Caithness, northern Scotland, has historically been an important breeding area for Great Black-backed Gulls Larus marinus, but monitoring at selected colonies shows that numbers have declined substantially over the past 20 years. To investigate this decline in more detail a survey of the whole of the Caithness coast was undertaken during the 2023 seabird breeding season. The survey found a total of 268 Great Black-backed Gull apparently occupied nests (AON) at 76 colonies. Birds were widely distributed around the coast of Caithness with the most significant numbers being on Stroma (24% of the population) and the coast south of Wick (63%). Colonies were mostly small, with 65% holding just a single breeding pair. The results confirm that a substantial population decline of 74% in the number of AON has taken place since the Seabird Colony Register Survey in 1985–88. Larger colonies have seen a gradual decrease in numbers since the latter half of the 1990s, except for Stroma where numbers were at a minimum in c. 2005 before recovering somewhat. The cause of the Great Black-backed Gull population declines remains unclear. Breeding productivity in 2023 was towards the upper end of the range found elsewhere in Britain (0.64 to 1.45 chicks per breeding pair) and, though lower in some previous years, appears not to have been a significant contributor to the declines. Fish and discards from fisheries are important components of the diet of Caithness Great Black-backed Gulls and so reductions in fish stocks or the availability of discards (based on landings of fish at harbours around the Moray Firth) may, in part, be contributing to their declines. Disturbance by ground predators such as Red Foxes Vulpes vulpes is implicated in some recent changes in the numbers of Great Black-backed Gulls breeding on the cliffs south of Wick, and the extinction of several former colonies. We discuss other potential factors contributing to the reduction in numbers and possible methods of halting and reversing the declines of Great Black-backed Gulls.

The resources available to breeding seabirds within their foraging ranges can influence productivity, either directly through the quality and quantity of food consumed by chicks, or indirectly by affecting the foraging behaviour and efficiency of parent birds.Where local resource availability is low, or the quality of resources are poor, species with flexible time-energy budgets can increase their foraging effort to provide adequate energy and nutrients to their chicks, although this may come at the expense of nest attendance.We investigated provisioning rates and nest attendance in European Herring Gulls Larus argentatus from seven colonies across southwest Scotland and Northern Ireland during two chick-rearing periods (2013 and 2014) in relation to the food resources used by these colonies.We observed variation in provisioning rates and nest attendance between colonies, and variation between years in nest attendance.We found no significant relationships between these behaviours and the proportion of intertidal prey consumed, suggesting that provisioning rate and nest attendance did not differ between resource types at the colony level.We also found no evidence that variation in behaviours was related to breeding success.Our results suggest that, within this region, the type of resources consumed had a greater influence on Herring Gull breeding success than differences in two proxies of foraging efficiency (provisioning rate and nest attendance), although other factors may also have influenced breeding success.Our work highlights the benefit of determining what food resources are provided to chicks, in addition to measuring foraging behaviours, to fully understand the consequences of consuming different resources on the breeding success of generalist foragers.

The removal of invasive species and mitigation of habitat loss are vital conservation tools for species such as seabirds. We surveyed habitats across the entirety of a small seabird islet reserve, Ilhéu da Praia, in the Azores, two decades on from mammalian eradication and floral restoration. Here, we present a fine-scale map, to a 12 metre resolution, representing the first full habitat survey of this islet. This resource can serve as a baseline for monitoring future habitat changes to this internationally important seabird islet. Following restoration efforts in the 1990s, the islet’s dominant habitats are meadow, grassland dominated by Festuca petraea, or a combination of the two. We also report a novel observation of both Band-rumped Hydrobates castro and Monteiro’s H. monteiroi Storm Petrels breeding in the cavities of Tamarix africana, an invasive tree species.

This study documents several types of abnormal eggs of the Common Guillemot Uria aalge collected from Bempton Cliffs, Yorkshire, UK, during the 1900s and currently housed in the Natural History Museum at Tring, Hertfordshire, UK. These eggs are abnormal in terms of size, shape, colour and surface topography. We suggest that the incidence of these abnormal eggs was relatively high because the manner in which they were collected -repeated visits to the breeding colonycaused considerable disturbance and stress that in turn disrupted the normal process of egg formation. We discuss the possibility of using abnormalities in avian eggs as a measurement of environmental stress.

Identifying at-sea foraging areas is a longstanding goal for seabird ecology and conservation.GPS tracks can reveal behaviour because slow, tortuous flight often indicates searching linked to feeding attempts, but two-dimensional (2D) paths may oversimplify three-dimensional (3D) flight.Here, we present the first 3D tracks for Ascension Frigatebirds Fregata aquila and assess whether incorporating flight altitude improves our ability to describe putative behavioural states.We compare results using altitude derived from GPS loggers and barometric altimeters deployed simultaneously.Tracked birds (three females) travelled at a mean altitude of 178 m and attained maximum heights of 1,658-1,871 m (measured by barometric altimeters).Hidden Markov models based on 2D tracks defined three states (interpreted as 'search', 'slow travel' and 'fast travel').However, with 59.5% of locations defined as 'search', identifying the most important foraging hotspots would be challenging.Including altitude was informative, allowing models to define two further states by introducing high-altitude 'soaring/thermalling' behaviour (3.4% of locations) and dividing 'search' into mid-altitude (44.7%) and low-altitude (12.2%), the latter being more likely to represent prey capture.Barometric altitude was less prone to large errors than GPS, but GPS altitude was highly correlated (r = 0.94) and state assignments overlapped by 88% overall.Using GPS altitude would reduce potential tag effects and allow us to model tracks in 3D for males and lighter females, which are too small to carry both loggers.Overall, incorporating flight height from either barometric altimeters or GPS loggers into behavioural models improved our ability to distinguish putative foraging events from high-altitude flight.

Results from seabird monitoring programmes are increasingly being used to assess the state of the marine environment, but data are time consuming to collect. We used monitoring data from a colony of Common Guillemots Uria aalge in the North Sea to determine whether temporal changes in breeding success over a 34- year period were reflected in six consistently monitored plots and if individual plots showed significant differences in breeding success. Annual mean breeding success showed a four-fold difference over the study period varying from 0.261 to 0.848 young fledging per pair laying. Although the annual pattern of change was broadly reflected in all six monitoring plots there were significant differences in annual breeding success and changes in breeding success over time among the plots. Monitoring any single plot thus gave an approximate indication of the overall patterns of change over time, including periods when breeding success was reduced. However, significant among plot differences indicated that at least at this colony, robustness of colony level estimates of breeding success and changes over time were improved by monitoring multiple plots.

Pseudo-eggs are foreign objects, resembling eggs, found inside the nests of birds (Conover 1985) and have been recorded in several ground-nesting seabirds (Coulter 1980; Conover 1985; Mellink 2002; DeStefano et al. 2013; Wagner et al. 2013; Witteveen et al. 2015). They are more common among species that have larger clutches or multiple brood patches (Coulter 1980; Wagner et al. 2013) where pseudo-eggs are included to increase their clutch size (Coulter 1980; Conover 1985; Wagner et al. 2013; Witteveen et al. 2015). Albatrosses and petrels however, only lay one egg; rare two-egg clutches result from two females laying in the same nest, with one of them being an inexperienced breeder (Ryan et al. 2007). The occurrence of pseudo-eggs has only been reported for Laysan (Phoebastria immutabilis) and Black-footed Albatrosses (P. nigripes; Bartholomew & Howell 1964; Grant 1982). We did not find any record of albatrosses breeding in the Southern Ocean that exhibited pseudo-eggs.

During an 11-year period starting in the mid-1960s, large numbers of fledgling Manx Shearwaters Puffinus puffinus were ringed and recaptured on Skokholm Island, Pembrokeshire, Wales. Since it is unlikely that any more will ever be found, this paper summarises the factors that affected the chances of a fledgling surviving long enough to be recaptured on the island. Both the date on which they were ringed and their weight at that time influenced the probability that they would be recaptured. Some implications for the annual cycle are discussed.

Skomer Island, Pembrokeshire, Wales is believed to have one of the largest colonies of Manx Shearwaters Puffinus puffinus in the World. In 1998 a census was made of the whole island, and the adjacent islands of Skokholm and Middleholm, in order to try to establish the size of the breeding population; the Skomer population was estimated to be just over 101,000 breeding pairs. A second census was carried out in 2011. First, a set of study burrows was opened and a tape of the male call (normally only males respond to these) was played down each burrow several times during the course of incubation in order to establish the male response rate. Then the same tape was played down all the burrows in each of 288 randomly selected plots across the island and the number of responses recorded. Extrapolating responses from census plots to the whole island yielded an estimate of 125,112 (CI 16,445) responses. Adjusting this figure to take account of the response rate yielded an estimate of 316,070 (SE 41,767) breeding pairs. This figure is greatly in excess of the estimate made just 13 years earlier. Possible reasons for this are discussed.

An abnormal movement of auks occurred in the eastern Skagerrak in the third week of September 2007. Large numbers of Razorbills Alca torda were reported along the coasts of southeast Norway and western Sweden, many thousands entered Oslofjorden (Norway), and their migration past the northern tip of Denmark into the Kattegat began a month earlier than normal. This preceded heavy mortality of the species that lasted several weeks, and numbered thousands of individuals. Unusually for the time of year, Razorbills greatly outnumbered Common Guillemots Uria aalge in reports of live and dead birds. Of 376 Razorbills collected in Oslofjorden, 87% were adults, 9% immatures, and 4% juveniles. Among 326 adults, females (71%) outnumbered males, and 18% showed two white inner bill grooves instead of the normal one. All birds were extremely emaciated and had presumably starved to death. Virtually all adults and older immatures were still regrowing their outer primaries after the post-breeding moult, whereas those of juveniles were fully grown. Most, if not all, belonged to A. t. islandica populations breeding in the British Isles, Faroes or Iceland, and few, if any, were from A. t. torda populations of the Baltic, Norway or Russia; the 23 ringed birds found in the Skagerrak and Kattegat, mostly adults, all came from Scottish colonies. Population effects at these colonies were not obvious, but adult survival in 2007–08 was low at one colony in eastern Scotland. Long-term beached bird data indicated that while not on the scale of that in the Skagerrak and Kattegat, Razorbill mortality was abnormally high over a wide area of the North Sea in autumn 2007. The age and sex structure of the mortality and its possible causes are discussed.