I I I I I I I I I I I I I I I I I I I I' I

NESTING DISTRIBUTION AND NESTING SUCCESS OF EIDERS ON

FORVIE NATIONAL NATURE RESERVE 2001

Report No. F01 LF15

For further information on this report please contact:

Alison Matheson Scottish Natural Heritage Forvie National Nature Reserve Stevenson Forvie Centre Little Collieston Croft Collieston, Ellon, Aberdeenshire AB418RU

This report should be quoted as:

Patterson, I.J., Aubry, A. & Thorpe, A.W., (2001) Nesting Distribution & Nesting Success of Eiders on Forvie National Nature Reserve 2001 Scottish Natural Heritage Report No. F01 LF15 (Unpublished report).

This report or any part of it should not be reproduced without the permission of Scottish Natural Heritage which will not be unreasonably withheld. The views expressed by the author(s) of this report should not be taken as the views and policies of Scottish Natural Heritage. © Scottish Natural Heritage 2002.

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SCOTTISH NATURA,L HERITAGE

[~~~]

COMMISSIONED REPORT

Summary NESTING DISTRIBUTION AND NESTING SUCCESS OF EIDERS ON FORVIE NATIONAL NATURE RESERVE 2001 Report No: F01 LF15 Contractor: University Of Aberdeen

BACKGROUND

Forvie NNR has a nationally important population of breeding eider duck. Research was commissioned to monitor the eider population as part of annual research. The aim of the 2001 study was to continue the monitoring of the nesting distribution of eiders on Forvie NNR and to measure nesting success, following a continuation of the programme of predator control which was started in 1995 and other SNH management eg the use of an electric fence to discourage foxes from entering the main nesting area.

MAIN FINDINGS

• The eiders' nesting distribution remained similar to that in previous years although the increase in density in the southern part of the reserve from 1999 to 2000 was reversed in 2001.

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• Laying was about one week later than in 2000 and mean clutch size decreased significantly lower from 4.06 in 2000 to 3.57 in 2001, the second consecutive year of decreased clutch size.

• Overall nesting success in the surveyed sample of nests was 41.5%,a non significant decrease from 48.8% in 2000. Success in the main Estuary-side nesting area also decreased, from 54.9% in 2000 to 43.1% in 2001':

• The mean number of fox tracks found on the transects was higher than in 20001, but the number of badger tracks decreased. Crow and gull numbers were again highest late in the season, rather than while the eiders were laying. The observed rate of nest predation (0.71 per hour) was the only slightly higher than in 2000 (0.65 per hour).

For further information on this project contact Alison Matheson, Area Officer, Forvie NNR, Little Collieston Croft, Collieston, Aberdeenshire, AB41 8RU Tel: 01358 751330

For further information on the SNH Research & Technical Support Programme contact The Co-ordination group; AdviSOry Services, 2 Anderson Place, Edinburgh~ Tel: 0131 446 2400

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NESTING DISTRIBUTION AND NESTING

SUCCESS OF EIDERS ON FORVIE

NATIONAL NATURE RESERVE, 2001

A report to S.N.H

1.1. Patterson, A. Aubry and A. W. Thorpe

Culterty Field Station, N ewburgh, Aberdeenshire

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NESTING DISTRIBUTION AND NESTING SUCCESS OF

EIDERS ON FORVIE NATIONAL NATURE RESERVE, 2001

1.1. Patterson, A. Aubry and A.W. Thorpe

Culterty Field Station, Newburgh, Aberdeenshire

SUMMARY

The aim of the 2001 study was to continue the monitoring of the nesting distribution

of eiders on Forvie NNR and to measure nesting success, following the continuation

of the programme of predator control started in 1995.

The eiders' nesting distribution remained similar to that of previous years, although

the increase in density in the southern part of the reserve from 1999 to 2000 was

reversed in 2001.

Laying was about one week later than in 2000 and mean clutch size decreased

significantly from 4.06 in 2000 to 3.57 in 2001, the second consecutive year of

decreased clutch size.

Overall nesting success in the surveyed sample of nests was 41.5%, a non significant

decrease from 48.8% in 2000. Success in the main Estuary-side nesting area also

decreased, from 54.9% in 2000 to 43.1 % in 2001.

The mean number of fox tracks found on the transects was higher than in 2000, but

the number of badger tracks decreased. Crow and gull numbers were again highest

late in the season, rather than when the eiders were laying. The observed rate of nest

predation (0.71 per hour) was only slightly higher than in 2000 (0.65 per hour).

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CONTENTS

Page

Introduction ........................................................................................... 2

Objectives .............................................................................................. 3

Methods

Study areas and transects .............................................................. 4

Nesting success ............................................................................. 6

Fox activity ................................................................................... 6

Bird predators .................... , ........................................................... 7

Statistical analysis ......................................................................... 8

Results

Nesting distribution ....................................................................... 8

Laying and clutch size ............................................ , ................... ,. 9

Nesting success ............................ , .............................................. 10

Causes of loss .............................................................................. 12

Discussion

Nest distribution and density ...... '" ............................................. 15

Laying and clutch size ................................................................ 16

Nesting success ........................................................................... 16

Predators and predation .............................................................. 17

Signs at predated nests ... , ............................................................ 19

Recommendations ........................................................... ' .................... 19

References ........................................................................................... 21

Appendices .......................................................................................... 23

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INTRODUCTION

A survey of eider duck Somateria mollissima nesting distribution and

nesting success on F orvie National Nature Reserve, Grampian in 1993

(Patterson and Laing 1993) concluded that the birds' distribution had

contracted dramatically since 1963, with most of the nests concentrated

(at much higher density than formerly) in a small area adjacent to the

Ythan estuary. Only 19.5% of the nests in that year and only 1% in 1994

succeeded in producing ducklings, with most eggs apparently taken by

herring gulls Larus argentatus, great black-backed gulls Larus marinus

and crows Corvus corone. Disturbance and predation by foxes Vulpes

vulpes were also thought to be important in the contraction of range and

in nest losses, the latter both by direct predation and by flushing

incubating eiders, leaving their nests vulnerable to subsequent bird

predation.

In response to the decline in the breeding success of eiders, SNH

implemented a successful programme of predator control in 1994/95.

This involved fox removal and partial protection of the estuary-side eider

nesting area by means of an electric fence around three sides leaving open

only the eiders' access to the estuary. An additional electric fence was

erected around part of the nesting area at the Point in 1999. Crows and

gulls were controlled in the same area by trapping and shooting, from

March to June.

Nesting success increased greatly in 1995, with 61 % of nests succeeding

in hatching ducklings, a rate close to the mean of 69% recorded in 1961-

1979. Following this encouraging result, the programme of predator

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control has been continued. The assessment of the effectiveness of

predator control in improving eider nesting success was complicated in

1996 by the late arrival and apparent poor condition of the eiders at the

start of the breeding season, possibly as a consequence of food shortage

on the wintering grounds. Overall nesting success was only 35.4%,

compared to 58.9% in 1995, at least partly as a result of the birds' poor

condition. However, success improved only slightly, to 38% in 1997

even though the eiders appeared to be in good physical condition.

Improved predator-control procedures were implemented in 1998 and

overall nesting success increased to 46% that year and to 62% in 1999.

Additional protection, involving the use of repellents, was introduced in

1999 and was continued in 2000, when success was 49%.

A detailed study of nesting, including laying dates and clutch sizes as

well as hatching success, was carried out in 2001 by Am'elie Aubry, to

compare nesting with that in 1996-2000. The results of the study are

incorporated into this report.

OBJECTIVES

a) to repeat the survey of the eiders' nesting distribution on Forvie, so as

to detect any extension of range;

b) to measure nesting success throughout the distribution, including a

detailed study of laying date and clutch size in the Estuary-side area;

c) to identify, as far as possible, causes of nest loss, and

d) to assess the success of the predator control measures, by monitoring

the activity of foxes, crows and gulls.

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METHODS

1. Study areas and transects

The detailed study of nesting was carried out on eight north-south

transect lines in the high density Estuary-side area surveyed in the

previous years' studies (Figure 1). The transects were visited twice

each week, at three or four day intervals, and a Srn-wide band (2.5m

one each side of the line) was searched for nests, which were marked

by short labelled canes placed on the line. In nests which were found

while the female was still laying, the date of the first egg could be

determined from the known laying rate of one egg per day, with two

days between the first and second eggs (Milne 1963). Final clutch

sizes were established by lifting incubating females gently with the

end of a cane until the eggs could be counted. The nests were then

left undisturbed until after hatching or predation had occurred.

To carry out the general survey of nesting distribution and success,

the transect lines established in 1994 were surveyed again in iate June

2001 (Figures 1 and 2), using exactly the same methods (Appendix

1). However, the area north of the Waterside to Rockend Path was

excluded, since very few nests had been found there in earlier years.

The Sand Cliff area (Figure 3) and 0.25 ha around the Stone Circles

(Figure 1) were included again, as were the areas surveyed for the

first time in 1995; the marsh beside the grassy car park, the mouse-

trapping grid in the valley south of the Waterside-Rockend Path and a

0.45 ha area near the south tip of the reserve (Figure 3). The latter

area was close to nesting terns in late June, so to avoid disturbance,

the survey here was delayed until early August. By this time,

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decomposition of the nest material and growth of the vegetation made

assessments of down, shell fragments and cover unreliable and not

comparable with other areas.

The nesting habitat used by the eiders was investigated in 2001. In the

Estuary-side study area, the nests were situated within three different

habitats; heath, grass or gorse. Since there were few nests in gorse (4

out of 13 7 nests), they were omitted from the investigation. For the

remainder, the habitat type within one metre of the nest was recorded.

F or nests where there was a mixture between grass (or moss) and

heath (8 nests), the predominant type was determined.

To test whether eiders tend to nest in one particular habitat, it was

necessary to compare the number of nests found in heath and grass

with the actual availability of these habitat types on the transects. The

habitats along the five of the eight transects in the Estuary-side area

were surveyed; transects 1, 7 and 8 were omitted, since differences in

habitat preference could have been associated with other factors

(transect 1 lies close to a walking path, while transects 7 and 8 are

located on higher dunes and mostly outside the electric fence; Figure

2). The number of (lm) steps made on grass (or moss) and those on

heath, in a strip 1 m wide, were recorded. This procedure estimated

the relative abundance of the two habitats; grass was found on 62 %

of the area. The expected number of nests in each habitat was then

calculated, assuming it to be proportional to the area covered by that

habitat.

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2. Nesting success

On the general survey, the outcome of each nest was determined by

using the same criteria ( down and shells) as in previous years

(Appendix 2). Any nests which still had sitting females at the time of

the survey were located with the GPS (east-west transects and mouse

grid) or were marked with labelled pieces of white adhesive tape

attached to short canes (Sand Cliff) and were re-visited later to

determine whether the eggs had hatched.

The success of nests in heath habitat was compared with that of nests

III grass.

3. Fox activity

The same two bands for fox tracking which were established across

the reserve in 1995 were surveyed again in 2001. The transect just

north of the north pebble beach tern colony, established in 1997, was

again not visited to avoid disturbance to the terns. Each tracking band

was surveyed on three consecutive mornings (Wednesday to Friday;

one by SNH staff) each week from 19 April to 29 June, if the weather

conditions were suitable. In some weeks, tracking was possible on

only one or two days. The aim on the first day was to find and mark

all existing fox tracks, so that new ones could be distinguished on the

subsequent days. However, in practice, preceding wind or rain

sometimes allowed fresh tracks to be distinguished and counted on

the first day.

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The fox tracks found were plotted on copies of a map derived from

aerial photographs of the dunes, with the transects plotted by GPS,

and were counted as separate tracks unless two or more similar ones

were close together, clearly linked and obviously made by the same

animal moving around a small area. Any distinguishing features (eg a

dragging foot) were noted, to help in estimating the number of

different foxes present. The mean number of separate tracks

encountered per morning was calculated for each week's tracking

days.

4. Bird predators

Counts of gulls and corvids and observations of their predation on

eider nests were carried out at least twice per week from a hide on a

vantage point on the high ridge to the east of the Estuary-side nesting

area (Figure 2) each week from 23 April to 29 June. The number of

bird predators present was counted every 15 minutes' for 2h

observation periods, starting usually in mid-morning. Counts were

subdivided into four zones; 1, south of the heather Calluna vulgaris

area; 2, the main, high-density nesting area in the south third of the

Estuary-side nesting area; 3, the middle third and 4, the north third of

the nesting area.

Throughout the observation periods, a watch was kept for any

instances of nest predation anywhere in the estuary-side nesting area.

The species and numbers of bird predators involved in each incident

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and those which consumed eggs were recorded and the species which

found the nest was identified where possible.

5. Statistical analysis

The statistical significance of apparent variations in clutch size

between different periods in the season was tested by Analysis of

Variance. Apparent differences in proportion (eg of nesting success

in different areas) were tested by X2 tests. Apparent correlations (eg

number of nests lost with number of predators) were tested with

Pearson's correlation tests. When data were found not to be normally

distributed, by an Anderson-Darling test, equivalent non-parametric

statistics (Mann-Whitney or Spearman rank correlation) were used.

RESULTS

1. Nesting distribution

As in 2000, the area of the reserve North of the Waterside to Rockend

path (Figure 1) was not searched in 2001, since only a few nests had

been found there in recent years.

The number of nests found in the 4.35 km (2.17 ha) of transect south

of the path decreased from 12 in 2000 to 4 in 2001 (Table 1),

equivalent to a decrease in density from 5.52 to 1.84 nests per ha.

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In contrast, the overall density in the Estuary-side study area was

similar to that in 2000, increasing only slightly, from 69.2 nests per ha

in 2000 to 71.4 per ha in 2001 (Table 2), a value similar to the density

found in 1998. The density in each separate lOOm zone varied from

12.5 to 223 nests per ha (Table 2). For the three densest lOOm

sections (section 300 of transect 3, sections 400 of transects 5 and 6,

all in the area of thickest heather), the mean number of nests per

hectare was the highest recorded since the beginning of the study; 360

nests per ha (compared to 340 per ha in 1999 and 320 per ha in 2000).

Nest numbers at the Point, Sand Cliff and Stone Circles (Figure 3)

decreased from 2000 to 2001 (Table 3), but numbers remained similar

in the Valley and increased slightly in the Marsh.

2. Laying and clutch size

The first clutch, of five eggs, was found on 4 May 2001. A

subsequent visit to the nest on 8 May showed that this was the final

clutch size, so that the first egg had been laid on or before 29 April

2001, later than the estimated first laying dates of 21 April in 2000

and 23 April in 1999. Two other nests were found with eggs on 4

May but these were subsequently predated by 8 May. The last clutch

was found in the week starting 17 June.

Most clutches on the Estuary-side study area were started between 6

May and 26 May (Table 4), later than in 2000 (between 29 April and

12 May) and in 1999.

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Most clutches were of four eggs (Table 5), with later clutches (after

20 May) significantly smaller than earlier ones (Table 4). The overall

mean clutch size of3.57 eggs in 2001 was significantly lower than the

mean of 4.06 recorded in 2000 (Table 5).

3. Nesting success

Hatching success

Overall nesting success, in all of the survey samples combined (Table

6), was 41.5% (N = 311 nests), a slight (and just non-significant)

decrease from 48.8 % in 2000 (X2 = 3.552, P = 0.059). The Sand Cliff

area showed a considerable and significant decrease in success, from

48.7 % in 2000 to 6.9 % in 2001, and success on the Estuary-side area

dropped from 54.9 % to 43.07 % (X2 = 3.774, P = 0.052). The nests at

the Point had similar success in the two years. South F orvie' s nesting

success was still very low, with only 4 % of nests hatched, but was

better than the complete failure of the 33 nests recorded there in 2000.

In 2001, each of the study areas was significantly different from each

of the others, apart from Sand Cliff and South Forvie, which had

similar low success (Table 6). The highest nesting success was found

at the Point, due largely to significantly higher success inside the

electric fence (65% hatched among 60 nests) than outside it (46.7%,

also among 60 nests; X2 = 4.089, P = 0.043)

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Success in relation to the laying week

In contrast to previous years, nests found in the first part of the season

(before 19 May 2001) were not significantly more successful. than

those found after 20 May (44.6 % of 56 nests compared'to 34 % of 79

nests; X2 = 0.110, P = 0.740). However, nests found before 19 May

were significantly more successful than those found in the latest part

of the season, after 27 May (21.6 % of 37 nests; X2 = 5.158, P =

0.023). As in 2000, the very earliest nests (found up to 12 May 2001)

seemed to be less successful than those found in the two subsequent

weeks (44.0% of 25 nests vs 53.4% of 73 nests) but the apparent

difference was not significant (X2 = 0.662, P = 0.416).

Success in relation to habitat

Nesting success for 109 nests in heath was 45.9%, compared to only

26.1 % for 23 nests in grass, but the apparent difference was not quite

significant (X2 = 3.044, P = 0.081). However, in spite of this, m,any

more nests were found in heath (95 compared to an expected 43)

compared to grass (17 compared to an expected 69; X2 = 51.036, P <

0.001)

Unlike in 2000 (but as in 1999), nests in the Estuary-side study area

with no cover were significantly less successful than those with cover

(Table 12).

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4. Causes of loss

Fox activity

The overall mean number of fresh fox tracks crossmg the sandy

transect line per night in 2001 (6.5) was higher than in 2000 (4.5), in

1999 (4.5) and in 1998 (3.4). However, it does not seem appropriate

to make any statistical analysis amongst years because the observation

of tracks depends on the weather conditions, which can vary

considerably from one year to another.

There was considerable variation on the number of fox tracks

throughout the season (Table 8), ranging from 14 tracks in the week

beginning on 29 April to only two tracks in the week beginning on 27

May. The number of tracks was lowest during the second half of May

but increased again at the beginning of June. Badger tracks were

found on only five of the 17 tracking sessions, a considerable

reduction on the frequency in 2000, when badger tracks were found

on most days.

Eight female eiders were found killed by predators in the Estuary-side

study area, a considerable reduction from the 19 found in 2000. Only

one of these birds had leg rings, in contrast to 2000, when 420/0 of the

dead birds had rings. Six of the birds found in 2001 were checked for

fox scent, but only one of them had a faint trace. The predator

concerned was clearly a large one, since some skeletal parts had been

bitten right through. Several freshly-dead bodies were examined for

mammal hairs, but all of those examined under the microscope were

rabbit ones, presumably picked up from the vegetation.

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Bird predators

The number of bird predators hunting in the Estuary-side study area

varied considerably through the season (Table 9). Numbers were not

highest during the peak of eider egg-laying period (6 May to 26 May;

Table 4), but increased later in the season, as in 2000.

In 2001, the mean numbers of bird predators were lower than in 2000.

The mean of the three highest weekly mean values decreased from 4.8

to 3.3 for crows and from 4.9 to 1.7 for gulls.

Gulls were the least frequent predators in the area, with a mean count

of more than one bird only at the end of May. Crow numbers

fluctuated around two to four birds per observation. As in previous

years, no rooks were seen until after the eiders started to lay. Rook

numbers were lower than in 2000, with more than five birds per count

only during two weeks and a peak in the week beginning on "10 June,

whereas in 2000 there were more than five birds per count from the

beginning of June until the end of the eider breeding season.

Eider nests were seen being attacked by bird predators during 10 out

of 20 two-hour observation periods from 26 April to 29 June, at a

mean rate of 0.71 nests lost per hour (Table 9), higher than in 2000

(0.65 per hour) and 1999 (0.64) but lower than in 1998 (1.03).

As in prevIOUS years, the mean weekly rate of loss was not

significantly correlated with either the mean or maximum numbers of

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bird predators (Spearman's rank-order correlations; r < 0.57 and p >

0.08 in all cases), presumably because the latter were highest later in

the season when the observed rate of predation was low (Table 9).

Signs at failed nests

Time of nest failure was judged by the amount of down in failed nests

(Appendix 2). For the Estuary-side study area and Sand Cliff, there

were more nests with a full amount of down than without down

(Table 7), showing that they had failed late in the laying period,

whereas at South F orvie, the commonest category was without down.

There was no significant difference between 2000 and 2001 in the

amount of down in predated nests (Table 7). However, when

comparing 1999 and 2001, it appears that predated nests in 2001

tended to have more down in them (X2 = 8.380, P = 0.015).

In the Estuary-side area, predated nests which were more than 200m

from the shore (measured from the middle of the 50m section at right

angles to the high tide mark) were significantly more likely to have a

full complement of down (as opposed to little or none), compared to

nests closer to the shore (54.2% of24 nests compared to 26.40/0 of 53; 2 X = 5.588, P = 0.018).

The overall mean percentage of failed nests which had shell fragments

in them in 2001 (39.40/0) was not significantly different to 2000

(31.8%; Table 10), despite the increase at the Sand Cliff (from 0 % to

26.9 %). In 2001, there was (as in 2000) significant variation between

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areas (Table 10), with a higher percentage of nests with shell

fragments in the Estuary-side area than the other two areas.

There was no significant difference between failed nests with different

amount of down in the proportion which had shells in them (Table

11). The proportion of nests with shell fragments, in relation to the

amount of down, was similar to that found in 2000.

DISCUSSION

1. Nest distribution and density

There was no consistent pattern of change in eider nesting distribution

and density between 2000 and 2001. The increase in nest density on

the east-west transects across the south part of the reserve recorded in

2000 was reversed in 2001, although there was no change between

2000 and 2001 in the central valley (Grid area). Similarly, the

decreases at the Point and Sand Cliff contrasted with no change in the

main Estuary-side nesting area. Overall, the picture was one of little

overall change, so the suggestion of an extension of range in 2000 was

not maintained.

As in previous years, an estimate of the minimum number of eider

nests on the reserve can be made from the surveys, since the transects

covered a known proportion of the area. The east-west transects south

of the Waterside to Rockend path surveyed 5m in every 250m (2% of

the area), so the four nests found there represented 200 nests in the

whole area. Similarly, since the Estuary-side transects covered 5m in

every 50m (10%), the 137 nests found there represented a total of

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1,370. The 29 nests at the Sand Cliff, the eight nests in the Marsh and

the 120 nests at the Point bring the total of known and estimated nests

to 1,727, a decrease of 18.2% from the 2000 estimate of 2, 111

(Patters on et al. 2000). This decrease resulted mainly from a drop of

400 in the estimated number of nests in the southern part of the

reserve generally.

2. Laying and clutch size

The later onset of laying in 200 1 (about one week later than in 2000),

together with the significantly smaller mean clutch size (3.57

compared to 4.06), suggests that the birds were again in poor

condition. The relatively late arrival of the bulk of the population,

three weeks later than in 2000 (Patterson and Thorpe 2001) tends to

confirm this possibility. Clutch size has now decreased for the second

year in succession, from a mean of 4.41 in 1999.

3. Nesting success

The decline in nesting success from 48.8% in 2000 to 41.5% in 2001,

although non significant, may have been associated with poorer

condition of the females (section 2, above) There was no increase in

the number of birds found killed by predators (below) and there were

fewer bird predators. However, the occurrence of dry periods during

the season may have forced females to leave their nests to drink and

so make their clutches vulnerable to bird predators. As in 2000, many

failed nests had a full complement of down, showing that they had

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been lost during the incubation period, when the nests are normally

secure from predation, provided that the female remains on the nest.

The total number of ducklings hatched on the reserve, estimated from

the calculated number of nests in each area (Section 1, above), the

measured success in each area (Table 6) and the mean clutch size

(from the Estuary-side area (Table 5), assumed to be the same

elsewhere), was 2,383, of which 2,108 (88.5%) were estimated to

have hatched in the Estuary-side area. These totals were considerably

lower than those in 2000 (3,346 and 2,964 respectively) and show a

second consecutive year of decrease. Mortality (of about 96%) after

leaving the nest reduced the estimated 2,383 ducklings which hatched

in 2001 to 143 which survived to fledge (Patterson and Thorpe 2001).

4. Predation and predators

F ox activity

The mean number of fresh fox tracks crossing the transect route in

2001 (6.5) increased considerably from the 4.5 recorded in 2000 and

was almost twice the value in 1999 (3.4). This was associated with

low success of fox control measures (Appendix 4), with only two

adults shot before the end of June, one of them in the far north of the

reserve.

In spite of the increase in the number of fox tracks, the number of

eiders found killed in the Estuary-side study area decreased from 19 in

2000 to eight in 2001. This may suggest (along with the virtual

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absence of fox scent on the bodies), that badgers may have been

involved in the predation.

Bird predation

The decrease in the number of crows counted in the Estuary-side

study area (Table 9) corresponded with an increase in the number

removed by shooting and trapping (59 in 2001 compared to 20 in

2000; Appendix 3). However, the more dramatic decline in the

number of gulls counted cannot be explained in this way, since the

number removed was slightly lower in 2001 than in 2000 (seven

compared to nine). It may be that the number of gulls foraging for

eider nests depends on feeding conditions elsewhere, but it is also

possible that the control measures are gradually removing eider nest

specialists.

The persistence of high numbers of crows and gulls until late in the

eiders' nesting season, similar to the situation in 2000, but unlike the

pattern in earlier years, may be related to the availability of some

nests late in their incubation periods (see below).

The estimated number of nests lost to bird predators, calculated by

applying the mean rate of nest losses (0.71 per hour) to an average 18

hour day for the seven weeks when predation was observed, was 630

nests. This estimate was lower than the 780 calculated from losses on

the transects (78 nests lost in a 10% sample of the area). However,

the two estimates are of a similar order, suggesting that bird predation

can account for most of the recorded losses.

19

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5. Signs at predated nests

The percentage of failed nests which had a full complement of down

(41.5%) remained similar to the value recorded in 2000 (40.5%),

suggesting again that females were leaving their nests, presumably to

drink, during the incubation period. This possibility is supported by

the finding that down was significantly more frequent in failed nests

that were furthest from the estuary, which would presumable have to

be left unattended for longer periods.

Failed nests in the Estuary-side area were again more likely to have

shell fragments left behind (Table 10), suggesting breakage in the

nest, consistent with the suggestion (above) that most losses can be

accounted for by bird predation.

RECOMMENDATIONS

The effectiveness of crow control improved considerably in 2001,

with the removal of about three times as many birds, so it would seem

desirable to maintain the same programme and timetable in 2002.

It is clear, however, that the existing fox control programme is

becoming less effective, possibly because experienced resident foxes

have learnt to avoid the operatives' lights and vehicles. It is difficult

to make recommendations other than those that have been made in

previous reports (Patterson et al. 1997, 1998 and 1999), which

20

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suggested strongly that new approaches to fox control should be

considered.

In 2001, there was continued suspicion that badgers might be involved

in predation in the Estuary-side area, in that a decrease in the number

of dead eiders was associated with a decline in the number of badger

tracks but did not correspond with the recorded increase in the

frequency of fox tracks. There was also little evidence of fox scent on

or near the bodies. A detailed survey of badger setts and the animals'

numbers and activity on Forvie would be very valuable. It is also

recommended that the use of electrified netting instead of tape should

be considered for the fence around the Estuary-side nesting area, since

mesh would be more effective than tape against badgers.

Since, as in 2000, the eiders which nested within the electric fence at

the Point were significantly more successful than those nesting

outside, it is recommended that this fencing be continued in 2002.

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REFERENCES

Baillie, S.R. 1981. Population Dynamics of the Eider (Somateria

mollissima) in North-east Scotland. PhD thesis, Aberdeen University.

Milne, H. 1963. Seasonal Distribution and Breeding Biology of the

Eider, So materia mollissima mollissima L., in the North-east of

Scotland. PhD thesis, Aberdeen University.

Milne, H. 1974. Breeding numbers and reproductive rate of eiders at the

Sands of Forvie National Nature Reserve, Scotland. Ibis 116: 135-

154.

Patterson, I.1. and Laing, R.M. 1993. Nesting distribution and nesting

success of eiders on Forvie National Nature Reserve, 1993. Report to

SNH.

Patterson, I.J. and Laing, R.M. 1994. Nesting distribution and nesting

success of eiders on Forvie National Nature Reserve, 1994. Report to

SNH.

Patterson, I.J., Kantola, P.S., Oldfield, S. and Cosgrove, P.J. 1997.

Nesting distribution and nesting success of eiders on Forvie National

Nature Reserve 1997. Report to SNH.

Patterson, I.1., Smits, M.1.A. and Cosgrove, P.J. 1998. Nesting

distribution and nesting success of eiders on Forvie National Nature

Reserve 1998. Report to SNH.

22

I I I I I I I , I I I I I I I I I

,I ! ;, I " U i'

I I

Patterson, 1.1., March, A. and Thorpe, A.W. 1999. Nesting distribution

and nesting success of eiders on Forvie National Nature Reserve

1999. Report to SNH.

Patterson, I.J., Shortridge, R. and Thorpe, A.W. 2000. Nesting

distribution and nesting success of eiders on Forvie National Nature

Reserve 2000. Report to SNH.

Patterson, 1.1. and Thorpe, A.W. 2001. The eider population of the

Ythan Estuary and Forvie National Nature Reserve, 2000. Report to

SNH.

23

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I I I I I I I I I I I I I I I I

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Appendix 1. Methods used to establish study areas and transects

Transects were set up between OS grid co-ordinates, usmg a Global

Position System (GPS), and the end-points were marked with wooden

stakes; the GPS methodology is described in detail in Patterson and Laing

(1994). Separate sets oftransects were used on, a) the reserve as a whole

and b) in the small area near the estuary which had a high nest density.

~

Transects over the reserve were established along east-west grid lines, at

500m intervals to the north of OS NK270 (Waterside to Hackley Bay)

and at 250m intervals from this line southward to the north end of the

mobile sand area at NK 244 (Figure 1 ).. Since detailed pegging-out of

transects up to 2.27 km long would have been very time-consuming, the

transect lines were followed by using the GPS. In almost all cases, the

line ended within 5m of the end marker stake, suggesting that the method

was adequate to ensure consecutive years' transects would sample the

same narrow bands of the reserve.

Transects in the Estuary-side nesting area were laid out at 50m intervals,

parallel to north-south grid lines (Figure 2). Such transects covered the

whole area systematically and confined disturbance to the narrow bands

being searched. Each transect line was defined by a 50m measuring line

stretched between adjacent marker canes. The first of these was located

at a precise right angle to the baseline by using a theodolite; subsequent

canes were placed by sighting on the first one and the marked starting

point on the baseline. An additional strip along a Sand Cliff on the edge

of the estuary, a mouse-trapping grid in the main dune slack, an area near

24

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I I ,I I ,I I I I I I I I I I I I I I I 'I

the southern tip of the reserve and a square of 0.25 ha around the Stone

Circles (Figure 1), were also surveyed.

On each transect, a 5m-wide band (2.5 on either side of the line) was

searched carefully for eider nests. The Sand Cliff area, mouse grid and

the 0.25 ha square were also divided into 5m-wide strips.

The positions of nests, in terms of their distances along the transect, were

recorded to allow subsequent measurement of nest density in different

parts of the area. The cover over each nest was also noted, using the

same scale as in 1993, from 0 for exposed sites to 5 for completely

hidden ones (Patters on and Laing 1993).

25

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Appendix 2. Criteria used to determine success and failure of eider nests

The signs left after predation and after successful hatching have been

described in detail by Milne (1963, 1974) and Baillie (1981) and these

were used to measure nesting success in the present study. Empty nests

were classified into the following categories.

(i) scrape, lined with sufficient vegetation to cover an egg but

without eider down or eggshells; this could be either a scrape in

which no eggs were laid or one from which newly-laid eggs had

been taken without being broken in the nest. Such scrapes can

be classified as unsuccessful nesting attempts, even though it is

not certain that eggs had been laid.

(ii) lined scrape without eider down but with fresh egg shells

(which could be distinguished easily from the previous year's)

albumen or yolk; predated early in the laying period.

(iii) lined scrape with some eider down and with or without egg

shells, albumen or yolk; predated late in the laying period,

when down is first deposited.

(iv) nest fully lined with down, with or without egg shells, albumen

or yolk; predated during incubation.

(v) nest fully lined with down, with the remains of several eggs

including characteristic leathery membranes; hatched

successfully.

26

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I I

Appendix 3. Numbers of bird predators trapped and shot in the Estuary-

side area in 2001. Data from J. Lewis and SNH.

I I Crows Gulls shot

I Week Beginning: Trapped Shot Total HG GBB

I April 16 0 0 0 0 0

I April 23 3 0 3 0 0

April 30 14 1 15 0 0

I May 7 6 2 8 0 0 May 14 8 0 8 2 0

I May 21 4 1 5 1 0

~I May 28 0 2 2 0 0 June 4 1 3 4 1 0 I June 11 3 1 4 0 0

June 18 0 4 4 2 0

I June 25 3 3 6 1* 0

I Total 42 17 59 7 0 I

* Trapped

I In addition, one jackdaw and four rooks were shot. I I I ,I

27

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Appendix 4. Summary of fox control on Forvie, 2001

F or the purposes of this summary, the reserve has been divided into two

areas; south of the Waterside to Rockend path and the remainder (the

"north"), which includes visits where the route taken was along the path

itself. Visits to the two areas have been counted separately, even ifboth

were visited on the same night. The summary is confined to the March to

June period (i.e. the eider nesting season).

Up to the end of June, 34 visits had been made. Of these, 28 (82%) were

to the north part of the reserve. Ten of the visits (29%) included part of

the Waterside to Rockend path.

Foxes were seen on six visits (17.6%), with similar success in the north

(17.9%) and in the south (16.7%). All of the encounters were at dens.

Two adult vixens were shot, one on 21 May in the northwest part.of the

reserve and one on 29 June, just north of the Waterside to Rockend path.

Both of these were shot at dens, along with cubs; no foxes were shot (or

indeed seen away from dens) on transect-type visits. Eight cubs were

shot, at four dens; two of these were in the northernmost part of the

reserve, one was just north of the Waterside to Rockend path and one was

just south of it.

Clearly, in 2001, transects across the reserve were very unsuccessful in

producing encounters with foxes, and control efforts were concentrated in

the north part of the reserve and at dens. This may well maximise the

28

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number of foxes killed, by concentrating on dens and on the shooting of

cubs, (which made up 80% of the kill), but does not necessarily reduce

fox activity in the eider nesting area. No adult foxes were shot before the

start of the eider nesting period; possibly associated with this, six of the

nine eiders found dead in the estuary-side study area were killed before

the first vixen was shot on 21 May.

29

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Rockeod

1 Km

Figure 1. Forvie National Nature Reserve, showing the position oftransects (solid

lines), The Stone Circles (asterisk) and the location of the estuary-side study area

(closely-spaced lines).

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Vthan Estuary

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\

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Sand cliff

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Figure 2. The estuary-side study area, showing the transect lines (solid straight

lines), the electric fence (dotted and dashed line), tracks (dashed lines), the Sand

Cliff and observation point (asterisk). Dotted cross bars on the transect lines show

100 m intervals from the baseline at the north end of each.

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D '\ Grid

Figure 3. Study areas other than transects (named) and the fox~tracking bands

(heavy lines to the north and south of Grid).

NESTING DISTRIBUTION AND NESTING SUCCESS OF EIDERS ON FORVIE NATIONAL NATURE RESERVE 2001SummaryCONTENTSINTRODUCTIONOBJECTIVESMETHODSRESULTSDISCUSSIONRECOMMENDATIONSREFERENCESAppendix 1Appendix 2Appendix 3Appendix 4