Fridtjof Mehlum

Daily energy expenditure and energy utilization of free-ranging Black-legged Kittiwakes

Rates of CO2 production by breeding Black-legged Kittiwakes (Rissa tridactyla) (mean mass, 386 g) were measured by using doubly-labeled water. Kittiwakes alternated days on and off the nest, while they brooded their nestlings. Field metabolic rates (FMR) in nonforaging birds averaged 2.43 ml CO2/g hr, or 596 kJ/day. This is 1.9 times the basal metabolic rate (BMR), measured in the laboratory to be 1.31 ml CO2/g-hr, or 314 kJ/day. FMRs in foraging birds averaged 4.04 ml CO2/g hr, or 992 kJ/day which is 3.2 times BMR. The rate of food consumption by an adult kittiwake, calculated on the basis of the chemical composition and digestibility of capelin (Mallotus villosus, the most important dietary item at Hopen Island) was 315 g of fresh matter per bird every other day. A colony of 3,000 breeding pairs of kittiwakes at Hopen Island, using the fishing grounds around the island, would consume about 1,245 kg of fresh fish per day, and add about 76 kg (dry matter) of guano to the marine ecosystem during the chick-rearing period.

An application of optimal diving models to diving behaviour of Brünnich's guillemots

Although theoretical models predict that the quality of foraging patches has little effect on optimal dive time with increasing depth, many empirical studies show that dive time at a given depth may vary. We developed a model that incorporated patch quality as a parameter of energy intake as a nonlinear function of time, and applied it to the diving behaviour of Brunnichs guillemots, Uria lomvia. The model indicated that optimal dive time can vary widely depending on the parameter. It also explained the convergence of observed dive times with travel time. Assuming the birds dived optimally, this parameter can be estimated from travel time and dive time for each dive. Foraging patches with larger estimated parameter values were favoured by the birds, suggesting that the parameter indicated patch quality. We used this parameter to test an optimal patch use model in divers. The results indicate that Brunnichs guillemots adjust their diving behaviour adaptively depending on patch quality, and that the optimal diving model is valid for prediction of observed dive patterns if patch quality is incorporated appropriately.

Diving behaviour and foraging habitats of Brünnich's guillemots (Uria lomvia) breeding in the High‐Arctic

The foraging behaviour of Brunnichs guillemots Uria lomvia was studied in a high-arctic fjord system (Kongsfjorden) in western Spitsbergen. The physical oceanographic characteristics of the water change from the head of the fjord and westward into the Greenland Sea, and are reflected in the vertical profiles of water temperatures in different parts of the area. Nine chick-rearing Brunnichs guillemots were instrumented with temperature-depth recorders, which generated vertical temperature profiles of the dives. These were compared to synoptic measurements of the water temperature characteristics of the region. This method was used to locate the foraging areas of the Brunnichs guillemots and to study the foraging site fidelity of individual birds. The results showed that only three of the nine birds foraged outside Kongsfjorden during the study period, and only 26 of the 186 dive bouts (14%) were conducted outside the fjord, 48–58 km from the colony. Most dives were probably made only a few kilometres from the colony. The data indicate that the birds showed strong fidelity to foraging areas at spatial scales of 1–20 km. However, the birds sometimes moved between feeding areas characterized by different vertical temperature profiles. The guillemots made 2229 dives during the study period and spent c. 10% of their time under water. The diving depth averaged 45 m, and the dive duration averaged 97 s. The deepest dive recorded was 136 m and lasted 196 s. We did not find any diel rhythm in the diving depths of the Brunnichs guillemots. Also, we found no diel pattern in diving frequency. These findings contradict the predominance of night-time diving observed in studies of guillemots undertaken further south.

The importance of prey aggregations to the distribution of Brünnich's guillemots in Storfjorden, Svalbard

We studied the influence of the distribution of prey and hydrographic fronts on the spatial distribution of foraging Brunnichs guillemots (Uria lomvia) in Storfjorden, southeastern Svalbard in late July 1992. Two large breeding colonies, comprising a total of 540000 individuals, were located adjacent to the study area, and large numbers of Brünnichs gullemots from these colonies foraged within the area, as well as to the south, outside of Storfjorden. Within the study area, most guillemots foraged on the west side of the fjord, coincident with a weak subsurface front between warm Atlantic water, which penetrated Storfjorden from the south, and cold Arctic water. Food samples from the guillemots collected in the study area contained primarily crustaceans (Parathemisto spp. and Thysanoessa inermis) and polar cod Boreogadus saida. Acoustic observations of prey were differentiated into two classes of signals, which we interpreted as originating from aggregated and dispersed organisms. The numbers of foraging guillemots were strongly correlated with the strength of echoes of the aggregated type, whereas correlations with dispersed echoes were consistently weaker. The distribution of foraging guillemots showed no significant correlations with either horizontal or vertical gradients of physical properties of the water column. Our finding that guillemots respond differently to aggregated and dispersed prey has important implications both for the interpretation of past work on the foraging ecology of marine birds, and for the management of fisheries.

PCBs in Arctic seabirds from the Svalbard region

Previous studies have indicated the presence of high levels of organochlorines, especially PCBs, in some species of arctic seabirds. The glaucous gull (Larus hyperboreus) in particular has shown high levels of organochlorine contamination. We present data on total PCB and isomer specific PCBs in liver samples from four species of seabirds from the Svalbard region. Two of the species were sampled both in the vicinity of the mining town Longyearbyen, where PCBs have been used in the past, and in the remote region of Nordaustlandet. We compared the levels obtained from these two localities in order to test for any indication of local contamination in the Longyearbyen area. No significant difference was found in total hepatic PCB between glaucous gulls collected at Longyearbyen and those collected at Nordaustlandet (grand mean ± S.D.: 15.59 ± 21.53 μg/g wet wt.; n = 22). Similarly, no difference was found in black guillemots (Cepphus grylle) from these two regions (grand mean ± S.D.: 0.14 ± 0.05 μg/g wet wt.; n = 20). However, in both species, we found significantly higher levels of higher chlorinated biphenyls in the Longyearbyen samples, and higher levels of lower chlorinated biphenyls in the samples from Nordaustlandet. This finding indicates that the birds sampled at the two localities might have been contaminated by different sources. Local contamination in the Longyearbyen area is one of several possible explanations for this difference. Total PCB levels in common eiders (Somateria mollissima) and Bru¨nnichs guillemots (Uria lomvia) were in the same order of magnitude as those for the black guillemots (mean ± S.D.: 0.04 ± 0.04 μg/g; n = 11 and 0.08 ± 0.04 μg/g; n = 8, respectively).

The importance of the “Polar Front” as a foraging habitat for guillemots Uria spp. breeding at Bjørnøya, Barents Sea

Abstract There are large breeding colonies of common guillemots Uria aalge and Brunnichs guillemots Uria lomvia at Bjornoya in the Barents Sea. We studied the foraging ecology of these guillemot populations during the breeding season by ship surveys off the island. The guillemots foraged in all directions from the island, but the main aggregations of foraging birds were encountered south of Bjornoya. Common guillemots tended to forage mainly on the southern side of the island. Most of the foraging aggregations were encountered 25–60 km from the island. These guillemot aggregations were located at the surface expression of the “Polar Front” and in the strongly stratified water on the offshore side of the front. The position of the surface “Polar Front”, which roughly follows the 100 m isobath, seems to be relatively predictable and is probably dependent on bathymetry and strong tidal currents. The euphausiid Thysanoessa inermis predominated in the diet of adult Brunnichs guillemots collected during the study, whereas fish were brought back to their young. Capelin Mallotus villosus is an important prey for guillemots in the Barents Sea, but in years when capelin is scarce in the region, guillemots may rely more on euphausiids for subsistence.

Thermoregulatory abilities in chicks of the Antarctic Petrel (Thalassoica antarctica)

SummaryWe studied the thermoregulatory capacity of Antarctic Petrel chicks, Thalassoica antarctica, breeding in a large colony in Queen Maud Land (71°53′S,5°10′E) on the Antarctic continent. Compared to newly hatched chicks of other birds, those of the Antarctic Petrel are characterized by a relatively high standard metabolic rate (SMR) and thermal conductance. Their metabolic scope is limited, however, being only 1.6 times the SMR, and they consequently depend on parental brooding to maintain Tb. At an age of 11 days the chicks become thermally independent and are left alone in the nest. The chicks keep a relatively high body temperature (>36°C) throughout their early development and we found no indication that they normally experience hypothermia. A significant positive relationship between latitude of breeding and SMR of the hatchlings is shown to exist for procellariiform birds. It is suggested that the high SMR found in Antarctic Petrel hatchlings could be a prerequisite for achieving a high growth rate, rather than being of any thermoregulatory significance.

Thermoregulation and Energetics of Arctic Seabirds

Svalbard and the Barents Sea are inhabited by one of the largest concentrations of seabirds in the world, comprising several million birds (Lovenskiold 1964, Norderhaug et al. 1977). These birds constitute a major component of the marine ecosystem and form an important link between the terrestrial and marine ecosystem by transporting organic material and nutrients from sea to land.

Seabird species associations and affinities to areas covered with sea ice in the northern Greenland and Barents Seas

Abstract Species associations and affinity to sea ice among arctic marine birds were studied during ship transects in the northern Greenland and Barents Seas in the period 1980–1984. Associations were investigated at the scale of visual contact, and the sampling units were 10-min periods, corresponding to a transect length of 1.5–3 km. In the Greenland Sea, three or four of the most abundant species, fulmar (Fulmarus glacialis), little auk (Alle alle), Brünnichs guillemot (Uria lomvia) and kittiwake Rissa tridactyla, composed a recurrent group in all years. In the Barents Sea, fulmars, Brünnichs guillemots and kittiwakes were most often clustered. A positive association with sea ice was found in more than one cruise in three seabird species: black guillemots, ivory gulls and little auks, whereas seven other species showed negative association with ice in more than one cruise. The observed species associations and affinities to sea ice reflect similarities in diet among the species involved.

Chinstrap and macaroni penguin diet and demography at Nyrøysa, Bouvetøya

Abstract Knowledge regarding interactions between predators and their prey is fundamental for understanding underlying links between climate change and ecosystem responses, including predator demographics, in the Southern Ocean. This study reports data on reproductive performance, total population size and diet composition for macaroni and chinstrap penguins breeding at Nyrøysa on Bouvetøya during the summers of 1996–97, 1998–99, 2000–01 and 2007–08. The breeding populations of these two species at Nyrøysa decreased significantly over the study period, with an 80% decline for chinstraps and a 50% decline for macaroni penguins, despite relatively high levels of chick production. During this period macaroni penguins at this site ate a diverse diet, dominated by myctophid fish and two krill species, whereas chinstrap penguins were Antarctic krill specialists. The population changes are probably primarily due to the expanding Antarctic fur seal population, and also to landslides that are the result of increased melting on the island which have destroyed penguin breeding sites. Additional impacts from global warming of the ocean might also be playing a role and could exacerbate the decline in these penguin populations if krill and other prey are negatively impacted in the future in this region. The local chinstrap penguin population would probably be most heavily affected given its narrow feeding niche and small current population size.