ECOGRAPHY 21: 48()-4»3. Copenhagen 1998

Dietary and microtopographical selectivity of Greenlandwhite-fronted geese feeding on Icelandic hayfields

J. N. Kristianseii, A. D. Fox, D. A. Stroud and H. Boyd

Kristiansen. J. N., Fox, A. D. Stroud. D. A., and Boyd, H. 1998. Dietary andmicrotopographical selectivity of Greenland white-fronted geese feeding on Icelandichayfields. - Ecography 21: 480 483.

The feeding ecology of Greenland white-fronted geese Amer albifrons ftaviroslrix wasstudied during .spring staging in Iceland 1997. Geese feeding on Poa pratensedominated hayfields ( > 80% cover) were highly selective, selecting for Deschampsiacaespitosa which comprised only lO'/u of the sward. Geese fed most on the south-fac-ing fringes of Deschampsia tussocks. Subsequent analysis showed that the southernfringes of Deschampsia tussocks supported significantly greater biomass (27% greatermass of green material) and that leaves growing on the southern faces had signifi-cantly higher protein content than those on the northern faces (33.9Vo vs 30.5°/ii)- Itappears that the geese maximise their nutritional intake in spring by selecting thegrass speeies of highest quality and taking the most nutritious parts of the plants.

J. N. Kristiansen and A. D. Fox, The National Environmental Research Institute, Deptof Coastal Zone Ecology. Kalo. Grendvej 12, DK-S4W Ronde, Denmark. - D. A.Stroud, Joint Nature Conservation Committee, Monkstone House, City Road, Peter-borough, U.K. PEI IJY. H. Boyd, Canadian Wildlife Service, Ottawa, ON, CanadaKIA OH3. (Present address of J.N.K.: (Jnkristiansen@zi.ku.dk) Univ. of Copenhagen,Dept of Population Biology, Vniversitetsparken 15, DK-2100 Copenhagen 0 , Den-mark.)

Arctic-nesting geese are relatively large herbivorousbirds which undertake long distance migrations be-tween breeding and wintering areas. Geese are highlyselective when feeding, ehoosing the plant species andorgans with the highest digestibility and nutrient con-tent (e.g. Boudewijn 1984, Madsen and Mortensen1985, Fox 1993). Geese face particular nutritional de-mands during the prelude to migration and breeding,when acquisition of stores of energy (to meet flightcosts and reproductive demands) and nutrients (forinvestment by the female in reproduction) are moreacute than other stages of their life cyele (Owen 1980.Krapu and Reinecke 1992).

Grass forms a major source of food for many north-em goose species in spring, yet not all grass speciesexhibit the same nutrient eontent. nor share similargrowth phenology, espeeially in northern latitudeswhere low ground temperatures restrict spring growth

early in the season. Fox (1993) showed that wherePhleum prutetue was the dominant grass in reseededhayfields in Ieeland, pink-footed geese Anserbrachyrhynchus fed mainly upon this, the speeies withthe highest protein and low crude fibre content. Thesame study demonstrated that over the course of fouror more years, the Phleum pratense component of thesward declined rapidly, as native grasses (especially Poapratense and Deschampsia caespitosa) invaded thehayfields and gradually dominated the sward. Little orno Phleum pratense is present in many hayfields inIceland thai are exploited by geese. What do these geesefeed on there and how do they optimise their intake ofother species of grass, to maximise nutrient acquisition?

Here we report a study of spring staging Greenlandwhite-fronted geese Anser athifrtms flavlrostris in west-ern Iceland, where birds stop for about three weeks enroute to breeding areas in west Greenland from their

Accepted 18 March 1998

Copyright © ECOGRAPHY 1998ISSN 0906-7590Printed in Ireland all rights reserved

480 ECOGRAPHY 2t

wintering areas in Ireland and Britain. Staging geeseaccumulate stores in Iceland in preparation for theironward tnigration across the Denmark Strait and theGreenland ice-cap to ultimate summering areas{Anonymous 1997). The present study describes thefeeding selectivity of Greenland white-fronted geese onhaylield swards and the exploitation of microtopo-graphical features by the geese to maximise their intake.

Study site

The study was carried out at Hvanneyri AgriculturalCollege in Borgafjordur, south-west Iceland (64°34'N,2I°46'W) during 16 April-9 May 1997. The area is awell known spring staging site for Greenland white-fronted geese (Francis and Fox 1987, Fox et al. 1994),comprising some 85 ha of relatively undisturbedhayfields (the college is a hunting free area) in closeproximity to safe roost sites. About 90 fields wereavailable to the geese within the Hvanneyri area, withPoa praten.se, Agrostis sp. and Deschampsia caespitosapredominant. Phleum praiense was the dominant grassin only five of the fields and the majority of feedinggeese exploited fields with httle or no Phleum pratensein the sward. Intensive fieldwork for the present studytook place on field no. 39, a 2.47 ha field whichcomprised mainly Poa I Deschampsia used by up to 94white-fronted geese at any one time in the spring of1997. On two occasions (5 and 8 May) two and fivebarnacle geese Branta leucopsis respectively were seentogether with the white-fronted geese. No other herbi-vores were seen during the study period.

Methods

Sward composition

The sward composition in the field was sampled byrecording the presence and percentage cover of allhigher plant species in 25 randomly placed 10 x 10 cmquadrats. Mean percentage cover was calculated fromall quadrats to give relative frequency of occurrence foreach species.

Diet

Twenty fresh droppings were collected randomly fromthe site, preserved in 70% ethanol and thoroughlymixed before being microscopically analysed followingthe procedure of Owen (1975). To identify plant frag-ments, reference slides were made from the plant spe-cies identified in the field. The relative frequencies ofplant fragments were determined by sampling 100 ran-dom points on each of ten microscope slides. We

compared species occurrence in the diet (d) with itsfrequency in the field (f) using Jacobs' index, D (Jacobs1974) to give an index of selectivity: D = (f-d)/(f+-d — 2fd). The index ranges from — 1 (complete avoid-ance) to -i- 1 (exclusive selection).

Tussock grazing

Once it was recognised the geese seleeted for D. caespi-tosa, thirty tussocks of this species were chosen ran-domly within the field (mean diameter 39.5cm + SE=1.02). From each tussock the number ofleaves (grazed and ungrazed) were counted in a 3 x 3cm square on the northern and southern quadrants ofthe tussocks (i.e. 45° either side of these cardinal points)and the proportion of grazed leaves recorded.

Nutrient content

From ungrazed tussocks green plant material was sam-pled from northern and southern sides and the outer(ca 2 cm) tips of fresh leaves (corresponding to the parttaken by the geese) analysed for nitrogen content usinga NA 1500 nitrogen analyser with leucin as standard.Crude protein was then measured by multiplying N-content by 6.25 (Hodgson 1983). The protein contentwas expressed as percentage of dry weight.

Results

Sward composition and diet

Comparison of plant frequencies in the droppitigs withthose in the sward shows that the geese selected D.caespito.sa and Phleum pratense (Fig. I). Poa pratense,the most abundant species (ca 80% cover) on the field,was avoided despite comprising 50% of material in thedroppings. Alopeeurus sp., Agrostris sp. and Ranunculussp. were all almost completely avoided.

Differences in shoot density

There were significantly more D. eaespitosa (27%)leaves on the southern faces of tussocks (mean 33.6 +1.3 SE 3 x 3 cm~') than the northern faces (mean26.5 + 0.96 SE 3 X 3 em ~ ') (pairwise comparison, t =4.57, DF = 29, p < 0.001).

Nutrient content

Leaf tips on the south-facing parts of D. caespitosatussocks had a significantly higher crude protein con-

ECOGRAPHY 21:5 (1998) 481

tent than those on the northern fringes (south mean33.85%+ 1.48 SE, north mean 30.54%+ 1.07 SE, arc-sine transformed data, pairwise comparison, t = 4.161.DF = 5, p<O.OI).

Tussock grazing

Geese fed more on the southern fringes of tussocks.(79.03%+ 3.77 SE grazed) than on the northernfringes (25.82'Ki + 5.19 SE grazed) (arcsine trans-fomied data, pairwise comparison, t = 8.466, DF — 29.p < 0.001).

Discussion

Fox (1993) showed that the grazing intensity of pink-footed geese in Iceland during spring was highly corre-lated with shoot density of Phleum praiense and thatIhis species had the highest protein content (togetherwith D. caespito.sa} of ail haylield grass speciesanalysed including Poa sp. (Fox 1993). In the studyfield considered here, however. Phleum pratense washighly restricted. The white-fronted geese showed ahigh preference for D. eaespilosa which made out ca3O'yii of the diet. Indeed, the leaf tips of D. caespitosaselected by geese in this study showed even higherlevels of protein content than the Phleum pratenseencountered in the earlier study. Poa praiense. themost abundant plain species in the sward, was activelyavoided although the diet still contained ca 50'yii ofthis species and hence, still might be an importantfood source during spring fattening. It would appearthai D. cae.spitosa offers food of sufficient quality in

Sward and diet composition

Cyp./Junc.

Festuca mbra

Ranunculus sp.

5 Agrostris sp.

J_ Alopecjrus sp

Poa pratense

Deschampsia caespitasa

Phleum pratense

n % in droppings

IS % in sward -1

-0.14

-0.63

0.S6

0.50

60

Percentage

I

80 100

Fig. I. Percentage frequency of phiiit species present in drop-pings (open bars) and llie sward (shaded) of (ield no. 39 alHvanneyri. spring 1997. [Jars indicate means + standard errorSE. ''D = Jacobs index value (see text) wliicli ranges from f 1(exclusive selection) to - I (complete avoidance), Cyp..JLin. =Cy peraeeae/J u ncaceac.

the absence of Phleum pratense which is, in any case,better forage than the abundant Poa pratense (Fox1993). Of course a comparison between sward and dietcould be biased if geese regularly moving betweenfields of different sward composition. However, ourclear impression was that geese usually stayed severaldays on the same field and hence, droppings in thisstudy most certainly were produced by geese from thestudy field. When exploiting I), eae.spirosa, the geeseencounter a plant species that grows in tussocksrather than an open sward and which apparentlyshows asymmetry of growth in terms of both biomassand crude protein. The geese responded to this asym-metry in the tussocks by feeding more intensively onthe southern fringes, avoiding the northern sides andin this way optimising their protein intake. Hence, itwould appear that shifting from one tussock to (henext after having grazed only the southern fringe is astrategy that represents a more profitable strategythan remaining to feed on the whole tussock. Exactlywhat causes this difference in biomass and quality wasnot investigated during the present work, but temper-ature differences between north and south on suchsmall scale tussocks is a phenomenon known to resultfrom the differentia] interception of solar radiation(Hansen 1973), while the prevailing northerly winds atthe study site (unpubl.) may have contributed to suchdifferences in this study. High temperatures will speedup the mineralisation in the soil and, hence, increasethe availabilily of for example nilrogen to the plants(Russell 1973. Lewis 1986). However, leaf growth, ofcourse, is also highly dependent on light intensity(Holmes 1980). Early in the growing season, the lowangle of incident solar radiation probably resulted ingreater light intensities on the soutlicrn fringes of thetussocks (creating higher temperatures and better con-ditions for photosynthesis) than on the northern faces.Eox (1993) showed how geese selected swards at the(ield level, but not on a smaller scale within fields.This study confirms the ability of geese also to makefine-grained foraging choices to maximise nutrient in-take by selecting between different species of food andby exploiting differences in forage quality resultingfrom microtopographic features affecting grassgrowth.

Acknowledgements This study was supporlai by fundingfrom the Becketi foundation. Nordisk Torskerutdun-ningsiikadcmi (NOR FA). Dansk Jagtforeniiigs Ju-bikeunisfoiid, and British Ornithologists" Union to JNK andADF. We acknowledge support of the Canadian WildlifeService to IIB and The Joint Niitiire Conservation Commiteeto DS. We thank Bjorn Thorsteinsson and colleagues Tortheir help and permission to carry out tlie field work atHvanneyri Agriciilturiil College and The Icelandic Inst. ofNational History, and we especially thank Arnoi- Sigfusson.Rikkiird Brynja!lasson and Oli Einarsson for practical help.We sincercl) acknowledge the help of Aime Kirsline Miiller.Hclle B. Fredcriksen and Soren Christcnsen wilh the nitrogenanalysis.

482 ECOCRAPHY 21:5 (1998)

References

Anonymous, 1997. Spring migration of Greenland white-fronted gecsc. Hvanneyri, West Iceland, April-May 1997. -Ibis i39: 127 128.

Boudewijn, T. 1984. The role of digestibility in the selectionof spring feeding sites by brent geese. - Wildfowl 35:97-105.

Fox, A. D. 1993. Pre-nesting feeding selectivity of pink-footedgeese Anser hrachvrhynchus in artificial grasslands. - Ibis135: 417-423.

Fox, A. D. et al. 1994, Greenland white-fronted gcesc inIreland and Britain 1982./83 1993/94. Greenland White-fronted Goose Study Research Rep. no. 8. GWGS/NPWS,Aberystwyth.

Francis, I, S, and Fox. A. D. 1987. Spring migration ofGreenland white-tronted geese through Iceland. Wildfowl38: 7-12,

Hansen, K. 1973. Microthermic observations in arctic vegeta-tion. Medd. om Grsnl., Biosdence 194 (6).

Hodgson, P. 1983. Sward measurement handbook. - BritishGrassland Soc London.

Holmes, W. (ed.) 1980. Cjrass, its production and utilization. -British Grassland Soc. London.

Jacobs, J. 1974. Quantitative measurements of tood selection.- Oeeologia 14: 413-417.

Krapu, G. L. and Reinecke, K. J. 1992. Foraging ecology andnutrition. - In: Batt. B. D. J. et al. (eds), Ecology andmanagement of breeding waterfowl, Univ, of MinnesotaPress, Minneapolis, pp. I 29.

Lewis, O. A. M. 1986. Plants and nitrogen. Studies in biologyno. 166. Edward Arnold.

Madsen, J. and Mortensen, C. E. 1985. Habitat exploitationand interspecific competition of moulting ceese in eastGreenland. - Ibis 129: 25 44.

Owen, M. 1975. An assessment of fecal analysis technique inwaterfowl feeding studies. - J. Wild. Manage. 39: 271-279.

Owen. M, 1980, Wild geese of the world: their life history andand eeology, - B.T. Batsford. London,

Russell. E, W, 1973, Soil conditions and plant growth. -Longman.

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