The lower extremities of 'general' non-passerine migrants were less developed than among residents. Wing muscles other than the Pectoralis major and the Supracoracoideus were lighter in migrant than in resident charadriiforms.

Not surprisingly, passerines were lighter on average than non-passerines. Aerodynamic constraints on small birds are relatively weak, which is why ecological influ- ences may prevail and why passerines, with the exception of the swallows, have low aspect ratios (Rayner 1988). The swallows in Hartman's data were not only distinguished by their aspect ratios (mean 2.44 f 0.1 16, n = 4), but also by the light musculature of the lower appendages (mean 2.52 f 0,5058, n = 4). Migrants of the more primitive Oligom- yodi (Tyrannidae including cotingas and manakins, Furnar- iidae. Formicariidae; classification after Haffer 1985) differed from tropical residents in several features: aspect ratios were higher (although body-mass tended to be less), the proportion of mass assigned to the lower extremities was substantially reduced, and minor flight muscles were less developed. The migrants among the nine-primaried parulid warblers were distinguished from their resident counterparts by higher aspect ratios, lighter hindlimbs, and heavier pectoral muscles. Finally, migrants in the remaining Passeres differed from more resident forms by possessing less developed lower appendages, bigger pectoral muscles, and higher aspect ratios.

The hypothesis that migrants show lower variability in some of their characters was explored by comparing groups of residents and migrants containing at least ten species each. Generally, non-passerine migrants fell within a narrower range of low or medium mass (47.2-1515 g) than residents ( 10.63-3700 g) and the variance of the proportion of the mass of the lower appendages was lower ( P < 0.06). Significantly lower variances in the lower appendages were also found in passerines (without swal- lows and parulids, P < 0.01 ) and in parulids ( f < 0.05).

Morphological correlates of migration in small passerines Resident tits ( n = 6 species) differed from long-distance migrants within the sylviids (distances greater than 4000 km; n = 15 species) in possessing shorter distal wing segments. lower aspect ratios, shorter and wider bills, shorter legs, and shorter femora ( P < 0.001 in all instances).

More detailed analyses of possible relationships between migration and morphology were carried out with data on 25 species of sylviids. First we examined which of t h e 32 variables in our character set correlated well with migration distance. The highest correlations were found

I992 ECOMORPHOLOCY OF M I G R A N T S 23

Residents Migrants

Morphological characteristic n mean s.e. n mean s.e.

Non-passeriformes excluding Trochilidae, Columbiformes. Charadriiformes

Weight Igl % Heart % Upper extremities % Lower extremities % Pectoralis % Supracoracoideus % 'Rest' of wing muscles Wing area/weight (cm2/g) Aspect ratio

Charadriiformes Weight Ig) % Heart % Upper extremities % Lower extremities % Pectoralis % Supracoracoideus % 'Rest' of wing muscles Wing area/weight (cm2/g) Aspect ratio

Weight lgl % Heart % Upper extremities % Lower extremities % Pectoralis % Supracoracoideus % 'Rest' of wing muscles Wing area/weight (cm2/g) Aspect ratio

Passeriformes, Passeres excluding Hirundinidae and Parulidae

Passeriformes, Oligomyodi

Weight (gl % Heart % Upper extremities % Lower extremities % Pectoralis % Supracoracoideus % 'Rest' of wing muscles Wing area/weight (cm2/g) Aspect ratio

Weight (g) % Heart % Upper extremities % Lower extremities % Pectoralis % Supracoracoideus % 'Rest' of wing muscles Wing area/weight (cm2/g) Aspect ratio

Parulidae

I35 I35 I10 123 I I3 I13 I12 I33 I33

7 7 6 6 6 6 6 7 7

94 94 79 89 86 86 79 94 93

I10 I10 94

I04 96 96 95 I10 I10

10 10 6 8 6 6 6

10 10

499.77 f 668.2 0.82f0.314

24.21 f 5.454 10.30 f 4.728 14.78 f 3.768 1.65f 1.371 7.74 f 2.038 2.73 f 1.072 2.08 f 0.440

360.28 f 276.3 I .03 f 0.205

23.6 I f 4.87 I 6. I4 f 2.296

15.86 f 4.226 1.60 f 0.840 6.23 f 0.495 2.85 f 0.588 3.43 f 0.588

26.66f 19.19 I . I3 f 0.269

26.12 f 5.191 7.18 f 2.770

16.97 f 3.912 1.9 I f 0.578 7.12f 1.266 5.06f 1.188 1.65 f0.139

45.60 f 6 1.98 I .I0 f 0.220

24.06 f 3.973 8.98 It 2.90 I

15.6 I f 2.998 I .56 f 0.300 6.77 f 0.998 4.14f 1.129 1.66 f 0.160

I1.50f2.386 1.23f0.1 12

20.91 f3.193 8.6 I f 1.580

13.18 f 2. I70 1.42 f 0.2 I6 6.02 f 1.003 6.30 f 1.043 I .62 f 0.092

17 17 14 I5 15 15 15 17 17

15 15 I I 12 I I I I I I 15 15

6 6 3 4 4 4 3 6 6

13 13 12 12 13 13 12 13 13

18 18 16 17 17 17 16 18 18

~

of the variables and tests.

387.46 f 388.0 1.02 f 0.226'

24.95 f 4.886 7.83 f 3.2 I2

16.22 f 3.654 1.695 1.373 7.35 f 1.899 2.79f 1.731 2.70 f 0.505***

131.02f 123.2 1.16 f 0.234

24.83 f 5.128 4.90 f 1.945

17.83 f 4.161 2.40 f I. I76 4.6 I f 0.904" 3.08 f 0.74 I 3.3 I f 0.642

24.l8f 12.56 I .22 f 0. I36

25.2 I f 0.534 3.62 f 0.936"

18.47f 1.129 1.93fO.I 15 5.40 f 0.836 5.91 f 1.198 I .86 f 0. I 19''

40.58 f 45. I7 1.18f0.168

25.93 f 3.088 6.29 f 1.507.''

17.44 f 2. I95 I .67 It 0.23 I 6.95 f 1.074 4.35 f 1.043 I .84 f 0.223'

12.52f4.731 1.1 4 f 0. I22

22.75 f 2.635 7. I4 f 0.964

15.39 f I .883 1.65f0.256 5.85 f 0.77 I 6.32 f 1.020 I .8 I f 0.083"'

Table I , Some morphological characteristics o\ resident (including short distance migrants) and migrant birds; percentages are relative to body-weight. Asterisks indicate significant differences ('P < 0.01, ** P < 0.002, *** P < o.oooz; these levels were chosen to account lor repeated testing 01 the same variable) of migrant means to respective values of residents. Data from Hartman I I 96 I I; see text for a detailed description

24 HANS W I N K L E R & B E R N D L E I S L E R IBIS I34 SUPPL. I

for characters which respectively describe long and pointed wings, or round and slotted ones (Table 2) . Step- wise regression analysis was used to search for character combinations which provide parsimonious predictions of migration distance. The best and sparsest set was formed b y the number of slotted primaries, which entered with a negative coefficient, and the length of the carpometa- carpus (Fig. I ) . To study whether the results obtained from the analysis of slyviid data could be extended to other groups, stepwise regressions were run with a set of five variables which formed a common subset among sylviids, turdids measured in their wintering grounds in East Africa, and parulids. Size was corrected with respect to humerus- length and data were log-transformed. Three skeletal characters, namely, femur (11, ulna (u ) and carpometacarpal length (c 1, were selected (tail-length and bill-width were not entered). Together they explained 8 1 % of the variance ( R 2 = 0.81 I , P < 0.001) in sylviid migration distances. Ulna and carpometacarpal lengths together explained 76.4% of the variance. The regression equation associated increasing migration distance mainly with allometric increase of distal wing elements Ic) and allometric decrease of proximal (u / ones. The equation was:

distance (in units of 1000 km) = 20.80 + 48.04~ - 2 I . I ~ u + 6.571.

When this equation was applied to the measurements of eight species of turdids. the Rock Thrush Monticola saxatilis ranked highest with a predicted migratory distance of approximately 6900 km; the Wheatear Oenanlhe oenanthe came next (3400 kml, followed by the lsabelline Wheatear 0. isabeliina (2 I00 km). and the Pied Wheatear 0. plewhanka 12000 km). The Capped Wheatear 0. gileata, an intra- African migrant, was estimated to migrate 740 km; the Ant

Table 2. Signilicanf correlations out 0132 characters, with migrationdistancelor 2 5 sylviid species. Length data were divided by the cuk-root ol weight and log-transformed. Correlations marked with asterisks aresigni/i~ant; P < 0.05,

** P < o.o i ,and** * P < 0001.

Character

Wing-length Tertials Length difference between 9th and 10th primaries Kipp's distance Number of notched primaries Aspect ratio Tail-length Carpometacarpus Pelvis-length Femur Bill-width

r

0.632"' 0.557" 0.8 19"' 0.834"'

-0.642"' 0.769"'

0.645"' 0.5 19' 0.4 19' 0.4 13'

-0.57 I **

8

A

E Y

0

0 0 6 Y Y

Q) 0

E i 4 +.. (0

-0

C 0

.-

'3 2 m

I

L

WJ .-

0

Figure

A A 0

0 2 4 6 8 W i n g morphology

I . The relationship between wing morphology and mig- ration distance in 25 species of sylviids. Morphology represents the prediction of migration distance through a multiple regression with the number of notched primaries and carpometacarpus- length as predictors (R' = 0.831, P < 0.0001; see main text for the variable transformations used). Unit distance is 1000 km. Filled circles denote Sylvia warblers, filled triangles Acrocephalus warblers, open circles Phyllo~opus warblers, open triangles Locustella warblers, and the open square represents Hippolais icterina.

Chat Myrmecocichla aethiops and Schalow's Wheatear 0. lugens schalowi were assigned negative values. The predic- tions generally agreed well with actual migration behav- iour, but failed when the migratory Whinchat Saxicola rubetra was placed among the more resident forms (470 kml. Predictions of the same equation applied to parulid measurements correlated with their migration distances quite well ( r = 0.637, n = 50, P < 0.00 I). However, predicted distances were mostly negative, which means that generalizations cannot be made in absolute terms but only in terms of the within-group ranking of migration distances. The difference was mainly due to the intercept; the slope of 0.8 did not differ significantly from I , indi- cating that the allometric relationships between morphology and migration distance were similar in both families. Therefore, the multiple regression of the three characters within the parulids did not improve t h e corre- lation substantially ( R = 0.734, P < O.OOOl), but did change the intercept (Fig. 2). The equation obtained was

distance ( in units of 1000 kml =

22.44 + 38.32~ - 18.21~ + 16.88f.

I992 ECOMORPHOLOCY OF MIGRANTS 25

E Y

0

0 0 6 7 Y

a, 0

5 4 ul

TI .-

C 0 .- - 2 L

CT) .- z

0 0 2 4 6 8

Morphology

Figure 2. The relationship between wing morphology and migra- tion distance in 50 species of parulids. Morphology represents the prediction of migration distance through a multiple regression with femur, ulna and carpometacarpus-length as predictors lR2 =

0.538, P < 0.0001; see main text for equation and the variable transformations used). Unit distance is 1000 km. Members of the genus Dendroica are marked with filled circles.

In a preliminary analysis of Dilger’s (1956) data on small North American thrushes (genera Hglocickla and Catharus 1. a strong relationship between migratory distance and the ratio of manus length to ulna-length (Spearman r, = 0.943, P < 0.05) was found, which again stresses the importance of the distal wingsegments for migration.

Body masses of sylviids did not correlate well with migratory distance ( r = 0.326), but within Sylvia w e found a strong correlation (r = 0.623, P < 0.05, n = I I ) . Acrocepkalus and Phglloscopus sample sizes were too small to be tested.

In sylviids, bill-length was weakly correlated with migra- tory distance (r = 0.389) as well as bill-depth (r = 0.260). Only in bill-width was a tendency for wider bills among migrants found ( r = 0.424, P < 0.005). There was no appre- ciable correlation between size-adjusted sylviid bill-length and migratory distance [ r = 0.185). Similarly, adjusted bill- depth was not correlated (r = 0.122) with migratory distance. Only relative bill-width of migrants tended to be wider ( r = 0.4 13, P < 0.05). Contrary to expectation, parulid bill-length was not correlated with migration distance ( r = -0.094).

Constraints Using the procedure described in the methods, data from ten species of Sylvia were examined for action of constraints with respect to migration distance and vege- tation height of the breeding habitats. Of the 32 charac- ters tested, two were constrained according to the definition and criteria we set. Of the total variance in the aspect ratio, 88% was explained by migration distance and vegetation height ( P < 0.0025). Migration distance contri- buted more (beta-weight = 0.628, P < 0.005) than vege- tation height (beta-weight = 0.464, P < 0.025). Femur-length was another constrained character: of its total variation among Sylvia, 62% was explained by the two predictors ( P < 0.05). Vegetation height was slightly more important (beta-weight = -0.849, P < 0.025) than migration distance (beta-weight = 0.622, P < 0.05). Kipp‘s distance was a further variable associated with migration and vegetation height.

To see whether constraints also acted at the level of linear character combinations, we ran a principal components analysis on 32 morphological characters (Table 3). The first and the second component together accounted for 65.6% of the total variance. That size-effects had been essentially removed through data transform- ations is evidenced by the occurrence of negative as well as positive loadings in the first component. Both compo- nents were subject to opposing constraints. The first component combined long and pointed wings and a short, ungraded tail with a wide bill and small feet. Vegetation height (beta-weight = 0.569. P < 0.025) and migration distance (beta-weight = 0.481, P < 0.05) together explained 81% of this component’s variance ( P < 0.005). The second morphological component represented the combination of long outer and hind toes with a long femur and unslotted wings; 76% of its variance (P < 0.0 I ) was accounted for by migration distance (beta-weight = 0.957, P < 0.005) and vegetation height (beta-weight = -0.635, P < 0.025).

D I S C U S S I O N

Our analyses suggest that several characters of the loco- motor apparatus influence and are influenced by migra- tion. Most features were directly linked to flight performance. Aspect ratio, the most important variable for flight costs (Rayner 19881, was generally higher in migrants. Flight styles among non-passerine birds are very diverse, so only a few general statements about adaptations for migration in this group could be made. The more uniform flight style of passerines (Rayner 1988) was more promising in this respect: migrants tended to have more attenuated wings with longer distal wing segments, whereas round, slotted wings, often in combination with long tails, were found among the less migratory birds. In no instance did wingload show any relation to migration. Engels ( I941 ) and Oehme ( I 990) believed that skeletal

26 H A N S W I N K L E R 6 B E R N D L E I S L E R I B I S 134 SUPPL. I

Table 3. Results of a principal component analysis of 32 morphological tharacters in Sylvia warblers. Important correlations lr > 0.6 for the first component, r > 0.5 for the second) of single characters with the components are shown. Length data were transformed as dexribed in Table 2 .

Correlation with

Character component I component 2

Wing-length Tertials Length difference between

9 t h and 10th primaries Kipp's distance Length of notch on 9th primary Number of notched primaries Wing-load Aspect ratio Tail-length Tail gradation Ulna Carpometacarpus Rictal bristle length Tarsus-length Hind toe Inner toe Middle toe Outer toe Hind claw Inner claw Middle claw Outer claw Foot-span ltoesl Foot-span (with claws) Pelvis-length Pelvis-width Femur Tibiotarsus Bill-length Bill-depth Bill-width Bill-bending

Variance explained

0.757

0.720 0.942

-0.695

0.924 -0.937 -0.940 0.756 0.793

-0.794 -0.880

-0.703 -0.832

-0.870 -0.857 -0.60 1 -0.894 -0.865 -0.822

-0.808

0.509 0.934

49.2%

0.573

-0.558 -0.584

0.769

0.847

0.613

0.525

0.56 I

16.4%

proportions were of little use for characterizing flight performance. Our results demonstrate the opposite, at least in certain taxonomic groups.

Although body-mass relates to flight performance (Rayner 1988), it is strongly influenced by other factors. Migrants can be as light as a few grams, as in humming- birds, or, like geese and bustards. weigh several kilograms. In t h e small birds analysed above, no relationship between body-mass and migration was found.

An important finding of this study was that migration apparently sets upper bounds on the development of the hind limb, especially in small birds. This also is probably

the basis of the little understood association of femur and pelvis-length with migration. Birds which need to cling strongly to perches tend to have shorter femora (Leisler et al. 1989). Within tits, independent and alternate use of the legs versus bipedal hopping correlates negatively with femur-length and they have much shorter femora than migratory sylviids. Because clinging and alternate use of the legs require more force and hence muscle mass, migrants are less likely to exhibit these modes of loco- motion.

Flight performance, morphology and foraging patterns are closely related (Norberg & Norberg 1988). Our new method of analysing constraints revealed that habitat use and migration may constrain each other, as had been suggested before (e.g. Caston 1974, Leisler & Winkler 1985, Winkler & Leisler 1985). Long-tailed birds with rounded and slotted wings and possibly strong legs seem well adapted for cluttered habitats but not for long- distance travel.

W e suggest that migration is an extra evolutionary factor selecting for efficient forward flight. Migratory sylviids and turdids prefer arboreal feeding on edges, in open habitats, and in the canopy. Flight is needed by these birds to hold large or even multiple territories; they make more use of their wings in foraging and they tend to change perches more often than comparable less migra- tory forms (Dilger 1956, Caston 1974, Leisler et al. 1983, Catchpole et al. 1985, Leisler 1990). In hummingbirds, the efficient fast forward flight required both for migration and territorial defence is not fully compatible with the efficient hovering found in trap-lining species (Feinsinger & Chaplin 1975) and it would be worthwhile to study the morphological attributes of these grhps. Among the parulids that rank high in the scores predicting long migration distances are the Bay-breasted Warbler Dei?droica castanea and the Cape May Warbler D. tigrina, which are also known for their pronounced numerical response to local outbreaks of Spruce Budworm Choriston- eura fumerifana (Morse 1978).

Migrants often occupy habitats which contain abun- dant but sporadically available resources (Robinson et al. 1988, Lovei 1989). It is possible that this explains the morphological differences in feeding apparatus between migrant and resident sylviids. The wider bills of migrant sylviids could be adaptations for opportunistically harvesting large, sporadically available prey (Creenberg I98 I , Leisler 1990).

The option to migrate appears to have arisen in many groups of birds with very different morphological and ecological prerequisites. Accordingly, comparisons and predictions (Monkkonen & Helle 1989) must take syste- matic grouping and phylogenetic correlates (Karr & James 1975) into account. For instance, when basic interfamilial differences between parulids and sylviids were accounted for, convincing evidence for convergent evolution with respect to migration distance was revealed. Analogous differences may have led to the rather unsuccessful

I992 ECOMORPHOLOGY O F MIGRANTS 27

estimate for the Whinchat's migratory behaviour in comparison to the wheatears and chats.

Studies on East African birds were supported by the Deutsche Forschungsgemeinschaft lLe 5 12/ 1 - 1 I , data on tit behaviour were obtained in the course of a study funded by the Fonds zu Forderung der wissenschaftlichen Forschung, Austria, grant 68586. Comments by H.Q.P. Crick, F. lames and I. Rayner were of great help in the revision of the manuscript. Miss D. Cracey and Miss S. Kleindorfer edited the English.

R E F E R E N C E S

Austen. M.I.W. 1988. Ecomorphology of North American wood warblers. MSc Thesis. London, Ontario: University of Western Ontario.

Averill, C.K. 1925. The outer primary in relation to migration in the ten-primaried oscines. Auk 42: 353-358.

Berthold, P. 1973. Relationships between migratory restlessness and migration distance in six Sylvia species. Ibis I 15: 594-599.

Berthold, P. 1979. Beziehungen zwischen Zugunruhe und Zug bei der Sperbergrasmiicke Sylvia nisoria: eine okophysiologische Untersuchung. Vogelwarte 30: 77-84.

Catchpole. C., Leisler. 6. & Winkler, H. 1985. Polygyny in the great reed warbler, Acrotephalus arundinaceus: a possible case of deception. Behav. Ecol. Sociobiol. 16: 285-291.

Cody, M.L. 1978. Habitat selection and interspecific territoriality among the sylviid warblers of England and Sweden. Ecol. Monogr. 48: 35 1-396.

Cody, M.L. & Walter, H. 1976. Habitat selection and interspecific interactions among Mediterranean Sylviid warblers. Oikos 27:

Cox, G.W. 1968. The role of competition in the evolution of migra- tion. Evolution 22: 180- 192.

Curry-Lindahl, K. 1981. Bird Migration in Africa, Vol. I . London: Academic Press.

Dilger, W.C. 1956. Adaptive modifications and ecological isolating mechanisms in the thrush genera Catharus and Hylocichla. Wilson. Bull. 68: 171-199.

Eaton. S.W.. O'Connor, P.D., Osterhaus. M.B. & Anicete, 6.2. 1963. Some osteological adaptations in parulidae. Proc. Int. Om. Congr. XIII: 71-83.

Engels. W.L. 1941. Wing skeleton and flight of hawks. Auk 58: 61- 69.

Feinsinger, P. & Chaplin. S.B. 1975. On the relationship between wing disc loading and foraging strategy in hummingbirds. Am. Nat. 109: 2 17-224.

Caston. A.]. 1974. Adaptation in the genus Phylloscopus. Ibis 116:

Greenberg, R. 1981. Dissimilar bill shapes in New World tropical versus temperate forest foliage gleaning birds. Oecologia 49:

Creenewalt, C.H. 1962. Dimensional relationships for flying

Creenewalt, C.H. 1975. The flight of birds. Trans. Am. Phil. Soc. N.S.

Haffer, 1. 1985. Passeriformes - S. In Glutz von Blotzheim, U.N. & Bauer. K.M. (eds) Handbuch der Vogel Mitteleuropas, Vol. 10. Wiesbaden: Aula.

2 10-238.

432-450.

143- 147.

animals. Smiths. Misc. Coll. 144 121: 1-46.

65 141: 1-67.

Hartman, F.A. 1961. Locomotor mechanisms of birds. Smiths. Misc.

Karr, I.R. & lames, F.C. 1975. Eco-morphological configurations and convergent evolution in species and communities. In Cody, M.L. & Diamond, I.M. ledsl Ecology and evolution of communities: 258-29 I . Cambridge, Mass.: Belknap Press.

Keast, A. 1980. Spatial relationships between migratory parulid warblers and their ecological counterparts in the Neotropics. In Keast, A. & Morton, E.S. ledst Migrant Birds in the Neotropics: ecology, behavior, distribution, and conservation: 109- 130. Washington. D.C.: Smithsonian Institution Press.

Kipp, F. 1942. Ober Fliigelbau und Wanderzug der Vogel. Biol. Zbl.

Leisler, B. 1990. Selection and use of habitat of wintering migrants. In Gwinner, E. led.) Bird Migration: 156-174 Berlin, Heidelberg: Springer-Verlag.

Leisler, B., Ley, H.-W. & Winkler, H. 1989. Habitat, behaviour and morphology of Acrocephalus warblers: an integrated analysis. Ornis Scand. 20: I 8 I - 186.

Leisler, B.. Heine, G. & Siebenrock, K.-H. 1983. Einnischung und interspezifische Territorialitit iiberwinternder Steinschmatzer loenanthe isabellina. 0. oenanthe. 0. plesthanka 1 in Kenia. 1. Om. 124: 393-4 13.

Leisler, B. & Winkler, H. 1985. Ecomorphology. Current Ornithol. 2: I 55- 186.

Leisler, B. & Winkler, H. 1991. Ergebnisse und Konzepte okomor- phologischer Untersuchungen an Voglen. 1. Orn. 132: 373- 425.

Lovei, G.L. 1989. Passerine migration between the Palaearctic and Africa. Current Ornithol. 6: 143- 174.

Meyer d e Schauensee, R. 1970. A Guide to the Birds of South America. Wynnewood, Pa.: Academy of Natural Sciences of Philadelphia, Livingston.

Monkkonen, M. & Helle, P. 1989. Migratory habits of birds breeding in different stages of forest succession: a comparison between the Palaearctic and the Nearctic. Ann. Zool. Fenn. 26: 323- 330.

Morse, D.H. 119781. Populations of bay-breasted and Cape May warblers during an outbreak of the spruce budworm. Wilson

Niemi, G.1. 1985. Patterns of morphological evolution in bird genera of New World and Old World peatlands. Ecology 66:

Niethammer, C. 1937. Ober die Beziehungen zwischen Fliigellange und Wanderstrecke bei einigen europaischen Singvogeln. Arch. Naturgesch.. N.F. 6: 519-525.

Norberg, U.M. & Norberg, R.A. 1988. Ecomorphology of flight and tree-trunk climbing in birds. Proc. Int. Om. Congr. XIX: 2271- 2282.

Oehme, H. 1990. Habitatwahl und Lokomotion: Anpassungen im Bereich der Vorderextremitit. Proc. Int. 100. Deutsche Om.- Ges. Meeting: 359-364.

Rayner, I.M.V. 1988. Form and function in avian flight. Current Ornithology 5: 1-66.

Robbins, C.S., Bruun. 6. Zim. H.S. 1966. Birds of North America. New York: Golden Press.

Robbins, C.S. & Van Velzen. W.T. 1969. The breeding bird survey I967 and 1968. Special Scientific Report - Wildlife No. 124. Wash- ington, D.C.: Bureau of Sport Fisheries and Wildlife.

Robinson, S.K.. Terborgh, 1. & Fitzpatrick, I.W. 1988. Habitat selec- tion and relative abundance of migrants in southeastern Peru. Proc. Int. Om. Congr. XIX: 2298-2307.

Stiles, F.G. & Skutch, A.F. 1989. A Guide to the Birds of Costa Ria .

Coll. 143 111: 1-99.

62: 289-299.

Bull. 90: 404-4 13.

1215-1228.

28 HANS WINKLER & BERND LEISLER I B I S 134 SUPPL. I

Ithaca, N.V.: Cornell University Press. Wiens. 1.A. 1989. The Ecology of Bird Communities, Vol. I . N.I.: Prentice-Hall.

Cambridge: Cambridge University Press. Winkler. H. & Leisler, B. 1985. Morphological aspects of habitat

selection in birds. In Cody, M.L. led.) Habitat Selection in Birds:

Zar. I.H. 1984. Biostatistical Analysis, 2nd edn. Englewood Cliffs,

Zbinden. N. & Blondel. 1. 1981. Zur Raumnutzung, Territorialitat und Legebeginn mediterraner Crasmucken (Sylvia rnelanocephala, S. undala, S. canlillans, S. hortensis) in Sudfrankreich. Om. Beob.

4 15-434. London: Academic Press. 78: 2 17-23 I.