Fresh Body Mass Research Articles

Using functional traits and phylogeny to understand local extinction risk in dragonflies and damselflies (Odonata).

Understanding the risk of local extinction of a species is vital in conservation biology, especially now when anthropogenic disturbances and global warming are severely changing natural habitats. Local extinction risk depends on species traits, such as its geographical range size, fresh body mass, dispersal ability, length of flying period, life history variation, and how specialized it is regarding its breeding habitat. We used a phylogenetic approach because closely related species are not independent observations in the statistical tests. Our field data contained the local extinction risk of 31 odonate (dragonflies and damselflies) species from Central Finland. Species relatedness (i.e., phylogenetic signal) did not affect local extinction risk, length of flying period, nor the geographical range size of a species. However, we found that closely related species were similar in hind wing length, length of larval period, and habitat of larvae. Both phylogenetically corrected (PGLS) and uncorrected (GLM) analysis indicated that the geographical range size of species was negatively related to local extinction risk. Contrary to expectations, habitat specialist species did not have higher local extinction rates than habitat generalist species nor was it affected by the relatedness of species. As predicted, species’ long larval period increased, and long wings decreased the local extinction risk when evolutionary relatedness was controlled. Our results suggest that a relatively narrow geographical range size is an accurate estimate for a local extinction risk of an odonate species, but the species with long life history and large habitat niche width of adults increased local extinction risk. Because the results were so similar between PGLS and GLM methods, it seems that using a phylogenetic approach does not improve predicting local extinctions.

Quantitative Parameters of the Body Composition Influencing Host Seeking Behavior of Ixodes ricinus Adults.

Ixodes ricinus, a hematophagous arthropod species with great medical importance in the northern hemisphere, is characterized by an ability to survive prolonged periods of starvation, a wide host spectrum, and high vector competence. The aim of the present study was to determine the quantitative parameters of questing I. ricinus ticks collected in eastern Poland during the spring peak of their activity. The study consisted in the determination of quantitative parameters characterizing I. ricinus females and males, i.e., fresh body mass, reduced body mass, lipid-free body mass, water mass, and lipid mass and calculation of the lipid index. A statistically significant difference was observed between the mean values of the lipid index in females collected during the first and last ten days of May, which indicates the progressive utilization of reserve materials in the activity period. Higher activity of I. ricinus female ticks was observed during the last ten days of May despite the less favorable weather conditions, indicating their strong determination in host-seeking behaviors accompanying a decline in the lipid content and the use of the “now or never” strategy.

Body mass and territorial defence strategy affect the territory size of odonate species.

The territory is a distinct mating place that a male defends against intruding conspecific males. The size of a territory varies between species and most of the variation between species has been found to scale allometrically with body mass. The variation that could not be explained by body mass has been explained with several variables such as habitat productivity, trophic level, locomotion strategy and thermoregulation. All previous interspecific comparative studies have been done on vertebrate species such as birds, mammals, reptiles and fishes, meaning that studies using invertebrate species are missing. Here, we studied the relationship of a species's territory size with its fresh body mass (FBM) in addition to other ecologically relevant traits using 86 damselfly and dragonfly (Odonata) species. We found that territory size is strongly affected by species FBM, following an allometric relationship similar to vertebrates. We also found that the territory size of a species was affected by its territorial defence strategy, constantly flying species having larger territories than species that mostly perch. Breeding habitat or the presence of sexual characters did not affect territory sizes, but lotic species and species without wing spots had steeper allometric slopes. It seems that an increase in a species's body mass increases its territory size and may force the species to shift its territory defence strategy from a percher to a flier.

Aroclor 1254 inhibits vasotocinergic pathways related to osmoregulatory and stress functions in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

The present study assesses the response of vasotocinergic system in the gilthead sea bream (Sparus aurata) after administering two doses of the polychlorinated biphenyl Aroclor 1254 (15 or 50 μg g−1 fresh body mass). Seven days post-administration, eight fish of each experimental group were sampled, and the remaining animals were challenged with a hyperosmotic stress by being transferred from seawater (36 ppt) to high salinity water (55 ppt) and being sampled 3 days post-transfer. Aroclor 1254 affected gene expression of avt, together with Avt concentrations in pituitary and plasma, inhibiting the stimulation observed in vasotocinergic system after hyperosmotic challenge. This was noted by the accumulation of Avt at hypophyseal level as well as by its undetectable values in plasma. Hyperosmotic transfer significantly changed branchial avtrv1a, avtrv2, atp1a and cftr mRNA expression levels in control fish, while in Aroclor 1254-treated fish they remained mostly unchanged. This desensitization also occurred for avtrs in hypothalamus, caudal kidney and liver. In addition, an enhancement in plasma cortisol concentration, together with the orchestration of several players of the Hypothalamic-Pituitary-Interrenal axis (crh, crhbp, trh, star), was also observed mostly at the highest dose used (50 μg g−1 body mass), affecting plasma and hepatic metabolites. Our results demonstrated that Aroclor 1254 compromises the hypoosmoregulatory function of vasotocinergic system in S. aurata, also inducing a concomitant stress response. In summary, this study demonstrates that Aroclor 1254 can be considered an important endocrine disruptor in relation with the correct arrangement of vasotocinergic, metabolic and stress pathways after their stimulation by transfer to hyperosmotic environments.

Validation of the flooding dose technique to determine fractional rates of protein synthesis in a model bivalve species, the blue mussel (Mytilus edulis L.)

For the first time, use of the flooding dose technique using 3H-Phenylalanine is validated for measuring whole-animal and tissue-specific rates of protein synthesis in the blue mussel Mytilus edulis (61mm shell length; 4.0g fresh body mass). Following injection, the phenylalanine-specific radioactivities in the gill, mantle and whole-animal free pools were elevated within one hour and remained elevated and stable for up to 6h following injection of 3H-phenylalanine into the posterior adductor muscle. Incorporation of 3H-phenylalanine into body protein was linear over time following injection and the non-significant intercepts for the regressions suggested incorporation into body protein occurred rapidly after injection. These results validate the technique for measuring rates of protein synthesis in mussels. There were no differences in the calculated rates following 1–6h incubation in gill, mantle or whole-animal and fractional rates of protein synthesis from the combined time course data were 9.5±0.8%d−1 for the gill, 2.5±0.3%d−1 for the mantle and 2.6±0.3%d−1 for the whole-animal, respectively (mean values±SEM). The whole-animal absolute rate of protein synthesis was calculated as 18.9±0.6mg protein day−1. The use of this technique in measuring one of the major components of maintenance metabolism and growth will provide a valuable and convenient tool in furthering our understanding of the protein metabolism and energetics of this keystone marine invertebrate and its ability to adjust and respond to fluctuations, such as that expected as a result of climate change.

Oxygen consumption of the earthworm species Dendrobaena mrazeki

Dendrobaena mrazeki is an endemic earthworm species inhabiting dry habitats such as pine and thermophilous oak forests in Central Europe. Metabolically, D. mrazeki showed some features typical for endogeic species and some of epigeic ones. In comparison with the related Dendrobaena octaedra, D. mrazeki was a larger earthworm with fresh body mass of adult and subadult individuals of W = 0.59 ± 0.05 g. Its body mass-specific oxygen consumption ( M/ W = 48 ± 5 μl O 2 g −1 h −1, at 15 °C) was the lowest of all earthworms studied ( Aporrectodea caliginosa, Aporrectodea rosea, D. octaedra, Lumbricus castaneus, Lumbricus rubellus and Octolasion lacteum), being strongly dependent on W ( b from the equation M/ W = aW b about −0.8). D. mrazeki had low relative water content (77.4% of fresh body mass) and small relative amount of dry weight of the intestinal content (20.1% of dry body mass), which is similar to the epigeic D. octaedra. The respiration rate of D. mrazeki remained the lowest even after recalculating M/ W to respiration rate per dry mass or per dry mass without the intestine content to correct for the differences among species in body water content and gut content.

Evidence for between-generation effects in carabids exposed to heavy metals pollution

This work represents one of very few studies showing intergenerational effects of terrestrial pollution with heavy metals in a terrestrial predatory invertebrate. We demonstrate that carabid beetles Pterostichus oblongopunctatus (Coleoptera, Carabidae) inhabiting metal polluted environment have altered life-history parameters in comparison to those from reference area populations. We observed decreased hatchability of eggs in field collected animals fed with uncontaminated food, which suggests that carabids from heavily polluted sites are not able to fully avoid the risk of secondary poisoning via contaminated prey. The adult fresh body mass of young imagines from the first laboratory generation reared in uncontaminated conditions was affected by pollution level at the sites of beetles' origin. However, we did not observe any effects of site contamination in the second laboratory generation. Therefore, we conclude that although genetic adaptation has not occurred in the populations chronically exposed to toxic metal concentrations, there is evidence of intergenerational maternal effects of metal pollution.

Fat Dynamics of Arctic-Nesting Sandpipers During Spring in Mid-Continental North America

Abstract We measured fresh body mass, total body fat, and fat-free dry mass (FFDM) of three species of Arctic-nesting calidrid sandpipers (Baird's Sandpiper [Calidris bairdii], hereafter “BASA”; Semipalmated Sandpiper [C. pusilla], hereafter “SESA”; and White-rumped Sandpiper [C. fuscicollis], hereafter “WRSA”) during spring stopovers in the Prairie Pothole Region (PPR) of North Dakota, and evaluated the contribution of stored fat to (1) energy requirements for migration to their Arctic-breeding grounds and (2) nutrient needs for reproduction. All spring migrant WRSA (n = 124) and BASA (n = 111), and all but 2 of 99 SESA we collected were ≥2 years old. Male and female BASA migrated through North Dakota concurrently, male SESA averaged earlier than females, and WRSA males preceded females. Fat indices (ratio of fat to FFDM) of male and female SESA and WRSA averaged approximately twice those of male and female BASA. Total body fat of male and female BASA increased with date in spring 1980, but not in 1981; slopes were similar for both sexes each year. Male and female SESA arrived lean in 1980 and 1981, and total body fat increased with date in both years, with similar slopes for all combinations of sex and year. Male and female WRSA arrived lean in 1980–1981 and 1981, respectively, and total body fat increased with date, whereas females arrived with fat reserves already acquired in 1980. Interspecific and sex differences in migration schedules probably contributed to variation in fat storage patterns by affecting maintenance energy costs and food availability. Estimated flight ranges of BASA suggest that few could have met their energy needs for migration to the breeding grounds exclusively from fat stored by the time of departure from North Dakota. Estimated flight ranges of SESA and WRSA, along with fresh body masses of both species when live-trapped on or near their breeding grounds in northern Canada, suggest that major parts of both populations stored adequate fat by departure from temperate mid-continental North America to meet their energy requirements for migration and part of their nutrient needs for reproduction. Dinámica de la Grasa en Chorlos que Nidifican en el Ártico durante la Primavera en el Área Continental Central de América del Norte

FAT DYNAMICS OF ARCTIC-NESTING SANDPIPERS DURING SPRING IN MID-CONTINENTAL NORTH AMERICA

We measured fresh body mass, total body fat, and fat-free dry mass (FFDM) of three species of Arctic-nesting calidrid sandpipers (Baird's Sandpiper [Calidris bairdii], hereafter “BASA”; Semipalmated Sandpiper [C. pusilla], hereafter “SESA”; and White-rumped Sandpiper [C. fuscicollis], hereafter “WRSA”) during spring stopovers in the Prairie Pothole Region (PPR) of North Dakota, and evaluated the contribution of stored fat to (1) energy requirements for migration to their Arctic-breeding grounds and (2) nutrient needs for reproduction. All spring migrant WRSA (n = 124) and BASA (n = 111), and all but 2 of 99 SESA we collected were ≥2 years old. Male and female BASA migrated through North Dakota concurrently, male SESA averaged earlier than females, and WRSA males preceded females. Fat indices (ratio of fat to FFDM) of male and female SESA and WRSA averaged approximately twice those of male and female BASA. Total body fat of male and female BASA increased with date in spring 1980, but not in 1981; slopes were similar for both sexes each year. Male and female SESA arrived lean in 1980 and 1981, and total body fat increased with date in both years, with similar slopes for all combinations of sex and year. Male and female WRSA arrived lean in 1980–1981 and 1981, respectively, and total body fat increased with date, whereas females arrived with fat reserves already acquired in 1980. Interspecific and sex differences in migration schedules probably contributed to variation in fat storage patterns by affecting maintenance energy costs and food availability. Estimated flight ranges of BASA suggest that few could have met their energy needs for migration to the breeding grounds exclusively from fat stored by the time of departure from North Dakota. Estimated flight ranges of SESA and WRSA, along with fresh body masses of both species when live-trapped on or near their breeding grounds in northern Canada, suggest that major parts of both populations stored adequate fat by departure from temperate mid-continental North America to meet their energy requirements for migration and part of their nutrient needs for reproduction. Dinámica de la Grasa en Chorlos que Nidifican en el Ártico durante la Primavera en el Área Continental Central de América del Norte

The density and biomass of Dreissena polymorpha living on submerged macrophytes in Lake Balaton (Hungary)

Dreissena polymorpha appeared and spread throughout Lake Balaton in the 1930 s. We studied the density, the body length-body mass relationships and the biomass of D. polymorpha living on the submerged macrophytes in the littoral zone at four sites of different trophic status from May to October 2000. The dominant submerged macrophyte was Potamogeton perfoliatus in May/June and July and Myriophyllum spicatum in October, the fresh biomass of submerged macrophytes ranged between 450.64 and 3,171.51 g/m 2 , dry biomass ranged between 61.54 and 381.31 g/m 2 . D. polymorpha represented 2.48-84.85 % of all animals on submerged macrophytes. The density of zebra mussels ranged between 421 and 749,032 ind./m 2 , between 1 and 282 ind./g macrophyte fresh mass, and between 9 and 2,032ind./g macrophyte dry mass. The body length-body mass relationships could be described by simple power function equations for fresh body mass with and without shell and dry body mass with and without shell. Zebra mussel biomass in Lake Balaton varied widely between 0.35 and 1,106.55 g fresh mass with shell/m 2 , between 0.01 and 50.96 g dry mass with shell/ m 2 , between 0.09 and 260.39 g fresh mass without shell/m 2 and between 0.002 and 6.49 g dry mass without shell/m 2 . The estimated respiratory organic carbon loss of total D. polymorpha population in the zone of submerged macrophytes ranged between 0.15 and 338.27 mg C/m 2 day, which is 0.04-154 % of planktonic primary production in different parts of the lake, illustrating the important role of this Ponto-Caspian invasive mussel in the matter-energy flux in Lake Balaton. The density of the zebra mussel (ind./m 2 ) significantly depends on the type of submerged macrophytes and on the water depth. The type of submerged macrophytes and water depth have significant additive and interactive effects on the length of animals. Only the water depth determined significantly the biomass of zebra mussel.

Avian forensics: predicting body fat and body mass from wing remains

We describe the development of a method to predict percent body fat of killed birds from the percent fat in the most distal wing tissue, which is often left uneaten by aerial predators. When combined with a measure of body structural size, such as tarsus, culmen or keel length, percent wing fat can be used to predict fresh body mass at the time of death. These techniques may prove useful in field studies of mass‐dependent predation risk.

Dynamic effects of parasitism by an endoparasitoid wasp on the development of two host species: implications for host quality and parasitoid fitness

Summary1. The study reported here examined growth and developmental interactions between the gregarious larval koinobiont endoparasitoid Cotesia glomerata (Hymenoptera: Braconidae) and two of its hosts that vary considerably in growth potential: Pieris rapae and the larger P. brassicae (Lepidoptera: Pieridae). At pupation, healthy larvae of P. brassicae are over twice as large, in terms of fresh body mass, as those of P. rapae.2. Clutch size of C. glomerata was manipulated artificially, and the relationship between parasitoid burden and the maximum weight of the parasitised host (= host–parasitoid complex) was measured. In both hosts, the maximum complex weight was correlated positively with parasitoid burden. Compared with unparasitised hosts, however, the growth of P. rapae was increased at significantly lower parasitoid burdens than in P. brassicae. Emerging wasp size was correlated negatively with parasitoid burden in both host species, whereas development time was less affected.3. After larval parasitoid egress, the weight of the host carcass increased slightly, but not significantly, with parasitoid burden, although there was a strong correlation between the proportion of host mass consumed by C. glomerata larvae during development and parasitoid burden.4. Clutch size was generally correlated positively with instar parasitised in both hosts, and greater in P. brassicae than in P. rapae. Sex ratios were much more female biased in L1 and L2 P. rapae than in all other host classes. Adult parasitoid size was correlated inversely with host instar at parasitism, and wasps emerging from P. brassicae were larger, and completed development faster, than conspecifics emerging from P. rapae.5. The data reveal that parasitism by C. glomerata has profound species‐specific effects on the growth of both host species. Consequently, optimality models in which host quality is often based on host size at parasitism or unparasitised growth potential may have little utility in describing the development of gregarious koinobiont endoparasitoids. The results of this investigation are discussed in relation to the potential effectiveness of gregarious koinobionts in biological control programmes.

Colony age, neighborhood density and reproductive potential in harvester ants.

At about age 5 years, colonies of the harvester ant, Pogonomyrmex barbatus, begin to produce winged, sexual forms (alates) that mate in large annual aggregations. We examined how colony age and neighborhood density affect the numbers, body mass, and body fat of alates produced by 172 colonies ranging in age from 4 to 17 years. Over one-third (36%) of all colonies produced no alates. Failure to reproduce was independent of colony age. Of those colonies that did produce alates, older colonies produced more alates than younger colonies. Older colonies produced lighter female alates (in dry mass), but the total biomass of additional alates produced by older colonies far outweighed the reduced allocation to female alate body mass. Body fat content was much higher in female alates (36.0% on average) than in males (3.7% on average). Alate body fat content was not related to colony age. The fitness of female alates may be related to their fresh body mass; that of females captured after mating and reared in the laboratory was positively correlated with egg-laying rate, although not with the total number of eggs in the first brood. Neighborhood density was not related to alate number, mass, or fat content, in contrast to the results of a 1995 study at the site, in which alate numbers were negatively related to neighborhood density. Thus the influence of crowding on reproductive output appears to vary from year to year, perhaps in response to variation in rainfall and food supply. Alate output by individual colonies was correlated among years. These results suggest that a few, older colonies dominate the pool of reproductives year after year.

Guts Don't Fly: Small Digestive Organs in Obese Bar-Tailed Godwits

We documented fat loads and abdominal organ sizes of Bar-tailed Godwits (Limosa lapponica baueri) that died after colliding against a radar dome on the Alaska Peninsula, most likely just after takeoff on a trans-Pacific flight of 11,000 km, and of birds of the same subspecies just before northward departure from New Zealand. We compared these data with data on body composition of godwits of the smaller lapponica subspecies obtained during a northward stopover in The Netherlands. As a consequence of high amounts of subcutaneous and intraperitoneal fat, and very small fat-free mass, Bar-tailed Godwits from Alaska had relative fat loads that are among the highest ever recorded in birds (ca, 55% of fresh body mass). Compared with northbound godwits from New Zealand, the Alaskan birds had very small gizzards, livers, kidneys, and guts. This suggests that upon departure, long-distance migrants dispense with parts of their metabolic machinery that are not directly necessary during flight. and rebuild these organs upon arrival at the migratory destination.

Controlling resource acquisition to reveal a life history trade‐off: egg mass and clutch size in an iteroparous seed predator, Prostephanus truncatus

1. A trade‐off constraining egg production was investigated and the consequences of egg mass for the offspring life history in Prostephanus truncatus investigated. Fresh egg mass was found to vary between 0.065 and 0.109 mg (about 20% of fresh body mass at emergence) and was correlated both with dry egg mass (r = 0.8) and with the mass of first‐instar larvae (r = 0.8).2. There was a negative correlation between egg mass and clutch size: doubling clutch size from eight to sixteen eggs resulted in a reduction in egg mass from 0.09 to 0.07 mg. Resource allocation per clutch was not constant but increased with clutch size. After allowing for the relationship between egg mass and clutch size, heavier females were found to oviposit both heavier eggs and more eggs in a clutch.3. By placing eggs in prepared seeds that minimized variation in resource acquisition, it was discovered that development period of females, but not of males, was negatively correlated with egg mass. Egg size was not correlated with body size at emergence in either sex.4. The results are interpreted as revealing a resource‐allocation trade‐off in egg production.

Basal metabolic rate in relation to body composition and daily energy expenditure in the field vole, Microtus agrestis.

Basal metabolic rate in the field vole (Microtus agrestis) was studied in relation to body composition and daily energy expenditure in the field. Daily energy expenditure was measured by means of doubly labelled water (D2 18O). In the same individuals, basal metabolic rate was subsequently derived from O2 consumption in an open-circuit system in the laboratory. Body composition was obtained by dissecting the animals and determining fresh, dry, and lean dry mass of different organs. Daily energy expenditure for free-living field voles ranged from 1.8 to 4.5 times basal metabolic rate, with an average of 2.9 times basal metabolic rate. Variation in both daily energy expenditure and basal metabolic rate was best explained by body mass. Gender or reproductive activity did not have significant additive effects. Daily energy expenditure and basal metabolic rate showed significant positive relationships to body mass with similar mass exponents of 0.493 and 0.526, respectively. Overall, there was a significant correlation between daily energy expenditure and basal metabolic rate, but the mass-independent residuals (deviations from the allometrically predicted values) did not correlate. Carcass analysis revealed that a number of organs were slightly better predictors for daily energy expenditure and basal metabolic rate than was fresh body mass. Mass-independent residuals of lean dry heart mass and basal metabolic rate were positively correlated, which is in agreement with the idea that basal metabolic rate reflects the size of metabolically active organs. The study does not provide support for an intraindividual association of basal metabolic rate with daily energy expenditure in the field.

Winter Starvation in Captive Common Barn-Owls: Bioenergetics during Refeeding

ABsTRACr.-The bioenergetics of eight captive Common Barn-Owls (Tyto alba alba) acclimated at 5?C were studied during the restoration of a 30% reduction in body mass following a period of total food deprivation. The eight-day period during which body mass was restored (Refeeding I) was compared with a five-day prefasting period (Feeding), corresponding to steady body mass and a six-day period (Refeeding II) of stabilization at a new steady state. Food was given ad libitum throughout the feeding periods. During Refeeding I, the rate of increase in body mass (13.9 ? SD of 1.0 g/24 h in females and 9.2 ? 0.8 g/24 h in males) was close to the maximum value for growth of captive or wild owlets. It was achieved by a 1.63-fold increase in gross energy intake and daily metabolized energy, respectively, of 370 ? 42 and 275 ? 31 kJ/d during Feeding. In contrast to the clear increase in food assimilation efficiency observed in other species during refeeding, the high rate of energy intake and body mass restoration in the Common Barn-Owl was associated with only a slight increase in assimilation efficiencies: 52.0 ? 2.2% versus 49.1 ? 1.0% during Feeding for dry mass; and 75.5 ? 1.1% versus 74.1 ? 0.6% for energy. This slight increase could only be attributed to a reduction of the energy lost in pellet production (i.e. to a higher effectiveness in gastric digestion). The energetic cost of daily change in body mass was estimated in both sexes and both feeding periods, and appeared to be constant (10.8 ? 1.1 kJ/g fresh body mass). Using this value, the part of the daily metabolized energy invested in the existence metabolism was calculated. After four days of refeeding, existence metabolism paradoxically appeared similar or even higher than before fasting, while the body mass was still lower than the initial value. Thus, in contrast to the laboratory rat (Rattus norvegicus) or humans, the Common Barn-Owl is unable to enhance restoration of body reserves by minimizing existence requirements when refed ad libitum after a period of starvation. This might be partly due to the maintenance of a high locomotor activity throughout starvation and refeeding. Received 3 October 1991, accepted 5 May 1992.

On the importance of fat reserves for the little auk (Alle alle) chicks.

The pattern of fat deposition and inter-year variation in the amount of deposited fat, lean dry mass (LDM) and water were studied in the chicks of little auk (Alle alle), an arctic alcid, at Spitsbergen in the 1984, 1986 and 1987 breeding seasons. The lipid index (lipid mass/LDM) rose from 0.29 at hatching to about 0.70 at the age of maximum body mass attained in the nest, the highest yet recorded for seabirds except procellariiforms. Just before fledging the index dropped to 0.38. Fat mass in 1984 chicks and also fresh body mass of older 1984 chicks was significantly lower than in the other two seasons, but there were no statistical year-to-year differences in LDM's of chicks. The amount of fat in chicks was significantly correlated with certain weather parameters. Fasting capability (FC) of the chicks (the time that chicks could survive when using only their lipid stores) was calculated from fat mass and previous data on metabolic rates of chicks. The FC's of all 108 chicks collected in three seasons were greater than maximum interval between two consecutive feeds to chicks reported in the study colony. Also the estimated fat reserves of 99.7% of chicks weighed in 1984 were sufficient to support them for longer than the maximum recorded intervals between feeds. In relation to death by starvation, little auk chicks, at least up to the age of maximum body mass, have a substantial surplus of fat. This is contrary to the hypothesis that fat depots in seabird chicks assist survival during the periodic fasts resulting from unpredictable feeding conditions.

Energy Content of Some Spiders and Insects on Branches of Spruce (Picea abies) in Winter; Prey of Certain Passerine Birds

Spiders and some insects were collected from branches of spruce, Picea abies, in September-October and February-March in southwest Sweden. At least 19 species of spiders were present. Spiders of family Thomisidae were most common with 37-45% by number, and the species-group Philodromus aureolus alone made up 35-39%. Family Linyphiidae came second with 27% and Araneidae third with 11-20%. The taxonomic composition is remarkably similar in September and March. This suggests that the birds, which severely reduce spider density over winter, prey on spiders with little or no selectivity as to taxonomy. A fitted power function of fresh body mass versus length has the exponent 2.39; this indicates that spiders of different size are geometrically dissimilar. In autumn the energy content per gram of dry mass is 24.0 kJ for spiders, 21.7 kJ for Psocoptera, and 22.0 kJ for Curculionidae. Average energy content per gram of dry mass of spiders decreased by 5.8% in four winter months. If this reduction is assumed to be caused by metabolism of stored fat only, the corresponding reduction of dry mass per spider would be 8.1% and the reduction of energy content per spider 13%. The energy cost of standard metabolism of spiders over winter was calculated to be a considerably larger proportion of the energy content of spiders in autumn.