Introduction

Since the end of the last Ice Age and the onset of the Holocene 11.6 ka BP (thousand years before present), there have been several major changes in the avifauna of northern Europe. The constant climate-induced succession of the woodlands, the formation of the North and Baltic Seas, later the anthropogenic clearing of the forests for livestock and fields, and finally the transformation from a natural landscape to a cultural landscape—all these factors must have had a deep impact on the composition and occurrence of breeding and migratory birds. With bird remains from archaeological excavations, a rich and, especially in more recent times, extensive material is available to analyze these developments, their causes, and consequences. This is also done from the discipline of archaeozoology so that the range history of many species is known in outline on the European level (von den Driesch and Pöllath 2010) and with more details on a regional scale (Ericson and Tyrberg 2004; Yalden and Albarella 2009; Goffette et al. 2017; Serjeantson 2023). Certain species have been extensively studied, such as the Great Auk (Pinguinus impennis; Hufthammer and Hufthammer 2022) or the Dalmatian Pelican (Crees et al. 2022; Nikulina and Schmölcke 2015). Sometimes, such studies include analysis of ancient DNA (Nikulina and Schmölcke 2015), give detailed insights into the evolutionary and ecological histories of birds (Holm and Svenning 2014; Wood and De Pietri 2015; Núñez-Lahuerta et al. 2018), and can be used for modeling future range shifts caused by the present climate warming (Lagerholm et al. 2016). However, despite the high potential of such archaeo-ornithological studies, they are rarely used in ornithology, in contrast to papers in molecular phylogeography, which reconstruct the distribution and population history of bird species based on their recent genome (Parau and Wink 2021).

The possibilities of archaeozoological investigations for ornithological research are manifold (Gál 2006; Wood and De Pietri 2015). They allow the determination and interpretation of range dynamics of individual species or species communities, the assessment of population developments and of the role of climate change, and the reconstruction of the evolution of bird migration. Archaeozoology provides data from deep in time on the abundance, structure, and spatial extent of past bird populations, and thus raises the conservation-relevant question: What are native and what are alien species? Finally, yet importantly, the interpretation of archaeozoological data also makes it possible to predict future biogeographical shifts in species, especially in times of climate change.

This paper will present the range history of two prominent species to demonstrate the relevance of archaeozoological research for conservation biology and ornithology. The species selected are of similar size and attractiveness. This prevents methodological problems when comparing the results.

The Eurasian Spoonbill (Platalea leucorodia Linnaeus, 1758) is a widespread, colony-breeding, and gregarious wetlands species throughout warm regions of the central and southern Palearctic (Cramp 1977; Hancock et al. 1992). In more temperate areas of its range, the populations are migratory, in the south of the breeding range they are resident. The recent Spoonbill distribution in Europe is very patchy and separated into two clusters of populations, one at the Atlantic coast from Portugal to Denmark and the other from northern Italy, the Danube River Basin, and the Carpathian Basin to the Black Sea area (Deinet et al. 2013, 189). However, it is widely assumed that it “formerly bred rather widely throughout Europe” (Hancock et al. 1992, 255), and that “the Atlantic population […] was much more expansive in the past” (Deinet et al. 2013, 186).

The White Stork (Ciconia ciconia Linnaeus, 1758) breeds today in large parts of Europe, north-western Africa, and westernmost Asia. The northern distribution boundary runs from Schleswig–Holstein in northernmost Germany and Denmark (only single breeding pairs) to Scania, southern Sweden (reintroduction program since 1989; Cavallin 1999) along the southern coast of the Baltic Sea to the Lake Ladoga (Thomsen et al. 2017). The White Stork colonizes open and semi-open landscapes. It prefers natural to extensively used wet grassland. The species is adaptable and uses intensively used grassland and even garbage dumps. The nest sites are usually located in human settlements, mostly on house roofs and poles, and less frequently on trees and rocks. Colonies build up under favorable conditions.

The White Stork is a migratory bird that winters in sub-Saharan Africa, south-western Europe, and North Africa (Köppen et al. 2017). There are two migration routes. The populations in Eastern Europe, South-eastern Europe, and Asia Minor migrate south-east across the Bosporus and the Gulf of Suez to East Africa and South Africa. The birds in Western Europe migrate across the Strait of Gibraltar to the West African Sahel. Since the 1980s, White Storks increasingly wintered on the Iberian Peninsula and in Morocco. A migratory divide with a broad mixed area runs through Central Europe.

Despite their importance for nature conservation as symbolic birds with positive connotations, the distribution history of both species has not yet been studied. Very brief outlines are available for the Great Britain (Serjeantson 2010) and, in the case of the White Stork, for the Netherlands (Esser and Verhagen 2001). Recently, a cursory look at the European distribution history of that species was published (Schmölcke 2022).

Materials and methods

This study uses bird bones found during archaeological excavations of prehistoric or protohistoric settlements. For both species, no postglacial remains from a non-archaeological context exist (see the complete list of records in the Supplementary Material). Depending on local preservation conditions and the varying intensity of human use of wild birds, hundreds or thousands of bird bones can be found per excavation, but often fewer. In addition to information about the cultural or ritual significance of birds, archaeological bird remains allow us to obtain details of the history of species distributions, landscape or bird migration, for example. To do this, it is first necessary to identify the species of the bones found. Extensive comparative collections with recent bones or speciation literature, such as Gruber (1990) for the species covered here, serve this purpose.

Our research is based on the huge Open Access data collection ‘The Holocene History of the European Vertebrate Fauna’, which was built under the leadership of Angela von den Driesch (University of Munich, Germany), Norbert Benecke (German Archaeological Institute, Berlin, Germany), and Dirk Heinrich (Kiel University, Germany) in the 1990s (Heinrich et al. 2016). The collection contains information on more than 7500 archaeological excavation sites with animal remains from the Late Pleistocene to the early modern period throughout Europe. 2915 of these sites contain remains of domestic or wild birds. Although the data collection contains only a few additions of bird bone finds since the year 2000, the data set with its more than 252,800 bird remains is so large that it can easily be used for studies on the distribution history of species. Nevertheless, in addition to the archaeozoological data of these 2915 archaeological sites, we also considered all published reports on (pre)historic White Stork and Spoonbill finds in Europe since the year 2000 and could add a few records of both species that were not listed in the data collection. In the end, the present study is based on 89 excavation sites where remains of White Storks were found and 22 sites with Spoonbill remains. All data on all records of both species inclusive of some comments were summarized in a table and presented in the Supplementary Material. This table includes geographical information and the dating of the finds, as well as every single reference to the sources, and the local number of finds. All records in the table were checked for their reliability. Determinations that were indicated by the authors in the primary literature as questionable or uncertain (in our case ‘Ciconia sp.’ or ‘C. nigra / C. ciconia’) were not taken into account. In addition, there are a few references to White Stork evidence that have also been excluded because they are proved to be unreliable due to different reasons. Details are given in the Supplementary Material. For all records, the dating of the archaeological site given in the data collection was proved to reflect the current state of research on the locations.

To reconstruct the history of species distributions by archaeological findings, it is necessary to take into account the former function of the respective sites. Most of the evidence considered in the present paper consists of bones found in settlement waste. The settlements differ in size from Stone Age camps to villages and urban-like contexts, but there are also finds from castles, trading centers, residences, or palaces. This functional context is always indicated in the table.

When reconstructing the history of former animal distributions based on archaeological data, the absence of evidence is not evidence of absence. Many factors influence the representation of animal species in archaeological finds, primarily the intensity of (bird) hunting, but also local preservation conditions. In addition, the tradition of archaeozoological analysis is not developed in the same way in all regions of Europe. Gaps in the archaeozoological findings can sometimes be compensated for by other archaeological or historical find groups (e.g. coins, figurines, drawings) or contemporary written sources. As can be seen below, this also applies in the case of White Stork and Spoonbill. Additionally, it cannot excluded from the start that the birds recorded in human settlements were brought there for food or ritual purposes from far away. All these aspects must be taken into account when interpreting and discussing zoological data so that this can only be done with proven interdisciplinary expertise.

It is not possible to give an exact total number of bones or individuals found of each species, as different measures were used in the primary literature. Sometimes the minimum number of individuals (MNI) is given, and sometimes the number of identifiable specimens (NISP). In some cases, only a list of species is published without any quantification. However, the total number of White Storks and Spoonbills archaeologically recorded (at one archaeological site) is not relevant to the present study, which is concerned with the development of the species’ ranges.

Dates are given in BP (years before present), if the long-term perspective is meant, or in Common Era (CE) and Before the Common Era (BCE) as an alternative to the original Anno Domini (AD) and Before Christ (BC) notations, if the information refers to periods or individual dates.

Results

The oldest evidence of White Storks in Europe after the end of the last Ice Age 11,600 years BP derives from two late-glacial sites in Spain (Gorham’s Cave) and south-eastern France (La Baume de Gigny). Both are ten thousand years old or a bit older. Only a little younger are White Stork remains from the Lower Rhine region (site Bedburg-Königshoven). From 11,600 to 4000 years BP, C. ciconia can be found at 14 more suitable archaeological sites, ranging from Brittany and Portugal in the west to Romania and northern Greece in the east (Fig. 1). Concentrations of findings are in south-eastern Europe (Romania, Bulgaria, northern Greece; n = 6), in the Upper Rhine and Rhône area (n = 6), and in the southern part of the Iberian Peninsula (n = 3). Between 4000 and 2000 years ago, this picture changed relatively little. Again, the records accumulate in Bulgaria and northern Greece (n = 4) and in Spain (n = 4). C. ciconia is also found again in the Upper Rhine region. Additionally, there is a find in Cornwall, England. In the following period from 2000 to 1000 years ago, the scenario changes. Almost all of the eleven relevant archaeological records of the White Stork are located to the northwest of the previous area of discovery, in a band that encompasses England and then runs down the rivers Rhine and Danube. Only two records lie outside this zone. One is on the northern coast of the Black Sea in southern Ukraine, the other in the foothills of the Harz Mountains in central Germany. Both the latter one as well as the record from the area of the Rhine mouth are somewhat spectacular. The White Stork record from the end of the second century CE found in The Netherlands at the archaeological site Midden-Delfland KR93 is a poorly but almost completely preserved skeleton of a bird that was deposited in a specially made pit as part of a ritual act (van London 1994). The pit belongs to a group of pits in which the remains of other deposited animals or selected skeletal parts were found (of a sheep and a foal). The record of C. ciconia at the Central German archaeological site Am Hetelberg/Gielde, a settlement continuously inhabited from the late 1st to the early seventh century CE, is a single bone, isolated spatially and temporally from all other contemporaneous finds. The identification nevertheless appears trustworthy, as the archaeozoologists responsible included reputable experts who also asked international specialists for their additional expertise.

Fig. 1
figure 1

Subfossil records of White Stork (Ciconia ciconia) in Europe during three periods between the post-glacial re-warming and 1000 years before present (yrs. BP). The background map shows the current breeding distribution in Europe in gray (EBCC 2022). The orange line marks the border of the Roman Empire around 100 CE. The blue-colored area marks the current migratory divide area between western and eastern storks. In Western Europe, the birds fly via Gibraltar to winter in Africa, in eastern Europe via the Bosporus

Full size image

In younger times, after 1000 CE, a clear expansion towards the northeast can be observed. Of the 50 archaeological sites with evidence of C. ciconia from 1000 to 1600 CE, 21 are well outside the previous distribution area before 1000 CE. At the same time, the geographical focus of the sites is also shifting.

From the period 1000 to 700 years ago, there are 20 archaeological sites with White Stork remains (Fig. 2). The former focus regions on the Iberian Peninsula, in the Upper Rhine area and the south-eastern Balkans are now only represented by a few individual finds. Most of the evidence now comes from the northern half of Germany (n = 5) and the western half of Poland (n = 5), added by three records in the Netherlands. In the last investigated period from 1300 to 1600 CE, 14 out of 19 records derive from the Netherlands or its immediate surroundings. At the same time, a further eastward expansion can be seen in Poland. Only widely scattered individual finds also confirm the occurrence of C. ciconia in its former, original distribution area in southern Europe and also in England.

Fig. 2
figure 2

Subfossil records of White Stork (Ciconia ciconia) in Europe during three periods between 1000 and 400 years before present (yrs. BP). The background map shows the current breeding distribution in Europe in gray (EBCC 2022). The blue-colored area marks the current migratory divide area zone between western and eastern storks. In Western Europe, the birds fly via Gibraltar to winter in Africa, in eastern Europe via the Bosporus

Full size image

In the case of the Spoonbill, even if there are only 22 locations with remains from the entire Holocene, spatially distributed from southern Scandinavia to the Mediterranean region, a consistent pattern emerges (Fig. 3). The oldest evidence of Spoonbills in Europe originates from Hungary (archaeological site Endrőd) and Romania (Hârşova) and is around 8000 years old. In the West, in Spain, P. leucorodia is first documented only much later in the second millennium BCE. For the entire pre-Christian period, there are finds from large parts of southern Europe, spreading from the Iberian Peninsula in the west to the mouth of the Dnipro in the east. The occurrence of the species in Hungary is documented twice and marks the northernmost evidence of the species in pre-Christian times. This picture changes shortly after the turn of the century. Spoonbills are now also being detected much further north, often in coastal areas, starting in the first decades of the CE with the archaeological site Velsen I in the Netherlands. This evidence is confirmed by a second, only slightly more recent Dutch record. In the second half of the first millennium CE, evidence that is even more northerly was found in Denmark and Sweden. Although the correct identification of the four different Scandinavian finds is not in doubt, it will be discussed below whether they indicate a former extension of P. leucorodia’s range to the Baltic Sea. From the second half of the first millennium CE onwards, Spoonbill can now also be found in England. It is unclear when the species immigrated there, as the (presumably) oldest evidence is only very imprecisely dated, but immigration must have taken place around 1000 CE at the latest. Two further archaeological remains continue the presence of the species in England into the 16th/seventeenth century.

Fig. 3
figure 3

Subfossil records of Spoonbill (Platalea leucorodia) in Europe during four periods between the post-glacial re-warming and 400 years before present (yrs. BP). The background map shows the current breeding distribution in Europe in gray (EBCC 2022)

Full size image

Discussion

The archaeological evidence of C. ciconia and P. leucorodia presented here reveals a large range expansion of both species from southern and western Europe. This general picture is completed by a few isolated finds, which can be attributed to stray visitors. This applies to the approximately 3000-year-old bone of a White Stork that was found almost 100 years ago on the Shetland Islands; its correct identification is not disputed in the specialist literature (Serjeantson 2010, 2023; Yalden and Carthy 2013; Barr 2018). The same applies to the equally undisputed, approximately 800-year-old evidence of a Spoonbill at the Baltic Sea island of Öland (Boessneck and von den Driesch 1979). When it comes to the interpretation of the results presented here, it must be taken into account that it is hard to say whether single archaeological finds can be interpreted as evidence of local breeding or whether they are animals on migration or, again, even stray visitors. Only in the case of two finds of bones from a young White Stork, a local brood is definitively proven; these are a 7000-year-old bone from northwest France (Tresset 2005) and three 600-year-old stork remains from the Netherlands (Esser and Verhagen 2001) and Central Germany (Boessneck 1982).

White Stork and Spoonbill in European prehistory up to the beginning of CE

The White Stork was up to 1500 years ago in Europe exclusively distributed in the South and West. Three centers of distribution have emerged: the Iberian Peninsula, the Upper Rhine region, and the Southern Balkans. It remains to be investigated whether this is caused by missing archaeological remains (i.e. by the state of research) or a further example of a disjunct distribution of a bird species in Europe caused by Pleistocene range retraction and fragmentation. Further examples of this phenomenon are White-Winged Snowfinch (Montifringilla nivalis), Rock Ptarmigan (Lagopus muta), Alpine Chough (Pyrrhocorax graculus), and Red-Billed chough (Pyrrhocorax pyrrhocorax) (Holm and Svenning 2014). If we take today’s migration routes to the wintering grounds as a guide, we could assume that the White Storks from the Iberian Peninsula and the Upper Rhine / Rhône region were westward migrants and the birds from the southern Balkans were eastward migrants (Fig. 1). This theory is also supported by the drift southward of the EuroSiberian–Mediterranean boundary during the Late Pleistocene discovered based on archaeological bird finds (Núñez-Lahuerta et al. 2018). This drift southward may have deepened the splitting of the populations, which ultimately led to the formation of two different migration routes to the wintering grounds. Schüz (1953, 1964) also assumed, when considering both migration routes of the White Stork that the post-glacial colonization of Europe ran from the southwest via the Iberian Peninsula and from the southeast via Asia Minor and the Balkans. Both populations then met in Central Europe, forming the migratory divide.

White Stork in Europe in Roman times

It is extremely remarkable and certainly no coincidence that the distribution boundaries of the White Stork at the end of Antiquity in the fifth century CE corresponded exactly to the extent of the Roman Empire during the first centuries CE, which encompassed large parts of western, southern and south-eastern Europe, inclusively parts of Britain and whose northern borders ran essentially along the rivers Rhine and Danube (Fig. 1). As many ancient written sources show, the White Stork was at that time already closely attached to humans, living synanthrope with nests on buildings in areas of open farmland and meadows, and a bird known to everyone in most parts of the Empire, at least in Italy and Greece (Arnott 2007; Lunczer 2009). Almost every ancient writer whose writings have come down to us mentions the species at some point in his œuvre (Arnott 2007). In the first century CE, Pliny even refers to the stork’s autumn migration in two directions, eastwards and southwards (Pliny HN 10.61–62), and in the early second century, a pair of storks once even nested on the roof of a temple to the goddess Concordia in the center of Rome (Juvenal SatI:116).

In addition to the written sources, the notable archaeological lack of stork remains in Italy is also filled by White Stork portrays on two different coins from the first century BCE as well as by depictions on two silver cups of an ancient Villa at Boscoreale near Pompeii, and an accurate wall painting in Pompeii itself, both dating to the first century CE (Watson 2002; Arnott 2007). Given this variety of sources, it is plausible to assume that the White Stork was a well-known breeding bird at that time in (at least in parts of) Italy and many other regions of the Roman Empire.

The northernmost find of C. ciconia on the European mainland in that period derives from the Netherlands and is a complete bird deposited 1200 years ago in a special pit (van London 1994). Likely, the deposition was part of a ritual act, since the pit belongs to a group of some more pits in which remains of a sheep and a foal were found (van London 1994). This record could indicate an (at least local) spiritual significance of the species and the borders of its distribution. However, there is no other evidence of something similar from this period.

Another northern find of C. ciconia from this period or a bit younger originates from a Central German settlement continuously inhabited from the late first to the early seventh century CE. Even if the species identification appears trustworthy, without direct radiocarbon dating, the bone should not be regarded as evidence for the presence of a White Stork far outside the actual range. Rather, local demand for exotic birds could play a role, because besides White Stork remains of Cinereous Vulture (Aegypius monachus) and Ural Owl (Strix uralensis) were also verified there. We will see in a moment that this explanation is not as outlandish as it may seem.

White Stork in Europe in historic times

Beyond the borders of the Roman Empire, in regions where human population density was much lower and agriculture and clearing were much less intensive—and which were thus dominated by woodlands—the White Storks did not yet find adequate habitats, in particular, because the species was in the Roman area already human-associated. It was not until 1000 years ago during the extensive Medieval clearings that conditions changed and a rapid expansion of the range began that can be observed both east and west of the migratory divide. In the west, the expansion possibly originated from a rapidly growing population in the Netherlands. Future archaeogenetic studies will show whether the first storks that appeared on the border with Scandinavia originated there. In the east, at the same time, the species seem to have spread northwards from the Danube lowlands, so that the Baltic Sea coast was already reached probably during the thirteenth century. 700–1000 years ago the migratory divide mixed area in Central Europe that is so prominent today was formed.

Although in northern Europe, the border to Scandinavia was reached already 1000 years ago, there was no further expansion of the area for a long time, unlike in the east. The earliest reference to the presence of the White Stork in Denmark is a written source from the sixteenth century CE (Løppenthin 1967). At this time, according to contemporary Swedish sources, White Storks were also breeding in Scania (Ericson and Tyrberg 2004). The White Stork population in Denmark reached its maximum in the mid-nineteenth century with 8000 and 10,000 pairs, in Scania with around 5000 pairs, when the population suddenly collapsed dramatically in 1856. This was probably caused by poor conditions during migration or in the wintering grounds and is referred to as a “disturbance year”. They remained there quite frequently until the middle of the nineteenth century when the population suddenly collapsed dramatically in 1856. By around 1890, the Danish White Stork population decreased to only 4000 pairs. The decline continued in the twentieth century until only one pair bred unsuccessfully in Denmark between 2001 and 2003. Since then, the population has recovered slightly (2023 – 10 pairs). The Swedish White Storks did not recover from this decline and were finally extinct in 1953 (Ericson and Tyrberg 2004). In 1989, a reintroduction project started so that 55 pairs were breeding in Sweden again in 2023.

According to our data, immigration to Poland began in the thirteenth century, and in the fifteenth century (precisely in 1584) Mateusz Cygański, the author of the first Polish ornithological study, called White Storks already them “domestic birds” (Nowak 1985), which again points to the synanthropic behavior of the species. At the same time, White Storks in Poland already fell under conservative and active protection, and Cygański reported care for disabled and injured birds (Dolata 2006).

White Storks nestled in Latvia only since the eighteenth century, when they lived in Courland up to the Daugava River (Ķuze 2008). Only in the first half of the nineteenth century, the number of storks began to increase rapidly, and they nested throughout Latvia since the mid-nineteenth century (Ķuze 2008). Today the breeding density in the country is one of the highest in Europe – up to 65 nests per 100 km2 (Janaus 2014).

There is no archaeological evidence of the White Stork in Estonia until 1800 (Ehrlich et al. 2023). The first breeding of the White Stork was recorded in Estonia in 1841 (Ots 2015). Around 1900, no more than 40 pairs bred in the country; by the end of the 1930s, the entire country was already populated. In 2014, between 4500 and 5500 pairs bred in Estonia. The southern parts of the country have the highest population density. The islands in western Estonia, on the other hand, are only very sparsely populated. In neighboring southwestern Finland, a breeding attempt was recorded for the first time in 2015 (Thomsen et al. 2017).

In the western regions of Russia, the first broods were recorded in the nineteenth century (Delyuk and Galchyonkov 2000). Before 1970, the White Stork bred in the Pskov and Bryansk regions and the western parts of Tver, Smolensk, Kaluga and Kursk. Between 1970 and 2000, the distribution range moved 100–120 km to the northeast (Pchelintsev and Ilyinsky 2000). In 2004, the border was located in the St. Petersburg, Kursk and Moscow regions.

While there has been a large range expansion in north-eastern Europe (which is continuing), C. ciconia has lost territories in other regions. In Britain, where storks immigrated during Roman times (first centuries CE), they soon disappeared again or became very rare. It was not until a thousand years later that individual records were found again in Medieval towns in the south of England. However, since the conspicuous storks do not feature in British folk tales, their presence was never common (Serjeantson 2023). After last breeding on the roof of the cathedral in Edinburgh in 1416 (Reid-Henry and Harrison 1988), C. ciconia became an occasional vagrant in Britain with some unsuccessful breeding attempts. A reintroduction project in England started in 2016 and in 2020, three pairs bred successfully (Lees and Metcalf 2020). In Italy, too, there is only sporadic evidence of the presence of White Storks after Roman times. For the years around 1241, there is evidence of breeding in Apulia in the form of a miniature of a White Stork in a nest (Kinzelbach 2008) and for Milano in a written source (Marotto et al. 2017). About 100 years younger is the only Italian post-Roman White Stork bone from Latium, origin from the sixteenth century, and additionally we have two written sources mentioning the species again for northern Italy (Marotto et al. 2017)—but all following reports of nesting after the sixteenth century doubtful (Marotto et al. 2017). The species returned suddenly in the 1950s and has since built up stable populations in various parts of the country with the support of reintroduction projects (Gallo Orsi et al. 1995; Bert 1999; Santopaolo et al. 2013).

Spoonbill’s history in Europe

For Spoonbills, the reconstruction of the former European distribution must be based on considerably less archaeological evidence. Despite its conspicuousness, this species was apparently largely outside the realm of human perception or use. This is certainly, because Spoonbills often live in impassable, damp lowland areas, such as inner river deltas and marine estuaries far from urban centers, and do not exhibit synanthropic behavior.

Our study suggests that Spoonbills lived in Southeast Europe (in the triangle Hungary–South Ukraine–Greece) and the Iberian Peninsula until two thousand years ago. Whether the populations of these two distinct regions were in contact or genetic exchange with each other remains unclear (cf. Brouwer 1964 for the modern situation), as the quantity of evidence is statistically insufficient. In addition to the archaeological finds, Aristotle (fourth century BCE), who knew the Spoonbill from Greece (Aristotle: Historia animalium, volume 2, 593b, lines 1–3; Arnott 2007), confirms the species’ appearance in the Aegean area. For the first millennium CE, a rapid, permanent, and widespread northern expansion of the occurrence is apparent, affecting mainly coastal regions of Western Europe. Remains of P. leucorodia from this period were found in Britain, the Netherlands, Poland, and even southern Scandinavia. Although the data situation is not nearly as good statistically as for the White Stork, the trend toward range expansion seems clear. However, not all archaeological findings should be taken as evidence of the local occurrence of the species discussed here, since during mid of the second half of the first millennium CE at the latest valuable animals became a commodity (Grimm 2018). Trading centers of supra-regional importance were established along the coastal lines of northern Central Europe and Scandinavia and served as a location for the trading of e.g. rare birds, such as peafowl and gyrfalcon (Schmölcke 2022). The Spoonbill records from Denmark mapped in Fig. 3 were likely such exotics used as a commodity. Two of the three Danish P. leucorodia records originate from elite residence sites, and another one is from a trading center of supra-regional importance (Gotfredsen 2014). A similar case seems to be the solitary White Stork bone found in Central Germany mentioned above, where at an archaeological site also Aegypius monachus and Strix uralensis, i.e., other very rare or even ‘exotic species’ in Central Europe, have been recorded (Schaal 1968).

The two findings from the Swedish island of Öland in the Baltic Sea (archaeological site Eketorp), which date to the period between 1000 and 1300 CE, lie far outside the familiar distribution range of the Spoonbill. Due to the proven expertise of the authors, who also published photos of the well-preserved bones, the identification is not in doubt (Boessneck et al. 1979). Unless we want to assume again the remote import of exotic animals, these are probably the remains of vagrant birds. Since there are no further finds in the spatial and temporal surroundings, a breeding occurrence of the Spoonbill in the central Baltic Sea at the beginning of the second century CE seems to be very unlikely.

An interesting case is the breeding occurrence of P. leucorodia in the Netherlands, the northernmost secure historical occurrence of the species and at the same time provided with a good number of different historical sources since it is also mentioned in contemporary documents and even paintings (de Rijk 2015). As the results presented here show, it is likely that the Dutch population already exists for at least two thousand years. Since today most Dutch Spoonbills wintering in Mauritania and Senegal with smaller numbers in France and Iberia (Lok et al. 2011, 2015), it is very likely that this population was founded by birds from Iberia. Repeatedly, it grew to such an extent that around 800 years ago the south of England and since the 1980s the eastern North Sea coastal area was also colonized from here. For the first few centuries, the Dutch population was hardly threatened by humans. The low number of identified Spoonbill remains implies that for a long time there was no hunting interest beyond the occasional killing of individual animals. Written sources show that this changed from the fourteenth century CE onwards. As the human population grew and the demand for farmland increased, the drainage of wetlands and thus of Spoonbill’s breeding habitats began, and also their eggs were now increasingly collected and eaten (Govaerts 2023). The species came into people’s focus more than ever before. Since 1500 CE P. leucorodia has been repeatedly depicted in drawings (Goddeeris et al. 2002). The birds were so common that their population remained intact when during the second half of the seventeenth century intensive hunting started (Govaerts 2023). Some large breeding colonies remained intact for the first instance—as late as 1851, a single colony near Nieuwerkerk still comprised about 1000 pairs—but in 1883, the largest Dutch colonies were destroyed (Brouwer 1964). By 1900, only two breeding colonies remained in the whole Netherlands, with a maximum of 300 pairs. At that time, the first pair nests in Denmark, possibly refugees from the Netherlands. The actual range expansion to the north, which continues to this day, only began in the 1980s after the Dutch population had recovered. In the Netherlands, 2530–3050 pairs are currently (2013–2015) breeding (SOVON 2018). For Germany, a population of 850 pairs (2011–2016) is reported (Gerlach et al. 2019).

From a historical perspective, Spoonbill’s behavior has not been very expansive. New suitable breeding habitats discovered by chance in the course of migrations of small flocks are accepted and then used constantly over long periods. In this way, the species has been able to expand its range over the last millennia slowly. It was helped by the fact that it prefers habitats that are avoided by humans, meaning that the birds were hardly ever hunted despite their unusual and attractive appearance. As a colony breeder, however, the species proved to be susceptible to the destruction (draining) of its habitat. For example, the losses suffered by the population living in the Netherlands were immense when the sites of their breeding colonies were destroyed. Unlike other, more sensitive colony breeders, however, it was quickly re-established in a suitable location, from where it has been spreading northwards along the eastern North Sea coast since around 1980.

Conclusions

Subfossil, well-dated bird bones, mostly from archaeological contexts, have a high potential for ecological, phylogenetic, genomic, and faunistic studies. This potential is once again demonstrated by the analysis presented here. The potential was recognized early on by archaeozoologists (e.g. Reichstein and Pieper 1986; Pieper and Reichstein 1995; Ericson and Tyrberg 2004), but in recent decades, only a few cases have been presented in ornithological journals (e.g. Boissaau and Yalden 1998; Stewart 2004, 2007; Buehler et al. 2006; Zachos and Schmölcke 2006; Nikulina and Schmölcke 2015; Langeveld 2020; Ponti et al. 2020; Crees et al. 2022). Nevertheless, the collaboration of archaeo- or paleornithology with ornithology creates an up-and-coming field of work (Wood and Pietri 2015), especially through the integration of methods, such as archaeogenetics (e.g. Nikulina and Schmölcke 2015), zooarchaeology using mass spectrometry (e.g. Eda et al. 2020) and investigations of the stable isotopes of bird bone finds (e.g. Su et al. 2023).

Our studies have investigated the long-term dynamics of the distribution range of two species using two example species, and at the same time show the advantages and disadvantages of archaeo-ornithological surveys. Their informative value often depends on the number of subfossil records of the species studied. Accordingly, we can present a detailed and well-founded picture of the history of the White Stork in Europe, whereas in the case of the Spoonbill, we have to rely in part on conjecture. Nevertheless, it seems clear that Spoonbills have lived on the Dutch Atlantic coast for at least 2000 years, far away from their core area in the Mediterranean. According to our study, White Storks prove to be real proviteurs of anthropogenic landscape change, especially of intensive clearing and large areas of agricultural land. Their advantage over many other species was and is that they have never been actively hunted across time and space. Humans’ admiration for White Storks has enabled them to open up new habitats and areas constantly, right up to the present day.