J. Zool., Lond. (1977) 181, 11-20

Contamination of Peregrine falcons (Falco peregvinus) with fulmar stomach oil

A N D R E W C L A R K E British Antarctic Survey, Madingley Road, Cambridge, England

(Accepted 8 June 1976)

Since 1971, four peregrine falcons, Fdco peregritrus, coated with an oil-like contamination, have been received for analysis at Monks Wood Experimental Station. All were from north or west Scotland. The contamination from one bird was examined and found to be a highly weathered oil of recent biological origin. The biochemical evidence did not indicate an unequivocal source for the oil, but was compatible with the hypothesis, for which there is strong circumstantial evidence, of fouling by stomach oil from a fulmar, Fulrnorus glacialis. The possible circumstances of the oiling are discussed. Stomach oil production by petrels and albatrosses is unlikely to have evolved solely in response to selection pressure for nest defence. Oiling by fulmars appears to a small, but possibly significant, cause of mortality in coastal peregrines.

Contents Page

Introduction . . . . . . . . . . . . . . . . . . . . 11 Materials and methods . . . . . . . . . . . . . . . . . . 12 Results . . . . . . . . . . . . . . . . . . . . . . 12 Discussion . . . . . . . . . . . . . . . . . . . . . . 17 Summary . . . . . . . . , . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . 19

Introduction The production of stomach oil in certain seabirds of the order Procellariiformes has

long been known. On St Kilda stomach oil from the fulmar, Fulmarus glacialis, held a reputation among the islanders as an emetic and general panacea, and in Tasmania stomach oil from the Short-tailed shearwater or Tasmanian mutton-bird, Pufinus ienui- rostris, has been utilized as a source of wax esters by the pharmaceutical and cosmetics industries.

A major function of petrel stomach oil appears to be chick nutrition (cf. Rice & Kenyon, 1962) and the bulk of the stomach oil in breeding adult seabirds seems to be derived directly from the food, although a little may be secreted (Cheah & Hansen, 1970a, b ; Clarke & Prince, 1976). However the ejection of stomach oil either aggressively or as a means of defence is also important. Oil ejection occurs in both adults and chicks and discharge at intruding humans is well known. Various species of petrel and albatross have also been recorded as ejecting stomach oil at members of the same species during sexual or territorial fighting (Brown, 1966), against other species of bird (Tulloch, 1971), sheep (Robertson, 1975) and even feral cats (K. R. Kerry, pers. comm.). Broad (1974) listed 20 species of bird recorded as having been fouled by fulmar oil, mostly on Fair Isle, Shetland.

11

12 A . C L A R K E

Since 1971 four Peregrine falcons, Falco peregrinus, have been sent for analysis to the toxic chemicals section at Monks Wood Experimental Station. These birds were all covered more or less extensively with a tacky, oil-like contamination. As peregrines have previously been noted as having been coated by fulmar stomach oil (for example the two sight records given in Broad, 1974), one specimen was analysed to determine whether or not the source of the contamination was fulmar stomach oil.

Materials and methods Contaminated feathers were carefully removed with clean scissors from the peregrine and

weighed. The feathers were then washed extensively with 900 ml methanol-chloroform 2/1 (v/v) and the solution filtered through glass fibre. Addition of 300 ml chloroform and 420 ml water produced separation into two phases (Bligh & Dyer, 1959). The lower, chloroform, layer was carefully removed, diluted with benzene and evaporated. The lipid was then weighed and made up to 100 ml with chloroform. Fulmar stomach oil lipid and peregrine preen gland lipid (obtained by maceration in methanol-chloroform) were purified by similar procedures.

Lipid extracts were examined by thin-layer chromatography (t.1.c.) on precoated silica gel plates (Merck, SG,,). The separated lipids were detected by spraying the plates with 0.01 % aqueous Rhodamine 6G and viewing wet under U.V. light (366 nm).

A rough quantitative assay of the various lipid components was obtained by separating with t.l.c., spraying the plate with 50% aqueous sulphuric acid, charring by heating to 120°C and then scanning the plate with a Joyce Loebl slit densitometer (reflectance mode, white light). Thin layer chromatography plates were cleaned prior to use by pre-running in solvents and samples were run at a variety of concentrations alongside standard calibration mixtures.

Pure lipid components were separated by t.1.c. for the preparation of derivatives. Fatty acid methyl esters were prepared by reaction under nitrogen with 0.5 N methanolic HCI and analysed by gas chromatography (g.c.) on a 20 % DEGS packed column at 185°C. Isopropylidene deriva- tives of long chain diols and monoalkylglycerols (glyceryl ethers) were prepared by reaction with dry acetone overnight at room temperature, in the presence of 10 mg anhydrous cupric sulphate as catalyst. Hydrocarbons were separated by column chromatography on 7 % hydrated florisil and analysed by temperature programmed g.c. on a 5 % Apiezon L packed column. The methods of analysis have been described in detail elsewhere (Clarke & Prince, 1976).

For chlorinated hydrocarbon analysis aliquot samples were measured out, evaporated and weighed. They were then dissolved in glass-distilled n-hexane, filtered, evaporated and redissolved in hexane. This procedure was repeated carefully 3 times to remove all traces of chloroform. The solution was then analysed by g.c. according to French & Jeffries (1971).

Results A total of four contaminated peregrines has been delivered to the toxic chemicals section

at Monks Wood Experimental Station. Details of these are given in Table I. Peregrine 4751 was examined to determine, if possible, the source of the contamination.

The contamination was extensive, covering the breast, flanks, underwing coverts, crown and lores. The contaminating oil was orange-brown and tacky to the touch. The smell, although distinctive, was not that of fulmar oil. In several areas the oil had matted the feathers badly and extended through to the underlying skin. From 40.45 g of contaminated feathers, 3.08 g of lipid were recovered.

For comparative purposes the preen gland was also removed and extracted. The excised preen gland weighed 242.3 mg, 0.052% of the body weight. Kennedy (1971)

C O N T A M I N A T I O N O F P E R E G R I N E F A L C O N S W I T H O I L 13

TABLE I Details of four Peregrine falcons, Falco peregrinus, received for analysis at Monks Wood Experimental Station

Monks Wood specimen number Sex Weight (9) Remarks

2844 0 840 Found dying, Dunnet Head, Caithness, 4 May 1971; died same night; oiled on head, breast and neck

3679 ? Died “covered in oil” in an Orkney garden, 24 June 1972; cause of death thought to be starvation and exposure

3908 0 902 Found alive John o’Groats, Caithness, 13 July 1973; died next day; oiled on primaries and secondaries of one wing, undersides of wings, tail, upper tail coverts and crown

475 1 6 465 Found oiled and with broken leg, Lerwick, Shetland, late June 1975; died Fair Isle, July 1975; oil contamination examined at Monks Wood

748

listed the weight of the preen gland relative to body weight for 171 individuals of 52 species of birds, with an indication of seasonal variation in one species. The only Falconi- form species listed were kestrel, Falco tinnunculus, and Brahminy kite, Haliastur indus. In these species the preen gland represented 0.075% and 0.094% of the body weight respectively. Although the weight of the preen gland will vary with the content of secretion, both these species and peregrine 475 1 fall at the lower end of the range of values presented by Kennedy (0.561 to 0.0193&0-0054% (s.D., n=5)). The similarity of the three values also implies that severe contamination of the plumage had apparently caused neither an

TABLE 11 Lipid composition of samples, as indicated by charring and reflectance densitometry

Feather- Peregrine Fulmar Fulmar washing preen gland stomach oil stomach oil

Lipid class lipid lipid sample F G I sample FG 2

- - Wax ester 11 86* Diol ester 4 8 Triacylgl ycerol 1 1 I 94 92 Free fatty acid 22 1 2 4 Free sterol 10 1 I .5 2 Monoacylglycerol

+ Diacylglycerol + Free fatty alcohol Polar lipid

- -

1 1.5 1

42 $ 3 1 1

*The wax ester band in the peregrine preen gland lipid was complex; ?hydroxy acid wax ester and normal (n-)

:This polar lipid was almost entirely degraded material with very low t.1.c. mobility. Data presented as % total uncorrected recorder response. Probable error

wax esters were assayed together.

10% stated value for components >50% mixture, * S O % stated value for components <50% mixture. Limits of detection approximately 1 % total sample. Lipid components not detected in any sample by t.1.c. and densitometry (e.g. hydrocarbons) not listed.

14 A . C L A R K E

inflamed nor an unduly wasted preen gland. The preen gland contained 181.6 mg lipid, 75 % of the fresh weight. This value includes both structural and secretory lipid.

The lipid washed from the feathers will have included some feather lipid and preen gland secretion as well as the contaminating oil. This feather-washing lipid was examined by t.1.c. alongside preen gland lipid and selected lipid standards. A rough quantitative assay of the relative proportions of the various components in each extract is given in Table 11.

The lack of any hydrocarbons detectable by t.1.c. indicated that the contamination was not a mineral oil. Hydrolysis of the complex wax ester band yielded long chain n-alcohols, n-fatty acids and other fatty acids, probably hydroxy- fatty acids. The diol esters were also hydrolysed and the diol backbone converted to the isopropylidene (IP) derivative. The products of this reaction were examined by t.1.c. according to Saito & Gamo (1973), alongside the 1P derivative of selachyl alcohol. This revealed several spots, one of which had a mobility corresponding to the IP derivative of long chain diols, although no standards were available for confirmation. Normal (n-) wax esters, hydroxy wax esters and esters of long chain diols are all common constituents of the secretions of avian preen glands. In a survey of the preen gland lipids of 14 species of bird, Haahti et a!. (1964) did not detect

T A B L E 111 Summary of fatty acid composition of selected lipid fractions

Preen gland Feather-washing Fulmar stomach Fulmar stomach oil FGl after lipid lipid oil stated number of days weathering

TAG TAG I day 3 days 3 days IOdays FFA TAG FFA TAG FGI FG2

16 : O/l6 : 1 3.0 4.0 5.3 1.3 1.5 1.4 2.8 3.4 3.1 4.3 18 : 1/18 : 0 0.9 1.0 1.5 2.8 6.6 6.4 10.6 10.8 10.1 5.3 22 : 0 (x total acids) 8.3 0.9 nd nd nd nd nd nd nd nd %saturated acids 605 56.6 59.8 42.6 22.9 28.0 36.1 42.7 38.9 50.1 % polyunsaturated

acids (4 or more nd nd 3.2 1.4 27.0 25.8 13.4 nd 3.7 nd double bonds)

Calculated iodine value 45 57 160 151 103 51 66 44

nd: not detected. FFA: free fatty acid; TAG: triacylglycerol; nd: not detected; shorthand notation for fatty acids is x : y where

The detailed composition data are available on request from the author. x is number of C atoms and y is the number of double bonds.

diol esters in kestrel or sparrowhawk, Accipiter nisus, preen gland secretions. Diol esters were however detected by Gamo & Saito (1971) in the Eastern buzzard-hawk, Butastur indicus.

The rough quantitative data in Table I1 indicate that although much of the contaminat- ing material had been degraded by weathering by the time of the analysis, the original oil was probably mostly triacylglycerol (TAG) and free fatty acid (FFA). The fatty acid composition of these fractions in both the feather-washing lipid and preen gland lipid was therefore examined. These were different (Table Ill), which implies that the feather- washing lipid TAG and FFA did not originate in the preen gland. The fatty acid methyl esters from the contaminating oil TAG and FFA needed clean-up on a small silica gel

C O N T A M I N A T I O N O F P E R E G R I N E F A L C O N S WITH O I L I5

column prior to analysis in order to remove degraded material which interfered with the g.c. analysis.

For comparison, two stomach oil samples were obtained from fulmar chicks on Skokholm, Pembrokeshire, and examined by t.1.c. and g.c. As found in previous analyses, these stomach oils were almost entirely TAG (Cheah & Hansen, 19706; Warham, Watts & Dainty, 1976; an early analysis by Rosenheim & Webster (1927) indicating a sub- stantial content of wax esters was possibly mutton-bird oil rather than fulmar oil). The TAG fractions were isolated and their fatty acid compositions analysed (Table 111). In common with previous analyses of petrel stomach oils, the fatty acid composition was typically marine with high contents of 16 : 1, 18 : 1, 20 : 1, 20 : 5 and 22 : 6 acids and high iodine values (the shorthand notation for fatty acids is x : y , where x is the number of C atoms and y is the number of double bonds). This composition was very different from both the preen gland and feather-washing lipid TAGS. However, several of the typical marine acids such as 20 : 5 and 22 : 6 are very unstable in the presence of light and oxygen. It is therefore possible that the observed composition of the feather-washing lipid TAG represents the result of weathering on a typical fulmar stomach oil TAG composition.

To test this hypothesis four bird wings were obtained, coated with pure fulmar stomach oil (sample FG 1) and exposed to the weather. The process of weathering was monitored by removing and analysing samples at set intervals. As previously, fatty acid methyl ester mixtures needed clean-up to remove interfering material. It can be seen (Table 111) that weathering slowly produced a composition similar to (but not identical with) that observed in the feather-washing lipid TAG. In particular, the polyenoic acids such as 20 : 5 , 22 : 5 and 22 : 6 were rapidly degraded with a concomitant drop in iodine value. In addition the smell changed from that typical of fulmar stomach oil to one similar to that of the oiled peregrines.

Although this evidence points to fulmar stomach oil as a possible source of the con- tamination, it is not conclusive. Alternative approaches were therefore attempted. Carotenoids were not investigated as possible indicators because of their sensitivity to photo-degradation. However several hydrocarbons such as pristane and squalene appear to be particularly associated with marine organisms, and can occur in significant amounts in some petrel stomach oils (Lewis, 1969; Clarke & Prince, 1976; Warham et al., 1976). Samples of the feather-washing lipid, preen gland lipid and fulmar stomach oil were therefore analysed for these hydrocarbons.

In all three samples the hydrocarbon (HC) fraction amounted to less than 1 % of the total lipid, confirming the t.1.c. data that the contaminating oil was not a mineral oil. The fulmar stomach oil HC fraction contained three major peaks, one of which was pristane. Pristane was absent from the preen gland HC fraction; the feather-washing lipid however did contain a small peak with a retention time identical with that of pristane. The general pattern of HC peaks also differed between the three samples. When compared with the preen gland lipid, the feather-washing lipid contained a much greater proportion of shorter chain-length HCs. Petrel stomach oil HC fractions are usually complex and contain a broad spectrum of chain lengths (Clarke & Prince, 1976). It is thus possible that the shorter chain-length HCs found in the feather-washing lipid may have been derived from fulmar stomach oil.

The feather-washing lipid and the two fulmar stomach oil samples were assayed for chlorinated hydrocarbon residues (Table IV). The residues in the feather-washing lipid,

16 A . C L A R K E

although marked, were nevertheless present only at trace level. Both the feather-washing lipid and the two fulmar stomach oil samples contained an unknown peak of long retention time. The low levels of pesticide residues detected would rule against run-off from a sheep dip (which can apparently contain quite large amounts of lanolin oil from the wool, as well as pesticide residues) as a source for the contamination. Dieldrin however is subject to photo-decomposition when exposed to light as it would be on the plumage. The dieldrin level, which is quite high, may thus be an underestimate. Furthermore, peregrines are known to be particular in their bathing behaviour (Baker, 1967) and so contamination from sheep dip run-off would seem unlikely.

The two fulmar stomach oil samples showed chlorinated hydrocarbon contents markedly lower than the feather-washing lipid. A similar low level (1.3 parts/lOs PCBs, presumably parts/106 wet weight) was found in a single sample of stomach oil from a fulmar collected

TABLE 1V Chlorinated hydrocarbon residues in feather-washing lipid and fulmar stomach oils

Sample p,p’-DDE HEOD (dieldrin) PCBs

pg parts/ 1 Oe pg parts/ I Oe Clg parts/lOe

Feather-washing lipid 110 35.7 26.67 8.7 400 129 Stomach oil FG 1 nd nd 10 .1 Stomach oil FG 2 nd nd < O . l

nd: not detected. Data are expressed as total weight residue (pg) in the sample, where known, and as parts/lOe (mg/g)lipid weight. Analyses were performed by M. C. French, L. A. Sheppard and R. J. Mellor of the analytical laboratory, Monks

Wood Experimental Station.

at sea (Bourne & Bogan, 1972). Since stomach oils appear to be derived directly from the food it is of interest that these observed PCB levels are comparable with contents reported for North Atlantic plankton. Williams & Holden (1973) analysed 26 samples of mixed zooplankton extending on a line from the Clyde estuary to the open ocean. PCB contents ranged from 0.01 to 2.20 parts/106 wet weight with the PCB/DDT ratio varying from 0.6 to over 40. In general the open sea values were considerably lower (0.01 to 0.07 parts/106 wet weight PCBs) than inshore values. Harvey et al. (1974) also examined Atlantic plankton for chlorinated hydrocarbon residues and, in contrast, found no evidence of latitudinal variations. Mixed zooplankton samples contained an average of 0.2 parts/lOs wet weight PCBs; a few values of over 1 parts/106 were associated with high phytoplankton contents. These data imply that much of the chlorinated hydrocarbon residues carried on the plumage of the peregrine originated in sources other than the contaminating oil. Atmos- pheric dust or the excretion of pollutants via the bird’s own preen gland are possibilities.

Because of the degradation caused by exposure to air and light, the biochemical evidence cannot indicate an unequivocal source for the contaminating oil. The contamination is not mineral oil, but of a recent biological origin and all the available evidence is compatible with the strong circumstantial evidence that it is stomach oil from a fulmar. Although only one of the four peregrines was analysed, it would seem reasonable to assume, on the basis of appearance and smell, that the source of contamination of the other three peregrines received at Monks Wood was also fulmar stomach oil.

CONTAMINATION O F PEREGRINE FALCONS W I T H O I L 17

Discussion The ejection of stomach oil by fillmar chicks appears to be an automatic reaction to

certain external stimuli, particularly disturbance. Oil ejection has even been recorded from fulmar chicks still within the egg (Lees, 1950), and Duffey (1951) recorded that it took fulmar chicks up to three weeks to cease reacting aggressively to a parent bird returning to the nest with food.

Armstrong (1951) discussed this behaviour in relation to a postulated Antarctic origin for the fillmarine petrels (Voous, 1949; but see Cramp, Bourne & Saunders, 1974: 62). Armstrong considered that the evolution of aggressive/defensive oil ejection behaviour must have taken place in the absence of ground predators and was primarily a means of defence against predation from the air; indeed he considered it to be additional evidence of the Antarctic origin of fillmars. However there are very few accounts in the literature of the use of stomach oil as a defence against flying predators, although Tulloch (1971) recorded the reverse, a fulmar in flight ejecting oil at a bird on the ground. Furthermore, in a species such as the Wandering albatross, Diomeden esulans, which nests in loose colonies on open flattish ground (and which has a well-developed ability to eject stomach oil), the distinction between a ground predator, sensu stricto, and a ground level attack by a scavenging skua, Catharacta skua, or Sheathbill, Chionis alba, is perhaps a fine one. It is of interest that on Macquarie Island, where cats are feral and a relatively recent addi- tion to the fauna, a Sooty albatross, Phoebetria pnlpebrata, chick has been seen to eject oil at a nearby approaching cat (K . R. Kerry, pers. comm.). Neither is oil production limited to those species which nest in the open. Many crevice nesting species (e.g. Snow petrel, Pagodroma nivea) and true burrow nesting species (e.g. Wilson’s petrel, Oceanites oceanicus, and Blue petrel, Halobuencr cnerulea) also produce quantities of stomach oil. I t is more likely that the varying degrees of ability to produce and eject stomach oil are a resultant of various selection pressures including both feeding ecology and agonistic behaviour, rather than nest defence alone.

Swennen (1974) has reported experimental evidence that severe coating of seabirds with fulmar stomach oil is usually fatal. Brown (1966) however reported that small scale coating with stomach oil during territorial/sexi~al fighting by male Snow petrels was normal, and that afterwards this was successfully removed by bathing in snow. In the four peregrines received at Monks Wood coating varied in intensity though it seems unlikely that the oil was the immediate cause of death. Exposure due to a loss of feather insulation or mal- nutrition consequent upon an inability to catch prey were more likely proximate causes of death. Starvation may have resulted in increased concentrations of chlorinated hydrocarbons in sensitive organs as the depot fat was mobilized and this may have contributed to the cause of death.

The four oiled peregrines sent to Monks Wood and the two instances of oiled peregrines cited by Broad (1974) all date from later than 1971, and all are from north or west Scotland. Recently two further peregrine oilings and the contamination of an immature Snowy owl, Nj’ctea scandiaca, have been recorded from Shetland (R. J. Tulloch, pers. comm.), and another example of peregrine oiling in Orkney during 1971 has also been published (Booth, 1976). It is possible that the lack of earlier records merely reflects a recent increase in observers and that oilings prior to 1971 were simply not detected. It is also possible however, that the relatively recent nature of these reported incidents is a reflection of the recent increase in the fulmar population.

18 A. C L A R K E

There has been a well documented increase in the fulmar population of the eastern Atlantic since the 18th century (for summaries see Fisher, 1952, 1956; Cramp et al., 1974). Fisher considered that the availability of offal from whaling and fishing fleets was a major cause of the population increase. Salomonsen (1965) and Brown (1970) however, sug- gested that changes in the oceanographic parameters which appear to govern fulmar distribution were a more likely cause. The present breeding population is particularly dense in NW Scotland where fulmars are now nesting on inland rock faces, dry stone walls and even rough ground in addition to the more normal sea cliffs. The utilization of new types of nest sites by fulmars in the Monach Isles, and the influence of factors such as weather, rabbits and sheep on the availability of sites have been discussed by Hepburn & Randall (1975). Fulmars nesting on inland crags have been found to foul with stomach oil the fleeces of browsing sheep which stray too close to the nests (Robertson, 1975).

On Fair Isle many species of bird have been observed with fulmar oil contamination. Broad (1974) listed 28 observations covering 20 species, including several passerines as well as two peregrines; 22 of these occurrences were since 1970. It is likely that oiling by fulmars was a contributory reason for the failure of the attempted reintroduction of the Sea eagle, Haliuetus albicilla, to Fair Isle (Dennis, 1971). Although recorded instances of the fouling of seven species of raptor may represent a general reaction to birds of prey as potential predators, such a reaction cannot explain the fouling of small passerines.

The circumstances surrounding the oiling of the peregrines remains unclear. It is possible that the contamination represents the successful retaliation by a fulmar to an attack, as peregrines in coastal areas are known to take fulmars as food (Ratcliffe, 1963). Alterna- tively, expansion of the fulmar population may have increased breeding density on the sea cliffs to the point where fulmars have started to nest within spitting distance of a traditional peregrine eyrie, with consequent oiling of one or both of the nesting peregrines. A further possibility is that the oiled peregrines were tired migrants, as seems to be the case with several of the oiled passerines recorded by Broad (1974), or may have been injured. The latter seems a distinct possibility with peregrine 4751 which had a broken leg when found. It is also possible that the peregrines were uncoordinated or moribund from sub-lethal contamination with chlorinated hydrocarbons or other pollutants (Jeffries & Prestt, 1966; Ratcliffe, 1972). On settling too close to a fulmar, oiling followed.

Since 1971 there have thus been at least nine recorded instances of peregrines being fouled with fulmar stomach oil (viz: four birds received at Monks Wood, of which one was analysed; two records in Broad, 1974; one record in Booth, 1976; two instances recorded by Tulloch, pers. comm.). This figure is obviously only a minimum estimate as other peregrines may have been oiled and then died before being discovered. Assuming that oiling of the sort observed inevitably leads to death by exposure or starvation gives a minimum estimate of 10 deaths in the period 1971-75. Although this is a small figure in comparison with the probable natural mortality of coastal peregrines in north and west Scotland from causes other than oiling by fulmars (cf. Ratcliffe, 1972), the estimate is an absolute minimum and it may nevertheless represent an important extra form of mortality. It is, however, difficult to assess the significance of this mortality in coastal peregrines t o the U.K. population as a whole.

Summary Since I97 1 four peregrines, Fulco peregrinus, have been received for analysis at Monks

C O N T A M I N A T I O N OF P E R E G R I N E F A L C O N S W I T H O I L 19

Wood Experimental Station. All were coated with an oil-like contamination. Analysis of one specimen indicated that the contamination was not mineral oil, but of recent biological origin. Thin-layer chromatography indicated that the oil was originally mostly triacyl- glycerol and free fatty acid. The fatty acid composition of the contaminating triacylglycerol was different from that of triacylglycerol isolated from the preen gland, but similar to that obtained by experimental weathering of stomach oil from a fulmar, Fulmarus glacialis. Because of the degradation caused by exposure of the contaminating oil on the plumage of the peregrine, the biochemical evidence cannot indicate an unequivocal source for the oil. Available evidence is, however, compatible with the hypothesis of fouling by stomach oil from a fulmar, for which there is also strong circumstantial evidence. The exact circumstances of the oiling are unknown, but the recent nature of the reports is probably a reflection of the increase of the fulmar population of the eastern Atlantic and the associated increase in breeding density in NW Scotland. Although these oilings probably represent a defensive reaction by the fulmar, it is likely that the varying degree of ability among seabirds to produce and eject stomach oil is the result of a combination of selection pressures including feeding ecology, rather than nest defence alone. Oiling by fulmars appears to be a small, but possibly significant, cause of mortality in coastal peregrines.

This work was undertaken whilst the author was employed by the British Antarctic Survey, to whom the author is grateful for permission to carry out the project. Thanks are due to M. C. French, D. J. Jeffries and A. A. Bell for presenting me with the problem, D. M. Stark, K. J. Derret and A. Reese for collecting the peregrine specimens, A. A. Bell for help with the weathering experiment, M. C. French, L. A. Sheppard and R. J. Mellor for the chlorinated hydrocarbon analyses, M. de L. Brooke(Skockho1m)for collecting the samples of fulmar chick stomach oi1,and W. N. Bonner, D. J. Jeffries, D. A. Ratcliffe and M. R. Payne for helpful constructive criticism of the manuscript.

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