I --I of Eiders on Forvie National Nature Reserve 2000 I...(at much higher density than formerly) in...

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 2000

Report No. FOOLF20

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 AB41 8RU

This report should be quoted as:

Patterson, I.J., Shortridge, R.J. & Thorpe, A.W. (2000) Nesting Distribution and Nesting Success of Eiders on Forvie National Nature Reserve 2000. Scottish Natural Heritage Commissioned Report No. FOOLF20.

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 2000.

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

SCOTTISH NATURAL HERITAGE

(~~~l

COMMISSIONED REPORT

Summary NESTING DISTRIBUTION AND NESTING SUCCESS OF EIDERS ON FORVIE NATIONAL NATURE RESERVE 2000 Report No: FOOLF20 Contractor: I.J. PATTERSON, R.J. SHORTRIOGE & A.W. THORPE

BACKGROUND

The aim of the 2000 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 started in 1995.

MAIN FINDINGS

• The eiders' nesting distribution remained similar to that in 1999, but nest density increased in most of the southern part of the reserve, and decreased in the nesting areas near the estuary.

• Laying was at the same time as in 1999 but mean clutch size was significantly lower, at 4.06 compared to 4.41 in 1999.

• Overall nesting success in the surveyed sample of nests decreased to 48.8%, from 61.7% in 1998. Success in the Estuary-side area was 54.9%.

• The mean number of fox tracks found on the transects was higher than in 1999 level, but dropped after vixens were shot. Crow and gull numbers were highest late in the season, rather than while the eiders were laying. The observed rate of nest predation (0.65 per hour) was the same as in 1999 (0.64 per hour). It is recommended that crow control be started in ear1y March and that new approaches to fox control should be considered.

TO BE COMPLETED BY SNH NOMINATED OFFICER For further information on this project contact: -Alison Matheson, SNH, Forvie National Nature Reserve, Cdllieston, Ellon. AB41 8RU: tel.no. 01358 751330 For further information on the SNH Research & Technical Support Programme contact The Co-ordination group; Advisory Services, 2 Anderson Place, Edil)burgh. Tel: 0131 446 2400

I I I I I I I I ,I I

1I I I I I I I I I I I

CONTENTS

Page

Introduction ........................................................................................ 1

Obj ectives ........................................................................................... 2

Methods

Study areas and transects ............................................................ 3

Nesting success ........................................................................... 4

Fox activity ................................................................................. 4.

Bird predators ............................................................................. 5

Statistical analysis ....................................................................... 6

c

Results

Nesting distribution .................................................................... 6

Laying and clutch size ................................................................ 7

Nesting success ........................................................................... 7

Causes of loss ............................................................................. 9

Discussion

Nest distribution and density ..................................................... 14

Laying and clutch size .............................................................. 15

Nesting success ......................................................................... 15

Predators and predation ............................................................ 16

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

Recommendations ............................................................................ 20

References ........................................................................................ 22

Appendices ....................................................................................... 24

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

1

INTRODUCTION

A survey of eider duck Somaleria mollissima nesting distribution and

nesting success on Forvie 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, arate close to the mean of 69% recorded in 1961-

1979. Following this encouraging result, the programme of predator


2

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.

A detailed study of nesting, induding laying dates and dutch sizes as

well as hatching success, was carried out by Richard Shortridge, to

compare nesting in 2000 with that in 1996-1999. 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, induding a

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

c) to identify, as far as possib1e, causes of nest loss, and


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

the activity of foxes, crows and gulls.

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 5m-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 late June

2000 (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

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

4

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

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

the survey here was delayed until 15 August. By this time,

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.

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.

3. Fox activity

The same two bands for fox tracking which were established across

the reserve in 1995 were surveyed again in 2000. The transect just

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

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

surveyed on three consecutive mornings (Wednesday to Friday; one

by SNH staft) each week from 10 April to 26 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


5

sometimes allowed fresh tracks to be distinguished and counted on

the first day.

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 3 April to 26 June. The number of

bird predators present was counted every 15 min for 2 h observation

periods, distributed throughout the day. 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


6

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 "1.2 tests. Apparent correlations (eg

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

Pearson's correlation tests.

RESULTS

1. Nesting distribution

The area of the reserve north of the Waterside to Rockend path was

not searched in 2000, since very few nests had been found there in

previous years, so that only very approximate estimates of density

could be made in spite of the considerable time and effort expended.

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

of the path increased from 8 in 1999 to 12 (Table 1), an increase in

density from 2.88 to 5.52 nests per ha.

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

decreased from 76.5 nests per ha in 1999 to 69.2 per ha in 2000

(Table 2), a value similar to the 71.4 per ha found in 1998. The

density in separate 100 m zones of the area (Figure 2) varied from


7

17.5 to 192.3 nests per ha (Table 2), with a mean value for the three

densest 100 m sections of transect (in the area of thickest heather) of

320.0 nests per ha, only slightly lower than the record value of 340/ha

found in 1999.

Nests numbers at the Sand Cliff, Marsh and Point decreased from

1999 to 2000 (Table 3), but increased slightly in the Valley Grid and

at Stone Circles.

2. Laying and clutch size

The first clutch, of five eggs, was found by J. Lewis on 26 April 2000.

~ A subsequent visit to the nest showed that this was the final clutch

size, so that the first egg had been laid on or before 21 April, a similar

date to the estimated first laying date of 23 April" in 1999. The first

laying date recorded on the transects of the Estuary-side study area

was 6 April 2000; most clutches there were started between 9 April

and 1 May (Table 4), with the latest new clutch found in the week

starting on 3 June.

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

(after 12 May) significantly smaller than earlier ones (Table 4). The

overall mean clutch size of 4.06 eggs in 2000 was significantly lower

than the mean of 4.41 recorded in 1999 (Table 5).

3. Nesting success

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

6), was 48.8% (N = 342 nests), a significant decrease from 61.7% in


. 8

1999 but a similar value to that in 1998 (46.1 %). All of the individual

survey areas showed a decrease in success, with the Estuary-side area

dropping from 65.7% to 54.9% and South Forvie from 32.0% to zero

(Table 6). At the Point, nests inside the electric fence had

significantly higher success (69.0% of 58 nests) than those outside

(44.4% of 81 nests; X2 = 8.01, p = 0.004 ). However, the total number

of successful nests in the Point study area as a whole decreased from

102 in 1999 to 76 in 2000. The nests inside the Point electric fence

were somewhat more successful than those in the fenced Estuary-side

area (above), with the difference just short of statistical significance

(X2 = 3.313, p = 0.069).

i As in 1999, the Estuary-side, Sand Cliff and Point areas had similar

nesting success (Table 6), but nests in South Forvie (on the east-west

transects, in the Mouse Grid area and around the Stone Circles;

Figures 1 and 3) were significantly less successful.

In contrast to 1999, there was no statistically significant variation

between areas in the stage at which nest failure occurred, as judged by

the amount of down in failed nests (Appendix 2; Table 7). A

consistent 22-24% had no down, showing that they had failed early in

the laying period. Compared to 1999, there was a tendency for fewer

failed nests to have no down and for more nests to have full down in

2000 (Table 7), although the apparent difference was not quite

statistically significant.

As in previous years, nests found in the first part of the season (before

19 May 2000) were significantly more successful (61.4% of 83 nests)

than those found later (42.6% of 47 nests; "I: = 4.321, p = 0.038).


9

However, unlike in earlier years, the earliest nests (found up to 5 May

2000) were less successful than those found in the two subsequent

weeks (43.3% of 30 nests vs 71.7% of 53 nests; 'X: = 6.506, P = 0.011).

4. Causes of loss

a) Fox activity

The overall mean number of fresh fox tracks crossing the transect

line per night in 2000 (5.7) was higher than in 1999 (3.6) and

1998 (4.0). There was again considerable variation through the

season (Table 8), with 8-9 tracks per night up to mid April, 13-14

per night on 21 April and 4-5 May and 4-5 per night in other

weeks up to 2 June. Track numbers then decreased through June

but were again high at the end of the month (Table 8). Badger

tracks were found on all but three of the 24 tracking sessions, with

a mean of 1.9 tracks per night. Some were heading towards the

Estuary-side area.

Six occupied dens with cubs were found by M. Sinclair

suggesting a larger fox population than in recent years, (although

in the two-month period involved, some could involve the ~ame

animals moving around). One of the dens was close to the

northern boundary of the reserve, so that the animals were

unlikely to have hunted in the main eider nesting area, but two

were south of the Waterside to Rockend path (one of these near

the Point). Vixens and cubs were shot at dens on 5 May (south of

the Waterside to Rockend path), 11 June and 13 June and a dog


10

fox was shot in August, after the end of the eider nesting season

(data from M. Sinclair and SNH).

Eleven female eiders with leg rings were found apparently killed

by predators, eight of them within the Estuary-side study area. A

further 11 killed females without rings were also found in the

Estuary-side area. Of the total of 19 kills in this study area, all but

two were within the electric-fenced area. The total found killed

represents a large increase from 1999, when only five birds were

found, (with only one inside the electric fence). In addition, two

ringed males (unusually) were found killed and four additional

ringed females were found dead from causes other than predation.

Within and around the Estuary-side study area, all dead eiders

found (whether with or without rings) were marked with labels so

that they could be distinguished from bodies found subsequently.

This allowed an assessment of the proportion of birds with rings;

(not possible with rings handed in by others, since there was no

corresponding count of dead birds without rings). The percentage

of killed females which had rings (42.1 % of 19 birds) was

significantly higher than among the females incubating on the

study transects (17.3% of 98; X2 = 5.806, P = 0.016). Females

found killed in the early part of the season (up to mid May) tended

to include more ringed individuals (57.1 %) than those found later

(33.3%), but the numbers involved were too small to allow

statistical analysis. Seventeen additional dead eiders were found

(by M. Sinclair) at fox dens; no rings were reported, but it is not

certain that the bodies were examined closely, so that no

comparison with the birds found in the study area can be made.


11

Sixteen of the female eiders found killed by predators were

recently dead, (ie killed during the three or four day interval

between visits to the transects, with some found within 24h) and

were checked for scent-marking by foxes. Only two of the birds,

both found on 8 May, were scent-marked; the other 14, although

injured and eaten to varying extents, had nothing to identify the

predator concerned.

b) Bird predators

As in 1999, the number of bird predators hunting in the Estuary-

side area varied considerably through the season (Table 9a).

Unlike 1999, however, numbers were not highest during the peak

in eider egg-laying, but occurred later in the season.

Gull numbers remained very low until after mid May and

increased only in the week starting on 22 May (Table 9a), well

after the start of eider egg-laying (24 April) and after the peak of

laying (8 May; Table 4). Numbers remained high (similar to peak

counts in 1999) until mid June, by which time few eiders were

laying, and declined only after 18 June.

Crow numbers showed some increase when the eiders started

laying and again at the peak of laying (Table 9a), but as with

gulls, the highest numbers occurred in late May and early June.

As in previous years, no rooks were seen until after the eiders

started to lay, with numbers then increasing throughout the


12

season, to reach their highest level in the second half of June

(Table 9a). Many of the rooks visiting the area late in the season

were accompanied by juveniles and foraged mainly in grassy

areas where there were few eider nests.

Eider nests were seen being attacked by bird predators during 16

out of 23 two-hour observation periods from 28 April to 22 June,

at a mean rate of 0.65 nests per hour, the same rate as in 1999

(0.64 per hour) and lower than in 1998 (1.03 per hour). The rate

9f loss was highest (0.8 to 1.8 nests per hour) in a three-week

period starting on 8 May (Table 9a), during and just after the peak

eider egg-laying period (Table 4). The mean weekly rate of nest

loss was not significantly correlated with either the mean or

maximum numbers of predators (r 0.05 in all cases),

presumabl y because the latter were highest later in the season

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

Gulls were the commonest participants seen at predated nests,

occurring at 85.2% of incidents (Table 9b) and consuming 83.8%

of the eggs seen being eaten. Crows were involved at fewer than

half of the nests (unlike 1999, when they were the main

participants) and were the least common finders of nests and

consumers of eggs (Table 9b). Rooks were seen finding as many

nests as gulls and were consumers of 25% of the eggs seen being

eaten.

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

c) Signs at failed nests

The overall mean percentage of failed nests which had shell

fragments in them in 2000 (31.8%; Table 10) was significantly

lower than in 1999 (61.3%), with a drop in percentage recorded in

all three areas. In 2000 there was (as in 1999) significant

variation between areas, with a higher percentage of nests with

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

(Table 10).

As in 1999, there was no significant variation between failed nests

with different amounts of down in the percentage which had shell

fragments in them (Table 11). The reduction between 1999 and

2000 in the percentage of faiJed nests with shell fragments, noted

above, occurred in all three categories of down, significantly in

nests with some or fu1l down (Table 11).

c) Success in relation to cover

Unlike in 1999, nests with thicker cover in the Estuary-side area

were not significantly more successful than those with little or no

cover (Table 12), although nests in cover categories 3-5 were

slightly more successful than those in lower categories.


14

DISCUSSION

1. Nest distribution and density

The increase in overall density of eider nests on transects in the south

part of the reserve (south of the Waterside to Rockend path), from

3.68 nests per ha in 1999 to 5.52 per ha in 2000 (Table 1), was

consistent with density increases in the Valley Grid and Stone Circles

(Table 3), both in the same South Forvie area. However, as in 1999,

no nests were found on the most northerly transect (267.50),

suggesting that eiders were not extending their nesting distribution

northwards.

In contrast to the increase in nest density on South Forvie, nest

numbers decreased in all other areas (Tables 2 and 3). This might

suggest some extension of range away from the dense nesting areas

close to the estuary, since the total reduction of 178 nests there

(Estuary-side, 140; Sand Cliff, 8; Marsh, 3; Point, 37) was of the

same order as the estimated increase of about 200 nests on South

Forvie. This may in turn have been related to the increased nesting

success (32.0%) on South Forvie in 1999 and if so, might be reversed

in 2001 following the complete failure of nests there in 2000.

Another factor could be the increased predation of sitting females

(and presumably increased disturbance by the predators) recorded

near the estuary in 2000, which may have caused females to move.

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,


15

south of the Waterside to Rockend path, surveyed 5 m in every 250 m

(2% of the area), so the 12 nests found there represent 600 nests in the

whole area. Since the Estuary-side transects covered 5 m in every 50

m (10%), the 133 nests found there represent a total of 1,330. The 37

nests at the Sand Cliff, the 5 nests in the Marsh and the 139 nests at

the Point bring the total of known and estimated nests to 2,111, a

decrease of 3.6% from the 1999 estimate of 2,189 (Patterson et al.

1999).

2. Laying and clutch size

The early onset of laying in 2000, on almost the same date as in 1999

• (21 April and 23 April respectively), was associated with an even

earlier arrival on the Ythan, with the peak count of females occurring

on 28 April 2000 compared to 7 May in 1999 (Patterson and Thorpe

1999, 2(00). The significantly lower mean clutch size in 2000 (4.06

compared to 4.41 in 1999),~however, suggests that the birds were not

in such good condition as in the previous year.

3. Nesting success

The significant decrease in nesting success in 2000 compared to 1999

may have resulted from poorer condition of the birds, suggested by

the significantly lower clutch sizes (above). However, the lower

success might also have been associated with the much higher number

of female eiders found killed by predators in 2000, since in addition

to the direct predation, the repeated presence of mammal predators in

the nesting area may well have caused birds to flush from their nests

or even to desert their nests permanently. Such uncovered nests


16

would be almost certain to fall prey to bird predators. The unusually

low nesting success of the earliest nests (before 5 May) may have

been the result of such disturbance, although the first dead birds were

found only from that date onwards.

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

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

elsewhere), was 3,346, of which 2,964 (HH.6%) were estimated to

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

lower than those in 1999 (5,554 and 4,259 respectively). Mortality

, (of about 94%) after leavi ng the nest reduced the 3,346 ducklings

estimated to have hatched in 2000 to 212 which survived to fledge

(Patterson and Thorpe 2(00).

4. Predators and predation

a) Foxes and badgers

In spite of reductions in the number of tracks recorded on the

transects after the shooti ng of one vixen on 5 May and two others

on 11 and 13 June (Table H), the overall mean number of tracks

was higher than in 199H and 1999. This is consistent with the

large number of dens found on the reserve in 2000.

The large increase in the number of eiders found killed in 2000 is

a cause for concern, particularly since so many (17) were found

inside the electric-fenced Estuary-side area. Part of the increase is

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

17

presumably related to an apparently increased number of foxes on

the reserve, but most is due to the failure of the electric fence to

deter the animals from entering the highest density nesting area

where eiders were very easy to find. Only two of 16 dead eiders

(both on R May) had fox scent on them and, although no

systematic checking was carried out on the smaller numbers killed

in previous years, it is thought that the proportion scent-marked in

2000 was much lower than usual. The regular finding of badger

tracks, some heading to or from the estuary, raises the possibility

that some (or even most) of the predation might have been carried

out by badgers. This could explain the ineffectiveness of the

electric fence in 2000, since hadgers would be less likely than

foxes to detect the fence visually and their lower posture and thick

coats would make them less likely to receive a shock when

passing under the tapes.

The surprising finding that the percentage of ringed birds among

the eiders found killed was significantly higher than among the

incubating birds as a whole, is difficult to explain, since the

proportion of females with rings did not vary significantly

between different parts of the area or between groups which

started laying in different weeks. It is possible that ringed

females, being much older than average (mean of 44 identified in

2000, 17.1 years), might sit more tightly and thus be more likely

to be killed. Alternatively, the predators might selectively carry

away to the den only birds without rings. The lack of any reports

of rings on the 17 dead eiders found at fox dens supports this

possibility. Two (separate) severed eider legs, each with a ring,

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

lR

were found in the study area, suggesting that predators might

reject rings.

b) Bird predators

Unlike in 1999, when crow and gull numbers were highest during

the peak of eider egg-laying, all of the bird predators in 2000

reached their highest numbers later in the season (Table 9a). As a

result, predator numbers continued to be high when the proportion

of newly-started eider clutches (the most vulnerable ones) had

become very low an~ when the rate of observed nest predation

had also decreased (Table 9a), so that there was no significant

correlation between predator numbers and observed predation

rate. Surprisingly, the lower success of predator control in 2000

(20 crows removed compared to 42 in 1999; 9 gulls compared to

29) did not result in higher numbers in the Estuary-side area,

where peak numbers were similar in the two years. It is possible

that the birds removed each year were quickly replaced by new

ones.

Rooks continued to be a particular problem, in that they were seen

to find as many nests as did gulls (Table 9b) but were not

susceptible to the control methods being used.

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

applying the mean rate of observed nest losses (0.65 per h) to an

average 18 h day from 28 April to 22 June (the period during

which predation was observed), was 644 nests compared to 600

from the transect study (60 nests lost in a 10% sample of the


19

area). The slightly (7.3%) higher estimate from direct observation,

which was very similar to the difference in 1999 (10.6% higher),

may have resulted from failure to identify some losses of one-egg

clutches from newly-started nests on the transects or from some

observed nest "predations" being in fact return visits to nests

attacked earlier. Several clear instances of the latter were

recorded (but not counted) where nest locations could be

pinpointed accurately. However, unless the observed losses were

seriously overestimated, it appears that bird predation can account

for most nest losses and that there was little direct egg predation

by mammals.

5: Signs at predated nests

The percentage of nests lost early in the laying stage (ie with no down

in the nest), which had decreased from 42'(}% in 199R to 29.0% in

1999, declined further to 22.5% in 2000, with similar values in all

areas (Table 7). This trend, together with the increase in the

percentage of failed nests with a full complement of down (ie during

incubation) from 24.7% in 1999 to 40.5% in 2000, suggests strongly

that most nests were lost late in the laying period or during

incubation. Since observed predation by birds can account for the

losses (above), the predated nests had presumably been left

undefended, either because the females had to leave to drink during

dry periods (Patterson et al. 1999) or because they were flushed (or

even killed) by mammal predators.

As in 1998 and 1999, failed nests in the Estuary-side area were more

likely than those elsewhere to have shell fragments left behind,


20

suggesting breakage in the nest. This is consistent with the

suggestion (above) that most of the losses can be accounted for by

bird predation. The significant decrease in the percentage of nests

without shell fragments between 1999 (72.4% in the Estuary-side

area) and 2000 (42.2%) is consistent with the higher proportion of

eggs seen to be consumed by gulls (83.3% compared to 27.6% in

1999), since these birds, especially greater black-backed gulls, can

carry eggs away without breaking them.

RECOMMENDATIONS

The efficiency of crow trapping could be improved by starting earlier in

the season, with prior pre-baiting and with the use of decoy birds from the

start. In 2000, although the traps were in position from 14 April, to allow

the crows to become familiar with them, baiting and trapping did not start

until 25 April, by which time the eiders had already started to lay. The

crows then had a supply of eider eggs and did not need to risk entering

traps. (Only highly unpalatable eggs were available in the concurrent

repellent trials; untreated eggs were last used on 30 March and all cached

ones appeared to have been recovered and eaten by mid April). Decoys

were not used until 1 May and only one crow was caught before 8 May,

after the peak of eider egg-laying.

It would be desirable to have the traps in position from early March, with

their doors wired open. Bait, placed first around the traps and later inside

them, should be renewed every few days from mid March onwards. If

possible, the trapper should obtain decoys in advance of the trapping

period, which should start in early April.


2L

Repellent trials may be continued in 2001, although only from mid April.

These will use simulated eider eggs, so it would be best if only white or

brown eggs were used in the traps.

The effectiveness of shooting bird predators, which was particularly low

in 2000 (only two crows and nine gulls compared to 14 and 29

respectively in 1999), might be improved by establishing baiting sites (eg

easily-visible simulated nests with hens' eggs; rabbit carcasses;etc), with

perches on poles for crows and rooks, in good positions for shooting from

the hides.

It is difficult to make recommendations regarding fox control, apart from

th"e introduction of new approaches, suggested in earlier reports

(Patterson et al. 1997, 199R, 1999). In 2000, fox control started at the

beginning of March, two months before the peak of eider laying, but was

unproductive in this period, with only three foxes seen and none shot in

21 nights (information from M. Sinclair and SNH). Subsequent successes

during the eider nesting period were all based on shooting at dens and

involved only vixens and cubs; no dog foxes were shot during the nesting

period, fox activity continued to be recorded on the tracking transects and

eiders continued to be killed. It is clear that, although the present fox

control programme removes some foxes and reduces activity to some

extent in the southern part of the reserve, it does not remove all of the

foxes hunting there or prevent predation. It is recommended that fox

control be reviewed and new approaches considered.

The possibility that badgers might have been responsible for some of the

predation in the estuary-side area suggests that electrified netting should

be used there instead of the present tapes. Netting would prevent the


22

animals passing underneath the fence without being shocked and might

also be more effective than tapes agai nst foxes.

Since the eiders which nested within the electric-fenced area at the Point

were significantly more successful than those nesting outside, it is

recommended that this fencing be continued. It would be advantageous

to increase the protected area if possible, by extending it further towards

the estuary.

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, Somateria 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, 1.1. and Cosgrove, PJ. 1998. The eider population of Forvie

National Nature Reserve, 1998. Report to SNH.

Patterson, 1.1. and Laing, R.M. 1993. Nesting distribution and nesting

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

SNH.


23

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.J., 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., Smits, M.J.A. and Cosgrove, P.J. 1998. Nesting

distribution and nesting success of eiders on Forvie National Nature

Reserve 1998. Report to SNH.

Patterson, I.J. and Thorpe, A.W. 1999. The eider population of the

Ythan Estuary and Forvie National Nature Reserve, 1999. Report to

SNH.

Patterson, I.J. and Thorpe, A.W. 2000. The eider population of the

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

SNH.


24

Appendix 1. Methods used to establish study areas and transects

Transects were set up between OS grid co-ordinates, using 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 of transects were used on a) the reserve as a whole

and b) in the small 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


25

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 Srn-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 Srn-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 () for exposed sites to 5 for completely

hidden ones (Patterson and Laing 1993).


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

successfull y .


27

Each marked nest which had a sitting female or entire eggs during the

transect surveys was visited again after the end of the breeding season

(late July). However, one visit to each nest was adequate in most cases to

distinguish success from failure, while minimising disturbance.

I -I

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

28

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

side area in 2000. All of the crows were first-year birds, ie hatched in

1999. Data from J. Lewis and SNH.

Crows Gulls shot

Week Beginning: Trapped Shot Total HG GBB

April 24 0 0 0 0 0

May 1 1 0 1 0 0

May 8 6 0 6 1 0 ,.

May 15 4 1 5 2 0

May 22 2 1 3 0 0

May 29 2 0 2 2 0

June 5 1 0 1 3 0

June 12 2 0 2 1 0

Total 18 2 20 9 o

I ,I

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

29

Table 1. Eider nests found on transects of Forvie (excluding the Estuary-

side area) in 2000 (with 1999 data for comparison). Locations are

shown in Figure 1. Transects are east-west OS grid lines (in square

NK), specified to the nearest 1 m, in the area south of the Waterside to

Rockend path.

2000 1999

Transect Length (m) Area (ha) Nests Nests/ha Nests/ha

267.50 894* 0.4470 0 0.00 0.00

265.00 1227* 0.6135 3 4.89 1.63

262.50 909 0.4545 2 4.40 8.80

260.00 727 0.3635 5 13.76 2.75

257.50 591 0.2955 2 6.77 6.77

Total 4348* 2.1740 12 5.52 3.68

* Shorter than in 1999 (area south of the path only); the 2000 lengths

have been used in calculating comparative 1999 densities.

I 30

I Table 2. Eider nests found in lOOm sections of transects in the Ythan

I Estuary-side area in 2000 (with 1999 data for comparison). A I

dash indicates that a transect did not extend into a section.

Locations are shown in Figure 2.

I I Section (m) Transect (W-E) Nests per ha I 1 2 3 4 5 6 7 8 Total 2000 1999 I 0

0 0 5 1 1 0 0 0 7 17.5 22.5

I 100 I

1 3 5 0 3 3 0 0 15 37.5 40.0

200

I 0 4 3 2 5 0 1 0 15 42.7 62.6 300

I 1 4 6 11 0 9 1 32 97.1 136.6

I 400

1 5 17 20 5 2 50 192.3 134.6

I 500 0 5 8 1 0 14 77.6 110.8

I 600

I Total 1 8 18 14 42 31 16 3 133 69.2 76.5 I I I I I


31

Table 3. Eider nests in areas other than transects on Forvie in 2000 (with

1999 data for comparison). Locations are shown in Figures 1 to 3.

2000 1999

Site Area (ha) Nests Nestslha Nests Nests/ha

Sand Cliff (linear site) 37 45

Marsh 2.R 5 l.R 8 3.85

Point 0.45 139 30R9 166 368.9

Valley Grid 2.00 19 9.5 16 8.0

Stone Circles 0.25 4 16.0 3 12.0

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

32

Table 4. Clutch size in relation to the week in which the first egg was

laid, in 2000. Nests lost prior to the start of full incubation have been

excluded, since their laying dates and clutch sizes could not be

determined. Seasonal variation in clutch size; F (60, 2) = 4.50, p = 0.015; clutches laid after May 12 significantly lower than both earlier

values (ANOVA with Tukey tests).

Week

Starting

April 22

April 29

May 6

May 13

May 20

May 27

June 3

June10

June 17

June 24

Number

of nests

2

16

23

8

9

3

1

0

0

0

Clutch

Mean SE

} 4.47 0.15

}

4.43 0.24

}

}

} 3.67 0.21

}


33

Table 5. Clutch sizes (of completed clutches only) in the Estuary-side

area in 2000.

Clutch

sIze

1

2

3

4

5

6

7

All

Number

of nests

1

6

16

38

28

1

2

92

Overall mean cl utch size; 4.06 ± O.ll

1999; 4.41 ± 0.10; t = 2.43, P = 0.016

Percentage

of nests

1.1

6.5

17.4

41.3

30.4

1.1

2.2

C_I_·~·"¥"··· .... ... . .. , .. , .... ~.~.-.",. .... ,. .......... .

I ,I I I I I I I I I I I I I I I I I I.

I 11

34

Table 6. Nesting success of eiders on Forvie in 2000 (with 1999 data for

comparison). Locations are shown in figures 1-3. South Forvie

includes the east-west transects south of the Waterside to Rockend

path, the Valley Grid and the Stone Circles.

Area Nests Percentage hatched

Estuary-side

Sand Cliff

Point

South Forvie

All areas

133

37

139

33

342

Overall X2 over the four areas

South Forvie vs Estuary-side;

South Forvie vs Sand Cliff;

South Forvie vs Point;

X2

X2

X2

X2

No other significant differences.

2000 vs 1999

=

=

=

=

2000

54.9

48.7

54.7

0.0

48.8

35.346, P < 0.001

32.330, P < 0.001

21.611, P < 0.001

32.327, P < 0.001

All areas; X2 = 12.508, P < 0.001

Estuary -side; X2 = 3.642, P = 0.057

South Forvie; X2 = 12.250, P < 0.001

No other significant differences

1999

65.7

64.4

61.5

32.0

61.7

I I I I I I I I :1 I I I I I I I I I I I

35

Table 7. The amount of down in predated eider nests in different areas of

Forvie in 2000 (with 1999 data for comparison). South Forvie areas

are as Table 6. There were no significant differences between areas;

between years, X2 = 5.698, P = (t058.

Area

Estuary-side

Sand Cliff

South Forvie

All areas

1999

Nests

60

18

33

111

93

Percentage of nests with

different amounts of down

None Some

21.7

22.2

24.2

22.5

29.0

45.0

27.8

27.3

36.9

46.2

Full

33.3

50.0

48.5

40.5

24.7

"1-"

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

36

Table 8. The number of fox tracks (mean per tracking day and maximum

on anyone day) found on the transects across the southern part of

Forvie in 2000. Each date is the starting date of the number of

tracking days shown. Additional preliminary surveys on 13 and 27

March revealed Rand 9 fresh tracks respectively.

Number of tracks:

Date Days . Mean Max.

April 14 1 9.0 9

Apri121 1 14.0 14

April 27 2 5.0 6

May 4 2 13.0 15 * May 11 2 4.0 5

May 18 2 5.0 7

May 25 2 4.0 6

June 2 1 4.0 4

June 8 2 2.0 2 ** June 14 3 3.0 6

June 22 2 0.5 1

June 29 2 8.5 10

Mean 5.7 7.1

* Adult foxes shot (information from M. Sinclair and SNH)

,.c·I"···'···~··'··m_"_~." . .c ....

I 37

I Table 9. Bird predators (mean count and maximum number seen at anyone time including periods between counts) and nest losses in the Estuary-side area of

I Forvie in 2000. All data are mean values for the weeks shown.

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

:1 I. I.

a) Counts

Week beginning

April 3

April 10

April 17

April 24

May 1

May 8

May 15

May 22

May 29

June 5

June 12

June 19

June 26

Obs. hours

10

4

4

2

4

4

4

8

8

8

4

4

4

Gulls

Mean Max.

0.0 0.0

0.0 0.0

0.1 0.5

0.6 2.0

0.2 1.0

0.9 9.0

0.8 3.0

5.1 10.1

4.2 13.3

2.2 5.5

5.4 28.5

0.7 2.5

1.4 3.0

Crows Rooks

Mean Max. Mean Max.

1.1 4.8 0.0 0.0

0.2 2.5 0.0 0.0

0.5 2.5 0.0 0.0

2.0 8.0 0.0 0.0

1.6 4.5 0.7 2.5

4.5 8.0 0.9 3.5

3.5 6.5 2.3 5.5

2.0 5.0 4.4 10.0

5.2 10.3 3.6 8.0

4.8 9.0 6.1 10.3

2.3 7.0 7.4 12.0

1.9 4.0 6.9 30.5

1.5 4.5 10.0 28.5

Nests lost per hour

0.5

0.5

1.0

0.8

1.8

0.4

0.3

0.3

0.3

0.0

~~'Im'~" .. m ___ "."._'" ,

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

38

Table 9 (Continued)

b) Involvement of gulls, crows and rooks in observed nest predation. N

shows the number of nests at which each role could be identified.

More than one species could participate and eat at anyone nest.

Role Percentage of nests involving:

Gull Crow Rook N

, Nest finder 39.1 21.8 39.1 23

Consumer of egg 83.3 16.7 25.0 24

Participant 85.2 48.1 55.6 27

Yl""'--'-'~'~"""W"""""W"""'-"'"

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

39

Table 10. The percentage of predated eider nests with shell fragments, in

different areas of Forvie in 2000, with 1999 data (from the same

areas) for comparison.

Percentage with shells

Area

Estuary-side

Sand Giff

South Forvie

" All areas

Nests

59

18

27

110

Overall X2 over the three areas

Estuary-side vs Sand Cliff;

2000

49.2

0.0

18.2

31.8

= 19.400, P < 0.001

Estuary-side vs South Forvie; X2 =

14.193, P < 0.001

8.612, P = 0.003

1999

72.4

43.8

42.1

61.3

Sand Cliff and South Forvie not significantly different, (X,2 = 3.709, P =

0.054*)

2000 vs 1999

Estuary -side; X2 = 13.033, P < 0.001 Sand Cliff; X2 = 9.917, P = 0.002* South Forvie; X2 = 3.508, P = 0.061

* ureliable; cells with expected val ues less than 5

I I I I I I

41

Table 12. The percentage of eider nests which hatched ducklings, in

relation to the amount of cover above the nest in the Estuary-side area

in 2000. Overhead cover was scored as absent (0) or present, in 20%

increments (from 1-20% (1) to 80-100% (5)).

Cover score;

o 1-2

Percentage hatching 53.8 52.3

Number of nests 65 44

No significant variation in percentage hatching with cover score;

X2 = 0.712, P = 0.701

3-5

62.5

24


t

---

1 Km

F».gme 1. Fome Natiooal Nature Reserve, showing the east-west ~ the

Stone G.rcles (~ri.sk) and the location of the estwuy-side study uea

(closely~ lines).


ythan Estuary

Sand Cliff

,

I

I

{- --, ,

I

I

F~ 2. 'I'he e.Wwy..&Qe study ~ showing the tDUect lim:I (lOHd ~

~), the electric fence (dotted and duhed), tDcb (~ the Sad

Qiff and the observation point (~). Dotted crou baD (8 the ~

lines show 100 m intervals from the basdine at the north ead of eId:L

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

I I I I I . ., I I

I ,

r , . __ - _-- ' ___ .1:~_ '_,

Field

I

-"'oL-" -... --~ ... "(,.

" b "\

, , , , ,

Grid

. , , 1

, ..... ____ I~

FJ.gme 3. Study areas other tUn tnmsects (named) ~ the fox-tnw:mug bmda

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

Nesting Distribution and Nesting Success of Eiders on Forvie National Nature Reserve 2000SummaryCONTENTSINTRODUCTIONOBJECTIVESMETHODSRESULTSDISCUSSIONRECOMMENDATIONSREFERENCESAppendix 1.Appendix 2.Appendix 3.Tables

Date post:	07-Feb-2021
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

I --I of Eiders on Forvie National Nature Reserve 2000 I...(at much higher density than formerly) in...

Documents