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In the 1970s and 1980s, the nominate subspecies of the Lesser Black-backed Gull (Larus fuscus fuscus) showed a dramatic drop in breeding numbers on the Norwegian Coast, and in 2000, the population in some colonies was only 10–20% of the population in 1980. This decline has been attributed to the collapse in the stock of Norwegian spring spawning herring (Clupea harengus). In this study, we examined whether local climate (sea and air temperatures), winter NAO (North Atlantic Oscilliation), and the year-class strength and size of 0-group herring could predict the relative changes in breeding numbers between years, mainly after the population collapse. Breeding birds were counted in 19 of the years between 1980 and 2007 in an archipelago on the coast of Helgeland, northern Norway. The best model predicting changes in breeding numbers for the period between 1980 and 2005 (for which data on 0-group herring was available) included mean local air temperature in winter (January–March) and winter NAO, explaining 57% of the variation between years, while the other factors had little effect. When also adding the years 2006–2007 (no herring data), the best model included only mean air temperature in winter, explaining 41% of the variation. In conclusion, the high positive correlation between breeding numbers and climatic factors probably resulted from a higher availability of important fish prey after mild winters, for which 0-group herring presently may only account for a limited proportion. However, this prey might have been of much more importance prior to the population decline.

In birds, there is ample evidence that the mother can manipulate the sex of the young and produce more of the sex, which gives the highest fitness return. This has previously been documented in gulls, Laridae. Gulls are sexually size dimorphic with males larger than females, and there is good evidence that parents in poor body condition switch their investment to the smallest sex. In the present study, we examined the primary sex ratio and the survival of male and female chicks of lesser black-backed gull (Larus fuscus fuscus) in relation to their blood levels of organochlorines (OCs), perfluorinated compounds (PFCs) and polybrominated diphenyl ethers (BDE-47). We show that females with high levels of OCs (but not PFCs and BDE-47) are likely to skew their sex ratio at hatching towards female offspring. Few females had very high levels of OCs, and the many females with low levels of OCs overproduced sons resulting in a male skew at hatching (59%). The survival of female offspring was lower than the survival of male offspring, causing an even stronger male skew in sex ratio (71%). There is evidence to conclude that circulating levels of OCs in the blood of females may have detrimental effect on the sex allocation strategy and could be of serious threat to the population.

Antarctic Petrel Thalassoica antarctica incubation and brooding effort was studied at Svarthamaren, Dronning Maud Land, during the austral summer of 1991–1992. The females probably left the nest site shortly after egg laying. The duration of incubation and brooding shifts as well as the daily weight loss (absolute and proportionate) were comparable with those of other similar-sized procellariform species. Males spent more time incubating and brooding than did females, suggesting higher female energy stress due to egg laying. Incubating birds which were below average weight were likely to desert the nests before their mates returned from feeding trips. Both males and females lost approximately one-fifth of their body-weight during their first incubation shifts. Nevertheless, they increased their initial weights from egg laying to hatching and had their highest initial weights when they returned to start the shift during which the egg hatched. No factors related to adult body-weight explained the duration of the incubation shifts. Both males and females gained weight at a higher rate when at sea than they lost it during incubation, and it is suggested that factors unrelated to food availability or individual feeding skills may be important in regulating the duration of the incubation shifts and the stay at sea.

Cormorants and shags are foot propelled pursuit divers that forage on benthic and pelagic fish. Previous studies suggested that diving in cormorants is extremely costly, and this is usually attributed to their partially wettable plumage and inefficient mode of propulsion. We investigated the energetic requirements of three Phalacrocorax species during diving. Our results indicate that, when the differences in experimental conditions and calculation methods are accounted for, energy expenditure during shallow horizontal diving in these species is similar and not considerably different from other avian divers. In the absence of direct measurements, thermodynamic modelling has been used to assess the impact of dive depth on the energetic costs of diving. Based on this, the energetic costs of Great Cormorants (Phalacrocorax carbo) diving during the winter in Greenland were estimated to be as high as 64 W kg−1 (∼21 × RMR). A recent study measured the effect of depth on the diving energetics of Double-crested Cormorants (P. auritus) to be much less drastic than suggested by this model. Extrapolating from the latter study to conditions encountered by birds wintering in Greenland shows that the thermodynamic model might greatly overestimate the energetic demand of Great Cormorants during diving. Using an improved model, the daily food intake of Great Cormorants wintering in Greenland was calculated to be ∼1,170 g. Taking into account the recorded time that birds spend diving every day, such food intake would require the highest prey-capture rate suggested so far for an avian pursuit diver (∼41 g min−1 underwater). However, little is known about the prey-capture capabilities of avian divers. We used an underwater video array to study the effect of prey density (live juvenile rainbow trout, Oncorhynchus mykiss) on the prey-capture performance of Double-crested Cormorants. We found that cormorant capture success greatly depended on prey density. Prey capture rate was highest at the greatest fish densities and easily surmounted 41 g min−1 underwater. This would suggest that cormorants in Greenland might be able to achieve these high capture rates, if prey densities are sufficiently high. However, what prey items are encountered by cormorants during the winter in Greenland and at what densities remains to be investigated.

AimSpecies are responding to climate change by changing their distributions, creating debate about the effectiveness of existing networks of protected areas. As a contribution to this debate, we assess whether regional winter abundances and distribution of the Smew Mergellus albellus, a migratory waterbird species listed on Annex I (EU Birds Directive) that overwinters exclusively in European wetlands, changed during 1990-2011, the role of global warming in driving distributional changes and the effectiveness of the network of Special Protection Areas (SPAs, EU Birds Directive) in the context of climate change. LocationEurope. MethodsWe used site-specific counts (6,883 sites) from 16 countries covering the entire flyway to estimate annual abundance indices and trends at country, region (north-eastern, central and south-western) and flyway scales, inside and outside SPAs. We fitted autoregressive models to assess the effect of winter temperature on the annual abundance indices whilst accounting for autocorrelation. ResultsThe Smew wintering distribution shifted north-eastwards in Europe in accordance with the predictions of global warming, with increasing numbers in the north-eastern region and declines in the central region. Trends in wintering numbers were more positive in SPAs on the north-eastern and south-western part of the flyway. However, a large proportion of the wintering population remains unprotected in north-eastern areas outside of the existing SPA network. Main conclusionsSPAs accommodated climate-driven abundance changes in the north-eastern region of the wintering distribution by supporting increasing numbers of Smew in traditional and newly colonized areas. However, we highlight gaps in the current network, suggesting that urgent policy responses are needed. Given rapid changes in species distributions, we urge regular national and international assessments of the adequacy of the EU Natura 2000 network to ensure coherence in site-safeguard networks for this and other species. (Less)

Steller's Eider Polysticta stelleri has a restricted arctic breeding range. The world population declined to c. 220,000 individuals in the late 1990s from an estimated 400,000–500,000 in the 1960s. The species has a limited global wintering distribution, occurring in marine habitats in north-east Europe, islands close to Kamchatka in Russia, and the eastern Aleutian Islands and south-west Alaska. European wintering numbers were estimated at 30,000–50,000 in the early 1990s, when the population was considered of favourable conservation status. Recent census data from the most important European wintering sites show annual declines of 8% in Norway since 1984, 9% in Estonia since 1994 and 22% in Lithuania since 1995, suggesting an overall 65% reduction in Europe. Counts in 1994 suggested that 30–50% of the European population wintered in Russia at that time. Current census data from Russia show similar declines along monitored sections of the Kola Peninsula wintering grounds since 1994. Accounting for trends in Russia, the current European wintering population could possibly stand at 10,000–15,000 individuals (a more than a 50% decline in 10 years), qualifying this population as Endangered under IUCN criteria. The changes in Baltic/Norwegian wintering numbers did not correlate with changes in the extent of ice-free marine waters in the Kola Peninsula/White Sea areas, but changes in annual numbers in Norway were correlated with winter North Atlantic Oscillation indices. Variation in annual numbers in the Baltic Sea correlated with projected number of juveniles among wintering birds. However, none of the possible causes discussed in this paper could fully explain the decline in Steller's Eider, confirming the need for comprehensive monitoring of the population throughout its winter range and for cohesive demographic monitoring to target effective conservation action.

Diving is believed to be very costly in cormorants (Phalacrocoracidae) when compared with other avian divers because of their poor insulation and less-efficient foot propulsion. It was therefore suggested that cormorants might employ a behavioural strategy to reduce daily energy expenditure by minimizing the amount of time spent in water. However, European shags (Phalacrocorax aristotelis) have been observed to spend up to 7 h day(-1) diving in water of around 5-6 degrees C. To gain a better understanding of the energetic requirements in European shags, we measured their metabolic rates when resting in air/water and during shallow diving using respirometry. To investigate the effects of water temperature and feeding status on metabolic rate, birds dived at water temperatures ranging from 5 to 13 degrees C in both post-absorptive and absorptive states. In parallel with respirometry, stomach temperature loggers were deployed to monitor body temperature. Basal metabolic rate (BMR) was almost identical to allometric predictions at 4.73 W kg(-1). Metabolic rate when resting on water, during diving and after feeding was significantly elevated when compared with the resting-in-air rate. During diving, the metabolic rate of post-absorptive shags increased to 22.66 W kg(-1), which corresponds to 4.8x BMR. Minimum cost of transport (COT) was calculated at 17.8 J kg(-1) m(-1) at a swim speed of 1.3 m s(-1). Feeding before diving elevated diving metabolic rate by 13% for up to 5 h. There was a significant relationship between diving metabolic rate and water temperature, where metabolic rate increased as water temperature declined. Thermal conductance when resting in air at 10-19 degrees C was 2.05 W m(-2) degrees C(-1) and quadrupled during diving (7.88 W m(-2) degrees C(-1)). Stomach temperature when resting in air during the day was 40.6 degrees C and increased during activity. In dive trials lasting up to 50 min, stomach temperature fluctuated around a peak value of 42.0 degrees C. Hence, there is no evidence that European shags might employ a strategy of regional hypothermia. The energetic costs during shallow diving in European shags are considerably lower than has previously been reported for great cormorants (Phalacrocorax carbo) and are comparable to other foot-propelled divers. The lower dive costs in shags might be the consequence of a more streamlined body shape reducing hydrodynamic costs as well as a greater insulative plumage air layer (estimated to be 2.71 mm), which reduces thermoregulatory costs. The latter might be of great importance for shags especially during winter when they spend extended periods foraging in cold water.

Summary 1Knowledge of the functional response of predators to prey densities conditions our understanding of food webs. Such links are still poorly understood within the higher trophic levels of marine ecosystems. 2We present the first field study recording the foraging effort and foraging yield of a seabird (the Great Cormorant, Phalacrocorax carbo) as well as the abundance and quality of prey within its foraging area. 3We confirm that Great Cormorants foraging off West-Greenland show the highest foraging performance recorded for a marine predator (between 17 and 41 g fish caught per minute underwater). Former work suggests that such high foraging yield should be based upon the exploitation of extremely profitable prey patches. 4Contrary to this hypothesis, average prey abundances estimated within the foraging areas of the cormorants were low (0·03–0·09 prey m−2, depending on methods), as was the average calorific value of the prey items (4·2 kJ g−1). 5Our study suggests that Great Cormorants remain highly successful predators even when exploiting modest prey resources. These findings have implications for our understanding of predator–prey relationships, and for the management of Great Cormorant populations.

Great Cormorant (Phalacrocorax carbo) diet was studied during three years (2001-2003) in an area where Arctic Kelp (Laminaria hyperborea) is extensively distributed off the central Norwegian coast. A total of 608 diet samples, 378 (62.2%) chick regurgitations, 22 (3.6%) whole fish, and 208 (34.2%) pellets were collected from the colonies at regular intervals during the chick-rearing period. From these samples a total of 1,013 food items (after pairing the otoliths) were isolated, representing 18 fish species. Gadoids, mainly Cod (Gadus morhua) and Saithe (Pollachius virens) dominated the diet (75% numerically, 86% by biomass). During the first year of the study, Cod represented nearly 50% of the diet, but decreased to 13% in 2003. At the same time, the occurrence of Saithe in the diet increased from 23% to 65%. For Saithe age II-group fish dominated the diet in 2001, and I- and II- group dominated in 2002 and 2003. For Cod 0-group fish dominated the diet in 2001 and 0- and I-group fish dominated ...

Weather extremes are one important element of ongoing climate change, but their impacts are poorly understood because they are, by definition, rare events. If the frequency and severity of extreme weather events increase, there is an urgent need to understand and predict the ecological consequences of such events. In this study, we aimed to quantify the effects of snow storms on nest survival in Antarctic petrels and assess whether snow storms are an important driver of annual breeding success and population growth rate. We used detailed data on daily individual nest survival in a year with frequent and heavy snow storms, and long term data on petrel productivity (i.e., number of chicks produced)at the colony level. Our results indicated that snow storms are an important determinant of nest survival and overall productivity. Snow storm events explained 30% of the daily nest survival within the 2011/2012 season and nearly 30% of the interannual variation in colony productivity in period 1985–2014. Snow storms are a key driver of Antarctic petrelbreeding success, and potentially population dynamics. We also found state dependent effects of snow storms and chicks in poor condition were more likely to die during a snow storm than chicks in good condition. This stresses the importance of considering interactions between individual heterogeneity and extreme weather events to understand both individual and population responses to climate change. Antarctic petrel, body condition, extreme event, individual state, offspring survival, Thalassoica antarctica.

Theoretical models, assuming an underlying conflict of interest between parents and offspring, suggest that begging can be an honest signal of offspring need provided that it is costly. Models on begging have been tested primarily on those birds in which parents provide care for several offspring. For these species, the underlying conflict selecting for extravagant (and apparently costly) begging displays might be sibling competition rather than parent–offspring conflict. We tested hypotheses on begging and parent–offspring conflict with the grey seal, Halichoerus grypus, as our model species, in which lactating females care for a single pup. As predicted from models of begging as an honest signal of need, pups begged at a significantly higher rate when hungry than when satiated. Furthermore, a mother was more likely to approach her pup shortly after the pup had uttered a begging call than within a randomly chosen period. We found no consistent support, however, for the assumption that there are strong conflicts of interest between mothers and pups. For example, the rate of suckling was not correlated with begging rate, suckling bouts terminated by pups were not longer than those terminated by mothers, and, although pups initiated the majority of suckling bouts, mothers did not terminate more suckling bouts than pups. These findings thus suggest that begging in species that care for a single offspring may evolve in the absence of strong parent–offspring conflict.  2001 The Association for the Study of Animal Behaviour

Environmental monitoring programmes are often confined by limited funds. By use of Monte Carlo simulations and GLM procedures, it is examined to what extent trends documented for some Norwegian seabird populations could have been obtained with less field effort. Changes in both breeding and wintering numbers are analysed. To minimise bias from merging different populations, only regional trends are considered. The results strongly suggest that some populations can be monitored adequately by less effort than that applied, i.e. still ensuring that the counts will reveal the various sources of variation in reliable proportions to the total variance in bird numbers. This may be achieved either by reducing the number of plots or by counting them less frequently, for example in alternate years only. General advise with respect to what changes deserve special attention from conservation authorities, and a discussion of the principles and considerations which should be taken into account when designing monitoring programmes for seabirds are presented.

We studied the behaviour of grey seals, Halichoerus grypus, during the breeding period at Froan, Norway, and compared our findings with existing studies on grey seals at breeding sites in Britain and Canada. The pups at Froan spent more time in water than pups at other breeding sites. While on-shore, the pups at Froan spent most of their time resting, behaviour similar to pups at other breeding sites. Lactating females at Froan spent most of their time in the sea, thus differing from females at most other breeding sites which spend most of their time on-shore. While in the sea, the females at Froan spent most time diving, typically interrupted by regular periods of surface swimming.

The survival of marine predators depends on behavioural plasticity to cope with changes in prey distribution. Variability in behaviour might predict plasticity and is easier to assess than plasticity. Using miniaturized GPS loggers over several breeding seasons in two Norwegian Northern gannet (Morus bassanus) colonies, we investigated if and how the variability within and between individuals, but also between colonies and years, affected foraging strategies. Results revealed strong individual variability (foraging trip durations, foraging effort and different foraging areas). Individuals from both colonies showed preferred commuting routes, flight bearings and feeding hotspots. Individuals from the largest colony used larger and more foraging areas than individuals from the small colony. Feeding hotspots and foraging ranges varied amongst years in the largest colony only. Our study demonstrated that gannets show flexibility by changing prey fields that are driven by shifting oceanographic conditions.

International audience; Although oriented migrations have been identified in many terrestrial bird species, the post-breeding-season movements of seabirds are generally regarded as dispersive. We used geolocator tags to reveal post-breeding movements and winter distribution of northern gannets (Morus bassanus) at a meta-population scale. By focusing on five breeding colonies of European gannets, we show that their breeding and wintering grounds areconnected by a major flyway running along the coasts of Western Europe and Africa. Moreover, maximum winter distance to colony was similar across colonies despite their wide latitudinal range. In contrast with the general opinion that large pelagic birds such as gannets have unlimited ranges beyond the breeding season, our findings strongly suggest oriented chain migration in northern gannets (a pattern in which populations move uniformly southward) and highlight the benefit of meta-population approaches for studying seabird movements. We argue that the inclusion of such processes in ocean management plans is essential to improve efforts in marine biodiversity conservation.

In 1988, first-year Herring Clupea harengus were the dominant prey fed to puffin chicks on Hernyken, Røst. Puffins carrying food loads were observed at least 137 km from the colonies in July. In early August, two major feeding areas were located about 20 and 85-105 km off Røst. These long foraging ranges and an insufficient availability of food are thought to be the main reasons for the poor chick growth this year. No relationships were found between the distribution of puffins observed at sea and survey station data on prey distribution, sea temperature or salinity, but this may have been due to inadequate sampling of these parameters. A recorded seasonal change in flight direction of adults returning to colony is discussed in relation to food quality and chick growth.

Despite global occurrence of several perfluorinated compounds (PFCs) the potential ecological effects of such substances on natural populations are not known. In endangered lesser black-backed gulls (Larus fuscus fuscus) on the Norwegian Coast, the blood concentrations of PFCs were as high as legacy organochlorines (OCs), and here we examined whether PFCs show associations similar to those of OCs to factors potentially affecting population growth, by evaluating relationships between contaminant concentrations and demographic parameters (reproductive performance and the probability of adults returning between breeding seasons). PFCs were not adversely associated with demographic parameters, while the most persistent OCs; notably PCB and p,p'-DDE, were adversely associated with early chick survival, and adult return rate. This study thus suggests that when the concentrations of PFCs and OCs are of similar magnitude in a gull population, OCs are more likely to cause adverse ecological effects.

The behaviour and oil vulnerability of Fulmars was studied when 30 t of crude oil was experimentally released at Haltenbanken, 150 km off the coast of Central Norway in July 1989. Evidence strongly suggests that the Fulmars deliberately avoided to settle on sea surface that was polluted with heavy oil. However, about 4% of the Fulmars in the area were slightly oiled, probably because they had been attracted to surrounding blueshine areas by food remains thrown overboard from the research vessel.

The present study focuses on the distribution and accumulation of persistent organochlorine compounds in different tissues and organs of grey seal ( Halichoerus grypus ) pups. Thus, levels of drins (aldrin, dieldrin, endrin), chlordanes (heptachlor, heptachlorepoxide, oxychlordane, transnonachlor), DDTs ( p,p′ -DDE, o,p′ -DDD, p,p′ -DDD, o,p′ -DDT, p,p′ -DDT) and 22 PCB congeners were determined in samples of brain, fat, and liver of 0–10 days old grey seal pups from the species' main breeding site in Norway. Whereas 10 different compounds were detected in the blubber, 8 compounds were detected in the liver. The concentrations of the two major classes of OCs (PCBs and DDTs) in liver were both about 75% of that in blubber. In cerebral tissue, only two PCB congeners were detected, and ϵPCB was only about 1% of that measured in the blubber. The distribution pattern of PCB-congeners in liver and brain differed significantly from that in blood and blubber tissue, indicating that the physico-chemical properties of the individual congeners and the lipid composition of the tissues are decisive for the tissue-specific pattern of congener distribution. A significant increase of the ϵDDT/ϵPCB-ratio as a function of blubber thickness indicates that DDT compounds are more readily accumulated in older pups.

We present data on sexual dimorphism in some morphological measurements (wing length, head length, bill depth and bill length) in the Antarctic Petrel Thalassoica antarctica. Males were on average larger than females for all measurements. Sexual dimorphism was on average largest for bill depths whereas wing lengths discriminated least between the sexes. A discriminant function including bill depth, head length and wing length correctly sexed 92% of the sample. Due to between-measurer variation it is recommended that morphometric measurements obtained by others on sexed birds are compared with ours before proceeding with the use of the discriminant function on unsexed individuals.

Protein-bound perfluorinated compounds (PFCs) and lipid-soluble polybrominated diphenyl ethers (PBDEs) and organochlorines (OCs) were measured in whole blood from a large number (n = 83) of breeding lesser black-backed gulls (Larus fuscus) caught during two distinct sampling periods in a colony on the coast of northern Norway. We analyzed 14 PFCs (seven were detected in more than 75% of samples), 10 PBDEs (only BDE 47 was detected), and 27 OCs, including 12 polychlorinated biphenyl (PCB) congeners (14 OCs were detected). Median total PFC concentration was higher than median total OC concentration (43 vs 39 ng/g wet wt). Perfluorooctane sulfonate (PFOS) was the dominant PFC (mean relative contribution of PFOS to total contaminant concentration in blood [Sigmatotal contaminants] was 38%), whereas total PCB (26% of Sigmatotal contaminants) and p,p'-DDE (2,2-bis(4-chlorophenyl)-1,1-dichloroethene; 13% of Sigmatotal contaminants) were the dominant OCs. No covariability was found between protein-bound and lipid-soluble compounds; individuals with high concentrations of PFCs did not have high concentrations of OCs or BDE 47. The concentrations of PFCs were lower in birds caught during the late sampling period compared to those of the early period, and females had lower levels of some PFCs compared with males, suggesting that females sequester fluorinated substances into eggs. For lipid-soluble compounds, no significant sex or sampling period differences were found, except that trans-nonachlor, cis-nonachlor, and p,p'-DDE concentrations were lower in birds caught during the late sampling period. The pattern of PFC compounds (relative to PFOS) and lipid-soluble compounds (relative to PCB 153) differed between sampling periods in females but not in males. Finally, PFCs were distributed more uniformly within the population than the lipid-soluble compounds, for which the distributions were strongly negatively skewed.

Frequent oil contamination of grey seal Halichoerus grypus pups is shown to be a severe problem within the Froan breeding area off central Norway. Since 1985, annual surveys have revealed that 30–60% of all pups born become oil-fouled during their first month of life. The location of the Froan archipelago within the coastal current serve to accumulate petroleum residues, and the main source of contamination of the pups is beached oil spots that melt when pups lay upon them. The proportion of oil contamined pups therefore increases with time spent ashore.

The winter diet of 522 Common Murres ( Uria aalge) killed in fishing nets off Ostfold, SE Norway was studied by analysis of stomach contents. Temporal variations throughout the winter 1989-1990 and sex and age specific differences in food choice were given special attention. A total of 1,864 food items were found in the 477 stomachs with contents. Otoliths and other fish remains constituted nearly 90% of the items, while 10% were remains of polychaete worms. Clupeids, gadids and gobids were the most common fish groups, both numerically and by frequency of occurrence. Although there were no sex and age specific differences in the frequencies of occurrence of the main prey groups, such differences were evident when data were expressed numerically. Immatures took more clupeids, gobids and polychaetes but fewer gadids than did adults. Males took more clupeids, gadids and polychaetes than did females; females took more gobids than did males. The frequency of occurrence of clupeids, gadids and gobids in adults and immatures showed no significant variation during the winter. There was, however, a significant seasonal variation in the numerical occurrence of gadid items, but not of clupeid items, in stomachs from adults andjuveniles during the three two-month periods in the winter 1989-1990. If this diet was representative, the total food consumption by Common Murres in Skagerrak during October 1989-March 1990 was about 12,520 metric tons, of which clupeids constituted 5,770 tons, gadids 6,435 tons, gobids 50 tons, and polychaetes 63 tons. The consumption of both clupeids and gadids totalled approximately 10% of the total landings by commercial fisheries in the North Sea and Skagerrak areas. Received 1 7June 1998, accepted 21 September 1998.

A large number of studies have reported a positive relationship between the egg size of birds and the subsequent growth and/or survival of nestlings, but such effects may partly be due to confounding variables, e.g. parental quality. In order to evaluate the potential effects of egg size, and of parental quality, on early nestling growth in the Antarctic petrel, we performed an experiment in which eggs of different size were swapped between nests. From a sample of 300 nests with eggs of known size, we selected eggs belonging to the lower quartile (small eggs), and those belonging to the upper quartile (large eggs), with respect to volume. Half of the small eggs were exchanged with small eggs from other nests, and the other half with large eggs. A similar procedure was used for large eggs. Growth and survival of the nestlings were recorded until 12 days old. Hatching success was positively related to egg size. Egg size influenced nestling body mass until the age of 3 days, and tarsus length was affected until 12 days old. However, these effects were not due to an effect of egg size on growth rates, but reflected instead the influence of egg size on hatchling size. In contrast to most previous studies, we found no effect of parental quality (as reflected in the size of own eggs) on foster nestling size or growth until 12 days old. This could be because egg size does not reliably reflect parental quality in the species, or because parental effects become evident only at later nestling stages. We discuss why egg size variation is maintained in this and other species where egg size influences parental fitness through the survival of eggs or nestlings.

Dabbling ducks (Anas spp.) are important migratory quarry species, protected as a shared resource under international legislation. However, there is a lack of sufficient high-qual- ity data on vital demographic rates and long-term trends in numbers to judge the conser- vation status of many duck populations at the flyway level. In response to reported de- clines in the North-West European flyway population of the Mallard, we compiled avail- able data on this species in the Nordic countries up to 2010. Generally, national breeding numbers showed increasing trends, wintering abundance showed variable trends, and productivity measures indicated stable or increasing trends. Major knowledge gaps were identified, namely the size of hunting bags, the influence of the released Mallards and the role of short-stopping in explaining changing patterns of wintering abundance across the North-West European flyway. Numerically the Nordic breeding population appears in “good condition”, and the wintering numbers have been either stable or increasing in the last two decades. The annual number of releases needs to be determined in order to judge the sustainability of the current levels of exploitation. Overall, none of the indicators showed alarming signs for the Mallard population in the Nordic countries when consid- ered in isolation. However, the widespread decline in wintering numbers elsewhere across North-western Europe requires urgent pan-European action.

This chapter focuses on Cormorantpopulation counts for both summer(i.e. breeding) and winter (i.e.migration, winter roosts) seasons. Italso explains differences in the datacollected from undertaking ‘day’versus ‘roost’ counts, gives somedefinitions of the term ‘numbers’,and presents two examples ofhow numerical data can be usedto calculate ‘Cormorant days’ andbreeding success.