The behaviour of a wintering flock of Mute Swans Cygnus olor in Southern Ireland

ELIZABETH M. KEANE and JOHN O’HALLORAN

The beha viour o f a wintering urban flock o f Mute Swans was studied o v e r a single winter 1990-91. D a ily and weekly activity patterns were monitored. Sw im m ing was the m ost com ­ m on activity representing 55% o f the time, with feeding and p reen in g being 36% and 15% respectively. The m ost com m on feeding strategies were bread feeding, surface feeding and feeding with neck submerged. Patterns o f daily activity differed from those o f oth er published studies, feeding increased significantly throughout the day, but the rate o f feeding o v e r the study p e riod did n ot vary. When data fo r Saturdays and Sundays were om itted (th e tim e o f m ost bread p ro vis io n in g), a different pattern o f bread feeding by swans was observed.

T h e M ute Swan Cygnus o lo r is the m ost fam iliar w ild fow l sp ecies in Ireland. It is w idespread, nesting throughout the coun­ try excep t w h ere land exceed s 300 m (H utchinson 1989). Little is known about its ecology, though recen tly som e data have been rep o rted fo r tw o Irish b reeding flocks (C ollins 1991, Sm iddy & O’Halloran 1991). Population estim ates v a ry betw een 5000-7000 individuals (Hutchinson 1979, M onval & P irot 1989), and a large p ro p or­ tion is con cen trated in urban inland and coastal w aters as in the United Kingdom . M any flocks o f non-breeding swans, con ­ gregating in such urban areas, are at least partially depen den t on humans for food (H utchinson 1979, Birkhead & Perrins 1986). Sears (1989) com p ared the feedin g b ehaviou r of M ute Swans in four habitats within the low lands o f the Tham es v alley and d escrib ed th eir utilisation o f bread. O ther studies have con cen trated on swans feedin g in tidal, brackish and saltmarsh areas (G illham 1956, Sparck 1958, Berglund et al. 1963, M athiasson 1973), but com ­ m ented little on the role o f bread in the d iet o f M ute Swans. This present study set out to d escrib e the diurnal and w eek ly activity/feeding pattern of a w in terin g flock of urban swans at Cork Lough, southern Ireland o v e r a single winter. 12 W ild fo w l 43 (1 9 9 2 ): 12-19

Study area A single flock c om p osed of immature, non­ breed in g and p ost breed in g adults was studied at Cork Lough, a freshw ater lake (6.1 ha in size), during the w in ter of 199091. T h e re is an alm ost com p lete absence of aquatic v egetation (K e lly 1985). Mute Swans and oth er w ild fow l sp ecies largely rely on feed in g by man. In the cen tre o f the lake th ere is a large island, w h ere w ater­ fow l roo s t and breed. T h e perim eter of the lake has grassland w hich is grazed by the w aterfow l o r m owed.

Data collection Data w e re colle c te d using tw o m ethods: scan sam pling and focal bird sam pling after Sears (1989). O bservations w ere m ade from dawn to dusk. 1) Scan sam­ pling: ob servation s w ere m ade on the flock e v e ry ten minutes throughout the day. Th e total num ber o f birds and the p rop ortion in vo lved in a range o f activities w ere record ed . 2) Focal bird sampling: uniquely ringed ( ‘D arvic’ rin gs) swans w ere ob s e rv e d continuously for a p eriod of about 20 minutes. During this time, the ty p e and duration of a c tivity was reco rd ed

M u te Swans in Ire la n d and the p ro p ortion of ob servation tim e spent in each a c tivity was calculated. All focal birds w ere chosen at random and w e re a sam ple of m ixed ages and sexes.

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the grass. 6) Walking: 7) Begging: (actively demanding food from peop le).

Analysis Activity types Eight types of activity w ere distinguished: l)F eeding: this could be subdivided into six categories: a ) feeding on bread (all other feeding activities excluded bread), b ) graz­ ing. c ) surface feeding, d ) head submerged, e ) neck subm erged and f) upending. 2) Swimming: 3) Preening: 4) Flying: 5) Resting: either on the w ater surface with neck under wing or in a similar posture on

T h e overall pattern of activity for the flock and focal birds was analysed to com pare these tw o m ethods of sam pling and to illus­ trate their activity and feeding strategy (see Figs 1 and 2). A separate tim e activity pat­ tern was determ ined for each period of observation based on the prop ortion of the flock engaged in each activity at the tim e of the scan: a standard ethological p rotocol for tim e budget analysis Altmann (1974). For investigation of diurnal and w eekly

F igure 1. C o m parison o f m ean (± s.e.) activity b u d g e ts fo r flock a n d focal Mute Sw ans. (538 scan o b s e r v a tio n s o f th e w h o le flock. Focal bird s 400 m in u tes o b s e rv a tio n , o n 20 sw a n s).

50 ■

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Scan ob servations of w hole flock n = 538 scans

EH

Focal sw ans n = 400 mins

a)

£ a> a>

ro

+■» c a> o i»



i Surface feeding

head submerged

neck submerged

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upending

Figu re 2. C o m parison o f m ean (± ) fe e d in g activity b u d g e ts fo r flock a n d focal Mute Sw ans. (538 sca n o b s e r v a tio n s o f th e w h o le flock, F ocal b ird s 400 m in u tes o b s e rv a tio n , o n 20 sw a n s).

grazing

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M u te Swans in Irela n d

T a b le 1. D etails o f the n u m b e r o f scan o b serv ation s o f a w h o le flock o f Mute S w an s o v e r 41 d a y s o f the study (17 d a ys in N o v em b e r; 15 d a y s in D ecem ber; an d 9 d a y s in J a n u ary).

Scans (n )

0

1

2

3

16

59

70

91

H ours s in ce daw n 4 5 53

activity patterns, the proportions of tim e spent in each activity w ere calculated as a mean of all observation periods grouped over that tim e interval. This approach was used in order to reduce bias in the data col­ lection and to ensure independence of the activity data (Bryant & Tatner 1988). Statis­ tical analysis, involving analysis of variance (follow in g arcsine transformation, after Snedecor & Cochran 1967) was carried out using Minitab (Pennsylvania State Universi­ ty ) (Ryan, Joiner & Ryan 1985).

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6

7

8

9

10

51

66

58

27

3

D iurnal a ctivity patterns T h e m ean percen tage tim e spent feeding, swim m ing and preening by M ute Swans varied during the day (feedin g: F = 7.34, df = 9, P