Waterbird monitoring of Cork Harbour: 1994/95-2002/03

Tom Gittings, Department of Zoology, Ecology & Plant Science, University College Cork.

Introduction

Cork Harbour is one of the most important sites in Ireland for wintering waterbirds (Crowe & Boland, 2004), and its waterbird populations have been monitored periodically since the 1970s (Hutchinson & O'Halloran, 1984; Smiddy et al., 1995). Since the winter of 1994/95, annual monitoring has been carried out, as part of the Irish Wetland Bird Survey (I-WeBS). This period has coincided with the “hibernation” of the Cork Bird Report. Therefore, the only published data from this period has been the summary data for selected species included in the I-WeBS reports (Colhoun, 1998, 2000, 2001a, b, 2002; Crowe & Boland, 2004; Delany, 1996, 1997). The present article continues the series of annual reports published in the Cork Bird Report in the early 1990s (Coveney, 1992; Leonard, 1993; Shorten, 1994) with the aims of: making available the results of the Cork Harbour counts; and reviewing trends in waterbird numbers and status during this period.

Coverage

For the purposes of carrying out waterbird counts, Cork Harbour is currently divided into 19 count sectors. These sectors are counted by nine or ten counters. The objective is for each count sector to be counted around high tide on either the Saturday or Sunday of the nominated weekend in each month between September and March. The actual level of coverage achieved is shown in Table 1. This shows that full coverage only occurred in nine of the 62 months, and only in the winter of 1996/97 was anything approaching full coverage achieved throughout the winter (with only one month having missing counts). In all the other winters, the majority of months have at least one missing count, and the level of coverage was particularly poor in 2000/01 and 2001/02. Several count sectors were not counted at all in particular winters: the Douglas Estuary in 1997/98, 1998/99, and 1999/00; Belvelly-Marino Point, Cuskinny and North Channel-Ballintubrid in 2000/01; and Ballynacorra, the Owenboy Estuary and Rathcoursey & Ahanesk in 2001/02. National summaries of I-WeBS results have generally not mentioned the fact that there has been incomplete coverage of Cork Harbour, with the exception of Crowe and Boland (2004). This latter publication describes coverage in 2000/01 as incomplete, but makes no mention of incomplete coverage in other winters.

Because waterbirds can move between count sectors, it is important try and co-ordinate counts to avoid either double-counting the same birds in more than one sector, or missing birds as they move between sectors. The objective aimed for in the Cork Harbour counts is for all counts to be carried out on the same weekend. Figure 1 shows that this objective was only achieved on 16% of the counts, while nearly 50% of counts included sectors counted a week or more apart, and 15% of counts included sectors counted two weeks or more apart.

Data analysis

The aims of the data analyses were to: assess the current status of the waterbird populations of Cork Harbour; and to identify trends in these populations across the period covered by this review.

The accepted method for assessing the status of waterbird populations is to calculate the five year mean of the peak annual counts (Colhoun, 2001a). Therefore, to assess current status the most recent five years should be used. However, in the current data set, the most recent five years include two winters (2000/01 and 2001/02) with very poor coverage (see Table 1). Therefore, five year means calculated from these years will inevitably underestimate the populations of many waterbird species. Those species whose peak numbers occur in the autumn will be particularly affected as the worst coverage was generally during the autumn months. Because of this problem, I have calculated a second set of five year means using the most recent five winters excluding 2000/01 and 2001/02: i.e., 1996/97-1999/00 and 2002/03. This second data set, however, includes two winters (1997/98 and 1998/99) during which the Douglas Estuary was not counted. Therefore, both sets of five year means are likely to be underestimates.

In order to identify trends in waterbird populations, I have calculated the annual maximum counts for each species. I also plotted out monthly count data for each winter to determine whether high counts may have been exceptional one-off peaks, and, for high counts, examined the dates on which individual sectors were counted to determine whether double-counting may have been involved. However, interpretation of these is complicated by the many gaps in coverage in the data set. The most significant gap in coverage is the absence of counts from the Douglas Estuary for the period 1997/98-1999/00. The Douglas Estuary, along with Dunkettle, forms a fairly discrete unit of Cork Harbour, which is physically separated from the other estuarine areas of Cork Harbour. Therefore, I have also calculated a second set of annual maximum counts excluding the Douglas Estuary and Dunkettle. This provides a more easily interpretable dataset for analysing annual trends. Even so, other gaps in coverage remain. Where the peak count of a species is in a month with gaps in coverage, I have examined the counts for the missing sector(s) in the same month of other winters and estimated an approximate value for the missing counts. I have also used a similar method to determine whether gaps in coverage in any particular winter could have resulted in the peak number in the dataset occurring in a different month from that in which the peak number actually occurred.

The methods described above assume that relatively predictable numbers occur in each count sector, or count sector combination. This is not always the case: sometimes exceptionally high or low one-off counts are recorded for particular count sectors. Therefore the interpretation of trends based on datasets that exclude the Douglas Estuary and Dunkettle and estimate approximate values for missing counts, will contain some errors. An alternative method of deriving population trends from datasets containing missing counts is the Underhill Index method, used by Crowe and Boland (2004). However, this method assumes that the three factors which determine variation between counts (month, year and site) are independent (Underhill & Prys-Jones, 1994). While I have not carried out any formal analyses, visual inspection of the Cork Harbour dataset suggests that the assumptions of independence between site and month factors and between site and year factors does not hold for many species.

All the following discussions of annual trends are based upon the dataset of annual maximum counts, excluding the Douglas Estuary and Dunkettle (Table 3). Because the 1994/95 season only included one full count (January), I have excluded this season from consideration of annual trends.

Overall results

Overall, 82 waterbird species were recorded on I-WeBS counts during this period. These included eleven rarities (Black-throated Diver, Pied-billed Grebe, Red-necked Grebe, Black-necked Grebe, American Wigeon, Green-winged Teal, Red-crested Pochard, Ring-necked Duck, Surf Scoter, Long-billed Dowitcher, and Laughing Gull) and one escape (Black Swan). Another 33 species were not recorded in every winter, because they are either summer/passage migrants, scarce winter visitors, or species that are not routinely monitored by I-WeBS counts (Water Rail, Jack Snipe and Kingfisher). There are also five regularly occurring waterbird species that are not reliably monitored by I-WeBS counts in Cork Harbour either because they are not counted in all sectors (Black-headed Gull, Common Gull, Lesser Black-backed Gull, Herring Gull and Great Black-backed Gull), or because I-WeBS count methodology is not appropriate for the species (Snipe). Where relevant, records of all the above species are included in the main body of this Cork Bird Report. The present article focuses on the 32 species that regularly occur in Cork Harbour during winter, and that are routinely monitored by I-WeBS counts.

Annual maximum counts for these species in each winter are presented in Tables 2 and 3.

Internationally Important Species

Two species (Black-tailed Godwit and Redshank) regularly occurred in internationally important numbers during this period (Table 4).

Black-tailed Godwit

Peak numbers in each winter were recorded in either September or October (Figure 2a). However, one of the two winters with peak numbers in October had many missing counts in September. In fact, peak numbers of this species may well occur in August before the I-WeBS counts start. For example, in 1997/98, I counted 1640 Black-tailed Godwits roosting in the Douglas Estuary on 20 August, which is substantially more than any I-WeBS count for this sector carried out during the period under review. Numbers generally decline sharply after the autumn peak and then fluctuate around a much lower level for the rest of the winter.

The annual maxima varied between 1411-3162 over this period, in part reflecting the absence of count data from the Douglas Estuary (one of the main sites for this species) from many of the winters. However, analysis of data, excluding the Douglas Estuary/Dunkettle, and taking account of the missing count sectors in 1995/96 and 2000/01-2002/03, indicates that there was a trend of increasing numbers from 1995/96-1998/99. This was followed by a sharp fall in numbers in 1999/00 with numbers increasing again over the following three winters to reach a similar level in 2002/03 to that attained in 1998/99. In 1998/99, the peak count of 2565 (September) probably represents an overall Cork Harbour population of over 3000, taking account of the lack of coverage of the Douglas Estuary. The peak count of 3162 in 2002/03 (October) was probably not affected significantly by gaps in coverage (as the count sectors not covered rarely hold many Black-tailed Godwits).

The trends described above do not match those reported at a national scale by Crowe and Boland (2004) for the winters 1995/96-2001/02. However, the latter are based on mid-winter (November-February) counts. In Cork Harbour there does not seem to be a consistent relationship between autumn and mid-winter numbers (Figure 3). In mid-winter, Black-tailed Godwit counts are highly variable because large flocks appear to spend most of their time feeding on fields, only visiting the estuarine habitats erratically. Therefore, I-WeBS counts, which largely do not cover fields around Cork Harbour, do not reliably represent the actual numbers of Black-tailed Godwits in the Cork Harbour area in mid-winter.

Redshank

Peak numbers in most winters were recorded in late autumn (usually November), with the exception of 1995/96 (January). In some winters, numbers remain high from the late autumn peak through the mid-winter period (December and January), while in other winters they decline sharply after the late autumn peak (Fig. 2b).

The annual maxima varied between 1005-2269 over this period. However, in the winters of 2000/01 and 2002/03 the key count sectors (Belvelly-Marino Point and North Channel-Ballintubrid) were not covered in the late autumn period. Excluding the winters of 2000/01 and 2002/03 reduces the variation in the annual maxima to between 2076-2269, suggesting a remarkable degree of stability in the Cork Harbour Redshank population. However, this does not take account of the missing counts from the Douglas Estuary (which can hold large numbers of Redshank). Excluding Douglas Estuary/Dunkettle, increases the variation in the annual maxima to between 1839 and 2249 for the same period. These adjusted maxima show a peak in the winters of 1997/98-1999/00 (2100, 2243 and 2249) with lower numbers in 1995/96, 1996/97 and 2002/03 (1839, 1840 and 1970). Given that the three winters with peak numbers lacked counts from the Douglas Estuary, it is likely that the Cork Harbour Redshank population peaked at over 2500 in the late 1990s.

 

Nationally Important Species

Nineteen species regularly occurred in nationally important numbers during the period under review (Table 4). In addition, while formal thresholds have not been set, the numbers of Little Egrets in Cork Harbour are surely of national importance: in each winter for which national data is available, the Cork Harbour maxima was at least 10% of the national maxima.

Three of these species (Shelduck, Dunlin and Curlew), regularly occur in numbers that are greater than 50% of the threshold for international importance and I discuss trends in the numbers of these species below.

Shelduck

Peak numbers in most winters occur in mid-winter (December and January). Much lower numbers usually occur outside this period, but exceptionally high numbers occurred in March 1996 (Fig. 2c).

The annual maxima varied between 722-2621 over this period. However, excluding Douglas Estuary/Dunkettle and the winters of 2000/01 and 2002/03 (which contain many missing counts) reduces the variation to between 1517-2205. Apart from high numbers in the winter of 1996/97, there appears to have been little annual variation in Shelduck numbers over this period. Taking account of the usual annual peak in the Douglas Estuary (c. 200) and the missing counts from Lough Beg and Monkstown Creek in January 2003 (usual combined annual peaks of 200-300), suggests that the Cork Harbour Shelduck population would have exceeded 2000 in every winter except 1997/98.

Dunlin

Peak numbers in most winters occur in mid-winter (December and January) with high numbers also sometimes occurring in November and February (Fig. 2d).

The annual maxima varied between 4155-12050 over this period. However, excluding Douglas Estuary/Dunkettle and the winters of 2000/01 and 2002/03 reduces the variation to between 3764-6750. These adjusted maxima show a peak in December 1997. However, on this count the Ballintubrid and Weir Island sectors (which held 1620 Dunlin on this count) were counted a week earlier than the adjacent Belvelly-Marino Point and North Channel-Ballintubrid sectors (which held 5450 Dunlin). As Dunlin numbers in the Ballintubrid and Weir Island sectors are very variable, it is quite possible that some double-counting occurred as a result. Taking this into account, and the missing counts from the Douglas Estuary, the adjusted maxima indicate that the Cork Harbour Dunlin population fluctuated around 10000-12000 in the late 1990s, with no evidence of any significant decline up to the winter of 1999/00. Much lower numbers were recorded from 2000/01 onwards, but interpretation of this data is complicated by the amount of missing counts. However, the peak numbers at most of the key sectors, when they have been counted, have been much lower than in the late 1990s indicating that there has been a real decline. In 2002/03, the peak number, allowing for the missing counts, probably did not exceed 5000 birds, a dramatic decline from the numbers present in the late 1990s.

Curlew

Peak numbers in most winter were recorded in either September or October. Numbers from November-February are generally, although not always, significantly lower than the autumn peak and show considerable fluctuations (Fig. 2e). This probably reflects the tendency for a large proportion of the Cork Harbour Curlew population to feed on fields during the winter, and to only use the estuaries as nocturnal roosts. Evening counts, which I have carried out, of roosting Curlews on the Glounthaune Estuary/Slatty Water suggest that I-WeBS counts routinely underestimate the mid-winter Curlew numbers.

The annual maxima varied between 1289-3031 over this period. Excluding Douglas Estuary/Dunkettle and the winters of 2000/01 and 2002/03 does not significantly reduce this variation (1131-2931). These adjusted maxima suggest that numbers were significantly higher between 1997/98-1999/00 compared to 1995/96-1996/97. The 2002/03 maximum suggest a return to the 1995/96-1996/97 levels, even taking into account the missing counts in September 2002 (which could have reduced the 2002/03 maximum by around 300). Taking account of the missing counts, it is likely that the Cork Harbour Curlew population was approaching the threshold for international importance (3500) during 1997/98-1999/00, but in 2002/03 did not significantly exceed 2000.

Other nationally important species

One other nationally important species, Lapwing, shows clear evidence of a substantial decline during the period under review. Interpretation of the data is complicated by the number of missing counts in the mid-winter period (when Lapwing numbers peak) in 2000/01 and 2001/02, and the fact that numbers at individual sub-sites tend to fluctuate substantially across the mid-winter months. However, even when poor coverage is taken into account, numbers in 2001/02 and 2002/03 probably did not significantly exceed 5000, compared to peak counts well over 10000 at the start of this period.

One nationally important species, Little Egret, shows a clear increase during the period under review. This is not surprising given its recent colonisation of Ireland. However, there also has been a change in the seasonal patterns of egret numbers in Cork Harbour (Fig. 2f). During the winters of 1995/96-1999/00 there were no strong seasonal trends, with numbers remaining fairly similar throughout the I-WeBS season. However, in 2000/01-2002/03 numbers show a marked peak in September/October with mid-winter numbers less than 50% of the autumn peak; note that this change in seasonal trends would be even more marked without the effects of the poor autumn coverage in 2000/01-2002/03. This change coincides with the development of the Cork Harbour breeding colony (Colony C in Smiddy, 2002) and presumably reflects the occurrence of young birds from this colony in autumn before they disperse away from Cork Harbour.

Taking account of the missing count data, most of the other nationally important species do not show any consistent trends of either increase or decrease across the period under review. In particular, it is important to note that there is no evidence for a decline in numbers of Bar-tailed Godwits in Cork Harbour, and it is likely that numbers have consistently remained above the threshold for national importance, contrary to Colhoun (2001a; 2001b) and Crowe and Boland (2004). The low counts in the winters of 1997/98-1999/00 were due to the lack of coverage of the Douglas Estuary during this period.

 

Conclusions

Waterbird populations of Cork Harbour, 1994/95-2002/03

Two species (Black-tailed Godwit and Redshank) regularly occurred in internationally important numbers during this period. Black-tailed Godwit numbers probably peaked at over 3000 in 1998/99 and 2002/03. Redshank numbers probably peaked at over 2500 in 1997/98-1999/00.

Twenty species regularly occurred in nationally important numbers during this period. Three of these species (Shelduck, Dunlin and Curlew), occurred in numbers that are greater than 50% of the threshold for international importance. Shelduck numbers peaked at over 2600 in 1996/97 but otherwise probably remained fairly stable at around 2000 each winter. Dunlin numbers were probably fairly stable at around 10000-12000 in the late 1990s, but have declined since 2000/01 to less than half this number. Curlew numbers probably peaked at around 3500 in 1997/98-1999/00. Other nationally important species that show strong trends across this period are Lapwing (decline of over 50%) and Little Egret (rapid increase). Contrary to published data, there has probably been no significant change in the status of Bar-tailed Godwits and numbers of this species remain nationally important. The decline in total waterfowl numbers in Cork Harbour reported by Crowe and Boland (2004) is probably largely due to the declines in Lapwing and Dunlin numbers.

Has it been worth the effort?

The level of coverage during this period is not impressive: in only one winter was anything approaching full coverage achieved. This is not to say that incomplete counts are worthless. Firstly, any count, however incomplete, that exceeds either national or international importance thresholds is of nature conservation (and possibly legal) significance and provides data to justify the continued conservation importance of Cork Harbour. However, it could be argued that, at this stage, the conservation importance of Cork Harbour is well established and the effort of annual I-WeBS coverage is not justified simply to confirm the status quo. Secondly, as I have attempted to do in this article, with sufficient local knowledge and taking gaps in coverage into account, even incomplete counts can indicate annual trends in species populations. Obviously, however, a considerable degree of caution needs to be attached to such interpretations and only large-scale trends (such as the 50% decline in Lapwing and Dunlin numbers) can be reliably detected. It is unfortunate that the national summaries of I-WeBS results have largely ignored the incomplete coverage of Cork Harbour, with the result that misleading interpretations of species status and trends may be derived from these summaries (e.g., the apparently non-nationally important status of Bar-tailed Godwit in Crowe and Boland, 2004).

One of the key objectives of I-WeBS is to monitor national waterbird populations. Therefore, a relevant question to consider is to what extent has the poor level of coverage in Cork Harbour affected national population estimates and trends? For several species, Cork Harbour holds a significant proportion of the national population (based on the data in Table 1 of Crowe and Boland, 2004): e.g., Shelduck (c. 30%), Black-tailed Godwit (c. 30%), and Redshank (c. 20%). For these species, the Douglas Estuary holds 20-30% (Black-tailed Godwit), or 10-15% (Shelduck and Redshank) of the Cork Harbour population. Moreover, although Cork Harbour only holds around 7% of the national Bar-tailed Godwit population, the Douglas Estuary holds around 90% of the Cork harbour population. Therefore, the lack of coverage of the Douglas Estuary in 1997/98-1999/00 will have reduced the overall national population estimates of these species by 6-9% (Black-tailed Godwit), 6-7% (Bar-tailed Godwit), 3-4.5% (Shelduck) and 2-3% (Redshank). As Crowe and Boland (2004) describe changes in population indices of greater than +2% and less than –1% as representing increases or declines, it seems that the lack of coverage of the Douglas Estuary in 1997/98-1999/00 could have had significant effects on detection of national trends in waterbird populations.

One potentially important factor that I have not considered in detail in this article is the potential effects of lack of co-ordination between count sectors on the accuracy of overall counts. Figure 1 shows that on many counts, different count sectors were counted days or even weeks apart. This is, however, a rather simplistic analysis because three groups of count sectors are relatively isolated and each group is counted by a single observer in one counting session: Saleen, Aghada and Whitegate; Monkstown Creek, Ringaskiddy-Luc Strand and Lough Beg; and the Owenboy Estuary. Therefore, lack of co-ordination of these count sectors with the overall count may not be a significant factor, at least over a period of a few days. However, movement between count sectors in the Inner Harbour and the North Channel will occur over this period of time, due to factors such as tidal cycles between spring and neap tides and weather conditions. Even over short time periods (within counts) movement can occur due to disturbance. There are also some predictable patterns of movement that occur, such as waders feeding on the silt lagoon at Dunkettle on the rising tide, and then moving to the Douglas Estuary roosts at high tide. All these factors mean that, in my view, counts carried out more than a day or two apart in different count sectors in the Inner Harbour and the North Channel are highly likely to have been affected by movement of birds between count sectors, and that, for certain groupings of count sectors, careful co-ordination of counts carried out on the same day is required to avoid this effect.

The future

It is clear from the information presented in this article that achieving adequate I-WeBS coverage of Cork Harbour is difficult. I want to emphasise that I am not criticising either the count organisers, or the counters (except for one individual, who shall remain nameless, who is responsible for the lack of coverage of the Douglas Estuary in 1997/98-1999/00!). As a counter throughout this period, and count organiser in recent years, I fully appreciate the difficulty of the task. There has been an attrition of experienced counters over the years, and a difficulty in finding replacements. Key sectors of Cork Harbour are difficult and challenging to count, and require counters with wader identification skills, and good local knowledge. Even when enough counters can be persuaded to take on sectors for a winter, inevitably some counters will not be able to do counts in particular months and, in these circumstances, it can be very difficult to provide cover given that familiarity with the count sector is necessary. Moreover, simply achieving the required number of counts is no guarantee that reliable data has been collected, but attempting to achieve close co-ordination of count dates and times would pose a further strain on the already fragile volunteer goodwill.

It seems to be the case that there simply is not a sufficient pool of willing and experienced volunteers to achieve adequate I-WeBS coverage of Cork Harbour at present. The laissez-faire attitude in which completion of I-WeBS counts is considered as an end in itself without any audit of the quality of the data generated is unsatisfactory, and, in my view, the point of continuing I-WeBS coverage of Cork Harbour in this manner must be seriously questioned.

 

Acknowledgements

Thanks are due to all those who participated in the counts: Anita Donaghy, Tom Gittings, Carla Hill, Harry Hussey, the Hutchinson family, Alec Jeffrey, Lesley Lewis, Eleanor Mayes, Paul Moore, Tony Nagle, John O'Halloran, Barry O'Mahony, Denis O'Sullivan, George Phipps, Mark Shorten, Pat Smiddy, Jim Wilson, Mark Wilson. The counts were co-ordinated by Mark Shorten (1994/95), Carol Styles (1995/96 and 1996/97), Paul Moore (1997/98-2001/02) and Tom Gittings (2002/03). Data were supplied by the Irish Wetland Bird Survey (I-WeBS), a joint scheme of BirdWatch Ireland, National Parks and Wildlife Service and The Wildfowl & Wetlands Trust, and I am grateful to Olivia Crowe for facilitating this and other assistance.

 

References

Colhoun, K. (1998) I-WeBS Report 1996-97: Results of the third winter of the Irish Wetland Bird Survey. Birdwatch Ireland, Dublin.

Colhoun, K. (2000) I-WeBS Report 1997-98: Results of the fourth winter of the Irish Wetland Bird Survey. Birdwatch Ireland, Dublin.

Colhoun, K. (2001a) I-WeBS 1999-00: summary of the sixth I-WeBS season. I-WeBS News, 2-14.

Colhoun, K. (2001b) I-WeBS Report 1998-99: Results of the fifth winter of the Irish Wetland Bird Survey. Birdwatch Ireland on behalf of the I-WeBS partners (BWI/NPW/WWT), Dublin.

Colhoun, K. (2002) Waterbird monitoring in Ireland 2000/01: Results of the seventh year of the Irish Wetland Bird Survey (I-WeBS). Irish Birds, 7, 43-52.

Coveney, J.A. (1992) Cork Harbour counts: an interim report. Cork Bird Report, 1991, 71-75.

Crowe, O. & Boland, H. (2004) Irish Wetland Bird Survey: Results of waterbird monitoring in Ireland in 2001/02. Irish Birds, 7, 313-326.

Delany, S. (1996) I-WeBS Report 1994-95: Results of the first winter of the Irish Wetland Bird Survey. IWC Birdwatch Ireland, Dublin.

Delany, S. (1997) I-WeBS Report 1995-96: Results of the second winter of the Irish Wetland Bird Survey. Birdwatch Ireland, Dublin.

Hutchinson, C.D. & O'Halloran, J. (1984) The waterfowl of Cork Harbour. Irish Birds, 2, 445-456.

Leonard, P.G. (1993) Cork Harbour Counts 1992-1993. Cork Bird Report, 1992, 74-80 and 100.

Shorten, M. (1994) Waterfowl counts in Co. Cork in the winters 1992/93 and 1993/94. Cork Bird Report, 1993, 69-72.

Smiddy, P. (2002) Breeding of the Little Egret Egretta garzetta in Ireland, 1997-2001. Irish Birds, 7, 57-60.

Smiddy, P., O'Halloran, J., Coveney, J.A., Leonard, P.G., & Shorten, M. (1995) Winter waterfowl populations of Cork Harbour: an update. Irish Birds, 5, 285-294.

Underhill, L.G. & Prys-Jones, R. (1994) Index numbers for waterbird populations. I. Review and methodology. Journal of Applied Ecology, 31, 463-480.


Table 1. Coverage achieved in I-WeBS counts of Cork Harbour, 1994/95-2002/03.

 

Count sectors not covered:

Winter

Sep.

Oct.

Nov.

Dec.

Jan.

Feb.

Mar.

1994/95

 

 

 

 

 

 

 

1995/96

Bn, DE, Dk, LB, MC, OE, RLS

DE, Dk, LB, MC, OE, RLS

 

Dk

 

LB, MC, OE, RLS

MC, OE, RLS

1996/97

 

 

 

LB, MC, OE, RLS

 

 

 

1997/98

DE

DE

 

DE, Dk

DE

DE, Dk

DE

1998/99

DE

DE

DE

DE

DE, Dk

DE, LB, MC, OE, RLS

DE, Dk,  LB, MC, OE, RLS

1999/00

DE, Dk

DE, Dk

DE

DE

DE, Dk

DE,

DE, Dk

2000/01

Bn, BMP, Ck, DE, Dk, LB, MC, NCB, OE, R&A, RLS

BMP, Ck, DE, NCB, RLS

BMP, Ck, Dk, LB, MC, NCB, OE, RLS

Bn, BMP, Ck, NCB, R&A

BMP, Ck, LB, MC, NCB, OE, RLS

BMP, Ck, LB, MC, NCB, OE, RLS

 

2001/02

Bn, BMP, Ck, DE, LB, MC, NCB, OE, R&A, RLS

Bn, BMP, Ck, Dk, LB, MC, NCB, OE, R&A, RLS

Bn, BMP, Ck, LB, MC, NCB, OE, R&A, RLS

Bn, LB, MC, OE, R&A, RLS

Bn, OE, R&A

Bn, Dk, OE, R&A

Bn, BMP, Ck, DE, GSW, LB, MC, NCB, OE, R&A, RLS

2002/03

BMP, Ck, Dk, LB, MC, NCB, OE, RLS

Bn, OE, R&A

OE

 

LB, MC, RLS

Dk

Dk

Count sectors: Bn = Ballynacorra; BMP = Belvelly-Marino Point; Ck = Cuskinny; DE = Douglas Estuary; Dk = Dunkettle; GSW = Glounthaune Estuary/Slatty Water; LB = Lough Beg; MC = Monkstown Creek; NCB = North Channel-Ballintubrid; OE = Owenboy Estuary; R&A = Rathcoursey & Ahanesk; RLS = Ringaskiddy-Luc Strand.

Blank cells indicate that full coverage was achieved. Cells with a diagonal line indicate that no co-ordinated I-WeBS count was carried out.

Coverage of the Douglas Estuary in 2001/02 was severely affected by bridge maintenance work, and many counts were considered to be gross underestimates.


Table 2. Annual maximum counts, including the Douglas Estuary and Dunkettle.

 

1994-95

1995-96

1996-97

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

Great Northern Diver

6

1

2

4

1

8

3

1

1

Little Grebe

64

54

67

75

56

50

58

59

60

Great Crested Grebe

282

287

330

275

166

218

171

287

240

Cormorant

347

991

564

219

284

556

244

392

326

Little Egret

2

7

10

16

20

18

27

39

61

Grey Heron

51

130

91

117

71

61

114

57

97

Mute Swan

28

39

57

31

46

42

25

15

42

Shelduck

1841

2124

2621

1517

1875

1870

722

1108

1903

Wigeon

2601

2178

2262

1403

1683

1402

1272

1519

1931

Teal

986

1381

912

1033

994

1214

1139

1079

1492

Mallard

343

441

619

617

671

572

431

362

489

Pintail

17

93

42

58

63

41

2

74

73

Shoveler

55

101

54

123

103

148

74

48

103

Pochard

31

83

198

32

38

11

19

21

27

Tufted Duck

58

87

139

41

34

20

46

36

29

Goldeneye

35

30

35

12

18

14

18

28

11

Red-breasted Merganser

116

134

138

101

110

128

64

77

95

Moorhen

25

36

115

22

28

21

21

19

24

Coot

91

28

79

28

35

96

24

13

26

Oystercatcher

1364

1150

2709

2412

1587

1421

1698

1061

1570

Ringed Plover

0

56

145

64

59

52

78

66

28

Golden Plover

4431

1554

7525

1520

3000

3432

4009

6888

4262

Grey Plover

114

136

51

173

72

44

5

6

108

Lapwing

15204

10280

12099

7232

4861

4116

7267

2816

4016

Knot

17

37

39

20

16

17

80

79

306

Dunlin

12050

11094

12769

9413

8847

8240

6632

5155

4924

Black-tailed Godwit

309

1411

1823

2060

2565

1692

1615

2128

3162

Bar-tailed Godwit

332

456

517

124

16

52

351

419

477

Curlew

1669

1421

1701

3031

2927

2223

1297

1329

1817

Redshank

1344

2269

2076

2146

2243

2269

1005

1138

2170

Greenshank

22

31

48

46

46

61

31

25

60

Turnstone

65

127

122

76

166

146

93

66

145


Table 3. Annual maximum counts, excluding the Douglas Estuary and Dunkettle.

 

1994-95

1995-96

1996-97

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

Great Northern Diver

6

1

2

4

1

8

3

1

1

Little Grebe

64

51

65

75

56

50

58

56

52

Great Crested Grebe

282

222

267

275

166

218

171

187

236

Cormorant

299

977

447

199

281

526

224

369

311

Little Egret

2

7

10

16

20

18

27

36

54

Grey Heron

30

107

76

95

71

61

94

37

48

Mute Swan

26

39

55

31

46

42

25

14

42

Shelduck

1719

1937

2205

1517

1875

1868

614

1005

1716

Wigeon

1692

1694

1749

1403

1683

1382

1022

1218

1606

Teal

902

1265

673

1033

994

1207

848

897

1210

Mallard

326

399

525

614

671

562

369

358

459

Pintail

17

93

42

58

63

41

2

74

73

Shoveler

48

100

54

123

103

148

74

48

95

Pochard

31

83

198

32

38

11

19

21

27

Tufted Duck

56

74

111

41

34

20

22

17

24

Goldeneye

20

4

14

12

18

14

1

2

6

Red-breasted Merganser

114

130

138

101

110

128

64

72

95

Moorhen

25

35

114

22

28

21

21

19

24

Coot

89

25

79

28

35

96

24

13

26

Oystercatcher

1352

1150

1439

1972

1489

1421

1698

944

1067

Ringed Plover

0

56

115

59

50

52

78

66

28

Golden Plover

630

1553

2670

1520

937

500

1130

1780

890

Grey Plover

114

130

51

173

72

44

5

5

91

Lapwing

11477

7400

8299

5832

4561

3116

5357

2266

2406

Knot

1

37

37

20

16

17

23

9

190

Dunlin

5493

6660

5769

9158

8297

6740

3332

4155

3764

Black-tailed Godwit

256

1096

1348

2010

2480

1692

1615

1880

2322

Bar-tailed Godwit

63

59

232

114

12

36

31

49

47

Curlew

1486

1131

1475

2931

2847

2223

1297

1194

1297

Redshank

1153

1839

1840

2100

2243

2249

847

1053

1970

Greenshank

22

31

46

45

46

61

28

22

59

Turnstone

60

127

122

71

166

146

93

66

145


Table 4. Mean annual five year maxima.

 

Five year maxima

Importance thresholds

 

98/99-02/03

96/97-99/00 and 02/03

International

National

Great Northern Diver

3

3

50

-

Little Grebe

57

62

-

30

Great Crested Grebe

216

246

-

35

Cormorant

360

390

1200

105

Little Egret

33

25

800

 

Grey Heron

80

87

4500

105

Mute Swan

34

44

2400

100

Shelduck

1496

1957

3000

125

Wigeon

1561

1736

12500

1000

Teal

1184

1129

4000

500

Mallard

505

594

20000

500

Pintail

51

55

600

20

Shoveler

95

106

400

40

Pochard

23

61

3500

350

Tufted Duck

33

53

10000

300

Goldeneye

18

18

3000

100

Red-breasted Merganser

95

114

1250

25

Moorhen

23

42

 

 

Coot

39

53

15000

300

Oystercatcher

1467

1940

9000

700

Ringed Plover

57

70

500

100

Golden Plover

4318

3948

18000

1500

Grey Plover

47

90

1500

50

Lapwing

4615

6465

20000

2000

Knot

100

80

3500

250

Dunlin

6760

8839

14000

1200

Black-tailed Godwit

2232

2260

700

80

Bar-tailed Godwit

263

237

1000

175

Curlew

1919

2340

3500

1000

Redshank

1765

2181

1500

250

Greenshank

45

52

3000

20

Turnstone

123

131

700

100

Internationally important species are shown in bold. Nationally important species are shown in italics.


Figure Legends

Figure 1. Degree of co-ordination of Cork Harbour counts. This graph shows the frequency distribution across all Cork Harbour I-WeBS counts of the number of days between the earliest and latest dates on which counts were carried out each month.

Figure 2. Seasonal trends in numbers of selected waterbird species in Cork Harbour (excluding Douglas Estuary/Dunkettle). For most species, no data is included for 2000/01 and 2001/02 due to the poor levels of coverage in those winters. Note that there was no count in November 1997.

Figure 3. Relationship between autumn and winter peak counts of Black-tailed Godwits in Cork Harbour. All counts exclude Douglas Estuary and Dunkettle. Data has been adjusted to take account of missing count sectors as follows: 1995/96 autumn + 150; 2000/01 autumn + 300; 2000/01 winter + 200; 2001/02 autumn + 300.