Herring Gull Larus argentatus

Breeding abundance

Figure 1: Trend in UK abundance index (solid line) of herring gull 1986-2011 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

Between 1969/70 and 1985-88, the UK herring gull population decreased by 48%. This decline continued between 1987 and 1990, with a subsequent recovery to 1994 (Figure 1). A further drop in abundance is apparent after 2000; although rapid at the start, this decline levelled off for a few years but now appears to be continuing again. At the time of the Seabird 2000 census, around 14% of the population nested on buildings, as compared with natural habitats; a proportion and total number that increased from 1976 (when just 63 pairs nested on roofs) to 1993-95¹ (10,900) and 1998-2002 (20,000). The abundant food supply in urban areas provided by street litter and insecure refuse bags/bins, combined with abundant safe nesting sites, has probably encouraged this increase¹. We do not know the current number of urban nesting gulls.

Despite the increases in urban-nesters, the total herring gull population is now at its lowest level since monitoring began in 1969/70. The reason for the decline is not well understood. Botulism is thought to have been a major factor in the decline between the first two censuses and possibly thereafter; refuse tips may be the source of the Clostridium botulinum bacterium that causes the disease, which also is widespread in wetland sediments². Decreases in the availability of food scavenged from refuse tips (associated with changes in refuse management in recent years)² and reductions in discards from fisheries³ have also likely played a role in decreasing herring gull populations. Ground predators have also had an affect at some colonies.

Productivity

Figure 2: Trend in UK productivity (no. of chicks fledged per pair) of herring gull 1986-2011. Based on SMP data; view the methods of analysis (PDF 158 kb).

Although there are big fluctuations in UK herring gull productivity between 1989 and 1999 there does appear to be an underlying declining trend during this period. From 2000 onwards productivity improved and has been relatively stable over the last decade although has never been high. Most information comes from a study of the effects of mink control on productivity of gulls and terns in western Scotland, which shows significant depressive effects of mink, for example by an estimated 26% in 2009, and by 30% in 2010⁴.

Recent analysis by Cook and Robinson⁵ found the mean breeding success of herring gulls at monitored nests was 0.75 and declined at a rate of 0.016 chicks per nest per year. This equated to a decline of 31% over the period 1986-2008. The quality of the existing dataset meant a change in breeding success greater than 10% could be detected with confidence. Population viability analysis (using available life history information such as population size, clutch size, age at first breeding and survival rates of different age classes) predicted that, were this rate of success to be maintained, herring gull populations would decline by 60% over 25 years. For the population to stabilize, breeding success would have to increase to 1.30-1.50 chicks per nest per year.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Figure 1: Trend in abundance index (solid line) of herring gull in Scotland,1986-2011 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

The trend for Scotland shown above shows a decreasing index during the late 1980s, followed by a period of relative stability before another decline from 2000 onward. Herring gull abundance in 2011 is now at its lowest point with in index currently only 42% of that in 1986. This comes on top of a longer term decline; numbers had already fallen by 42% between Operation Seafarer and the Seabird Colony Register. In summary, herring gull numbers are now far lower than at any time since 1969/70.

Numbers nesting on buildings in towns and cities increased from 1976 (55 pairs) to 1993-95¹ (3,568) and 1998-2002 (5,843). The current size of the population in towns is unknown. The increases in urban-nesters do not make up for the overall declines recorded at coastal colonies.

Productivity

Figure 2. Trend in productivity (no. of chicks fledged per pair) of herring gulls in Scotland, 1986-2011. Based on SMP data; view the methods of analysis  (PDF 158 kb).

The graph above closely matches that shown for the UK as much of the data is collected in Scotland. The trend in productivity for Scotland appeared to be declining during the first half of the recording period and was especially low from 1997-1999. This was probably due to predation by American mink at colonies on the west coast. Since 2000, productivity has been relatively stable, perhaps in response to trapping programmes at colonies where mink were active.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Figure 1: Abundance of herring gull at South Walney, 1986-2011.

In common with herring gull populations in Scotland and Wales, numbers in England declined greatly between the censuses in 1969/70 and 1985-88. By Seabird 2000, although the population had increased, numbers were still some 18,000 pairs lower than during Operation Seafarer. The trend in abundance, calculated from colonies sampled for the SMP, over-estimates this increase, rendering it unrepresentative. However, numbers at South Walney, the largest colony in England holding about one-fifth of the national population, had fallen by three-quarters between 2000 and 2011. Of other large colonies (>1,000 pairs) monitored regularly over the last decade, Rockcliffe, Orfordness and Outer Trial Bank have all declined with only Steep Holm increasing. In contrast, the number of roof-nesters increased greatly, from 1,960 pairs in 1976 to 6,383 pairs in 1993-95¹ and to 12,284 pairs by Seabird 2000. The current size of the urban population is unknown, though recent increases have occurred in towns in NW and SW England.

Productivity

Relatively few data are available on the productivity of herring gulls at English colonies. There was no statistically significant variation over time; on average approximately 0.71 chicks fledged per pair per year between 1990 and 2011.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Herring gull numbers fell by 77% in Wales between Operation Seafarer and the Seabird Colony Register and although an increase (of 26%) was detected by Seabird 2000, numbers recorded were still 25,000 pairs lower than in 1969/70. Further losses may have occurred over the last decade; 19 colonies counted in 2011 held 4,782 pairs compared with 5,435 pairs during Seabird 2000, representing a fall of 12%, although this change could easily be accounted for by other sources of error e.g. observer differences, timing of survey relative to timing of nesting.

Roof-nesters increased from 772 pairs in 1993-95¹ to 1,826 pairs in Seabird 2000. In 2011, a survey of Cardiff urban gulls alone recorded 640 AON. This represents a remarkable turn around in fortunes as supposedly no roof-nesting herring gulls were recorded in Cardiff during Seabird 2000. Previous estimates indicated 425 pairs there in 1975 falling to 4 pairs by 1993.

Productivity

Figure 1. Trend in productivity (no. of chicks fledged per pair) of herring gulls in Wales, 1986-2011. Based on SMP data; view the methods of analysis  (PDF 158 kb).

The number of herring gull chicks fledged at colonies in Wales has been declining since 1994. Birds were very successful in that year, fledging almost two chicks per pair but between 1998 and 2011 herring gulls have usually fledged less than one chick per pair. Productivity was particularly low in 2008 due to unknown factors.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Figure 1: Trend in abundance index (solid line) of herring gull in Northern Ireland,1986-2011 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

Seabird 2000 found that herring gull numbers in Northern Ireland had declined severely since the previous census. Between Operation Seafarer and the Seabird Colony Register, numbers were buoyant when populations in other UK countries, and in the Republic of Ireland, were falling. The subsequent massive decline of 96% left just 709 pairs by Seabird 2000. Botulism has been suspected as the main cause for large losses at some colonies e.g. Rathlin Island, the Copeland Islands and Strangford Lough. Figure 1 reveals that there has been only a very limited increase in abundance during the last decade, mostly during the last few years. Few herring gulls have been recorded nesting on roofs in Northern Ireland.

Productivity

Very little systematic data have been collected on the productivity of herring gulls in Northern Ireland as part of the SMP.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

National census data show the herring gull population of the Republic of Ireland has declined steadily since Operation Seafarer; the Seabird Colony Register recorded a 65% fall with a further decline of 64% by the time of Seabird 2000. Few colonies are monitored frequently, or in any one year (e.g. just five small colonies in 2011, most holding fewer than 40 pairs), but available data suggest that the decline has continued over the last decade; six colonies surveyed in 2010 held 1,098 pairs compared with 2,556 pairs during Seabird 2000, a fall of close to 60%. Relatively few herring gulls have been recorded nesting on roofs in the Republic of Ireland.

Productivity

Very few systematic data have been collected on the productivity of herring gulls at colonies in the Republic of Ireland as part of the SMP.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses, so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Figure 1: Trend in abundance index (solid line) of herring gull throughout Ireland, 1986-2011 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis (PDF 158 kb).

The trend in abundance of herring gull for the whole of Ireland using the SMP sample (Figure 1) closely matches that shown for Northern Ireland, where the majority of samples were collected. National census data showed that herring gull numbers had declined severely between Operation Seafarer and Seabird 2000, although numbers in Northern Ireland were actually stable between the first two censuses. The abundance trend using the SMP sample (Figure 1) suggests only a very limited recovery during the last decade. Relatively few herring gulls have been recorded nesting on roofs in Ireland.

Productivity

Very few systematic data have been collected on the productivity of herring gulls at colonies throughout Ireland as part of the SMP.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses, so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

Figure 1: Abundance of herring gull on the Calf of Man, 1986-2011.

Between Operation Seafarer and the Seabird Colony Register there was a decline of 9% in the number of herring gulls nesting on the Isle of Man. A larger decline then occurred so that by Seabird 2000 numbers had fallen a further 21% to 7,126 pairs. The current status of herring gull on the Isle of Man is unknown as only one colony, on the Calf of Man, has been surveyed since Seabird 2000. In the late 1980s and early 1990s this colony regularly held over 10% of the Isle of Man population. The most recent count available is from 2010 when 447 pairs were recorded, compared to 670 pairs in 1999. Numbers may have been underestimated in this colony in 2006; just 88 pairs were recorded. Relatively few herring gulls on the Isle of Man have been recorded nesting on roofs. 

Productivity

No systematic data have been collected on the productivity of herring gulls at colonies on the Isle of Man as part of the SMP.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Note: Inland colonies were not counted during the two earlier national censuses, so to enable direct comparison the Seabird 2000 figure refers to the coastal population only.

Breeding abundance

In common with other areas of the British Isles, the number of herring gulls breeding in the Channel Islands also declined between Operation Seafarer and the Seabird Colony Register, although the size of this fall, a decline of 11%, was less severe than elsewhere. Numbers increased by 22% between the Seabird Colony Register and Seabird 2000. Few data have been collected in the region since 1998-2002, so the current status of the population is unknown. 

Productivity

No systematic productivity data have been collected for herring gull in the Channel Islands as part of the SMP.