Studies of West Palearctic birds: Turtle Dove Stephen Browne and Nicholas Aebischer

Ray Scally ABSTRACT The Turtle Dove Streptopelia turtur has declined, in terms of both range and abundance, throughout much of northern over the last 30 years. Until recently, the was relatively poorly studied in the modern agricultural landscape in Britain. Concerns over its conservation status prompted an intensive research programme to gather information on its breeding ecology, identify the causes of the recent decline and make recommendations to aid its recovery and conservation.Turtle Doves require tall, overgrown bushes for nesting and short weed-rich areas for feeding, but agricultural intensification has markedly reduced the availability and suitability of these habitats. Over the last 40 years,Turtle Doves have switched from foraging in ‘natural habitats’ to those created by humans, and their diet is now primarily seeds from cultivated .The number of chicks fledged per pair per year is today almost half that in the 1960s, while autumn migration has become significantly earlier. Many management options to help to conserve the species can be achieved within the current UK agri-environment policy framework.

58 © British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove

he Turtle Dove Streptopelia turtur is a throughout Europe prompted The Game Con- summer migrant to Britain and Europe, servancy Trust, with support from English Tbut perhaps most people in Britain Nature and the World Wide Fund for Nature would associate the bird with the second day of (UK), to establish a dedicated research pro- Christmas rather than high summer, thanks to gramme focused on the species’ breeding the popular carol The Twelve Days of Christmas. ecology. In this paper, we outline the biology of This subversive, pro-Catholic hymn was sup- the species based on the results of a number of posedly written at a time when it was illegal to studies undertaken across Europe. We also make direct reference to Catholicism, and the present the findings and recommendations of ‘two Turtle Doves’ are thought to represent the our intensive four-year study, undertaken Old and New Testaments. Historically, human between 1998 and 2001, to show how the interest in the Turtle Dove was associated with breeding biology of the species has changed the bird’s faithfulness, and because it was an over the last 40 years. emblem of hope and peace. The writings of Saint Jerome (c. AD 320-420) and of Alain of Range and distribution Lille, in his twelfth-century work The Complaint The Turtle Dove is a small, slim member of the of Nature, state that a Turtle Dove would not Columbidae, with a thin neck, a protruding seek another mate should its original partner head and deep chest, giving it a pigeon-like die. Indeed, it was thought that if a Turtle Dove form, but with a long, wedge-shaped tail and lost its mate then it too would soon die. It was swept-back wings. The sexes are broadly similar, not until the eighteenth century that the species but females are slightly smaller than males and became more noted for its migratory abilities, somewhat less brightly coloured. Four races of being referred to in at least two of Gilbert Turtle Doves occur in the Western Palearctic, White’s letters. Today, however, most bird- with nominate turtur found throughout much watchers in southeast England and much of of Europe and western . Slightly smaller Europe would associate its purring calls with and paler, with more white on the belly, S. t. warm summer evenings, rather than love or arenicola occurs across North (including peace. In recent years, the calls of this small, the Balearics) and into the Middle East. The attractive and once-common dove have been two remaining races are much more restricted heard less frequently and its population decline geographically, with S. t. hoggara (also smaller and range contraction in Britain and and paler than nominate turtur, with broader Gordon LangsburyGordon 23. Turtle Dove Streptopelia turtur,Austria, May.

British Birds 98 • February 2005 • 58-72 59 Studies of West Palearctic birds: Turtle Dove

2

1.5

1 CBC Index

0.5

0 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99

Fig. 1. Index of abundance of Turtle Doves Streptopelia turtur in Britain from 1963 to 1998, derived from BTO Common Birds Census data.The index (solid line) and the 95% confidence limits (dashed lines) are shown. edging on the wing-coverts and on the tail) loway 1997). Some local declines were apparent inhabiting the central Saharan mountains, and from the 1950s (Goodwin 1989), but trends S. t. rufescens (more distinct than the other from census work suggest that the period of races, being smaller and more richly rufous- general increase lasted until about 1978/79 coloured) in Egypt and northern Sudan (Marchant et al. 1990). A few local studies (Cramp 1985; Gibbs et al. 2001). Both turtur showed that numbers of Turtle Doves fluctu- and arenicola are true migrants, spending the ated in a pattern similar to the national trend winter (late October to late March) chiefly in (Hongell & Saari 1983; Miller 1992). From the the Sahel region of Africa, roughly between late 1970s, however, a sustained decline in the 10°N and 20°N. The other two races are breeding population in Britain became thought to be sedentary or undertake only apparent, and this continues today (Baillie et al. small migratory movements (Cramp 1985). 2002) (fig. 1). The decline has been so severe In the breeding season (early May to mid that the majority of the British population is August), the range of turtur extends from the now restricted to southern and eastern counties Mediterranean to all but the most northern of England and, by extrapolation from the areas of Europe. In Britain, at the northwest 1988-91 census and subsequent rates of decline, edge of the species’ breeding range, it is a probably numbered only about 30,000 pairs in lowland bird, favouring warm, dry conditions 2001. These population trends are of such and avoiding the higher ground and rainfall of concern that Turtle Dove is now recognised as a the west and north (Gibbons et al. 1993). Con- ‘Red List’ species of conservation concern in the sequently, Turtle Doves are concentrated in the UK (Gregory et al. 2002), and the UK Govern- most intensively farmed, and now predomi- ment has placed it on the list of priority species nantly arable, areas of Britain. considered by the UK Biodiversity Action Plan. One of the recommendations of the UK Species Population trends in Britain and Europe Action Plan for the Turtle Dove is to undertake Survey and census work organised by the BTO an autecological research project to identify the suggests that numbers of Turtle Doves in cause of the recent decline, in order to form a Britain declined by 70% between 1968 and 1999 recovery plan (Anon 1998). (Baillie et al. 2002), with a 25% contraction in This pattern of range expansion followed by range between the 1968-1972 and 1988-1991 recent decline has been repeated elsewhere in breeding Atlases (Gibbons et al. 1993). This Europe, with evidence of local downturns being sharp decline commenced in 1979, following a noted from the 1950s onwards (Holzwarth lengthy period of apparent increase and range 1971; Kraus et al. 1972; Cederwell 1978; expansion from at least the mid nineteenth Hongell & Saari 1983; Bijlsma 1985; Yeatman- century (Spencer 1965; Duckworth 1992; Hol- Berthelot & Jarry 1995). Although census and

60 British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove migration data are often rudimentary or non- (Nankinov 1994a, Nankinov 1994b), (the existent, it is believed that, on a European scale, former) Czechoslovakia (Pikula & Beklova the decline of the Turtle Dove occurred from 1984), France (Genard 1989), Germany the mid 1980s onwards, particularly in western (Holzwarth 1971; Kraus et al. 1972), The Europe (Tucker & Heath 1994; Heath et al. Netherlands (Bijlsma 1985), Portugal (Dias & 2000). Turtle Dove is now a Category 3 species Fontoura 1996; Dias et al. 1996), Spain (Peiró of European conservation concern (SPECs): a 1990), Sweden (Cederwell 1978), and in the ‘species whose global populations are not con- southern Urals (Kotov 1974). Other studies centrated in Europe, but have an Unfavourable have looked at specific aspects of Turtle Dove Conservation Status in Europe’ (Heath et al. biology, including diet (Garzón 1974; Kiss et al. 2000). 1978; Jimenez et al. 1992; Dias & Fontoura 1996) and habitat requirements (Aubineau & Previous research on the Turtle Dove Boutin 1998). Turtle Dove migration was docu- Until recently, the only major ecological study mented by, for example, Ash 1956, Rappe 1965, of the Turtle Dove in Britain was completed in Marchant 1969, Bourne & Beaman 1980, the early 1960s (Murton et al. 1964; Murton Mountfort 1981, Genard 1989, Nankinov 1994b 1968). In 1996, a pilot study was undertaken (by and Aebischer 2002, and the biology of the The Game Conservancy Trust, funded by species on its wintering grounds in Africa by English Nature) to collect basic information on Morel & Morel 1979, Morel 1985 and Morel the ecology of the Turtle Dove and to test the 1987. methodology for a more detailed study (Calla- dine et al. 1997). The factors causing its recent Migration decline, in a modern agricultural environment The Turtle Dove is the only British member of which has changed considerably since the 1960s the pigeon family to undertake a long-distance (Grigg 1989), and the stages of its life history at migration, travelling up to 4,000 km twice a which those factors operate, were therefore year between breeding and wintering grounds. unknown before a study undertaken by The The species’ annual migration, combined with Game Conservancy Trust in the late 1990s its exclusively granivorous diet, sets it apart (Browne & Aebischer 2001; Browne 2002). from all other farmland bird species in Britain. More widely, the breeding biology of the After breeding, Turtle Doves begin to leave Turtle Dove has been investigated in Bulgaria Britain in August, with the last birds departing Stephen Browne 24. Turtle Doves Streptopelia turtur are found in a variety of habitats on their wintering grounds in western Africa, including scrub, open woodlands, savannah and agricultural land; the open scrub with low-density cattle browsing shown here (in The Gambia) would be a typical backdrop for encountering the species in winter.

British Birds 98 • February 2005 • 58-72 61 Studies of West Palearctic birds: Turtle Dove in October and November. Their migration likely that factors other than temperature (e.g. route takes them through western France, day length) may trigger the start of migration central and western Iberia, along the Atlantic for this species (Lofts et al. 1967). One conse- coast of Morocco, and through Mali and quence of this lack of response in migratory Senegambia into western Africa. The main behaviour to increasing global temperature is migration period is between mid August and that, like some other migrant species, such as late October, when most birds arrive in western Pied Flycatcher Ficedula hypoleuca (Both & Africa. Migration is thought to be mainly noc- Visser 2001), the timing of the Turtle Dove’s turnal, but there is a diurnal component at breeding season and food supply may now be times (Guyomarc’h 1998). Turtle Doves tend to asynchronous. Studies have shown that the migrate in groups of 5-30 individuals, but fruiting of various plants now occurs earlier, in flocks of over 100 are reported regularly; large response to increasing temperature (e.g. congregations, of up to 1,000, can occur in Walther et al. 2002), and it is possible that the food-rich areas, such as fields of ripe sunflowers peak period of Turtle Dove breeding is now out Helianthus (Aebischer 2002). Spring migration of phase with the peak in food availability, a sit- commences during February-March, when uation which may have contributed to the huge flocks of many thousands of birds can species’ decline in recent years (Browne & occur in Mali and Senegambia (Curry 1974; Aebischer 2003a). Morel & Morel 1979, 1988). Turtle Doves arrive in Britain from mid April through to June, with Hunting the main influx during May (see Aebischer 2002 Little accurate information is available on the for an overview). numbers of Turtle Doves taken by hunters (see In recent years, the autumn migration of Boutin 2001). The Turtle Dove is a traditional Turtle Doves in the UK has taken place eight quarry species in many European countries, days earlier, on average, than in the 1960s particularly those bordering the Mediterranean, (Browne & Aebischer 2003a); concomitantly, and hunting is legal in seven EU countries in their breeding season is now some 12 days autumn: Austria, France, Greece, Italy, Malta, shorter, on average, than 40 years ago (fig. 2). Portugal and Spain. All these countries operate For some bird species, it has been shown that a an open season, and although national or recent increase in average temperatures, attrib- regional legislation controls the exact opening uted to global warming, has altered the timing date of that season, EU regulations ensure that of migration, but this relationship has not been this is not before 15th August. This prevents established for Turtle Doves (Tryjanowski et al. resident breeding populations from being tar- 2002; Browne & Aebischer 2003a) and it is geted specifically, and it is primarily migrating

130

120

110

100

Length of residency (days) Length of residency 90

80 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99

Fig. 2. Length of residence of Turtle Doves Streptopelia turtur in Britain during the period 1963 to 2000. The values represent the difference between mean arrival and departure dates at six bird observatories in south and east England. Redrawn from Browne & Aebischer (2003a).

62 British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove birds which are shot. A bag limit per hunter (i.e. are thought to have contributed to the decline the number each hunter can shoot legally per of the species (Marchant et al. 1990; Jarry day) is set in Greece, Portugal and Spain. In 1995), although this is unsubstantiated by any addition, Turtle Doves are hunted illegally in recent studies. France during the spring. Although accurate data on the numbers hunted each year do not Habitat use on the breeding grounds exist, and estimates are difficult, the total The habitat requirements of Turtle Doves away annual hunting bag for the EU is thought to be from the nest-site have been little studied. In of the order of 2-4 million birds (Boutin 2001); general landscape terms, Turtle Doves occur in it is not possible to assess the long-term trend a range of open lowland habitats which are of the EU hunting bag. In Morocco, the esti- interspersed with hedges, scrub and small mated bag is up to 140,000 birds, and because woods (e.g. Kraus et al. 1972, Bijlsma 1985). the open season runs from mid June to early They avoid open areas such as heathland and August, most are of the race arenicola. Hunting also large tracts of extensive woodland, but of Turtle Doves is not permitted in their win- occur in young plantations and managed tering areas, and information is so limited that (thinned) woodland (e.g. Genard 1989). Turtle the numbers of any taken illegally cannot be Doves appear to favour warm areas, being estimated. found in those parts of Germany where the mean daily maximum July temperature is at Overwinter ecology least 17°C (Kraus et al. 1972), and in Britain Little is known about the ecology of Turtle where the equivalent temperature is at least Doves on their wintering grounds (see Cramp 19°C (Norris 1960). 1985 for overview), certainly in recent times. An analysis of 30 BTO Common Birds The overwintering range of the migratory Census (CBC) plots showed that, by 1995, the turtur and arenicola is thought to extend from mean density of Turtle Doves was 0.8 territories Senegambia and southern Mali south to the per km2 on 15 farmland plots and 10.1 terri- Gulf of Guinea, and from the Atlantic coast tories per km2 on 15 woodland plots (Browne et east to Cameroon and Nigeria. Although areni- al. 2004). Browne & Aebischer (2004) recorded cola probably occurs in the east of this range, farmland densities of 4.1-4.6 territories per km2 with turtur in the west, there appears to be con- in Suffolk and 0.3-0.5 territories per km2 in Lin- siderable overlap. Both races are known to colnshire. Densities of 6.5 territories per km2 in occur in Senegal and Mauritania during winter. woodland and over 40 territories per km2 in They are found in a variety of habitats, including acacia scrub, open woodlands, savannah plains and agricultural land. Large flocks have been recorded feeding on wheat fields, harvested rice fields and on quaysides where peanuts are being loaded (Barlow et al. 1997). They eat a wide variety of seeds from wild and cultivated plants. Huge flocks, of up to a million birds, most likely to be arenicola,have been recorded at food sources, water and at roost, typically in acacia scrub or waterlogged woodland. Turtle Doves tend to drink at first light or at sunset, when the largest congrega- tions are usually seen. Although they appear able to feed during the intense heat of the day, they will take shelter in shade under trees and bushes during extreme heat (Curry 1974); they often associate with Vinaceous Doves Strep- topelia vinacea while foraging or resting (Morel & Morel 1988). Recent poor rainfall in the Sahel, deforestation, scrub clearance and Olaf Lessow 25. Turtle Dove Streptopelia turtur, improvements to agriculture in western Africa Austria, June 2000.

British Birds 98 • February 2005 • 58-72 63 Studies of West Palearctic birds: Turtle Dove scrub have been recorded in northeast Essex On farmland, based on information (C. F. Mason pers. comm.). Other reported den- extracted from 15 farmland CBC plots, density sities for Turtle Doves in Britain are 1.4 territo- was related to the amount of suitable nesting ries per km2 on farmland and 2.2 in woodland habitat on each plot (Browne et al. 2004). As the during 1968-72 (Sharrock 1976); corresponding length of hedgerow and length of woodland figures of 0.6 and 2.6 territories per km2 during and scrub edge decreased within farmland, 1988-91 (Gibbons et al. 1993); and 1.6-2.1 terri- Turtle Dove density also decreased (fig. 3). tories per km2 on farmland in eastern England The home range of British Turtle Doves is (Mason & Macdonald 2000). Other studies highly variable (on average occupying some across the species’ breeding range have shown 83.5 ± 23.9 ha at one site and 497.3 ± 22.5 ha at that Turtle Dove density varies from 1.4 to 30.0 another site), depending on habitat availability, pairs per km2 in a range of wooded and farm- and ranging from 0.3 ha to 1,130 ha (Browne & land habitats (Holzwarth 1971; Kraus et al. Aebischer 2003c). Information from radio- 1972; Bijlsma 1985; Genard 1989; Dias & Fon- tracking suggests that Turtle Doves choose their toura 1996). territories in a non-random way. Cropped In Britain, it appears that suitable woodland arable habitats were avoided and wooded ones areas support densities of Turtle Dove terri- most preferred, relative to availability. The latter tories up to 6.5 times higher than on farmland. reflects the species’ behaviour of loafing near This probably reflects the species’ propensity to the nest-site or in tall trees and hedges, which is nest in overgrown bushes, with woodland areas also where most territorial behaviour is con- being used predominantly for nesting and the ducted. arable areas for feeding. Studies by Fuller & Moreton (1987) and Hinsley et al. (1995) Social behaviour showed that use of woodland by Turtle Doves Turtle Doves are monogamous and may form was governed by nest-site selection. Turtle pairs which last for more than one breeding Doves were associated with shrubby vegetation, season (Cramp 1985). Some pairs are formed avoided dense woodland and did not hold terri- during migration but, in most cases, it would tories in coppice woodland until five years after seem that the males arrive on the breeding coppicing, when mean tree height was 5.6 m grounds first, begin to deliver their continuous and canopy cover was 66%. Within woodland purring calls immediately and attract females habitats, Turtle Doves appear to favour scrub quickly. Males generally call most frequently rather than pure woodland stands (Mason & early in the morning and in the evening, and Macdonald 2000). Woodland area is also from favoured song-posts (Calladine et al. important, with the minimum required being 1999). The calls may be followed by a display around 0.2 ha (Mason 2001). flight, which is usually triggered by the arrival

0.25

0.20

0.15

0.10

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Change in Turtle Dove density Dove Turtle Change in -0.10

-0.15 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 Change in the availability of suitable nesting habitat Fig. 3. Relationship between the amount of suitable nesting habitat and the density of Turtle Doves Streptopelia turtur on 15 BTO farmland CBC plots during 1965-1995. Redrawn from Browne et al. (2004).

64 British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove Stephen Browne 26. During the breeding season,Turtle Doves Streptopelia turtur will use a range of open lowland habitats. Most nests are found in hedgerows and scrub, with smaller numbers in young plantations and woodland, and in isolated bushes. Nests are typically in thorny bushes, but conifers, elder Sambucus and fruit trees are also favoured; dense woodland is generally avoided.This photo also shows the type of broad, weedy-edge habitat which is important for feeding. of another Turtle Dove, apparently to further Breeding ecology attract females or discourage males. The display The breeding season begins upon arrival on the flight consists of a steep, upward flight, with breeding grounds in late April, with the peak of rapid wingbeats producing wing-clapping, fol- nesting activity being in early June. Turtle lowed by a long, slow, circular descending glide Doves defend only a small area immediately with wing- and tail-feathers outstretched, around the nest-site, but utilise a much larger returning the bird to its original take-off point. area for foraging. The size of these defended If joined by a female, the calling male will also territories around the nest ranges from 0.75 to undertake a bowing display, in which he fluffs 8.90 ha, and they contain a higher proportion out his feathers, particularly around the throat, of woodland, grassland and other non-crop bobs his head up and down and takes small, habitats, and a lower proportion of cropped two-footed jumps towards the female. habitats, than expected by chance (Browne & Pairs tend to aggregate in suitable nesting Aebischer 2004). The majority of nests are habitat and adjacent nests can be as close as 3 m found in hedgerows and scrub, with some (Cramp 1985). Further nesting attempts are within young plantations and woodland, and in made close to the first nest, often in the same isolated bushes; most are in thorny bushes, but bush and occasionally on top of the old nest. also in conifers, elder Sambucus and fruit trees Breeding activities, including nest-building, (Browne & Aebischer 2004; Browne et al. 2005). incubation and tending the young, are under- The nest is usually a small platform of thin taken by both parents, although the male sticks, built by the female with the occasional appears to take on more of these activities than assistance of the male. Sometimes other mater- the female. During the breeding season, birds ials, such as thin wire and plastic, are utilised tend to roost near their nests, although occa- too. Many nests are built with climbers as an sionally they roost communally. Soon after integral part of the nest (Aubineau & Boutin breeding, young and adults disperse and do not 1998; Browne & Aebischer 2004), and it is form family groups. Consequently, Turtle Doves believed that these provide additional support are usually observed singly or in pairs on their to the nest structure. Nests are usually 0.1-20.0 m breeding grounds, although small flocks may above ground level, the majority being 1-3 m form around food sources. high (Browne & Aebischer 2004). Nest height

British Birds 98 • February 2005 • 58-72 65 Studies of West Palearctic birds: Turtle Dove varies according to habitat; for example, nests in Turtle Doves laid 2.9 ± 0.1 clutches per year, conifers tend to be higher as the lower levels of which produced on average 1.6 ± 0.1 fledged conifers are generally unsuitable. The majority young per pair. Today, each pair produces 2.1 ± of nests are located within 1 m of the edge of 0.3 clutches and 1.3 ± 0.2 young fledge per pair the bush or tree. (Browne & Aebischer 2004). This decline in Clutches vary from one to three eggs, with productivity is a result of fewer breeding two being typical. Turtle Doves may produce up attempts and is related to a contraction of the to three successful broods in a season, but may breeding season (see above and fig. 2); for nest more than three times if a brood is lost and example, in the 1960s, 24% of nesting attempts a replacement clutch laid. Incubation is under- were started in August compared with just 5% taken by both sexes and lasts for 14 days. during the 1990s (Browne & Aebischer 2004; fig Nestlings are cared for by both parents and 4). This, in turn, links in with the species’ leave the nest after 15 days. Birds are able to markedly earlier autumn migration from breed in their second calendar-year. About half Britain (discussed above), and implies that the the eggs laid are successful, with the remainder reduced number of nesting attempts and earlier being predated, deserted or failing to hatch cessation of breeding identified by Browne & owing to infertility (Murton 1968; Cramp 1985; Aebischer (2004) is likely to apply on a wide Browne & Aebischer 2004). geographical scale. Furthermore, an analysis of The likelihood of various outcomes of approximately 1,900 BTO Turtle Dove Nest modern-day nesting attempts is different from Record Cards has shown that there has been no that during the 1960s (Murton 1968; Browne & discernable difference in any aspect of the Aebischer 2004). During Murton’s study, 6% of species’ breeding ecology over the last 40 years nests were abandoned, 56% of nests were lost to (Browne et al. 2005). It is clear that the reduc- predation and 39% fledged young, compared tion in the number of nesting attempts per bird with 15%, 37% and 47% respectively during the per year has caused the reduction in breeding late 1990s. In other words, abandonment rates performance. were lower and predation rates higher in the 1960s, but in the 1990s hatching success was Diet on the breeding grounds higher, yet fledging success was lower. Overall, Early studies identified seeds from wild plants the success of an individual breeding attempt (weeds) as the main component of Turtle Dove appeared to be approximately the same in the diet, with seeds of locally cultivated crops 1990s as in the 1960s. making up the remainder. The seeds from two In recent years, the breeding productivity of species, Common Fumitory Turtle Doves has fallen dramatically. In the and Common Chickweed Stellaria media,were 1960s, Murton (1968) found that, on average, particularly important (Murton et al. 1964). In

30

25

20

15

10 % of nests started

5

0 May 2 Jun 1 Jun 2 Jul 1 Jul 2 Aug 1 Aug 2

Fig. 4. Proportion of nests started in each half-month period of the Turtle Dove Streptopelia turtur breeding season in the early 1960s (black bars) and the late 1990s (white bars). Redrawn from Browne & Aebischer (2004).

66 British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove

100

80

60

40 % of weed seeds in diet % of weed 20

0 Adult Nestling

Fig. 5. Proportion of weed seeds in the diet of adult and nestling Turtle Doves Streptopelia turtur in the early 1960s (black bars) and the late 1990s (white bars). Error bars show ±1 standard error. Redrawn from Browne & Aebischer (2003c). areas where cultivated seeds were taken, this tats for feeding nowadays, but also undertake usually coincided with harvest time. Today, relatively large foraging trips. On average, Turtle seeds from cultivated plants (chiefly wheat and Doves travelled 0.5-1.5 km per trip during the rape) are the main constituents of Turtle Dove 1990s, but some feeding sites were located up to diet, and comprise, on average, 69% of the seeds 10 km from the nest (Browne & Aebischer identified in the faecal samples of nestlings, and 2003c). Such relatively long trips probably 60% of the seeds taken by adults (Browne & reflect a lack of suitable feeding opportunities Aebischer 2003c; fig. 5). Forty years ago, the closer to nesting areas. percentages were 23% and 5% respectively The greatest influence on these dietary (Murton et al. 1964). It is likely that these dif- changes is likely to be the spatial and temporal ferences are real and do not reflect different availability of food during the breeding season. methodologies. The seeds from crops are generally most widely The foraging behaviour of Turtle Doves is available immediately before, during and after now markedly different from that recorded in harvest, at the end of the Turtle Dove’s breeding the 1960s, when they fed predominantly on season. Earlier availability is dependent on spilt clover leys, hay fields and stooked wheat grain, which usually occurs during its transport (Murton et al. 1964). Today, they feed in a range from storage. When cereal prices are high, farm- of different habitat types, but principally those based grain stores are emptied earlier than which include spilt grain: in farmyards, animal during times when prices are low. Conse- feed and non-arable habitats. In almost all quently, in some years, spilt grain may be avail- cases, birds recorded on crops are feeding on able to Turtle Doves during the breeding the weed strip around the edge of fields, weedy season, in other years it may not, and this areas that sprayers have missed, on crops that depends solely on market pressures. Cultivated have limited herbicide use (e.g. daffodils) and seed availability is not only limited and variable on stubbles after harvest (Browne & Aebischer temporally, but also spatially. Whereas a weed- 2003c). Recent changes in agricultural practices rich farming landscape would provide food for have removed or reduced many of the feeding Turtle Doves throughout their home range, opportunities available in Murton’s day. At the there may be only one or two patches of spilt same time, increased use of herbicides and fer- grain across a wide geographical area, forcing tilisers and more efficient screening procedures birds to travel large distances between nesting have greatly reduced the abundance and diver- and feeding habitats. sity of weeds and weed seeds throughout the farmed environment, compared with 40 years Reasons for the species’ decline in Britain ago (O’Connor & Shrubb 1986). Habitat use and feeding ecology Turtle Doves not only utilise different habi- Hedgerow and scrub removal has long been a

British Birds 98 • February 2005 • 58-72 67 Studies of West Palearctic birds: Turtle Dove Gary Bellingham 27. First-winter Turtle Dove Streptopelia turtur, Scilly, October 2003.

feature of agricultural intensification (Pollard et the Turtle Dove’s breeding season means that al. 1974; Barr et al. 1993), and remaining hedges the number of nesting attempts would now be are often intensively managed. Most of these are expected to be at least 20% lower than in the cut annually (Macdonald & Johnson 2000), cre- 1960s. The observed reduction in the number ating hedgerows which are usually too low and of clutches each pair lays is 45%, from 2.9 in the not wide enough for the Turtle Dove’s needs. 1960s to 1.6 in the 1990s. In turn, the number The territory distribution of Turtle Doves of young that successfully fledge per pair has appears to be linked to availability of suitable dropped from 2.1 in the 1960s to 1.3 in the nesting habitat, primarily bushes and trees in 1990s. This reduction in breeding output would scrub, hedgerows, woodland edge, etc. Both the lead to a per annum decrease of approximately quantity and the quality of suitable habitat have 17% in the British breeding population of declined in the modern farming landscape. Turtle Doves if replicated throughout its British As described above, Turtle Doves now range. The ultimate cause of the reduction in occupy relatively large home ranges, undertake breeding output is not known, but it is possible long foraging trips and make little use of that changes in the spatial and temporal avail- natural feeding sites, being much more depen- ability of food and the associated shift in diet dent on (for example) spilt and stored grain may affect adult body condition. Birds may and animal feed. The results from experimental struggle to achieve and maintain suitable body work suggest, however, that, at the local scale, condition throughout the breeding season and food provided by humans does not appear to as a result may finish breeding earlier, although improve breeding densities or success (Browne this remains unproven (Browne & Aebischer & Aebischer 2002). Diet has changed as well as 2003b). feeding behaviour, from weed seeds to culti- vated seeds (in broad terms). Although it Hunting appears that diet does not have a direct effect on The limitations of the available data make it dif- breeding success, it seems likely that all the ficult to assess the importance of hunting. For factors outlined here will combine to have a example, a worst-case scenario, using the lowest detrimental impact on the species. European population and highest bag estimates (Hagemeijer & Blair 1997; Boutin 2001) and a Breeding ecology breeding productivity of 1.3 fledged young per Our data suggest that the reduction in length of pair (Browne & Aebischer 2004), could predict

68 British Birds 98 • February 2005 • 58-72 Studies of West Palearctic birds: Turtle Dove up to 40% of the autumn population being hinsberg 2000) and Yellowhammer Emberiza killed, but the comparable best-case scenario citrinella (Bradbury & Stoate 2000) as well as of (highest population and lowest bag estimates) Turtle Dove. A reduction in breeding perfor- predicts that only 4% is killed. Until accurate mance, brought about by a falling number of information on the numbers of Turtle Doves nesting attempts per pair, has consequences for being hunted is available, it is impossible to the population size of Song Thrush Turdus make a scientifically sound statement on the philomelos (Thomson & Cotton 2000) and contribution of hunting to the decline of the Linnet Carduelis cannabina (Moorcroft & Turtle Dove. Wilson 2000), as well as of Turtle Dove. The decrease in food availability, attributable either Changes on overwintering areas directly or indirectly to pesticide use, has been For some migrants that overwinter in sub- shown to affect Grey Partridge (Potts 1986), Sky Saharan Africa, population declines have been Lark Alauda arvensis (Donald & Vickery 2000), linked with drought on the wintering grounds Red-backed Shrike (Vanhinsbergh 2000), Yel- (e.g. Winstanley et al. 1974, Cowley 1979, lowhammer (Bradbury & Stoate 2000) and Marchant et al. 1990, Peach et al. 1991). Corn Bunting E. calandra (Brickle & Harper Decreased rainfall, rising temperature and other 2000), as well as Turtle Dove. Such findings changes linked to desertification in the Sahel, make it difficult to separate the decline of the perhaps linked to global warming, may indeed Turtle Dove, and of many other farmland bird have important consequences for Turtle Doves species, from changes in land management breeding in Europe. Nonetheless, the decline of associated with recent agricultural intensifica- the Turtle Dove did not immediately follow the tion, although the potential negative effects of severe drought of 1968/69, when many other hunting and changes on the overwintering species that winter in the Sahel suffered a severe grounds cannot be dismissed. population crash (Marchant et al. 1990). Indeed, Turtle Doves increased during the 10-15 Conservation measures years following the 1968/69 drought, and it was The Turtle Dove UK Species Action Plan (Anon not until 1980 that the population began to decline (Marchant et al. 1990). Unlike the species that were badly affected by that drought, the Turtle Dove is solely granivorous; it is pos- sible that its food supply was less severely affected and it may have adapted to become more mobile, and exploit new food sources, such as rice and peanuts, that arose from improved agriculture in the region (Cramp 1985; Marchant et al. 1990; Barlow et al. 1997). In addition, forest and scrub clearance in over- wintering areas, for agriculture and to provide fuel, has also been cited as a possible cause of the Turtle Dove’s decline (Jarry 1994), particu- larly through the removal of suitable roosting sites. The impact of this is likely to be relatively small, however.

Common factors causing Turtle Dove and other farmland bird declines Recent studies have highlighted a number of ecological changes that have affected Turtle Stephen Browne 28. Edge habitats are now crucial for Turtle Doves Doves and other farmland species alike. The Streptopelia turtur in the modern agricultural loss of nesting habitat, primarily hedges and landscape. During the breeding season, most birds scrub, is thought to restrict the territory distrib- recorded feeding on cropped land are concentrated ution of Grey Partridge Perdix perdix (Rands on the strip of weeds around the edge of fields, weedy areas that sprayers have missed, farm tracks 1986), Red-backed Shrike Lanius collurio (Van- or on crops that have limited herbicide use.

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1998) had the following objectives and targets: systems. Ongoing reform of the Common Agri- • In the short term, halt or reverse the decline cultural Policy, scheduled for 2005, should in numbers of the Turtle Dove by 2003 so encourage farmers to manage land in a more that the Breeding Bird Survey (BBS) index is environmentally friendly fashion. This will at least at 1996 levels; allow the introduction of compulsory cross- • In the long term, see a sustained recovery in compliance, whereby a farmer receives agricul- numbers so that the BBS index is at least tural subsidy (e.g. Arable Area Payments) 50% higher than 1996 levels by 2008. conditional on compliance with environmental The following recommendations will help to standards; payments may be reduced or can- deliver these targets in the UK. Although tail- celled if standards are not met. Future policy ored towards Turtle Doves, these are also likely also needs to address those areas which are cur- to help other farmland wildlife. rently not adequately covered, including the widespread management of arable field Management options margins, the re-establishment of arable fields in Nesting habitat pasture-dominated areas, the planting and Turtle Doves have specific requirements for the management of scrub and the provision of sup- types of tree and bush in which they nest, and plementary food. management needs to recreate suitable hedgerows and patches of woodland or scrub, Acknowledgments and ensure that intensively managed hedgerows The study undertaken by The Game Conservancy Trust was funded by The Game Conservancy Trust, English are restored and replanted. Hedges should be Nature, WWF-UK and, in part, by The Habitat Research allowed to become overgrown with climbers Trust. We thank all landowners, farm managers and their and reach a minimum height of 4.5 m and gamekeepers for allowing access to their estates and farms. Alastair Burn, Julie Ewald, Jim Fowler, Phil Grice and width of 3 m. Becky Halahan provided useful advice during the study. Mike Armitage, Sarah Coe,Victoria Edward, Abigail Knight, Food availability Stephen Murphy, Lynsey Robinson, Blair Urquhart, Turtle Doves like to feed amongst short, sparse Nicholas Watts and Georgios Yfantis assisted with the fieldwork. We thank all the BTO bird ringers, CBC and vegetation with a predominance of seed-rich Nest Record Card surveyors and bird-observatory staff weedy plants. Management needs to encourage for their efforts over the last 50 years in collecting some patches of arable plants and provide alternative of the data used here. We are also grateful for help from the Bird Observatories Council (BOC), in particular Peter sources of seed. Within or adjacent to arable Howlett and Dick Loxton, and the BTO, in particular the fields, areas should be tilled annually each Ringing Unit staff, Humphrey Crick, John Marchant and autumn and receive limited herbicide applica- Richard Thewlis. tions (only those targeted specifically at perni- References cious agricultural weeds) to allow the Aebischer, N. J. 2002.Turtle Dove Streptopelia turtur. In: establishment of weed-rich areas, with low open Wernham, C.V.,Toms,M. P., Marchant, J. H., Clark, J. A., vegetation cover. Alternatively, or additionally, Siriwardena, G. M., & Baillie, S. R. (eds), The Migration such areas can be established by sowing seed Atlas: movements of the birds of Britain and Ireland: 420- mixes. Existing herb-rich grassland should be 422. Poyser, London. Anon. 1998. UK Biodiversity Group Tranche 2 Action Plans. protected and managed for a late hay crop (cut English Nature, Peterborough. after 15th July). These grasslands should be Ash, J. S. 1956. On the movements and survival of encouraged by de-intensifying the use of Woodpigeons and Stock Doves. Brit. Birds 49: 298-305. Aubineau, J., & Boutin, J.-M. 1998. L’impact des modalités de improved grassland or by arable reversion. gestion du maillage bocager sur les colombidés Post-harvest cereal, rape and pea stubbles (Columbidae) nicheurs dans l’ouest de la France. Gibier should be left until at least the end of August to Faune Sauvage, Game & Wildlife 15: 55-63. Baillie, S. R., Crick, H. Q. P., Balmer, D. E., Beaven, L. P., allow good pre-migratory feeding. Supplemen- Downie, I. S., Freeman, S. N., Leech, D. I., Marchant, J. H., tary food, such as waste grain or tailings, is best Noble, D. G., Raven, M. J., Simkin, A. P.,Thewlis, R. M., & provided close to suitable nesting habitat. Wernham, C.V. 2002. Breeding Birds in the Wider Countryside: their conservation status 2001.BTO Research Report No. 278, BTO,Thetford. Policy options (www.bto.org/birdtrends) The current framework of agri-environment Barlow, C.,Wacher,T., & Disley,T. 1997. A Field Guide to policies allows many of the conservation man- Birds of The Gambia and Senegal. Pica Press, Robertsbridge. agement recommendations for Turtle Doves to Barr, C. J., Bunce, R. G. H., Clarke, R.T., Fuller, R. M., Furse, be incorporated within modern agricultural M.T., Gillespie, M. K., Groom, G. B., Hallam, C. J.,

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