Breeding abundance

The annual sample of common gull colonies is insufficient to produce reliable trend information for the UK as a whole. Note that the only comparable data from national censuses relate to coastal-nesting common gulls. Coastal nesting birds increased by 24% between 1969-70 and 1985-88, with another increase of 36% up to Seabird 2000.  The reason for the increase in abundance of coastal nesters is not known; it is possible that it may have been an artefact due to less complete survey coverage during the earlier censuses. With Scotland holding about 98% of the UK population, the trend there can be used as a proxy for the UK situation post Seabird 2000, and suggests that numbers have declined since the last census. American mink Neovison vison are known to have severe negative effects at a local level, taking both eggs, chicks and adults, and causing colony abandonment^1,2, but it is unknown whether this is the main reason for the apparent decline nationally.

During Seabird 2000 over half (57%) of the total population in Britain and Ireland bred inland. Due to colonies being surveyed infrequently no trend can be generated from data submitted to the SMP. However, some large inland common gull colonies in Scotland are known to have declined severely, although the reasons are unknown.

Productivity

Figure 1: Trend in UK productivity (no. of chicks fledged per pair) of common gull 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

The sample of colonies for which productivity was studied may not be representative of the UK. Most information comes from a study of the effects of American mink control on productivity of gulls and terns in western Scotland², which shows significant negative effects of mink, although results in some years may be partially clouded by predation of common gull eggs by larger gulls. Common gull breeding success data collected from this study area between 1996 and 2013 found colonies with successful mink control fledged an average of 0.71 chicks per pair per year, compared to 0.30 at colonies with no, or unsuccessful, mink control; on average breeding success was 57% (range 27-77%) lower at colonies in the latter group. In 2014, success at these two groups of colonies was 0.68 and 0.19 chicks fledged per pair, respectively - a difference of 72%³.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

Figure 1: Trend in abundance index (solid line) of coastal-nesting common gulls in Scotland, 1986-2015 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

Coastal nesting common gulls in Scotland have been increasing since 1969-70 according to national census data. Numbers recorded during Seabird 2000 were 35% higher than during the Seabird Colony Register, and 67% higher than during Operation Seafarer. The abundance trend using the SMP sample agrees with the national census data over the same period, although suggests a slightly higher abundance at the time of Seabird 2000. Since 2005, the trend has been downward, with the index in 2015 at 22% below that of 1986.

Numbers at some large inland common gull colonies, not part of the analysis above, are known to have declined severely, for unknown reasons. For example, the first systematic survey of colonies at the Correen Hills and Mortlach Hills in 1988-89 found 24,500 and 16,200 AON, respectively. By 1995, the Correen Hills colony had declined to 6,400 AON, and by 1998, had become extinct. The Mortlach Hills colonies have also declined since 1998 when they held 18,136 AON; 6,565 AON were recorded in 2003 and 6,240 AON in 2007/08. It is doubtful whether decreases at both these areas have been compensated for by increases at existing colonies or by the establishment of others. Few large colonies are routinely surveyed as part of the SMP. Two major colonies (Tom Mor and Tips of Corsemaul both Moray) held just 4,156 and 2,084 in 2007 and 2008 respectively. No additional data has been collected at any inland colony holding at least 2,000 AON since then.

Productivity

Figure 2: Trend in productivity (no. of chicks fledged per pair) of common gull in Scotland, 1986-2016. Based on SMP data;  view the methods of analysis (PDF 158 kb).

The productivity of common gulls in Scotland shows no clear trend across the entire recording period but does appear to have declined since the late 1990s with poor breeding seasons in 2008, 2011, 2013 and 2015. Most information collected is from a study of the effects of American mink control on productivity of gulls and terns on west coast islands², so may not be representative of Scotland as a whole. This mammal can have a significant depressive effect on breeding success. Common gull breeding success data collected from this study area between 1996 and 2013 found colonies with successful mink control fledged an average of 0.71 chicks per pair per year, compared to 0.30 at colonies with no, or unsuccessful, mink control; on average breeding success was 57% (range 27-77%) lower at colonies in the latter group. In 2014, success at these two groups of colonies was 0.68 and 0.19 chicks fledged per pair respectively - a difference of 72%³. Trapping in recent years, specifically targeting colonies where the American mink are most active, has helped to raise the number of young fledged. However, trapping effort increased in the late 1990s but may have decreased since, possibly explaining the decline in overall productivity over the last decade shown in Figure 2.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

Few common gulls nest in England: eight pairs were recorded during Operation Seafarer rising to 31 pairs by the Seabird Colony Register. During Seabird 2000, 15 colonies were known with total numbers close to that recorded by the SCR. Since Seabird 2000, numbers of common gulls in England have probably remained at least stable and may even have increased. For example, between 2003 and 2014 reports were received from a sample of between five and nine colonies annually and numbers ranged from 20 AON (2004 and 2005) to 64 AON (2008). However, only 21 pairs were reported from six colonies in 2015; Havergate Island (Suffolk) and Holkham NNR (Norfolk) are the main colonies holding 6 and 7 AON respectively.

Productivity

With only a handful of pairs nesting in England, few meaningful data on productivity are received. Monitored pairs tend to be in colonies containing terns which receive most of the targeted effort toward recording breeding performance. Complete failure is usually noticed and recorded, but successful years may not be recorded. Hence, productivity data for this species may be biased toward collecting zeros so the estimated average productivity of 0.23 chicks fledged per nest per year (there was no significant difference over time) may be low due to this potential bias. 

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

Common gull no longer breeds in Wales. Two pairs were recorded during Operation Seafarer but none were found during the later censuses. 

Productivity

This species ceased to breed in Wales before the SMP started so no data on productivity are available.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

Figure 1: Abundance of common gull at Strangford Lough (Co. Down), 1986-2015.

National census data show the number of common gulls nesting along the coast of Northern Ireland increased between Operation Seafarer and Seabird 2000, and this increase appears to have continued. Common gull numbers at Strangford Lough (Co. Down, Figure 1), one of the largest and most frequently counted colonies in the region, increased steadily from the late 1980s to 1999. A sharp decline occurred between 1999 and 2002 (access restrictions due to foot and mouth disease prevented counting in 2001) as numbers fell from 138 to 28 AON. Numbers then increased rapidly to a peak of 532 AON in 2010 but have declined since with only 229 AON recorded in 2015. A further 93 pairs were estimated at three other colonies in 2014. The Copeland Islands (Co. Down), another major colony which held 452 AON in 2012, were not counted since then, although numbers there have decreased since 2009 when 850 AON were estimated to be nesting. Thus, coastal colonies visited in 2015 hold a minimum of 350 AON, with unsurveyed colonies likely to hold a few hundred more, so the total population will be above that recorded by Seabird 2000.

Inland colonies, which held 174 AON during Seabird 2000, have not been surveyed to any great extent in recent years although 164 AON were recorded at the largest one on Lower Lough Erne (Co. Fermanagh) in 2015.

Productivity

Data submitted to the SMP on the productivity of common gulls in Northern Ireland are sparse; thus, no meaningful average productivity value can be given.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

During Seabird 2000, 586 pairs of common gull were recorded in the Republic of Ireland, five times as many as had been recorded by the Seabird Colony Register, but still 100 pairs fewer than were found by Operation Seafarer. Few data have been collected since, with no regular monitoring at all but the smallest colonies, and so the current status of the population is unknown.

Productivity

Data submitted to the SMP on the productivity of common gulls in the Republic of Ireland are sparse; thus, no meaningful average productivity value can be given.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

National census data show numbers increased greatly between the Seabird Colony Register and Seabird 2000, after a large decline from that recorded by Operation Seafarer. Large increases have been recorded at some colonies in Northern Ireland over the past decade but the trend in the Republic of Ireland is unknown due to few colonies of any size being surveyed. However, the total Irish population probably now lies slightly above that recorded by Seabird 2000. The small sample of colonies counted between 2012 and 2015 (12 of about 100 known colonies during the last census, both coastal and inland) were entirely in Northern Ireland (which held c.35% of the Irish population during Seabird 2000) with a composite figure suggesting they hold around 1,000 nesting pairs; the total coastal and inland population during Seabird 2000 was just over 1,600 pairs.

Productivity

Data submitted to the SMP on the productivity of mew gulls from colonies throughout Ireland are sparse; thus, no meaningful average productivity value can be given.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.

Breeding Abundance

Only a few pairs of common gull nest on the Isle of Man. Five pairs were found during the Seabird Colony Register and six pairs during Seabird 2000. No data have been received recently although the one colony is surveyed near-annually for other species; it is possible that common gulls no longer breed on the Isle of Man.

Productivity

No systematic data on the productivity of common gulls on the Isle of Man have been submitted to the SMP.

Common gull does not breed on the Channel Islands.