First records of lesser black-backed gulls Larus fuscus crossing the Sahara non-stop

Lesser black-backed gulls Larus fuscus migrate regularly along coastlines or the Nile to their wintering grounds in sub-Saharan Africa. They usually avoid the interior of the Sahara, but occur occasionally far inland when moving upstream along rivers. We discovered several flocks of lesser black-backed gulls crossing the western Sahara about 500 km east of the Atlantic coast. Their concentrated flight directions along a northeast-southwest axis indicate that the gulls were on an intended migratory flight and not incidentally drifted inland. Ground speed of 8 flocks of gulls averaged 20 m/s and was considerably larger than the mean air speed (12 m/s) demonstrating that the gulls were strongly assisted by tailwinds. Highest ground speed was 26 m/s. Warmest temperature encountered when crossing the study site was 13° C due to relative high flight altitudes of 3,500 m above sea level. Thus, lesser black-backed gulls migrated under favourable conditions with respect to energy and water consumption. Our observations strongly suggest that the gulls performed long non-stop flights between the eastern Atlantic coast of sub-Saharan Africa and the Mediterranean Sea.     

Incubation capacity limits maximum clutch size in black-tailed gulls Larus crassirostris

Factors determining clutch size of birds have long been the central issue in studies in life histories. It is assumed that the configuration of brood patches could limit the maximum clutch size. To test this hypothesis we manipulated clutch sizes and measured egg temperature as well as reproductive consequences in black-tailed gulls Larus crassirostris , which usually lay two egg clutches and have three brood patches. Mean egg temperature in 4-egg clutches (32.6±1.0°C) was significantly lower than in 2-egg (34.6±0.4°C) and 3-egg clutches (34.1±0.4°C), because egg temperature of the coolest egg within a 4-egg clutch was often substantially lower than the other three eggs. The proportion of eggs hatching from 4-egg clutches (11.6%) was lower than those of 2-egg (49.1%) and 3-egg clutches (52.0%). Four-egg clutches had longer incubation periods (29.6±1.3 day) than 2-egg (28.1±1.7 day) and 3-egg clutches (28.0 ±1.3 day). The results indicate that incubation capacity, which may be determined by the configuration of brood patches, limits the maximum clutch size in black tailed gulls, but not the actual clutch size typically laid.     

Nitrite poisoning in herring gulls (Larus argentatus) and ring-billed gulls (Larus delawarensis)

Landfill disposal of a fertilizer manufacturing waste product was associated with a die-off of gulls in New Hanover County, North Carolina. An estimated 250 herring and ring-billed gulls were found dead at the site following the initial disposal of this material. Chemical analyses revealed that the fertilizer waste contained predominately calcium (12.0 to 22.2%) and nitrite (3.0 to 15.2%). Contents of the proventriculi and gizzards of dead gulls also contained calcium (3.0 to 10.9%) and nitrite (1,730 ppm). Fertilizer waste administered orally to 16-day-old domestic turkeys resulted in acute, progressive signs of depression, respiratory distress, pallor, convulsions and death. The mean percentage methemoglobin in blood from convulsing turkeys (90.6) was significantly increased from that of normal control turkeys (3.6). The ante-mortem signs and increased blood methemoglobin concentrations in the experimental turkeys support the conclusion that the toxic principle in the fertilizer waste was nitrite, and that nitrite poisoning was the cause of the die-off of gulls.     

The effect of dehydration on salt and water balance in gulls (Larus argentatus and L. fuscus).

The effects of a variety of dehydratory stresses, hypersalinity, heat and water deprivation on renal and extrarenal handling of a standard salt load have been studied. Concommitant measurements of plasma and tissue electrolytes and of pituitary prolactin levels have also been made and the possible correlation between prolactin levels and the degree of dehydration are discussed along with the possible ecological significance of the reported findings.     

Age-related migration patterns in Larus fuscus spp.

Migration is a critical period in a bird’s life that can affect the fitness of individuals. Intra-population migratory patterns and the way different sex and/or age classes within a population differ in timing and/or distance of migration are not completely understood. The present study aims to observe inter- and intra-population migratory patterns in the western population of Lesser Black-backed Gulls (Larus fuscus spp.), shedding light on age-related differences of temporal patterns of occurrence in the Portuguese coastal areas during migration and winter. One thousand seven hundred and fifty-four colour ring records were analysed matching a 30-year period of observations on the Portuguese coast between 1975 and 2005. During migration, the graellsii population represents 90% of the migratory flow of L. fuscus through Portugal with the intermedius accounting for 9% and the fuscus population, being vestigial in this period, accounting for 1%. Nevertheless, interesting significant differences were observed between the age classes of the three populations during this period, the graellsii population having a large number of first winters (40% of the migratory contingent of this population) followed by immatures and adults whilst in the intermedius and fuscus populations, the largest age class is the adults. During winter, no inter-population differences were found. When comparing migration and winter periods, intra-population differences were found in the graellsii and fuscus populations regarding distribution and age classes. These results indicate different migratory routes amongst different populations suggesting a leapfrog migration in L. fuscus and also a differential age-related migration pattern that might result from first winters migrating further south in search of a wintering place since adults heavily occupy the closest wintering quarters in their attempt to arrive earlier at their breeding ground.     

Interspecific differences in foraging preferences, breeding performance and demography in herring (Larus argentatus) and lesser black-backed gulls (Larus fuscus) at a mixed colony

Herring gulls Larus argentatus and lesser black-backed gulls Larus fuscus breeding at Walney Island, Cumbria, the largest breeding colony of the two species in the UK, have recently shown very different population trends. The former has declined sharply, whereas numbers of the latter have been maintained for several years. Here we compare aspects of the feeding and breeding ecology of the two species in order to examine whether or not this suggests explanations for their different population trends. Comparison of the ratio of the two species in flight lines leading to different feeding sites and their diet composition showed that the lesser black-backed gulls fed more at sea and the herring gulls fed more in the intertidal zone. Urban resources were used by both these species. These differences have been consistent over the last three decades. Susceptibility to death from botulism at the breeding colony was the same for the two species. The availability of the intertidal zone for foraging appears to have declined in recent years, and this may have had a more negative impact on the herring gull. However, the breeding success of the two species remains relatively high. This study suggests that differences in foraging behaviour and food availability during the breeding season are unlikely to be responsible for the marked differences in demographic trends in the two species. Changes in local food availability during the winter would be expected to have more effect on the resident herring gull. This work highlights the need for more detailed studies of the ecology of both species during the breeding season and in winter in regions showing differing patterns of population change.     

The effect of age and environment on extrarenal salt excretion in juvenile gulls (Larus argentatus and L. fuscus)

Young gulls captured from an essentially marine colony with no access to freshwater showed a significantly greater ability to excrete a hypertonic salt load than did birds of approximately the same age captured from an inland colony.
This ability was reflected by higher extrarenal secretion rates from the heavier nasal gland of the marine birds. That this increased ability was due to environmental exposure and not to genetic variations was shown by the fact that these differences disappeared when the two groups of birds were maintained on a freshwater diet for four weeks.
The main environmental factor stimulating the development of the nasal gland in the marine birds appeared to be non-availability of freshwater, as analysis of the diet of both colonies showed only minor differences.     

Biochemical genetic variation in populations of Larus argentatus and Larus fuscus in northwestern Europe

The techniques of biochemical population genetics were used to examine the relationships between two apparently closely related species and their component subspecies which form the Larus argentatus/fuscus species complex in northwest Europe. The systematics and taxonomy of these populations in this part of the circum-polar ring are complex and it was thought that this type of analysis might clarify the taxonomic relationships. Samples were obtained from breeding colonies along a transect from northern France (47°N), through Britain to arctic Norway (70°N), with additional samples from the Camargue on the Mediterranean coast (42°N). Twenty-one enzyme systems were examined using starch gel electrophoresis. No interspecific differences were found and only one locus (glutamate oxaloacetate transaminase) was polymorphic. There were no allelic differences within geographical groups of populations, although there were some differences between some of the subspecies. The low levels of heterozygosity ( H = 0.0081 and H = 0.0031) are considered to arise from a combination of two factors: the low levels of heterozygosity which appear to be characteristic of birds and population effects. Furthermore, no interspecific differences were detected ( I = 0.999) indicating the morphological changes rather than changes at structural gene loci may have been more important in speciation.     

Intermittent breeding in the Herring Gull Larus argentatus and the Lesser Black-backed Gull Larus fuscus

Thirty-three percent and 37% of adult Herring Gulls Larus argentatus and 34% and 40% of adult Lesser Black-backed Gulls Larus fuscus , all with some previous breeding experience, failed to breed in 1993 and 1994, respectively. About half of these intermittent breeders of both species failed to breed in both years. Common amongst the intermittent breeders were smaller individuals, birds with low survival chances and relatively unsuccessful breeders.     

Kelp gulls Larus dominicanus as predators in kelp Macrocystis pyrifera beds

Summary Minimum daily consumption of bivalves Gaimardia sp by kelp gulls in a Macrocystis kelp bed at Porvenir, Tierra del Fuego, was calculated to be ca. 525 000 individuals, corresponding to an energy removal of ca. 21 kJ·m^-2·d^-1. This is far in excess of energy removal by any other higher-trophic-level predator in southern Chilean Macrocystis beds, but previous work has ignored kelp gulls as a component of the kelp bed community.     

CCK-induced pancreatic growth is not limited by mitogenic capacity in mice

In mice fed trypsin inhibitor (camostat) to elevate endogenous CCK, pancreatic growth plateaus by 7 days. It is unknown whether this represents the maximum growth capacity of the pancreas. To test the ability of CCK to drive further growth, mice were fed chow containing camostat (0.1%) for 1 wk, then fed standard chow for 1 wk, and finally returned to the camostat diet for a week. Pancreatic mass increased to 245% of initial value (iv) following 1 wk of camostat feeding, decreased to 147% iv following a 1 wk return to normal chow, and increased to 257% iv with subsequent camostat feeding. Camostat feeding was associated with significant increases in circulating CCK and changes in pancreatic mass were paralleled by changes in protein and DNA content. Moreover, regression of the pancreas following camostat feeding was associated with changes in the expression of the autophagosome marker LC3. Pancreatic protein synthetic rates were 130% of control after 2 days on camostat but were equivalent to control after 7 days. Changes in the phosphorylation of 4E-BP1 and S6, downstream effectors of mammalian target of rapamycin (mTOR), paralleled changes in protein synthetic rates. Cellular content of Akt, an upstream activating kinase of mTOR, decreased after 7 days of camostat feeding whereas expression of the E3 ubiquitin-ligases and the cell cycle inhibitor p21 increased after 2 days. These results indicate that CCK-stimulated growth of the pancreas is not limited by acinar cell mitogenic capacity but is due, at least in part, to inhibition of promitogenic Akt signaling.     

Circadian photosynthetic reductant flow in the dinoflagellate Lingulodinium is limited by carbon availability

Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide a selective advantage to cells adapted to daily light/dark cycles. However, the biochemical links between the clock and the overt rhythms in cell physiology are generally not known. Here, we examine the circadian rhythm in O₂ evolution by cultures of the dinoflagellate Lingulodinium, a rhythm previously ascribed to rhythmic electron flow through photosystem II. We find that O₂ evolution rates increase when CO₂ concentrations are increased, either following addition of DIC or a rapid decrease in culture pH. In medium containing only nitrate as an electron acceptor, O₂ evolution rates mirror the circadian rhythm of nitrate reductase activity in the cells. Furthermore, competition between photosynthetic electron flow to carbon and to nitrate varies in its relative efficiency through the day–night cycle. We also find, using simultaneous and continuous monitoring of pH and O₂ evolution rates over several days, that while culture pH is normally rhythmic, circadian changes in rates of O₂ evolution depend not on the external pH but on levels of internal electron acceptors. We propose that the photosynthetic electron transport rhythm in Lingulodinium is driven by the availability of a reductant sink.     

Strong environmental determination of a carotenoid-based plumage trait is not mediated by carotenoid availability

Carotenoid-based colours are recognized as having an important signalling function, yet the nature of the mechanisms that maintain their honesty is not well understood. By combining a carotenoid-feeding experiment with a quantitative genetic experiment in a wild population of blue tits (Parus caeruleus), we were able to test predictions that differentiate between proposed mechanisms. If variation in carotenoid ingestion underlies variation in carotenoid-based colour expression, then carotenoid-supplemented birds should have reduced variance in colour. In this study, carotenoid supplementation produced a small but significant change in plumage colouration, but no significant change in variation. These results suggest that variation in carotenoid acquisition is not an important source of variation for this colour trait, and that variation in post-ingestion processes are likely to be more important. The low heritability of this colour trait suggests environmental factors are likely to underlie the majority of variation in these processes.     

Age-dependent changes in plasma biochemistry of yellow-legged gulls (Larus cachinnans)

The study of avian plasma chemistry is providing useful reference values for the management of endangered and game species, supporting veterinarians in their diagnostics, and also bringing to light relevant physiological adaptations during periods of food-shortage. Age is an important source of variability for plasma chemistry. Here I report plasma chemistry of yellow-legged gulls Larus cachinnans from different ages, between post-independence and adulthood, a 5-year interval. Increase in plasma cholesterol concentration and decreases in uric acid, inorganic phosphorus and alkaline phosphatase values were seen. Body mass corrected by body size (i.e. body condition) increased with age, plasma cholesterol being positively correlated in females, but not in males. Moreover, cholesterol was also positively correlated to gonad size in both sexes. Long-term developmental changes in this species, such as gonad development and the acquisition of an optimal body mass for reproduction, could explain these findings. Finally, inorganic phosphorus and alkaline phosphatase, both traditionally related to osteogenesis, were not associated to deferred skull ossification, as originally was suggested in other species.     

Nonbreeding and nests without eggs in the Lesser Black-backed Gull Larus fuscus

Estimates of the number of breeding Lesser Black-backed Gulls Larus fuscus at the Tarnbrook Fell gullery, Lancashire, have been made from annual counts of nests since 1981. During all of these surveys, the mean percentage of nests which did not contain eggs has been remarkably constant from year to year (54%± 1.9%). A study of specific nests at the colony in 1992 showed that the great majority of these "empty" nests did not subsequently receive eggs. in 1993, a study of a sample of territory-holding gulls was made on a 0.41-ha study plot to investigate and to quantify the occurrence of empty nests. Of the 62 pairs that defended a territory and constructed a complete nest, 27% subsequently failed to produce eggs. These birds attended their territory as a pair significantly less frequently than pairs that produced clutches and achieved significantly fewer apparently successful mountings. Sixty percent of pairs constructed more than one nest, and 58% of all nests built received no eggs. The construction of empty nests was not found to be related to the density of nesting gulls. Since 1981, estimates of the number of gulls in the colony have been based on the assumption that one nest represents one pair of gulls. This has been shown not to be the case, and a correction multiplier of 0.61 must be applied to counts of nests at the colony to obtain an estimate of the number of breeding gulls.     

Biomass and carotenoid pigment production by patagonian native yeasts

Summary New yeast isolates from unexplored Patagonian habitats were studied for the production of biomass and carotenoids as the first step towards the selection of hyper-producing strains and the design of a process optimization approach. Patagonian yeast isolates considered as potential biomass and carotenoid sources were studied using ammonium sulphate and urea as nitrogen sources in semi-synthetic medium (MMS), and agro-industrial byproducts (cane molasses, corn syrup, raw malt extract) as carbon sources. Maximum pigment production (300 μg g⁻¹) was achieved by Rhodotorula mucilaginosa CRUB 0195 and by novel species Cryptococcus sp. CRUB 1046. β-carotene, torulene and torularhodin were the major carotenoids found.     

Sex-biased mortality in the Lesser Black-backed Gull Larus fuscus during the nestling stage

Theory predicts that skewed progeny sex ratios should be relatively common in vertebrate populations. In most birds this has proved hard to substantiate due to the difficulties associated with identifying the sex of large samples of chicks. This study reports the success of a new molecular DNA technique in determining the sex of 601 newly-hatched Lesser Black-backed Gulls Larus fuscus
There was no evidence of any adaptive sex ratio within broods. Male chicks were found to be disproportionately large and to grow at a faster rate than females. The overall sex ratio changed significantly from 0.484 (male/male + female) at hatching to 0.399 by fledging, probably due to male susceptibility to starvation. Mortality also increased significantly with hatching order, an effect often observed in species like the Lesser Black-backed Gull where hatching is asynchronous. I discuss the possibility that hatching asynchrony may in fact be a strategy employed to prevent excessive skews developing in progeny sex ratio whenever variable differential mortality is likely.
The results appear to vindicate Fisher's (1930) hypothesis which predicts the overproduction of the 'cheaper' sex. However, as the skewed sex ratio may be determined more by unpredictable environmental factors, such as food supply and weather conditions rather than parental strategy, this interpretation should be treated with caution.     

Respiration in postharvest sugarbeet roots is not limited by respiratory capacity or adenylates

Control of respiration has largely been studied with growing and/or photosynthetic tissues or organs, but has rarely been examined in harvested and stored plant products. As nongrowing, heterotrophic organs that are reliant on respiration to provide all of their metabolic needs, harvested plant products differ dramatically in their metabolism and respiratory needs from growing and photosynthetically active plant organs, and it cannot be assumed that the same mechanism controls respiration in both actively growing and harvested plant organs. To elucidate mechanisms of respiratory control for a harvested and stored plant product, sugarbeet (Beta vulgaris L.) root respiration was characterized with respect to respiratory capacity, adenylate levels and cellular energy status in roots whose respiration was altered by wounding or cold treatment (1 degrees C) and in response to potential effectors of respiration. Respiration rate was induced by wounding in roots stored at 10 degrees C and by cold temperature in roots stored at 1 degrees C for 11-13d. Alterations in respiration rate due to wounding or storage temperature were unrelated to changes in total respiratory capacity, the capacities of the cytochrome c oxidase (COX) or alternative oxidase (AOX) pathways, adenylate concentrations or cellular energy status, measured by the ATP:ADP ratio. In root tissue, respiration was induced by exogenous NADH indicating that respiratory capacity was capable of oxidizing additional electrons fed into the electron transport chain via an external NADH dehydrogenase. Respiration was not induced by addition of ADP or a respiratory uncoupler. These results suggest that respiration rate in stored sugarbeet roots is not limited by respiratory capacity, ADP availability or cellular energy status. Since respiration in plants can be regulated by substrate availability, respiratory capacity or energy status, it is likely that a substrate, other than ADP, limits respiration in stored sugarbeet roots.     

Validation of water flux and body composition in glaucous gulls (Larus hyperboreus)

Water influx rates (WIR) measured with tritiated water dilution were compared with direct measures of water and energy intake in glaucous gulls (Larus hyperboreus). Total body water (TBW) measured isotopically was also compared with TBW determined by body composition analysis (BCA) of the same birds. Seventeen wild gulls were captured and studied in outdoor enclosures at Ny-Alesund, Svalbard, in July 2002. Gulls were hand-fed known quantities of Arctic cod (Boreogadus saida) or given water on the basis of one of four experimental treatments: (A) fasting, (B) fish only, (C) water only, or (D) fish and water. Water and energy content of Arctic cod was also determined. WIR of gulls (after subtracting metabolic water production) in treatments A, B, C, and D were 0, 101 +/- 5, 62 +/- 19, and 122 +/- 21 SD g d(-1), respectively. Measured water intake in each group was 0, 111 +/- 2, 64 +/- 3, and 134 +/- 15 SD g d(-1), respectively. On average, WIR underestimated measured water intake in each group. Errors were lowest but most variable for gulls fed water only (-2.2% +/- 32.8%) compared with gulls fed fish only (-9.0% +/- 5.4%) or fish and water (-9.0% +/- 7.0%). Compared with measured water intake, errors in WIR were relatively low overall (-6.9% +/- 17.4%) and comparable to previous validation studies. The difference in TBW determined by BCA versus isotopic dilution ranged between -1.02% and +8.59% of mass. On average, TBW measured isotopically (632 +/- 24 g kg(-1)) overestimated true body water by a factor of 1.033.     

Geographic variation in reproduction and survival of kelp gulls Larus dominicanus vetula in southern Africa

Different populations of a species tend to vary in survival and reproduction, but the extent and scale of such spatial variation are poorly known. We estimated survival and clutch size of kelp gulls Larus dominicanus vetula across their entire African range. At this large geographic scale, we found no evidence for spatial variation in survival, and there was no variation in clutch size. However, there was considerable variation in clutch size among colonies within regions. Over the whole study, mean annual survival of juvenile and adult birds was 0.44 and 0.84, and mean clutch size was 2.2 eggs. A matrix population model showed that population growth was least sensitive to variation in clutch size, and the observed variation in clutch size could not fully account for the observed variation in population growth among colonies and regions. Our results thus suggest that dispersal and/or variation in survival (including egg/nestling survival) at a small spatial scale are also important for the spatial pattern of kelp gull population dynamics. These results are consistent with a metapopulation approach to spatial population dynamics.