Philopatry and Population Growth of Red Kites, Milvus milvus, in Wales

Philopatry and Population Growth of Red Kites, Milvus milvus, in WalesAuthor(s): I. Newton, P. E. Davis and D. MossSource: Proceedings: Biological Sciences, Vol. 257, No. 1350 (Sep. 22, 1994), pp. 317-323Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/50139 .

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Philopatry an(d population growth of red kites, Milvus milvus, in Wales

I. NEWTON1, P. E. DAVIS2 AND D. MOSS1 1 Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE7 2LS, U.K. 2Felindre, Aberarth, Aberaeron, Dyfed SA46 OLP, U.K.

SUMMARY

Between 1946 and 1993, the number of territorial red kites, which form an isolated relict population in mid-Wales, has increased from 7 pairs to 113 pairs. Population growth has been approximately exponential at a mean rate of 5 0 per year. Breeding success was generally poor, but improved from an average of 0.53 young per pair in 1946-1960 to 0.71 young per pair in 1991-1993. Annual losses from the whole population (including juveniles) was estimated during 1946-1960 at 22 o, reducing to 11 % during 1961-1993. As the population grew, the area used for breeding expanded slowly. Despite wandering widely in their first year, birds returned to breed close to their natal area. For the most part, they expanded their breeding range progressively on a 'rolling front', rather than striking out into distant unoccupied areas.

1. INTRODUCTION

The red kite (Milvus milvus) was once widespread in Britain, breeding in every county, but as a result of persecution, mainly in the 19th Century, the species was eliminated everywhere except for a small area in central Wales. By 1900, the total remnant British population almost certainly numbered less than 20 pairs, decreasing to less than 10 pairs in the 1930s (Davis 1993). With protection of the nests (which did not completely prevent killing and egg robbing), numbers increased progressively from the 1940s, reaching more than 100 territorial pairs in the 1980s, plus a number of non-territorial, non-breeding birds. In this paper we document the population increase and the associated pattern of range expansion, and sum- marize information on reproductive and mortality rates.

The paper is based on data collected during 1946-1993, when attempts were made each year to find all territorial pairs and non-territorial individuals, and record which pairs built nests, laid eggs and raised young. For most breeding pairs, clutch and brood sizes were also recorded. Not all pairs were found in the first year they established themselves in a new area, and not all nests were found or nest contents recorded. However, it was often possible to fill in gaps in subsequent years, as further information came to light. In consequence, we have a reasonably complete picture of numbers and nest success over the 48 years concerned. Few expanding populations can have been documented in such detail.

Like many other birds of prey (Newton 1979), the Welsh kites tended to nest in the same restricted localities (here called nesting territories) year after

year. Each territory held up to several nests, built or refurbished in different years. As the population grew, new territories became established in the same general area. However, not all previously used territories were occupied in any one year. Unpaired birds in their first few years of life wandered more widely than breeders, and showed no clear site attachment.

The area of central Wales where kites now breed covers an area of about 100 km x 50 km, and includes: (i) low ground (mainly below 200 m) of moderate fertility, with enclosed farmland (chiefly pasture), villages and small towns; and (ii) high ground (mainly above 200 m), consisting of open grassland grazed by sheep and plantation forests of conifers at different growth stages (further details in Walters Davies & Davis 1973; Newton et al. 1981). Most kites nested in the remnants of native oak woods, found chiefly at the boundary between the low farmland and the upland, but some nested in trees elsewhere. To obtain their food, the birds foraged over wide areas of open land around their nesting territories, taking a broad range of live prey items from earthworms to medium-sized birds and mammals (Davis & Davis 1981). They also often took prey which were moribund or dead, including sheep carrion. In autumn and winter, they fed in numbers at local rubbish dumps and slaughterhouses, where they obtained some food by kleptoparasitism of carrion crows (Corvus corone).

2. RESULTS

(a) Population expansion

Over the period 1946-1993, the known territorial population increased from 7 pairs to 113 pairs (figure 1). For most of this period, the growth of the territorial

Proc. R. Soc. Lond. B (1994) 257, 317-323 317 C 1994 The Royal Society Printed in Great Britain



318 I. Newton and others Philopatry and population growth of red kites

120 - territories nests

/ clutches 80

40 r broods 40

0 1950 1960 1970 1980 1990

year Figure 1. Increase in the territorial red kite population in Wales, 1946-1993, together with various measures of breeding performance: territories occupied, nests built, clutches laid and broods raised.

2.5

.175 134

2.0 101

,cl.S, . D1.5

1.0

05,, 1940 1960 1980 2000

year

Figure 2. Exponential increase in the territorial red kite population in Wales, 1946-1993. The solid line shows the mean trend, and the broken lines the 95 % confidence limits. Lines are extrapolated to give the predicted population in the year 20.00.

Table 1. Exponential growth of territorial red kite population in Wales, 1946-1993

rate of 95 % confidence closeness of annual limits fit to increase exponential (%) lower upper model, r2

1946-1960 4.64 1.86 7.49 0.505 1961-1970 6.51 5.54 7.50 0.969 1971-1980 3.54 2.26 4.83 0.834 1981-1990 6.90 5.50 8.31 0.945 1946-1993 5.29 5.00 5.58 0.969

population was close to exponential, averaging 5.3 00O

per year (figure 2, table 1 ). The main variations in this rate of growth occurred in 195 1-1955 when the known population remained constant at 15 pairs, in the 1970s when population growth was mostly lower than

before 1961 1961 - 1970 1971 - 1975 1976- 1980 1981 - 1985 1986- 1990 1991 - 1992 now unoccupied

Figure 3. Pattern of spread of territorial red kites in Wales 1946-1992. Years refer to the period when particular 5 km squares were first occupied.

average, and in the 1980s when growth was mostly higher than average. If the mean rate of growth observed during 1946-1993 continues, in the year 2000 a territorial population of 134 pairs would be expected (with 950O confidence limits of 101-175 pairs), and a population of 200 pairs would be expected by the year 2008 (with the 95 0 confidence interval spanning the years 2002-2014).

As the Welsh population grew, it gradually spread from its original areas. The pattern of spread of nesting pairs is shown in figure 3 on the basis of 5 km squares. The squares are based on the national grid, and bear no consistent relation to habitat or kite nest sites. Each square was counted as occupied once a territorial pair settled there, and in many squares additional pairs settled in subsequent years. Once occupied, almost all squares remained so to the present day, and the apparent desertion of 10 (10O ) squares by 1992 can probably be attributed either to pairs shifting their nest sites from one square to a neighbouring one or to short- lived attempts to establish nesting territories in areas that were quickly abandoned.

In general, the spread in breeding distribution over the years has taken place progressively from one square to the next, or to the next but one; that is, new territories have mostly been established within 10 km of existing territories. This has given a pattern in which

Proc. R. Soc. Lond. B (1994)



Philopatry and population growth of red kites I. Newton and others 319

0 100 km

Figure 4. Locations of red kites marked as chicks in the breeding area (shaded) and subsequently reported outside the breeding area. All were in their first year of life and most were found dead. Points joined by a line represent successive reports of the same individual. The point off the east coast represents a bird found on a gas platform.

areas in the centre of the present range have been occupied for the longest time, and areas on the edge for the shortest time and most recently. The spread has taken place mainly to the north and south. To the west the birds are constrained by the sea. To the east the habitat looks suitable, but expansion has almost certainly been checked by the persistent use of poison baits (by sheep farmers for predator control), which could have continually removed potential colonists

and prevented them from establishing. The gap in the centre of the present distribution is occupied by high ground (>300 m), much of which is also heavily forested. The outward spread over the years has resulted in an increasing proportion of the population nesting on low ground, particularly to the south. In 1946-1960, only I0O% of nests were on ground less than 200 m in elevation, but by 1986-1991 this proportion had increased to 33 00.

The slow expansion of the breeding population, and its confinement throughout to mid-Wales, occurred despite the widespread dispersal of some kites in their first year of life (figure 4). Most of the young kites raised in Wales during the last 30 years were fitted with numbered metal rings, and many also with coloured wing tags, so they could be identified from a distance (Newton et al. 1989). Subsequent records of these birds showed that most remained within the breeding area, but some moved away, with 28 found at distances up to 400 km in their first year. Most of these long- distance birds were found dead, but three tagged birds seen at more than 100 km from their natal sites were later seen back within the breeding area, and at least one of them subsequently bred. It seemed that, despite dispersing widely in their first year (winter and summer), survivors returned to breed near where they were raised.

(b) History of performance on individual territories

The expansion of any species raises the question whether the initial low population was concentrated in particularly favourable localities, and whether, as numbers grew, an increasing proportion of pairs was forced to occupy poorer areas. If such a pattern occurred in kites, the birds should, on average, have performed best on the longest established territories and less well on more recently established ones. We therefore examined overall breeding performance on territories that were established in successive periods as

Table 2. Mean performance score of red kites on territories established at different dates through the study (robbed nests excluded)

(Each previously established territory scored annually as 0 (unoccupied), 1 (occupied), 2 (nest built), 3 (eggs laid) or 4 (young raised).)

years number of established territories mean score s.d. s.e. minimum maximum

(a) Including unoccupied and occupied territories pre- 1960 19 2.348 0.864 0.198 0.610 3.421 1961-1970 17 2.130 0.821 0.199 0.292 3.290 1971-1975 15 1.990 0.862 0.222 0.429 3.500 1976-1980 14 1.853 0.923 0.247 0.563 3.462 1981-1985 25 2.109 1.195 0.239 0.250 4.000 1986-1990 28 2.425 1.402 0.265 0.200 3.833 1991-1993 40 2.521 1.220 0.193 0.000 4.000 (b) Including only occupied territories pre- 1960 19 3.015 0.433 0.099 1.882 3.421 1961-1970 17 2.953 0.297 0.072 2.333 3.476 1971-1975 15 2.790 0.543 0.140 1.500 3.600 1976-1980 13 2.832 0.625 0.173 1.800 3.846 1981-1985 25 2.983 0.690 0.138 1.500 4.000 1986-1990 29 2.816 1.080 0.201 1.000 3.833 1991-1993 38 2.877 0.985 0.160 1.000 4.000

Proc. R. Soc. Lond. B (1994) 22 Vol. 257. B




Table 3. Breeding performance of red kites in 1991-1993 on territories first established at different dates before this

(Restricted to territories established before 1991, and in each year each previously established territory was scored as 1 (occupied), 2 (nest built), 3 (eggs laid) or 4 (young raised). There is no significant variation in performance between territories of different ages: X6 = 5.28, p > 0.5 (combining scores 1-2 and pairs of age classes).)

number of nesting attempts years since achieving following scores territory first mean established 1 2 3 4 score

1-5 1 3 14 27 3.49 6-10 2 3 11 34 3.54 11-15 1 2 7 20 3.53 16-20 6 2 10 9 2.81 21-25 0 2 13 10 3.32 26-30 3 1 2 11 3.24 31-40 1 1 4 5 3.18

> 41 3 2 11 20 3.33

the population grew (table 2). For each year for each territory we allocated a performance score, based on the stage of breeding reached: 0, unoccupied; 1, occupied; 2, nest built; 3, eggs laid; 4, young produced. The average scores of territories established in successive periods showed no consistent or significant trend with time. They thus revealed no evidence that kites tended to occupy progressively worse (or better) territories over the past 48 years as their numbers grew. This conclusion held whether the analysis was based on all territories (occupied and unoccupied, minimum score = 0) or on occupied territories alone (minimum score = 1) (table 2).

As a further analysis of trends in performance, we examined whether the performance on particular territories changed with time since first occupation. This analysis included all territories used during 1946-1993, regardless of when they were first established. If we included for each territory all years from first occupation, scoring years of nil occupancy as 0, most of the 156 territories showed no significant trend in performance score over the years, but six territories (occupied over periods of 24-48 years) showed a significant improvement in performance score over the years, and 13 (occupied over periods of 21-48 years) showed a significant decline. If we included only the years that a territory was occupied (so that in each year the minimum score was 1), most territories again showed no significant trend in performance score over the years, but six (occupied over 23-47 years) showed a significant increase in score, and three (also occupied over 23-47 years) showed a significant decline. On a sample of this size, significant trends in the scores of some territories would have been expected by chance, but taken as a whole the records gave no firm evidence for any systematic deterioration or improvement of kite performance on individual territories over the time periods considered. This was consistent with another finding, namely the lack of any relation between nest success and age of territory. Thus, in recent years, no difference in nest success was

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PPhilopatry and population growth of red kites I. Newton and others 321

Table 5. Breeding performance in areas of different base status

(NT, number of territories occupied; NS, number successful. Differences in success between base-poor and base-rich areas: 1976-1980, p =0.087 (Fisher's exact test, two-tailed); 1981-1985, x2 = 0.46, n.s.; 1986-1990, x2 = 9.51, p = 0.002; 1991-1993, x2 = 9.57, p = 0.002; overall (1976-1993), X 2 = 17.32, p < 0.001.)

overall 1976-1980 1981-1985 1986-1990 1991-1993 (1976-1993)

NT NS (%) NT NS (0) NT NS (0) NT NS (0) NT NS (%)

base poor 197 75 (38) 234 80 (34) 298 108 (36) 254 118 (46) 983 381 (39) base rich 6 0 (0) 27 11 (41) 65 37 (57) 58 40 (69) 156 88 (56)

apparent between kites that bred on recently established territories and those that bred on territories established decades previously (table 3).

(c) Breeding From 1723 records of pairs on territory during

1946-1993, 87 0 were known to reach the nest- building stage, 7700 laid eggs, and 3900 produced young (table 4). Most failures occurred at the egg stage or soon after hatching. Successful pairs produced an average of 1.39 young per brood, which is equivalent to 0.71 young per nest and 0.54 young per territorial pair per year. However, the proportion of territorial pairs which raised young increased in recent years, reaching 400o in 1986-1990 and 50?, in 1991-1993 (table 4). Mean clutch size also increased, from 1.81 in 1946- 1960 to 2.44 in 1991-1993 (on regression analysis of individual clutch sizes against year, b = 0.013, p < 0.001), giving an increase in mean brood sizes in successful nests from 1.32 to 1.49 (on regression analysis, b = 0.003, p = 0.070).

These long-term improvements in breeding performance could not be attributed solely to an increase over the years in the proportion of pairs nesting on low ground (< 200 m). Overall success was little better on low ground than high (460% and 4300 of territorial pairs raised young, respectively), and the improvements in performance were evident when nests on high ground alone were considered. However, in one area of low ground in the south of the current range, success has been particularly high (560% of territorial pairs raised young). Throughout this century, most of the Welsh kites nested on areas of Silurian or Ordovician rocks, where the overlying soils are markedly acidic. But in 1978, as the birds spread southwards, a pair settled in an area of sandstone and carboniferous rocks, where the soils were more basic. In this area numbers subsequently increased at an average rate of 20 0 per year, compared with 500 for the whole population. The birds here also showed significantly higher nest success than the rest of the population (table 5), and significantly higher clutch and brood sizes. On casual impression, this area seems to have a more plentiful supply of prey.

The proportion of nests known to have been robbed by egg collectors has fluctuated from year to year but has shown no long-term trend (table 4). Overall, it has affected about 6 0 of territorial pairs, and about 8 0 of clutches laid. If, in the absence of robberies, these

clutches had showed the same success as other clutches, then the proportion of clutches that produced young would have increased from 51 0 to 55 0, and the proportion of pairs that produced young from 39 0 to 42 0. These figures give a minimum assessment of the effect of egg collecting, because it remains possible that the failure of other nests robbed by egg collectors was wrongly attributed to natural causes, including non- laying.

(d) Annual losses

From knowledge of the number of birds present each spring, and the number produced each year by breeding, the annual losses of full-grown birds from the population could be calculated from year to year, as shown in table 6 (minor changes in some of the pre- 1981 figures from those given in Davis & Newton (1981) result from the inclusion here of later information). Thus, in 1951, 31 full-grown birds (breeders and non-breeders) were found in spring, and during the summer nine chicks fledged, giving an estimated total post-breeding population of 40 kites. The next year, 31 birds were again present in spring, so it was assumed that nine (23%) had been lost over winter. Proceeding in this manner enabled the losses to be calculated for each year, and then averaged for particular periods of years. These net annual losses reflected the combined effects on the population of mortality and of permanent emigration-immigration (if they occurred). Net losses reached 36.4 0 per year, but over the whole period they averaged 13.7 + 1.2 0. Losses were higher in the 1950s (1951-1960, mean = 22.1 + 3.0 o) than subsequently (1961-1993, mean = 11.4 + 0.9 %O). They referred to all full-grown kites and did not distinguish between age groups. An analysis of tagged breeders alone for 1977-1985 indicated an annual mortality of only 5.6 + 2.0 o (Newton et al. 1989), so the younger age groups must have a much higher rate of loss, as would be expected. The main recorded cause of mortality is illegal poisoning (Davis & Newton 1981; Evans 1994).

3. DISCUSSION

The general pattern of gradual outward spread from existing occupied areas was most plausibly attributed to high natal philopatry, with individuals showing a strong tendency to breed near where they themselves were raised, or near to other kites. This was despite the fact that, in their pre-breeding years, kites wandered

Proc. R. Soc. Lond. B (1994) 22-2




Table 6. Annual losses of full-grown red kites in Wales, 1951-1992

full-grown birds in spring (breeders total and non- chicks birds if no birds lost since

year breeders) fledged mortality previous year (o)

1951 31 9 40 1952 31 7 38 9 (22.5) 1953 29 11 40 9(23.7) 1954 31 13 44 9 (22.5) 1955 28 1 29 16 (36.4) 1956 25 7 32 4 (13.8) 22.1 +3.0 1957 26 8 34 6 (18.8) 1958 32 5 37 2 (5.9) 1959 28 8 36 9 (24.3) 1960 25 10 35 11 (30.6) 1961 33 6 39 2 (5.7) 1962 37 7 44 2 (5.1) 1963 38 4 42 6 (13.6) 1964 41 7 48 1 (2.4) 1965 44 11 55 4 (8.3) 10.7 + 1.8 1966 45 11 56 10 (18.2) . 1967 48 11 59 8 (14.3) 1968 55 12 67 4 (6.8) 1969 58 16 74 9 (13.4) 1970 60 17 77 14 (18.9) 1971 59 16 75 18 (2.3) 1972 67 19 86 8 (10.7) 1973 76 14 90 10 (11.6) 1974 78 13 91 12 (13.3) 1975 75 24 99 16 (17.6) 1976 80 18 98 19 (19.2) 11.9+1.5 1977 89 17 106 9 (9.2) 1978 94 22 116 12 (11.3) 1979 105 19 124 11 (9.5) 1980 106 27 133 18 (14.5) 1981 118 21 139 15 (11.3) 1982 117 23 140 22 (15.8) 1983 108 24 132 32 (22.9) 1984 131 24 155 1 (0.8) 1985 139 25 164 16 (10.3) 10.9+ 1.9 1986 140 29 169 24 (14.6) . 1987 158 39 197 11 (6.5) 1988 178 39 217 19 (9.6) 1989 202 50 252 15 (6.9) 1990 227 74 301 25 (9.9) 1991 260 62 322 41 (13.6)1 1992 294 96 390 28 (8.7) 13.9+3.1 1993 314 80 394 76 (19.5)4

widely, and appeared in localities up to 400 km from where they were raised. The 28 ringed or tagged birds from mid-Wales that were found elsewhere in recent years is testimony to their widespread dispersal. In fact, many of the additional wintering birds seen in England in recent decades may have been of Welsh origin, although the situation has changed since 1989 following the release of kites in other areas (see below). There is as yet no evidence from ringing that continental kites winter in Britain in any numbers, although some pass through eastern counties (and occasionally further west) on migration.

It is remarkable that, despite wide dispersal in the first year of life, the breeding population throughout this century (until released birds started to nest in 1991) remained confined to mid-Wales. Over this whole period, there was only one definite breeding attempt outside Wales, in Devon in 1913. The pair concerned might well have been derived from the Welsh population, as the next nearest kites bred about 700 km away in France and Germany. One bird from this pair is believed to have been killed so the attempt failed. In addition, there were unsubstantiated reports of unsuccessful breeding from Inverness in 1917, Cornwall in 1920, Devon in 1947, and Cumbria in 1977-1978. The situation has now changed, however, because in the last 5 years a reintroduction programme has led to the establishment of two local breeding populations of continental kites in southeast England and northeast Scotland (Pienkowski & Evans 1991; Evans & Stowe 1993; Evans 1994). Kites from these releases dispersed widely in Britain during their first year but, like the Welsh birds, later returned to breed near their respective 'fledging' areas.

The pattern of territory establishment within Wales over the years implied that kites showed extreme philopatry, spreading out from existing territories on a 'rolling front' as their numbers grew. This view has recently received support from genetic studies which, by use of blood samples taken from nestlings, has revealed only two haplotypes within the Welsh population (May et al. 1993). The oc-haplotype was shown by female chicks from 83 0 of nests sampled, and the P-type by female chicks from 17 % (n = 53 nests in 1992 with female chicks). But while the oc-type was found throughout the Welsh range, the rarer ,B- type was markedly associated with the southernmost nest sites (main population 38cz, 4j; southern region 6cz, 5jp; Fisher's exact test, p = 0.013). The birds in this southern area therefore appeared somewhat distinct genetically from the rest of the population, even though several birds from this area are known to have bred in the main area. The first nest in the southern area can be dated to about 1978, and the others may have been derived mainly from this one pair. The other interesting finding was that this particular haplotype was found frequently in kites from Germany, but not in kites from Sweden and Spain (May et al. 1993). It is possible, then, that a German kite behaved unconven- tionally, and settled in Wales in the 1970s, founding part of the existing population. The kite bearing a German ring which was found dead in Wales in July 1972 constitutes the only concrete evidence for immigration to Wales, although this bird (a yearling) was extremely unlikely to have bred. The alternative explanation for the existence of two haplotypes is that they were both present in the original Welsh population, and have survived until now. But the fact that one haplotype is concentrated in one part of the existing range provides further evidence for extreme site fidelity, with young returning close to their natal areas to breed.

Reproduction of kites in Wales was poor compared with kites elsewhere and with other similar raptors (Walters Davies & Davis 1973; Newton 1979; Davis &




PPhilopatry and population growth of red kites I. Newton and others 323

Newton 1981), but some aspects of performance improved during the study. Increases occurred in mean clutch and brood sizes, and (especially in recent years) in the proportion of territorial pairs which produced young. Part of this overall improvement was linked with the colonization in recent years of an area with more productive soils and apparently greater food supply. In addition, a more general increase in food supply may also have occurred in mid-Wales over the years, associated with afforestation and other land-use diversification, and with greater sheep densities, but no relevant measurements were made.

From a knowledge of numbers and productivity, an average of 140% of kites were estimated to have been lost from the population each year, ranging between 1 00 and 360% in individual years. Of all the figures given in this paper, these were the ones most subject to error, as a result of birds being missed at the spring count, including some that were temporarily absent from the area. Some tagged first-year birds were absent from central Wales (= not seen) during their first spring, but had returned to the area (= were seen) in a later spring. These bircls formed only a small proportion of the total population. They would have slightly inflated the estimate of loss in their year of absence, and slightly depressed the estimate in their year of return. Over the period as a whole, the absence of one group of birds in each spring would have been partly compensated by the return of another, thus reducing the overall error.

The exponential population growth at about 500

per year during 1946-1993 is unlikely to have represented the maximum growth possible, considering the loss of eggs and birds to human predation in this time (Davis & Newton 1981). The period of slowest growth, in the 1950s, corresponded with the period of highest overwinter losses. If the same mean rate of increase continues, however, the Welsh population could reach 200 pairs during the years 2002-2014. There is clearly no shortage of suitable habitat for

further expansion either in Wales or in Britain as a whole.

The data analysis for this paper was supported by funding from the Forest Authority and the Countryside Council for Wales. We thank these bodies, and the many observers who contributed observations over the years.

REFERENCES

Davis, P. E. 1993 The red kite in Wales: setting the record straight. Br. Birds 86, 295-298.

Davis, P. E. & Davis, J. E. 1981 The food of the red kite in Wales. Bird Study 28, 33-40.

Davis, P. E. & Newton, I. 1981 Population and breeding of red kites in Wales over a 30-year period. J. Anim. Ecol. 50, 759-772.

Evans, I. M. 1994 Experimental reintroduction of the red kite to England and Scotland. The Raptor 21, 22-25.

Evans, I. M. & Stowe, T. J. 1993 Red kite reintroduction progresses well. In Britain's birds in 1990-91: the conservation and monitoring review (ed. J. Andrews & S. P. Carter), pp. 52-54. Peterborough: Joint Nature Conservation Com- mittee.

May, C. A., Wetton, J. H. & Parkin, D. T. 1993 Poly- morphic sex-specific sequences in birds of prey. Proc. R. Soc. Lond. B 253, 271-276.

Newton, I. 1979 Population ecology of raptors. Calton: Poyser. Newton, I., Davis, P. E. & Moss, D. 1981 Distribution and

breeding of red kites in relation to land-use in Wales. J. appl. Ecol. 18, 173-186.

Newton, I., Davis, P. E. & Davis, J. E. 1989 Age of first breeding, dispersal and survival of red kites Milvus milvus in Wales. Ibis 131, 16-21.

Pienkowski, M. W. & Evans, I. M. 1991 Red kite reintroduction to Scotland and England. In Britain's birds in 1989-90: the conservation and monitoring review (ed. D. Stroud & D. Glue), pp. 124-127. Peterborough: Nature Con- servancy Council.

Walters Davies, P. & Davis, P. E. 1973 The ecology and conservation of the red kite in Wales. Br. Birds 66, 183-224,241-270.

Received 23 June 1994; accepted 30 June 1994




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Philopatry and Population Growth of Red Kites, Milvus milvus, in Wales