Gannet Eggs Research Articles

The influence of nest location and the effect of predator removal on Cape Gannet Morus capensis egg predation by Kelp Gulls Larus dominicanus vetula

The breeding range of the Cape Gannet Morus capensis currently extends to six of the ten islands formerly utilised by this species. The Cape Gannet is classified as an endangered species with a rapidly declining population. Since the mid-1950s, the global population has declined by 51% due to multiple causes, including egg predation by the Kelp Gull Larus dominicanus vetula. To assess the effect of this predation, we monitored 100 nests over an 11-week period in 2018 at the Lambert’s Bay colony in South Africa. To assess the effect of selective predator removal on the likelihood of predation, data were collected from 2006 and 2018. Our objective was to assess whether nest location and predator removal affected the likelihood of egg predation. The peripheral nests saw a higher level of egg loss (average 1.5 eggs per week) compared with the central nests (average 1 egg per week). Predator control of Kelp Gulls was implemented in 2015, 2017 and 2018. Between years, selective culling decreased the number of Cape Gannet eggs predated. However, within years, except for 2015, the predation rate on Cape Gannet eggs increased post-culling during the same year of implementation. In all three of the implementation years, predation started again (within 48 hours) after the culling commenced. Predation by this indigenous gull species is natural; however, certain human activities might have supported larger populations of Kelp Gulls leading to elevated predation intensity. The most notable being the ever-increasing existence of dumpsites and other sources of food. Predation is affecting the Cape Gannet breeding population; therefore, we suggest that an alternative, long-term, and sustainable solution be planned and implemented to reduce the effects thereof.

Persistent pollutants in Northern Gannet Morus bassanus eggs in Ireland: Levels and colony differences.

Seabird eggs are considered a favourable matrix for monitoring marine pollutants and are widely used as higher trophic level indicators. Persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and other organochlorine compounds (OCs) as well as metals have been shown to have deleterious impacts on seabirds. The Northern Gannet Morus bassanus is an avian sentinel; the largest breeding seabird in Ireland and an obligate piscivore. Gannet eggs were collected from two island colonies off the east coast of Ireland in locations with divergent history of industrialisation. Contaminant levels were measured and differences in concentrations between colonies compared. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were measured in each egg to understand the influence of diet and trophic position on contaminant levels detected. Significantly higher levels of Σ14PCBs, Σ7PBDEs and total mercury were detected in Gannet eggs from Lambay Island near Dublin (Ireland's industrialised capital city) compared to Great Saltee Island. No differences were observed in levels of other OCs (HCB, ΣHCH, ΣCHL, ΣDDT) between the two colonies. Though Gannets travel significant distances when foraging for food, tracking studies have demonstrated that birds from proximal breeding colonies maintain exclusive feeding areas. Stable isotope ratio analysis in this study demonstrated that Gannets at both locations occupy similar dietary niches, indicating that dietary differences may not be the driver of differing contaminant levels between colonies. Levels of persistent pollutants in the Gannet eggs fall below most existing thresholds for adverse effects and are within internationally reported values. Recent population growth and range expansion of Gannets in Ireland suggest that persistent pollutants are not having an immediate impact on the Gannet population. This study will inform potential monitoring programmes that can help Ireland achieve good environmental status under the European Union's Marine Strategy Framework Directive.

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and flame retardants in northern gannet (Morus bassanus) eggs from Bonaventure Island, Gulf of St. Lawrence, 1994–2014

Northern gannet (Morus bassanus) eggs from Bonaventure Island, Québec, Canada, were collected to monitor concentrations of contaminants. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) and non-ortho polychlorinated biphenyls (PCBs) were measured in eggs from 2004 and 2009, and several brominated and nonbrominated flame retardants (FRs) were measured every 2–5 years in eggs from 1994 to 2014. The sum (Σ) concentrations of PCDDs/Fs were significantly lower in 2009 relative to 2004, but the total toxic equivalent concentrations for PCDDs, PCDFs, and PCBs showed no significant differences (196 ng/kg wet weight (ww) in 2004 and 220 ng/kg ww in 2009). The mean ΣFR concentrations decreased significantly between 1994 and 2014, from 58 ng/g ww to 19 ng/g ww. Hexabromocyclododecane (HBCDD) was the principal nonbrominated FR detected in gannet eggs and ranged from <1.0 ng/g ww to 6.9 ng/g ww. The PCDD/F and nonortho PCB profiles were dominated by 2,3,7,8- tetrachloro-dibenzofuran (2,3,7,8-TCDF; from 26.2 ng/g ww to 34.8 ng/kg ww) and PCB-77 (from 1580 ng/g ww to 2650 ng/kg ww), respectively. Although the values of both ecological tracer stable isotopes of carbon (δ13C) and nitrogen (δ15N) showed differences among the years, no temporal trends were observed, which indicates relatively stable adults' diet and foraging area over this time period. The trends over time in concentrations of the studied contaminants likely reflect a decrease in environmental contamination. The mean 2012 eggshell thickness was 10% lower than the pre-DDT value and corresponded to a year of poor reproductive success.

Temporal trends of mercury, organochlorines and PCBs in northern gannet (Morus bassanus) eggs from Bonaventure Island, Gulf of St. Lawrence, 1969–2009

Since 1969, northern gannet (Morus bassanus) eggs from Bonaventure Island, Québec, have been collected to monitor concentrations of contaminants. Levels of p,p′-DDE, which caused low breeding success of Bonaventure gannets in the 1960s, decreased by 99.4% from 1969 to 2009 (17.1–0.1 mg/kg ww), with concomitant improvement of hatching success. PCBs, most organochlorines and mercury also showed decreasing trends. Stable isotopes of carbon (δ13C) and nitrogen (δ15N) were measured to track the possible influence of diet changes on concentrations of contaminants over time. The confounding effect of the combustion of fossil fuels on baseline values of δ13C (the Suess effect) was taken into account. No temporal trends were observed in δ13C and δ15N values in gannet eggs. Hence trophic level or foraging area had a negligible influence on temporal trends of contaminants.

Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the Eggs of Predatory Birds in Britain

The eggs of gannets from two Scottish colonies (Ailsa Craig, Bass Rock) of golden eagles from the Hebrides and Highlands and of merlin eggs from the Scottish borders were analyzed for 52 PAHs, including 2-7 ring parent and alkylated PAHs. Phenanthrene was the most abundant PAH in gannet eggs from Ailsa Craig, and methylnaphthalenes predominated in the eggs from other locations and species. Most PAHs were detected in eggs but none were at likely embryotoxic concentrations. The sum concentrations for all the PAHs analyzed (3.1-5.7 ng g(-1) wet wt.) and for the U.S. EPA 16 priority PAHs (2.0-4.3 ng g(-1) wet wt.) did not differ significantly between species or locations. This uniform, low-level accumulation suggests background exposure to diffuse sources. PCA indicated that 3 ring parent and alkylated PAHs predominated in the eggs of merlins and gannets from Ailsa Craig and Hebridean golden eagles; other eggs had a more mixed profile. Source signature diagnostics largely suggested a petrogenic origin for the PAHs in the merlin eggs that we analyzed but otherwise gave equivocal results and further work is needed to determine which diagnostics can be successfully applied to PAHs in eggs.

Temporal and spatial trends of PCB congeners in UK gannet eggs.

Gannet (Sula bassana) eggs collected from Ailsa Craig, Western Scotland between 1977-1998 have been analyzed retrospectively for several PCB congeners. Concentrations of a range of congeners were determined in 8-10 eggs analyzed separately for several individual years. All congeners declined in concentrations throughout the time period, but the rates of decline differed for different congeners. Declines were first order and half-lives varied between 5.4 years for PCB-101 to 10.1 years for PCB-180. Egg concentrations reflect the maternal body burden, which itself is controlled by the birds rate of intake (principally via the diet) and losses (via metabolism and other clearance mechanisms). The declining concentrations in eggs, therefore, broadly reflect reductions in prey concentrations (principally herring and mackerel) and--in turn--water column concentrations. Rates of change in PCB concentrations from this study were similar to those noted in fish-eating birds from the Baltic Sea and North American Great Lakes, and ambient air in the UK. This provides indirect evidence that gannet eggs are broadly reflecting regional/global scale clearance/removal mechanisms which are controlling ambient PCB concentrations.

Temporal and Spatial Trends of PCB Congeners in UK Gannet Eggs

Temporal and Spatial Trends of PCB Congeners in UK Gannet Eggs

Trends in organochlorine and mercury levels in Gannet eggs.

Levels of DDE, HEOD, PCBs and mercury were measured in Gannet eggs from several colonies around Britain during 1971-1987. At two colonies (Ailsa Craig and Bass Rock) sampled throughout this period, organochlorine levels declined between the early 1970s and 1983, and then increased again. The trends at other colonies, sampled over shorter periods, were generally consistent with those at Ailsa Craig and Bass Rock. Trends in mercury levels were more variable, and increases were observed at four colonies and declines at two. Some shell-thinning occurred in association with DDE contamination. However, levels of this chemical were too low to affect breeding success in the years concerned. The same was probably true of the other chemicals.

Organochlorines and eggshell thinning in northern gannets ( Sula bassanus) from Eastern Canada, 1968–1984

The northern gannets ( Sula bassanus) nesting on Bonaventure Island, Quebec, were studied from 1968 to 1984 in order to measure environmental contaminant levels and their relationship to productivity. Fresh eggs in 1969 contained a mean DDE level of 18·5 mg kg −1 and had shells which were 17% thinner than pre-1947 samples. Unhatched eggs in 1969 had no outer calcified layer, a mean thickness 20% less than the pre-1947 mean, and mean DDE concentration of 30·6mg kg −1. Significantly higher levels of eight contaminants were measured in unhatched than in fresh eggs collected in 1969. DDE and shell thinning were also intercorrelated with nine other contaminants; these data strongly implicate toxic chemicals, particularly DDE, as the main cause for the low breeding success of Bonaventure gannets from 1966 to 1974. Extensive use of DDT to control forest insects around the Gulf of St Lawrence ceased in 1969. Use of DDT, dieldrin and PCBs was restricted in North America during the early 1970s. Residues of DDT, DDD, DDE, PCBs, dieldrin, HCB and chlordane-related compounds in gannet eggs decreased significantly during this study. Heptachlor epoxide remained constant while α-HCH appeared to increase. Estimated half-lives ranged from 3·1 years for DDD to 35·4 years for oxychlordane. The breeding success and population of the colony have coincidentally increased.

Breeding Biology of the Australasian Gannet Morus Serrator (Gray) at Motu Karamarama, Hauraki Gulf, New Zealand I. the Egg

Breeding biology of the Australasian Gannet was studied over three breeding seasons (1978-80). The nest sites and density, first date and duration of egg-laying, median date of laying, clutch size and replacement laying, incubation period and egg dimensions, were measured. Similar information is available for the Atlantic Gannet and the Cape Gannet, allowing comparisons between the three Gannets to be made. The Australasian Gannet varies more in the first and median dates of laying than the Atlantic Gannet. This is thought to be related to weather and food supply. Most Australasian Gannet eggs that are lost are lost and replaced after three- quarters of the spread of laying has elapsed. In the Atlantic Gannet eggs are mostly lost and replaced before the mid-laying date. The Australasian Gannet has a proportionally larger egg than the Atlantic Gannet. These differences probablv result from the Australasian Gannet exoeriencing a less seasonal and predictable environment than the Atlantic Gannet.

Mercury, DDE, and PCBs in eggs from a Norwegian gannet colony.

Eggs taken from gannet nests in Norway were analyzed for mercury, DDE, and PCB's. Eggs collected in 1972 had mercury levels averaging 0.58 ppM, DDE levels averaging 2.1 ppM, and PCB levels averaging 7.7 ppM. While 1978 egg samples yielded lower DDE and PCB concentrations (0.66 ppM and 3.5 ppM respectively), mercury levels increased to 0.80 ppM. DDE levels were too low to affect eggshell thickness of gannet eggs. (14 references, 1 table)

Size, organic composition and energy content of north atlantic gannet Morus bassanus eggs

1. 1. Eggs averaged 3.6% adult weight. Percentage of yolk (15.5%), lipid level of the dry matter of the yolk and albumen (25.8%), and energy content (0.897 kcal·g −1) are the smallest yet recorded for any avian egg. 2. 2. Albumen, water, and nonlipid dry matter increased in direct proportion to egg weight. Yolk size and lipid content were independent of egg size. Egg size was more strongly correlated with water content than with any other component. 3. 3. Gannet eggs resemble those of other altricial species, having low lipid and high water levels. The energy content of the egg is very small compared to adult metabolic rate. which suggests that gannets invest little in egg production.

THE BREEDING BIOLOGY OF THE GANNET SULA BASSANA ON THE BASS ROCK, SCOTLAND

THE BREEDING BIOLOGY OF THE GANNET SULA BASSANA ON THE BASS ROCK, SCOTLAND