Towards the map of the homing pigeon?

Anita. Behav., 1990,40, 65-78

Towards the map of the homing pigeon? J O R G U. G A N Z H O R N

Abteilung Verhaltensphysiologie, Beim Kupferhammer 8, 7400 Tiibingen, Federal Republic of Germany Abstract. The behaviour of pigeons, Columba livhT, homing from different sites was used to generate a geographical map based on empirical data. With the help of cluster analysis, release sites were grouped into clusters of sites according to similarities in the initial orientation of the pigeons when released. These similarities in initial orientation were assumed to reflect similarities in the information of the map component. The initial orientation of samples of pigeons was characterized by the length of the mean vector and the angular deviation of the mean vanishing direction from the home direction. According to this analysis the map information is distributed in distinct patches extending over several tens of kilometres. Exposing pigeons to air collected within one of these patches but releasing them after anaesthesia of their olfactory mucosae at a site opposite to the home loft within a different patch resulted in disorientation. This experiment, however, yielded significant differences between control and experimental pigeons within only two out of four distinct patches. This suggests that the map has an airborne component. Parts of the map, however, are based on other physical cues. How these 'landmarks' could be used for navigation even when the perception of one or the other component has been eliminated is discussed.

Many hypotheses have been put forward to explain how pigeons, Columba livia, home from unfamiliar sites (reviewed by Schmidt-Koenig 1970, 1979, 1985; W. Wiltschko & Wiltschko 1978, 1982, 1987; Gould 1982; Wallraff 1988a). The most persistent hypothesis is Kramer's concept of a two-step navigation process involving a map and a compass (Kramer 1953). Though little is known about the physical basis of the map, this concept is favoured because homing pigeons do have and actually use compasses during their initial orientation (Schmidt-Koenig 1958; Walcott & Green 1974; F/iller et al. 1983; W. Wiltschko 1983). Wallraff (1974) favoured a map based on environmental gradients; in this case a compass could be involved in the homing process, but it would not necessarily be needed. Many of the recent approaches to elucidate the actual pattern of the map components have been concerned with testing Wallraff's (1974) proposal. Among other things his concept is compatible with the idea that the initial orientation of pigeons has a preferred directional tendency at all sites. Whereas Wallraff considers this idea confirmed (Wallraff 1978, 1982, 1986), others have pointed out that release site biases (i.e. angular deviations of the mean vanishing direction of a sample of pigeons from the home direction) are too variable to be consistent with a general (loft-specific) directional tendency (Gr/iter et al. 1982; R. Wiltschko & 0003-3472/90/070065 + 14 $03.00/0

Wiltschko 1985b, c). With the help of multivariate analyses we have been able to disentangle sitespecific from directional effects and have demonstrated, at least for our lofts at T/ibingen, that there is a directional as well as a site-specific component in the parameters describing the initial orientation of pigeons (Ganzhorn 1989; Ganzhorn & SchmidtKoenig 1989). However, separating the relative importance of these two components does not help us to understand the geographical distribution of information relevant for the orientation process. The discussion about the physical basis of the information used for navigation is equally unclear. Potential candidates to form gradients and/or mosaic-like maps are the earth's magr~etic field (Gould 1982; Walcott 1982, 1986; Lednor 1982; W. Wiltschko et al. 1986; Lednor & Walcott 1988), airborne information (Papi 1975, 1982; Wallraff 1980, 1983, 1988a; for critical reviews see SchmidtKoenig 1987; Waldvogel 1987, 1989; SchmidtKoenig & Ganzhorn in press), or topographical features (Dornfeldt 1982; for a discussion of his findings see Ganzhorn & Schmidt-Koenig 1989). It is most likely that varying combinations of all these factors are involved in the homing process during ontogeny (R. Wiltschko & Wiltschko 1985a), at different distances from the home loft (Schmidt-Koenig 1970; W. Wiltschko & Wiltschko 1987), in pigeons from different lofts (W. Wiltschko et al. 1987b), and in pigeons raised under different 9 1990The Association for the Study of Animal Behaviour 65

66

Animal Behaviour, 40, 1

conditions (W. Wiltschko et al. 1987a). Given this high variability, crucial tests on the physical basis of the map components and their relative importance for the homing process would be greatly facilitated if we had a precise idea of the quantitative or at least of the qualitative distribution of this information. In this paper, I first present a new methodological approach, which generates, based on empirical data, a map used by the pigeon. This map is derived from the behaviour of pigeons upon release. If pigeons released at different sites oriented similarly and vanished in similar directions, I assumed that they used the same information at these sites. If there were statistically significant differences in the pigeons' behaviour when released at different sites, I assumed that these sites are characterized by different map information. Certainly, different sources of information might lead to the pigeons' initial orientation having similar characteristics at different sites. This, however, is not a principal flaw of the methodology but rather a problem of resolution. Nevertheless, this problem should be kept in mind lest the present interpretations be accorded more importance than they perhaps deserve. I then investigate whether or not this map information might have an airborne component as suggested by Papi (1975, 1986) and Wallraff (1980, 1983, 1988a). According to Benvenuti & Wallraff (1985) and Kiepenheuer (1985, 1986) airborne components characterizing release sites can be collected in airbags. After pigeons had been exposed to this kind of information collected at one site, their olfactory mucosae were anaesthetized to prevent them from collecting further olfactory information. Released at a different site pigeons that have smelled 'false-site' odours are either disoriented (Kiepenheuer 1986) or they vanish in a direction away from home (Benvenuti & Wallraff 1985; Kiepenheuer 1985). If the map generated in the first part of this paper has an airborne component, it should allow very precise predictions about the outcome of airbag experiments using air collected within different regions of this map and presenting them to pigeons prior to release (i.e. the experimental design developed by Kiepenheuer 1986). Some of these predictions were checked for goodness of fit by reinterpretation of published data (SchmidtKoenig & Ganzhorn 1989) and analysis of yet unpublished airbag experiments. All these airbag experiments had been carried out before the map

was generated. Therefore I recognize that the experimental design of the airbag experiments is not the best for testing the predictions. MATERIALS

AND METHODS

Generating the Map Pigeons raised and housed at our lofts near Tiibingen (Hohenentringen and Rosenau) were released at 25 different sites located 9-69 km around their home loft. I used only those sites that had also been used in the airbag experiments (Ganzhorn & Schmidt-Koenig 1989; and results given below). All pigeons had the experience of single homing flights before being used in the experiments. According to the criteria of R. Wiltschko & Wiltschko (1985c), none of the pigeons can be considered to be 'unfamiliar to the site', since all of them had been released within 20 km of the respective release sites prior to the experiments. In fact, most of the pigeons had homed from or had presumably passed over the release site before. Pigeons were released singly. I recorded their vanishing directions with respect to magnetic north and plotted them with respect to the home direction (0 ~ in Fig. 4). Vanishing directions were taken with 7 x 50 binoculars with a built-in compass. Each release per site consisted of at least seven vanishing bearings. Three to 15 releases (total of 207 releases) were carried out per site. Some of the data have been used and published in previous analyses (Ganzhorn 1989; Ganzhorn & SchmidtKoenig 1989). Releases per site were combined by vector addition. The combined vanishing bearings per site are characterized by the length (a) of the mean vector and its mean compass direction a H transformed with respect to the home direction (0~ The compass direction of the mean vector was split into its sine and cosine component. The sine and cosine of the mean compass direction and the mean vector length were standardized and transformed in a principal component analysis to remove correlations between variables. The three resulting principal components were used in a cluster analysis according to Ward (Deichsel & Trampisch 1985). This analysis combines into clusters sites where the pigeons show similarities in their initial orientation. Significance levels for differences between clusters were determined with the Hotelling test (Batschelet 1981). F o r this test the single releases per site were used. Two sites were combined when the releases

Ganzhorn: Map of the homingpigeon of the two sites were not significantly different (P>0'05). Procedures of circular statistics were performed according to Batschelet (1981). Principal component and cluster analyses were run using SAS/STAT (1987) for personal computers. Nonparametric tests of linear data were performed according to Siegel (1956).

Airbag Experiments I carried out these experiments in the summers of 1987 and 1988 with pigeons from our loft at Rosenau. These releases are independent from the releases used in the analysis of the 'map'. The pigeons had training flights of up to about 10 km and were unfamiliar with the release sites. Only pigeons older than 12 weeks were used, i.e. when their orientational and navigational capabilities are thought to be fully developed (R. Wiltschko & Wiltschko 1985a). Release sites used in these experiments (except site W D H which had not been used for releases generating the 'map') are listed in Table I and shown in Fig. 1. Natural air was collected in 750-1itre plastic (PVC) containers at two sites located at equal distances to, but in opposite directions from, the home loft (e.g. sites A and B). They were brought back to the loft and five to seven pigeons were placed in each of them for about 2 h. Still inside the container, their olfactory mucosae were anaesthetized with Gingicain. Gingicain is effective for about 6 h after application (Groebe 1979) though the time course of recovery certainly varies between pigeons (Wallraff 1988b). To assure anaesthesia of the olfactory mucosae throughout the experiment Gingicain was reapplied after 3 h. After anaesthesia the pigeons were separated into two groups. Controis kept in air collected at site A were transported to and released at site A. Experimental birds kept in air collected at site B were transported to and released at site A (and vice versa). Whenever possible we released untreated pigeons as super controls alternating with controls and experimental birds. Vanishing directions of the different groups were summarized by vector addition and compared with the Watson U 2 test (Batsehelet 1981). RESULTS

Generatingthe Map The cluster analysis of release sites, characterized by vanishing bearings recorded with respect to

67

home (Table I), yields four main clusters of sites (Fig. 2). Main clusters differ with P < 0.001 according to the Hotelling test. The main cluster (cluster 2) combining release sites north of the home loft contains two subclusters which differ significantly on the 1% level according to the Hotelling test (Fig. 3). Towards the south, release sites are clearly separated into two main clusters (clusters 3 and 4). Cluster 1 stretches as a band of release sites from west-northwest towards the east of the loft. At four out of these five sites in cluster 1, vanishing bearings show a bi- or multimodal distribution. Therefore the behaviour of pigeons released at these sites might be considered to be intermediate between that of pigeons released at sites in clusters 2 and 3. Despite some geographical overlap between clusters the nearest neighbour of any given site belongs more often to the same cluster of sites than would be expected assuming random distribution of sites betwen clusters (Z2=9-72, df= 1, P<0.01). Thus, the observed pattern is far more organized than expected by chance.

Airbag Experiments A total of 42 releases were performed in this series ofairbag experiments (Appendix). Due to the small number of vanishing bearings obtained per release, there was never a significant difference in vanishing directions between controls and experimental birds of a single release (P > 0-05 according to Watson U 2 test when applicable). Assuming that the different main dusters of the previous analysis represent air of different quality, the following working hypothesis was deduced: air north and south of the loft has distinct qualities which can be recognized by the pigeons. In the south there are two regions of different quality (clusters 3 and 4 in Fig. 2). Towards the north there is but one quality (cluster 2 in Fig. 2). Sites in cluster l, located from the east to the west-northwest, represent an area where the different air qualities from the north and the south mix and thus provide ambivalent information for orientation and navigation. Based on this working hypothesis, the airbag experiments were pooled into the following data sets: (1) experiments including one of the sites combined in cluster 1; (2) experiments including one of the sites of cluster 3; and (3) experiments including one of the sites of cluster 4. If the working hypothesis were correct, we would expect the following results.

Animal Behaviour, 40, 1

68

Table I. Directional means of untreated pigeons released at 25 sites around T/ibingen

Site

Number of releases

Number of vanishing bearings

aN

an

a

ALT B(3H DUR DUS ECK EHN FRO HAP HEC HIM HOC IHI LER M1]N OBE PLI ROM SCH SPI STW TIG TOM WAL WIL ZEP

3 8 7 9 12 10 13 7 7 15 8 8 9 8 10 3 7 8 8 6 8 8 11 7 7

31 97 95 143 180 118 141 87 95 199 97 97 150 116 115 30 93 100 121 69 90 99 152 83 88

257 ~ 341 ~ 206 ~ 6~ 65 ~ 118 ~ 52 ~ 134~ 49 ~ 360 ~ 15~ 26 ~ 125~ 136~ 97 ~ 297 ~ 9~ 195~ 109~ 122~ 327 ~ 269 ~ 192~ 197~ 13~

10~ 65 ~ 77 ~ 24 ~ 1~ 322 ~ 7~ 295 ~ 26 ~ 26 ~ 345 ~ 224 ~ 345 ~ 309 ~ 349 ~ 76 ~ 98 ~ 1~ 25 ~ 333 ~ 8~ 354 ~ 339 ~ 5~ 343 ~

0.19 0.19 0.38 0.46 0.84 0.47 0.58 0.51 0.71 0.55 0.82 0.21 0.34 0,24 0.38 0.35 0.06 0.44 0.59 0.54 0.64 0.30 0.31 0.28 0.73

The geographical locations of sites are given in Fig. 1. %/%: mean vanishing direction with respect to north/home; a: length of mean vector.

(1) In the experiments including one o f the sites o f cluster 1, differences between control and experimental pigeons are unlikely to be detected. Here, at least at one site, the air collected contains ambiguous information, the quality o f which could be either identical or different to that o f the air collected at the site opposite to the h o m e loft. Given the high variability in the vanishing directions o f h o m i n g pigeons, any difference is likely to be missed. Thus, these experiments involving sites o f cluster 1 are unsuitable to test the working hypothesis. We can only check w h e t h e r or not the results o f this series m a k e sense under the working hypothesis. (2) Experiments c o m p a r i n g the behaviour o f pigeons exposed to air: collected at the sites o f clusters 3 or 4 versus air collected at sites o f cluster 2 should yield significant differences between controls and experimental birds.

The p o o l e d experiments involving sites o f cluster 1 and cluster 3 did not yield any significant differences between controls and experimental pigeons (Fig. 4, Table II). The large scatter o f the pooled vanishing bearings in these data, however, cannot be attributed to the anaesthesia o f their olfactory mucosae. All o f t h e m had clear directional preferences which are very similar to the mean vanishing direction o f untreated controls released during the same experiment (Table II). Obviously, in these experiments, control and experimental pigeons relied o n the same kind o f i n f o r m a t i o n as the untreated controls. Perception o f this information, however, could not be influenced by anaesthesia o f the olfactory mucosae. Experiments involving sites from cluster 4 (i.e. presenting air f r o m sites o f cluster 4 and cluster 2 to the pigeons) resulted in significant differe~aces in the initial orientation o f controls and experimental

Ganzhorn: Map of the homing pigeon

0

/

69

sto.oo.

f

/|

--/ I0

20

~0

km

Figure 1. Location and abbreviations for release sites used in the cluster analysis to generate the map (Figs 2 and 3). The black hut marks the location of the home lofts. birds ( P < 0.02 Watson U2 test, Fig. 4, Table II). On average, controls showed a significant directional preference and the 95 % confidence interval of the mean vector does include the home direction. But here, some of the experimental pigeons vanished in the opposite direction to controls. Together with the rest of the experimental birds which vanished towards home, this results in a very small length of the mean vector of their combined vanishing directions (Fig. 4). Also, when pooled per release the homeward component h (h = a*cosan) of controls is consistently larger than the homeward component of experimental birds (N=12, T = 5 , P=0.01, Wilcoxon matched-pairs signed-ranks test). This significant difference is no longer apparent when the data are pooled with respect to untreated controls. However, in this comaprison, the sample size is very small and a trend seems to point to the same results as obtained by pooling the data with respect to home (Table II). Though on a statistically weak basis, the outcome of the experiments involving sites o f cluster 4

supports the idea of an airborne component of the map o f the homing pigeon.

DISCUSSION The map of the homing pigeon presented in this paper is characterized by regions including several release sites. The initial orientation of homing pigeons varies significantly between regions but is fairly consistent between sites within a region. Towards the north and south of the home loft these regions appear fairly distinct. Along a band of sites located from the east to the northwest of the loft the initial orientation of pigeons is inconsistent within a single release and/or between releases at the same site. I assume that the pigeons' behaviour is an indicator of the quality of the information used for orientation and navigation. If this is true, the cues available north or south of the home loft provide sufficient information about where to fly.

70

Animal Behaviour, 40, 1

@

@

@

|

|

0

o/

I0

20

1

I

30 km ,

U

Figure 2. Distribution of the four main clusters of release sites. 9 cluster I; @: cluster 2; ~ : cluster 3; O: cluster 4. The large variability in the pigeons' behaviour at the sites located in the region running from the east of the loft to the northwest might indicate poor or contradictory information. Since this band of sites lies somewhat between regions with more precise information north and south it could be interpreted as a region of conflicting or mixed information content. This scenario seems to support parts of Wallraff's system's analysis resulting in the 'null-axis' hypothesis and the idea of a 'preferred compass direction' (Wallraff 1974). The existence of a preferred compass direction has already been tested and rejected for pigeons from Tfibingen and I shall not reiterate here the conclusions arrived at (for discussions of this issue see Wallraff 1982, 1986; R. Wiltschko & Wiltschko 1985b, c; Ganzhorn 1989; Ganzorn & Schmidt-Koenig 1989 and references cited therein). Negation of a preferred compass direction, however, does not necessarily eliminate the idea of a null-axis. According to this hypothesis, pigeons fly up or down a gradient until they arrive at values of the gradient that characterize an axis running through

their home loft (the null-axis). When arriving at, or on being released along, this axis, pigeons should have difficulties in determining whether or not they fly towards home or away from home. This prediction seems to be confirmed by the present analysis. Here, the band of sites where pigeons show extreme variability in their initial orientation (cluster 1 in Fig. 2) could be interpreted as a null-axis. Previously I have argued that if the idea of a null-axis were correct, pigeons should approach their home loft from only two directions, i.e. along the nullaxis (Ganzhorn 1989). Tracks of homing pigeons, however, do not confirm this prediction (Michener & Walcott 1967; Schmidt-Koenig & Walcott 1978). Also, the band of release sites characterized by high variability of the pigeons' initial orientation does not separate two regions where pigeons show differences in their initial orientation. Rather, it cuts through the northwestern region where pigeons show uniform initial orientation (cluster 2 in Fig. 2). This region with similar information content extends on both sides of the null-axis and thus does not support the assumption that the region of poor or varying initial orientation is equivalent to a null-

Ganzhorn."Map of the homingpigeon ~.,._~

F_~[

DU R P .L:.l BOH ROM IHI

~

p

I.

71

LER OBE WAL SCH TOM WIL ALT

9 Cluster I

. Cluster 2

EHN

STW

HAP MON

I

Hoc}

I

ZEP ECK

Cluster 3

I-E., I SPI DOS

Cluster 4 I--" FRO L--TIG j HEC

LI I o,ool

I O.Ol

I o.o5

I I-O

significence levels for differences between groups

Figure 3. Result of the cluster analysis according to Ward. Significance levels between groups were calculated with the Hotelling test.

Table II. Results of airbag experiments Pooled with respect to home Experiments involving sites of

No. of releases

No. of bearings

aH

Cluster 1 C E

15t 15t

94 92

Cluster 3 C E

14 14

Cluster 4 C E

12 12

Pooled with respect to untreated cor~trols No. of releases

No. of bearings

auc

a

U2

0.099

9 9

50 49

3~ 337 ~

0"68** 0"50**

0"106

0.20* 0.17

0.066

14 14

82 89

357 ~ 352 ~

0"47** 0'42**

0'031

0.37** 0.07

0.264*

6 6

29 29

14~ 10~

0.59** 0.37*

0-120

a

U2

342 ~ 36 ~

0.10 0.13

82 89

29 ~ 23 ~

61 62

348 ~ 329 ~

The initial orientation and vanishing bearings drawn with respect to home and pooled for experiments involving different clusters of release sites are shown. C: control; E: experimental bird. Samples were tested for directionality with the Rayleigh test. Groups were compared with the Watson U2 test: *P<0.05; **P<0-001. a: direction of the mean vectors with respect to home (all) and untreated controls (auc). For further details see Appendix. "tOne release was deleted from this analysis because none of the control pigeons gave a vanishing bearing.

Animal Behaviour, 40, 1

72

OC

Ca) C

(b)

-

(c)

Figure 4. Results of airbag experiments pooled with respect to home (0 ~ marked by the dashed line). Symbols at the periphery mark the vanishing direction of single pigeons. The arrow represents the mean vector. Vector length 1 would equal the radius of the circle. O, Controls: pigeons exposed to air collected at the later release site. O, Experimental birds: pigeons exposed to air collected at a site located in the opposite direction to the home loft. (a) Experiments including sites from cluster 1. (b) Experiments including sites from cluster 3, (c) Experiments including sites from cluster 4. Statistical details are given in Table II.

Ganzhorn: Map of the homingpigeon axis. Certainly, if pigeons knew that there were a band of insufficient information and if they knew that this band extends between regions with better information content then they should show the bimodal or variable directional behaviour as predicted by the idea of a null-axis. The underlying causes and navigational mechanisms, however, would be very different from those suggested previously (Wallraff 1974). Despite these objections, the existence of a null-axis has not actually been tested yet. Thus neither acceptance nor rejection of this hypothesis is justified. The analysis of airbag experiments supports the idea of an airborne component in the map of the homing pigeon. But it also suggests that, at least around Tfibingen, this airborne information is just one factor in a multi-cue navigational system. According to the data presented here, there are two regions with different airborne information transportable in PVC containers. One region is to the south of the home loft (cluster 4), the other is to the north (cluster 2). When air from one region is presented to pigeons that later, after anaesthesia of their olfactory mucosae, are released in the region at the opposite side of the home loft, the pigeons are disoriented. Though the effect is fairly weak, it is consistent with previous experiments (Benvenuti & Wallraff 1985; Kiepenheuer 1985, 1986). But there are also regions where olfactory manipulations do not show any effect. These regions extend into the 'olfactory' regions, creating some kind of mosaic. In contrast to the ideas of Papi (1975), however, this mosaic does not seem to consist of air of different types but rather of altogether different physical qualities. Another explanation of the lack of effect of olfactory manipulation at some sites could be that the inherent odour of the PVC bags used in this experiment covered any olfactory cue. If this were the case, we also would not expect to find differences in the initial orientation of experimental birds and controls. But, if these masked olfactory cues were essential, we would observe samples of vanishing bearings without directional preference in both groups under the present experimental conditions. Since this is not the case, olfactory cues at these sites are of no or at the most of minor importance and the pigeons rely on other information. In any case, it is extremely hard to imagine how the observed pattern of initial orientational characteristics might come about, since, from all we know about the atmospheric dispersion of airborne com-

73

ponents, it is very unlikely that distinct patches of olfactory information persist predictably in a given area for some period of time (Becker & van Raden 1986; Waldvogel 1987, 1989). Thus, any sharp boundary such as between release sites belonging to cluster 3 (where olfaction does not seem to be of much relevance for homing pigeons) and some adjacent sites of cluster 4 (where olfaction seems to be important) are unlikely to reflect reality if airborne cues are involved in the map. Rather we might be dealing with a continuum which is split into subgroups by virtue of our statistical methods. This continuum is likely to be composed of several physical components. Pigeons might then weight these different modalities differently at different sites. Despite its speculative nature, the picture presented here might be able to explain many unsolved and debated phenomena in pigeon orientation. There seem to be axial components in the map of the pigeons, as represented by the sites of clusters 1 and 3. These could suggest axial determinants in the homing mechanism as proposed by Wallraff (e.g. 1974, 1986). But along one cardinal direction there seem to be changes of mechanisms on a geographically small scale (i.e. sites of clusters 3 and 4 towards the south). These changes could provide an explanation for the Wiltschkos' results. Overall, they found extremely strong evidence for directional preferences in the vanishing bearings of pigeons from Frankfurt. But on a smaller scale, they found variations that do not support this idea of uniform directionality (Grfiter et al. 1982; R. Wiltschko & Wiltschko 1985b, c; see also W. Wiltschko & Wiltschko 1987). The analysis could also explain why some (in this example magnetic) effects can be observed at only one site, and not at another (Kowalski et al. 1988). The geographical arrangement of sites combined in one cluster also explains why we did not find any difference between control and experimental pigeons in a previous series of airbag experiments (Schmidt-Koenig & Ganzhorn 1989). There, we had presented air collected at sites located at different distances from, but in the same cardinal direction to, the pigeons. Released from one site after anaesthesia of their olfactory mucosae, controls and experimental birds on average vanished in the same direction. In retrospect, we had often collected air from two sites belonging to the same cluster of sites as revealed in this analysis.

Animal Behaviour, 40, 1

74

Though highly speculative and neglecting the information pigeons might collect en route (Kiepenheuer 1978; R. Wiltschko et al. 1978; Baldaccini et al. 1982; Benvenuti et al. 1982; W. Wiltschko & Wiltschko 1982; R. Wiltschko & Wiltschko 1985a, 1988; Wallraff & Sinsch 1988a, b), the different clusters and subclusters in Fig. 3 could reflect landmarks based on different physical cues. In our case, clusters 2 and 4 might represent different 'olfactory landmarks', whereas clusters 1 and 3 are based on something else. Further post factum analyses indicate that disturbances of the earth's magnetic field affect pigeons when released at sites of clusters 1 and 3 but not at sites of clusters 2 and 4 (Schmidt-Koenig & Ganzhorn, 1989). Experimental elimination of the perception of one of these cues will result in an impoverished map. But it is still a map and pigeons will be able to find their way home, though initially they might be disoriented and they might need longer to home. Also, pigeons with different experiences during ontogeny will weight these landmarks differently and thus respond differently to experimental manipulations (Keeton 1974; W. Wiltschko et al. 1987a, b). These landmarks (i.e. clusters of sites where pigeons behave similarly) might be used for navigation by similar mechanisms as suggested by Cartwright & Collett (1987) for honey bees, Apis mellifera. In short, they suggested that bees have an album of mental snapshots of the landscape. Each snapshot is mentally linked to a vector characterized by the home distance and home direction

from the place where the mental image has been registered. After being displaced, they select the snapshot that matches the actual landscape best, and take offin the direction indicated by the vector associated with it. Since the mental snapshot will often represent only an approximation of the actual site to which the animal had been displaced, the animal will make errors. These errors can be corrected during flight when a new mental snapshot takes precedence (for extensive discussions of similar potential navigational strategies see W. Wiltschko & Wiltschko 1978, 1987). This mechanism would explain the phenomenon of release site biases as well as the slow homing speed of pigeons which must be due to extensive detours. Also, this kind of map would be fairly robust against disturbances of one component or the other. Thus, the evolution of this mechanism is easily conceivable. Due to its descriptive nature, the present analysis is unable to test any of the pending questions in pigeon navigation. My aims are, first, to draw attention to a potential methodological shortcoming in the study of pigeon orientation. By pooling releases from different sites located symmetrically around the loft we are likely to combine orientation mechanisms based on different cues. Certainly this will blur our results. Second, in contrast to previous attempts, the kind of cluster analysis presented here might allow us to formulate precise predictions yielding testable hypotheses. This approach might finally make the map of the homing pigeon experimentally accessible.

APPENDIX

The results of the airbag experiments (the geographical locations of sites are given in Fig. 1)

Date

Site

Distance (km)

fl

Group

No. released

No. bearings

an

a

h

HEC HEC MON MON ROM ROM OBE OBE LER LER DUS

23.6 23.6 33.9 33.9 12.6 12.6 19.5 19.5 13.4 13.4 9.2

23~ 23~ 187~ 187~ 271~ 271~ 108~ 108~ 140~ 140~ 342~

C E C E C E C E C E C

7 7 7 7 7 7 7 7 7 7 7

4 5 5 6 6 6 5 6 5 5 6

321~ 314~ 5~ 130~ 247~ 288~ 71~ 39~ 17~ 185~ 30~

0.77 0.75 0.41 0.22 0.32 0.31 0.35 0.54 0.40 0.21 0.49

0.60 0.52 0-41 -0.14 -0.13 0.10 0-11 0.42 0.38 -0.21 0.42

1987

14 July 14 July 14 July 14 July 16 July 16 July 16 July 16 July 24 July 24 July 24 July

continued

Ganzhorn." Map of the homing pigeon

75

APPENDIX

Continued

Date

24 J u l y 17 A u g u s t 17 A u g u s t 17 A u g u s t 17 A u g u s t 19 A u g u s t 19 A u g u s t 19 A u g u s t 19 A u g u s t 21 A u g u s t 21 A u g u s t 21 A u g u s t 21 A u g u s t 29 A u g u s t 29 A u g u s t 29 A u g u s t 29 A u g u s t 29 A u g u s t 29 A u g u s t 3 September 3 September 3 September 2 October 2 October 2 October

Site

Distance (km)

fl

Group

No. released

No. bearings

an

a

h

DUS FRO FRO SCH SCH HIM HIM IHI IHI OBE OBE ROM ROM ROM ROM ROM ECK ECK ECK ZEP ZEP ZEP WIL WlL WIL

9.2 15.8 15.8 14.9 14.9 21.0 21.0 23.7 23.7 19.5 19.5 12.6 12-6 12.6 12.6 12.6 18.0 18.0 18.0 45.1 45.1 45.1 44.3 44.3 44.3

342 ~ 45 ~ 45 ~ 194 ~ 194 ~ 334 ~ 334 ~ 162 ~ 162 ~ 108 ~ 108 ~ 271 ~ 271 ~ 271 ~ 271 ~ 271 ~ 64 ~ 64 ~ 64 ~ 30 ~ 30 ~ 30 ~ 192 ~ 192 ~ 192 ~

E C E C E C E C E C E C E UC C E UC C E UC C E UC C E

7 7 7 7 7 7 7 7 7 7 7 7 7 9 7 7 7 7 7 11 14 14 10 14 14

7 6 5 6 5 5 5 5 5 6 4 5 5 7 5 4 6 3 2 7 11 14 7 11 13

354 ~ 328 ~ 243 ~ 3~ 84 ~ 16 ~ 121 ~ 253 ~ 240 ~ 169 ~ 148 ~ 360 ~ 166 ~ 205 ~ 187 ~ 214 ~ 337 ~ 350 ~ 6~ 343 ~ 336 ~ 358 ~ 111 ~ 106 ~ 111 ~

0.58 0.58 0.77 0.15 0'73 0.28 0.24 0.65 0.85 0.20 0.82 0.27 0.30 0.67 0.99 0.80 0.84 0.78 0.99 0.75 0.47 0-70 0.79 0.88 0.87

0.58 0.49 -0.35 0.15 0.08 0.27 -0.12 -0.19 -0.43 -0.20 --0.70 0.27 -0.29 -0.61 -0.98 -0.66 0.77 0.77 0.98 0.72 0.43 0.70 - 0.28 -0.24 -0'31

SPI SPI SPI BOH BOH B(3H BOH BOH SPI SPI SPI SCH SCH SCH HEC HEC HEC STW STW STW HIM HIM HIM DUS DUS DUS EHN EHN

31.4 31.4 31.4 35.1 35.1 35.1 35.1 35.1 31.4 31.4 31.4 14.9 14.9 14.9 23.6 23.6 23-6 34.0 34.0 34.0 21.0 21.0 21.0 9.2 9.2 9.2 16.3 16.3

84 ~ 84 ~ 84 ~ 276 ~ 276 ~ 276 ~ 276 ~ 276 ~ 84 ~ 84 ~ 84 ~ 194 ~ 194 ~ 194 ~ 23 ~ 23 ~ 23 ~ 149 ~ 149 ~ 149 ~ 334 ~ 334 ~ 334 ~ 342 ~ 342 ~ 342 ~ 156 ~ 156 ~

UC C E C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C

11 15 13 14 14 13 13 14 18 13 14 7 7 6 4 7 7 7 7 7 7 7 7 7 7 7 7 7

4 9 7 12 13 12 11 13 I0 9 13 4 6 6 1 5 5 5 4 5 6 3 6 7 6 4 7 5

36 ~ 17 ~ 348 ~ 177 ~ 50 ~ 176 ~ 206 ~ 93 ~ 352 ~ 360 ~ 321 ~ 311 ~ 339 ~ 353 ~ 69 ~ 24 ~ 34 ~ 332 ~ 282 ~ 212 ~ 204 ~ 226 ~ 184 ~ 25 ~ 81 ~ 112 ~ 296 ~ 295 ~

0.62 0.73 0.93 0.14 0.57 0.36 0-59 0.35 0.64 0.84 0.45 0.66 0.83 0.70 -0'82 0.73 0.83 0.82 0.59 0.38 0.42 0.75 0.20 0.57 0.51 0.75 0.61

0.50 0.70 0'91 -0-14 0.37 -0.36 - 0.53 -0.02 0.63 0.84 0.35 0.43 0.77 0.69 -0-75 0.61 0.73 0.17 -0'50 -0.35 -0.29 --0.75 0.18 0.09 --0.19 0.33 0.26

1988 22 A p r i l 22 A p r i l 22 A p r i l l0 J u n e 10 J u n e 14 J u n e 14 J u n e 14 J u n e 15 J u n e 15 J u n e 15 J u n e 29 J u n e 29 J u n e 29 J u n e 29 J u n e 29 J u n e 29 J u n e 1 August 1 August 1 August 1 August 1 August 1 August 4 August 4 August 4 August 4 August 4 August

contmued

Animal Behaviour, 40, 1

76

APPENDIX

Continued

Date 4 August 5 August 5 August 5 August 5 August 5 August 5 August 8 August 8 August 8 August 8 August 8 August 8 August 9 August 9 August 9 August 9 August 9 August 9 August 10 August 10 August I0 August 10 August 10 August 10 August 16 August 16 August 16 August 16 August 16 August 16 August 17 August 17 August 17 August 17 August 17 August 17 August 18 August 18 August 18 August 18 August 18 August 18 August 19 August 19 August 19 August 19 August 19 August 19 August

Site EHN ZEP ZEP ZEP WlL WIL WIL HOC HOC HOC HAP HAP HAP FRO FRO FRO PLI PLI PLI HOC HOC HOC HAP HAP HAP OBE OBE OBE ROM ROM ROM ECK ECK ECK ALT ALT ALT WIL WIL WlL ZEP ZEP ZEP ECK ECK ECK WDH WDH WDH

Distance (km)

fl

Group

No. released

No. bearings

aH

a

h

16.3 45.1 45.1 45.1 44.3 44.3 44.3 67.2 67-2 67.2 63.6 63.6 63.6 15.8 15.8 15.8 23.4 23.4 23.4 67.2 67.2 67.2 63.6 63.6 63.6 19.5 19.5 19.5 12.6 12.6 12.6 18.0 18.0 18.0 14.3 14.3 14.3 44.1 44.1 44.1 45.1 45.1 45.1 18.0 18.0 18.0 11.4 11.4 11.4

156 ~ 30 ~ 30 ~ 30 ~ 192 ~ 192 ~ 192 ~ 30 ~ 30 ~ 30 ~ 199 ~ 199 ~ 199 ~ 45 ~ 45 ~ 45 ~ 221 ~ 221 ~ 221 ~ 30 ~ 30 ~ 30 ~ 199 ~ 199 ~ 199 ~ 108 ~ 108 ~ 108 ~ 271 ~ 271 ~ 271 ~ 64 ~ 64 ~ 64 ~ 247 ~ 247 ~ 247 ~ 192 ~ 192 ~ 192 ~ 30 ~ 30 ~ 30 ~ 64 ~ 64 ~ 64 ~ 245 ~ 245 ~ 245 ~

E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E UC C E

7 5 7 7 5 7 7 7 7 7 7 7 7 7 7 7 6 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7

3 5 5 7 3 6 6 5 5 5 6 7 6 6 6 3 6 3 3 6 5 3 7 7 5 3 4 2 4 0 2 4 4 5 6 4 4 6 4 7 5 4 5 5 5 4 3 4 5

273 ~ 155 ~ 85 ~ 73 ~ 296 ~ 354 ~ 129 ~ 358 ~ 339 ~ 352 ~ 278 ~ 281 ~ 284 ~ 310 ~ 314 ~ 343 ~ 128 ~ 82 ~ 100 ~ 348 ~ 321 ~ 350 ~ 254 ~ 222 ~ 243 ~ 37 ~ 59 ~ 51 ~ 229 ~ . . 316 ~ 305 ~ 12~ 310 ~ 51 ~ 141 ~ 226 ~ 123 ~ 117 ~ 90 ~ 38 ~ 352 ~ 341 ~ 340 ~ 7~ 344 ~ 237 ~ 20 ~ 106 ~

0.41 0.40 0.60 0.11 0.40 0.49 0.42 0.91 0.96 0.82 0.81 0.37 0.44 0.41 0.48 0.79 0.21 0.66 0.82 1.00 0.36 0.97 0.38 0.41 0.61 0.70 0.97 0.99 0.31 . . 0.68 0.48 0.39 0.57 0.95 0.68 0.45 0.31 0.85 0.46 0.91 0.68 0.85 0.59 0.94 0.42 0.46 0.17 0.63

0.02 -0.37 0.05 0.03 0.18 0.49 -0.27 0.91 0.89 0.81 0.11 0.07 0.11 0.26 0-33 0.76 -0.31 0.09 -0.14 0.98 0.28 0.96 - 0.11 -0.31 -0.28 0.56 0.50 0.62 -0.20 0.49 0.27 0.38 0.37 0.60 -0.53 -0.25 -0.17 -0.39 0.00 0.72 0.67 0.81 0.55 0.93 0.40 -0.25 0.16 -0.17

Distance, fl: distance and home direction of release sites. C: controls: pigeons exposed to air collected at one site and released at the same site after anaesthesia of their olfactory mucosae. E" experimental birds: pigeons exposed to air collected at one site but released at a site opposite to the home loft after anaesthesia of their olfactory mucosae. UC: untreated controls, an, a: direction and length of the mean vector with respect to the home direction (0~ h: homeward component (h = a ' c o s % ) .

Ganzhorn: Map o f the homing pigeon ACKNOWLEDGMENTS I thank A. Ganzhorn, E. Haydt, A. Kfihner-Arnold and C. Kunze for their help in the releases and in the preparation of the manuscript. H. Mauch took excellent care of the pigeons. A. G a n z h o r n wrote the computer programs for circular statistics. R. R. Baker, K. Schmidt-Koenig and an anonymous referee made very helpful comments on drafts of the manuscript. The work was supported by the Deutsche Forschungsgemeinschaft, SFB 307.

REFERENCES Baldaccini, N. E., Benvenuti, S., Fiaschi, V., Ioa16, P. & Papi, F. 1982. Pigeon orientation: experiments on the role of olfactory stimuli perceived during the outward journey. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 160-169. Berlin: Springer Verlag. Batschelet, E. 1981. Circular Statistics in Biology. New York: Academic Press. Becker, J. & van Raden, H. 1986. Meteorologische Gesichtspunkte zur olfaktorischen Navigationshypothese. J. Ornithol. 127, 1-8. Benvenuti, S., Baldaccini, N. E. & Ioa16, P. 1982. Pigeon homing: effect of altered magnetic field during displacement on initial orientation. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 140-148. Berlin: Springer Verlag. Benvenuti, S. & Wallraff, H. G. 1985. Pigeon navigation: site simulation by means of atmospheric odors. J. comp. Physiol. A., 156, 73~746. Cartwright, B. A. & Collett, T. S. 1987. Landmark maps for honeybees. Biol. Cybern., 57, 85-93. Deichsel, G. & Trampisch, H. J. 1985. Biometrie: Clusteranalyse und Diskriminanzanalyse. Stuttgart: G. Fischer Verlag. Dornfeldt, K. 1982. Dependence of the homing pigeons' initial orientation on topographical and meteorological variables: a multivariate study. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 253-264. Berlin: Springer Verlag. Ffiller, E., Kowalski, U. & Wiltschko, R. 1983. Orientation of homing pigeons: compass orientation vs piloting by familiar landmarks. J. comp. Physiol. A, 153, 55 58. Ganzhorn, J. U. 1989. Multivariate analysis of initial orientation in homing pigeons: is there a 'preferred compass direction'? J. Ornithol. 130, 161-173. Ganzhorn, J. U. & Schmidt-Koenig, K. 1989. Initial orientation of homing pigeons around Tfibingen. In: Proceedings of the International Centennial Meeting of the Deutsche Ornithologen-Gesellschaft, Current Topics in Avian Biology, Bonn 1988 (Ed. by R. v.d. Elzen, K.-L. Schuchmann & K. Schmidt-Koenig), pp. 305-309. Bonn: Verlag der Deutschen OrnithologenGesellschaft. Gould, J. L. 1982. The map sense of pigeons. Nature, Lond., 296, 205-211.

77

Groebe, G. 1979. Dressur von Brieftauben (Columba livia) auf nat/irliche Geruchsstoffe. Diplomarbeit, Universit~it Tiibingen. Gr/iter, M., Wiltschko, R. & Wiltschko, W. 1982. Distribution of release-site biases around Frankfurt a.M. Germany. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 222-231. Berlin: Springer Verlag. Keeton, W. T. 1974. The orientational and navigational basis of homing in birds. Adv. Study Behav., 5, 47132. Kiepenheuer, J. 1978. Inversion of the magnetic field during transport: its influence on the homing behavior of pigeons. In: Animal Migration, Navigation and Homing (Ed. by K. Schmidt-Koenig & W. T. Keeton), pp. 135-142. Berlin: Springer Verlag. Kiepenheuer, J. 1985. Can pigeons be fooled about the actual release site position by presenting them information from another site? Behav. Ecol. Sociobiol., 18, 75-82. Kiepenheuer, J. 1986. Are site specific airborne stimuli relevant for pigeon navigation only when matched by other release-site information? Naturwissenshaften, 73, 42-43. Kowalski, U., Wiltschko, R. & Fiiller, E. 1988. Normal fluctuations of the geomagnetic field affect initial orientation in pigeons. J. comp. Physiol. A., 163, 593-600. Kramer, G. 1953. Wird die Sonnenh6he bei der Heimfindeorientierung verwertet? J. Ornithol. 94, 201219. Lednor, A. J. 1982. Magnetic navigation in pigeons: possibilities and problems. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraf0, pp. 109-119. Berlin: Springer Verlag. Lednor, A. J. & Walcott, C. 1988. Orientation of homing pigeons at magnetic anomalies. Behav. Ecol. Sociobiol., 22, 3-8. Michener, M. C. & Walcott, C. 1967. Homing of single pigeons: analysis of tracks. J. exp. Biol., 47, 99-131. Papi, F. 1975. La navigazione dei colombi viaggiatori. Le Scienze, 78, 66-75. Papi, F. 1982. Olfaction and homing in pigeons: ten years of experiments. In: Avian Navigation. (Ed. by F. Papi & H. G. Wallraff), pp. 149-159. Berlin: Springer Verlag. Papi, F. 1986. Pigeon navigation: solved problems and open questions. Monitorezool. ital., 20~471 517. SAS/STAT 1987. Guide for Personal Computers. Cary, North Carolina: SAS/STAT. Schmidt-Koenig, K. 1958. Experimentelle EinfluBnahme auf die 24-Stunden-Periodik bei Brieftauben und deren Auswirkungen unter besonderer Beriicksichtigung des Heimfindeverm6gens. Z. TierpsychoL, 15, 301-331. Schmidt-Koenig, K. 1970. Entfernung und Heimkehrverhalten der Brieftaube. Z. vergl. Physiol., 68, 39-48. Schmidt-Koenig, K. 1979. Avian Orientation and Navigation. New York: Academic Press. Schmidt-Koenig, K. 1985. Hypothesen und Argumente zum Navigationsverm6gen der V6gel. J. Ornithol. 126, 237-252. Schmidt-Koenig, K. 1987. Bird navigation: has olfactory orientation solved the problem? Q. Rev. Biol., 62, 31-47.

78

Animal Behaviour, 40, 1

Schmidt-Koenig, K. & Walcott, C. 1978. Tracks of pigeons homing with frosted lenses. Anita. Behav., 26, 480-486. Schmidt-Koenig, K. & Ganzhorn, J. U. 1989. On the role of airborne information for the initial orientation of homing pigeons: test of the mosaic map hypothesis. In: Proceedings of the International Centennial Meeting of the Deutsche Ornithologen-Gesellschaft, Current Topics in Avian Biology, Bonn 1988 (Ed. by R. v.d. Elzen, K.-L. Schuchmann & K. Schmidt-Koenig), pp. 299-304. Bonn: Verlag der Deutschen OrnithologenGesellschaft. Schmidt-Koenig, K. & Ganzhorn, J. U. In press. On the problem of bird navigation. In: Perspectives in Ethology, Vol. 9 (Ed. by P. P. G. Bateson & P. H. Klopfer), New York: Plenum Press. Siegel, S. 1956. Nonparametric Statistics. Tokyo: McGraw-Hill Kogahusha. Walcott, C. 1982. Is there evidence for a magnetic map in homing pigeons? In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 99-108. Berlin: Springer Verlag. Walcott, C. 1986. A review of magnetic effects on homing pigeon orientation. In: Biophysical Effeets of Steady Magnetic Fields. (Ed. by G. Maret, N. Boccara & J. Kiepenheuer), pp. 146-147. Berlin: Springer Verlag. Walcott, C. & Green, R. P. 1974. Orientation of homing pigeons altered by change in the direction of an applied magnetic field. Science, 184, 18~182. Waldvogel, J. A. 1987. Olfactory navigation in homing pigeons: are the current models atmospherically realistic? Auk, 104, 369-379. Waldvogel, J. A. 1989. Olfactory orientation by birds. In: Current Ornithology. Vol. 6 (Ed. by D. M. Power), pp~ 269-321. New York: Plenum Press. Wallraff, H. G. 1974. Das Navigationssystem der V6gel. Miinchen: Oldenbourg Verlag. Wallraff, H. G. 1978. Preferred compass directions in initial orientation of homing pigeons. In: Animal Migration, Navigation andHoming (Ed. by K. SchmidtKoenig & W. T. Keeton), pp. 171-183. Berlin: Springer Verlag. Wallraff, H. G. 1980. Olfaction and homing in pigeons: nerve-section experiments, critique hypotheses. J. comp. Physiol. A, 139, 209-224. Wallraff, H. G. 1982. Homing to Wiirzburg: an interim report on long-term analyses of pigeons. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraf0, pp. 211-221. Berlin: Springer Verlag. Wallraff, H. G. 1983. Relevance of atmospheric odours and geomagnetic field to pigeon navigation: what is the 'map' basis? Comp. Biochem. Physiol., 76A, 643-663. Wallraff, H. G. 1986. Directional components derived from initial orientation data of inexperienced homing pigeons. J. comp. Physiol. A, 159, 143 159. Wallraff, H. G. 1988a. Navigation mit Duftkarte und SonnenkompaB: das Heimfindeverm6gen der Brieftauben. Naturwissenshaften., 75, 380-392.

Wallraff, H. G. 1988b. Olfactory deprivation in pigeons: examination of methods applied in homing experiments. Comp. Biochem. Physiol. A, 89, 621-629. Wallraff, H. G. & Sinsch, U. 1988a. The role of'outwardjourney information' in homing experiments with pigeons: new data on ontogeny of navigation and general survey. Ethology, 77, 10 27. Wallraff, H. G. & Sinsch, U. 1988b. The 'outward journey problem' in pigeon homing: reply to Wiltschko & Wiltschko (1988). Ethology, 78, 254-255. Wiltschko, R., Wiltschko, W. & Keeton, W. T. 1978. Effect of outward journey in an altered magnetic field on the orientation of young homing pigeons. In: Animal Migration, Navigation andHoming (Ed. by K. SchmidtKoenig & W. T. Keeton), pp. 15~161. Berlin: Springer Verlag. Wiltschko, R. & Wiltschko, W. 1985a. Pigeon homing: change in navigational strategy during ontogeny. Anita. Behav., 33, 583-590. Wiltschko, R. & Wiltschko, W. 1985b. Pigeon homing: does initial orientation include a 'preferred compass direction'? J. comp. Physiol. A, 157, 469476. Wiltschko, R. & Wiltschko, W. 1985c. Pigeon homing: can release site biases be explained by a 'preferred compass direction'? Monitore zool. ital., 19, 197-206. Wiltschko, R. & Wiltschko, W. 1988. The role of 'outward-journey information' in homing experiments with pigeons: comment to Wallraff & Sinsch (1988). Ethology, 78, 251-253. Wiltschko, W. 1983. Compasses used by birds. Comp. Biochem. Physiol. A, 76, 709-718. Wiltschko, W., Nohr, D., Fiiller, E. & Wiltschko, R. 1986. Pigeon homing: the use of magnetic information in position finding. In: Biophysical Effects of Steady Magnetic Fields. (Ed. by G. Maret, N. Boccara & J. Kiepenheuer), pp. 154-162. Berlin: Springer Verlag. Wiltschko, W. & Wiltschko, R. 1978. A theoretical model for migratory orientation and homing in birds. Oikos, 30, 177-187. Wiltschko, W. & Wiltschko, R. 1982. The role of outward journey information in the orientation of homing pigeons. In: Avian Navigation (Ed. by F. Papi & H. G. Wallraff), pp. 239-252. Berlin: Springer Verlag. Wiltschko, W. & Wiltschko, R. 1987. Cognitive maps and navigation in homing pigeons. In: Cognitive Processes and Spatial Orientation in Animals and Man (Ed. by P. Ellen & C. Thinus-Blanc), pp. 201 216. Dordrecht: M. Nijhoff. Wiltschko, W., Wiltschko, R., Griiter, M. & Kowalski, U. 1987a. Pigeon homing: early experience determines what factors are used for navigation. Naturwissenshaften, 74, 196-197. Wiltschko, W., Wiltschko, R. & Walcott, C. 1987b. Different effects of olfactory deprivation in different countries. Behav. Ecol. Sociobiol., 21, 333-342.

(Received 18 February 1989; initial acceptance 11 April 1989;final aceeptance 6 May 1989; MS. number: 3356)