Endocrine Correlates of Seasonal Body Mass Dynamics in the Collared Lemming (Dicrostonyx groenlandicus)

Many winter-active temperate rodent species show seasonal, photoperiod-mediatedchanges in body mass that correlate with changes in food availability,gaining mass when food is abundant. The collared lemming (Dicrostonyxgroenlandicus), an arctic species, also undergoes a seasonaltransition in body mass, but one that is temporally out of phasewith that observed in species from lower latitudes; whereastemperate species increase in mass when exposed to relativelylong day lengths, collared lemmings do so under long but decreasingday lengths. This adaptation may be in response tothe timingof peak above-ground biomass in the arctic. Validation of thishypothesis requires a more thorough examination of both collaredlemmings and other arctic species. In the collared lemming, photoperiod-mediated changes in bodymass are correlated with changes in serum concentrations ofprolactin, thyroid hormones, corticosterone, and growth hormone,and pineal concentrations of melatonin. These observations arecompared to those obtained with temperate small mammals, andpossible cause-and-effect relationships between body mass andhormonal parameters are discussed.     

Use of Supplementary Feeding Dispensers by Arctic Foxes in Norway

Supplementary feeding is often used as a conservation tool to reverse the decline of food-limited populations. The arctic fox (Vulpes lagopus) is one of the most endangered mammals in Norway and has been the target of several conservation initiatives for almost 3 decades, including supplementary feeding. To measure and improve the efficiency of supplementary feeding as a conservation action, we used passive integrated transponder (PIT)-tags in arctic foxes and 6 feeding stations equipped with PIT-tag readers to monitor individual use of supplemental food between 2013 and 2018. We tested hypotheses about the potential influence of temporal and spatial patterns, individual characteristics (i.e., age, sex, reproductive status), and food abundance (abundance of small rodents and amount of food filled) on the frequency and intensity of use of supplementary feeding stations by arctic foxes. The feeding stations were visited ≥1 time by 196 PIT-tagged individuals. We detected 54% of juveniles born in the study area between 2013 and 2017 at the feeding stations. More arctic foxes used the feeding stations during the pre-breeding period than during the other seasons, and the visits occurred mostly at night. The closest feeding station to each natal den was systematically used by the established pair and by the juveniles born at this den. Juveniles did not use the feeding stations more than adult foxes. Older foxes, and breeding adults, visited the feeding stations more than younger and non-breeding adults. Foxes used feeding stations more intensively when prey was scarce and with greater amounts of supplemental food. This study highlights that supplemental feeding is important for breeding adults, especially in periods of low prey abundance. Understanding the use of feeding stations will contribute to the optimization of supplemental feeding as a conservation action and help wildlife managers to carefully plan and manage its discontinuation. © 2020 The Authors. Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.     

Life cycle of Cyclops vicinus in relation to food availability, predation, diapause and temperature

The seasonal cycle of Cyclops vicinus was studied during a 5year period in the shallow and hypertrophic Lake Søbygård.The annual number of generations varied between three and sixand sometimes included midsummer generations. Naupliar and copepoditedensity was extremely high, the maximum recorded being 1313and 745 1^–1 respectively. The seasonal fluctuation inthe abundance of C.vicinus was related to the concentrationof edible phytoplankton (EDP): when diatoms and cryptomonadswere abundant, nauplii and copepodites were also abundant, whereaswhen greens such as Scenedesmus spp. were dominant, no cohortswere observed. The maximum density of copepodites in the separatecohorts and the amount of EDP, expressed as carbon content,were found to be significantly correlated. The development ofthe second cohort also seemed to depend on the occurrence ofa peak in rotifer density. High number of eggs per female generallycoincided with high biovolume of EDP, suggesting that algaeconstituted a major part of the diet of adult C. vicinus. Theduration of the naupliar stage was inversely related to temperatureand is one of the shortest times that have been recorded inthe literature. The short duration is probably attributableto the abundance of food. Fish composition and the calculatedsex ratio of C.vicinus indicate low predation pressure fromplanktivorous fish. The high density of C.vicinus during thesummer, when the whole population would be expected to haveentered diapause, is probably attributable to the concurrenceof low predation and the abundance of food.     

Trophic interactions in a high arctic snow goose colony

We examined the role of trophic interactions in structuringa high arctic tundra community characterized by a large breedingcolony of greater snow geese (Chen caerulescens atlantica).According to the exploitation ecosystem hypothesis of Oksanenet al. (1981), food chains are controlled by top-down interactions.However, because the arctic primary productivity is low, herbivorepopulations are too small to support functional predator populationsand these communities should thus be dominated by the plant/herbivore trophic-level interaction. Since 1990, we have beenmonitoring annual abundance and productivity of geese, the impactof goose grazing, predator abundance (mostly arctic foxes, Alopexlagopus) and the abundance of lemmings, the other significantherbivore in this community, on Bylot Island, Nunavut, Canada.Goose grazing consistently removed a significant proportionof the standing crop (     

Seasonal and Acute Changes in Adrenocortical Responsiveness in an Arctic-Breeding Bird

The Lapland longspur,Calcarius lapponicus,times its breeding season so that chicks hatch coincident with the brief period of food abundance in the high arctic. This synchronization requires that all reproductive activities occur in over a much shorter period than at lower latitudes. Because of the known influence of stress hormones on delaying breeding in temperate-zone birds and the detrimental effects of such delays in the arctic, we expected the performance of the hypothalamic–pituitary–adrenal (HPA) axis of arctic-breeding birds to show less sensitivity to environmental stress than their mid-latitude counterparts. We found that adrenocortical responsiveness to the standardized stress of capture and handling, measured by taking five serial blood samples for corticosterone during the course of a 1-hr period, was similar to many temperate passerines and was also similar both between male and female longspurs and between the migratory and reproductive phases. However, the profile of plasma corticosterone during capture stress was significantly damped in longspurs sampled as they began their postnuptial molt. In addition, we had the opportunity to examine endocrine responses to a natural environmental stress in 1989 during a 3-day snowstorm which concealed available food resources. During this storm longspurs formed progressively larger flocks each day, with females abandoning incubation duties by the third day. Birds captured during the storm showed highly significant increases in both the rate of plasma corticosterone increase during capture and the peak postcapture level compared with birds sampled before the storm. This increased adrenal potential suggests increased activity of the HPA axis in response to severe conditions and is reminiscent of the response to fasting. Although the storm occurred during incubation, and reproductive hormone levels had begun to decline, we measured significant reductions in luteinizing hormone in both males and a subset of females captured during the storm.     

The marine side of a terrestrial carnivore: intra-population variation in use of allochthonous resources by arctic foxes

Inter-individual variation in diet within generalist animal populations is thought to be a widespread phenomenon but its potential causes are poorly known. Inter-individual variation can be amplified by the availability and use of allochthonous resources, i.e., resources coming from spatially distinct ecosystems. Using a wild population of arctic fox as a study model, we tested hypotheses that could explain variation in both population and individual isotopic niches, used here as proxy for the trophic niche. The arctic fox is an opportunistic forager, dwelling in terrestrial and marine environments characterized by strong spatial (arctic-nesting birds) and temporal (cyclic lemmings) fluctuations in resource abundance. First, we tested the hypothesis that generalist foraging habits, in association with temporal variation in prey accessibility, should induce temporal changes in isotopic niche width and diet. Second, we investigated whether within-population variation in the isotopic niche could be explained by individual characteristics (sex and breeding status) and environmental factors (spatiotemporal variation in prey availability). We addressed these questions using isotopic analysis and Bayesian mixing models in conjunction with linear mixed-effects models. We found that: i) arctic fox populations can simultaneously undergo short-term (i.e., within a few months) reduction in both isotopic niche width and inter-individual variability in isotopic ratios, ii) individual isotopic ratios were higher and more representative of a marine-based diet for non-breeding than breeding foxes early in spring, and iii) lemming population cycles did not appear to directly influence the diet of individual foxes after taking their breeding status into account. However, lemming abundance was correlated to proportion of breeding foxes, and could thus indirectly affect the diet at the population scale.     

The influence of snow conditions on the date of breeding of wading birds in north-east Greenland

The young of wading birds that breed in some parts of the arctic hatch when their insect food supply is most abundant. This appears to be the ultimate factor determining the date of egg-laying. In various other arctic birds the date of breeding may be influenced, directly or indirectly, by the time at which snow or ice melts. The Joint Biological Expedition to N.E. Greenland 1974 studied Ringed plovers Charadrius hiaticula , Dunlins Calidris aplina , Sanderlings Calidris alba , Knots Calidris canutus , and Turnstones Arenaria interpres breeding in various areas within 80 km of each other.
In 1974 the thaw was two or three weeks later than normal in the region. The time at which snow cleared and the dates of breeding of the waders differed considerably between valleys: breeding was delayed in valleys that cleared late. In all areas egg-laying ceased early in July, probably because chicks hatching from eggs laid later would not be ready to migrate by the end of the summer. Hence the mean date and length of the egg-laying period were determined by the date of snow clearance from the breeding areas.
Studies of the potential food resources indicate that the waders in N.E. Greenland do not appear to time their breeding so that the young hatch at some peak of food abundance. Sufficient food resources are probably available over a long period of time.     

Temporal Patterns of Territorial Behavior and Circulating Testosterone in the Lapland Longspur and Other Arctic Passerines

We studied territorial aggression in relation to circulatingtestosterone levels in free-living birds of four species innorthern Alaska. The Lapland longspur, Calcarius lapponicus,is an abundant breeding passerine on the arctic tundra. Unlikemany passerines at lower latitudes, male Lapland longspurs donot defend a "multiple-purpose territory" that serves to providenest sites, food and shelter. Rather, after arrival on the breedinggrounds, they perform aerial display flights over a looselydenned "nest area" for a very brief period of two days or so,showing tolerance of other males. This song display may be involvedin courtship. During this phase, male longspurs show a briefand pronounced peak in circulating testosterone levels, andare not aggressive toward simulated territorial intrusions (STIs).Males then "guard" their sexually receptive mates for aboutten days, during which they are highly aggressive toward STIs,but do not sing as much. During the next phase, incubation,the males become very tolerant of conspecific males. Their circulatingtestosterone levels decline to baseline levels, and they generallydo not sing or display aggression in response to STIs. Threeother passerines, the white-crowned sparrow, Zonotrichia leucophrysgambelii, American tree sparrow, Spizella arborea, and savannahsparrow, Passerculus sandwichensis, show patterns of territorialaggression typical of species studied at lower latitudes. Welldefinedterritories are defended for several weeks, during which thereis a prolonged peak in plasma concentrations of testosterone.These three species continue to sing and display aggressioneven late in the season, unlike the longspurs. The peak of testosteronein the longspurs occurs simultaneously with the peak in songdisplay, while in mid-latitude species it occurs with the peakin reproductive aggression. These data suggest that the interrelationshipof testosterone and aggression in Lapland longspurs may be differentfrom that of passerines with multiple-purpose territories, andmay be related to the constraints of breeding in the open arctictundra.     

Arctic zooplankton prefer living ice algae: a caution for zooplankton excretion measurements

Regardless of how they were killed, dead ice algae were lessdesirable as food to several arctic copepods (Pseudocalanussp., Calanus glaciahs, Metridia longa) than living ice algae.For Pseudocalanus, the only species tested, the presence ofdead ice algae also depressed respiration and ammonia-excretionrates. In the short run, food quality (i.e. whether living ordead) had a greater effect on copepod metabolism than food quantity.Pre-conditioning for 48 h, and conditions in the natural environmentto which the animals had become acclimated, also had a markedeffect on their metabolic performance, but did not mask theeffect of morbidity in the food supply. We conclude that deadalgae should not be used as a substitute ration for living foodin certain types of metabolic experiments without prior comparisonof suitability.     

Resource use for reproduction depends on spring arrival time and wintering area in an arctic breeding shorebird

Resources for egg production may come from body reserves stored before breeding (“capital breeders”) or from food acquired at the breeding site (“income breeders”). Arctic migrants were long thought to be capital breeders, because they often arrive at a time when local food availability is still limited. However, later evidence suggested that arctic breeding shorebirds are primarily income breeders, or that they use a mixed strategy depending on laying date. We explored the relationship between laying date and resource use for reproduction in the pectoral sandpiper Calidris melanotos breeding in the Alaskan arctic by contrasting carbon isotope (δ¹³C) values of the local diet and of maternal plasma, cellular blood, feather and claw with those of the eggs produced. Our results revealed that early breeding females utilize resources for egg production that were acquired recently at staging areas, whereas later breeding females mostly relied on nutrients derived from local food sources. These findings suggest that the resource allocation strategy used for reproduction differs among females, and varies depending on the timing of arrival and the start of reproduction. The arrival date at the breeding ground and laying date may critically depend on non‐breeding season events such as winter habitat choice, staging areas or migration routes. By comparing maternal feather δ¹³C, claw δ¹³C and feather δD, we examined whether non‐breeding season events influenced the use of resources for egg production through variation in capture date or clutch initiation date. Female pectoral sandpipers originating from moulting areas characterized by higher (more positive) δD signatures were caught earlier and started laying earlier, and they used stored resources for reproduction. Using regional maps of δD values for precipitation in the wintering sites in South America, we compared the spatial variation in the observed feather δD signatures. This analysis indicated that female pectoral sandpipers with higher δD signatures, presumably coming from more north‐easterly wintering sites in southern America, started laying earlier and used mostly stored resources for egg production, compared to females that wintered (or at least moulted) further south. Our results thus show that winter moulting habitat is linked to breeding resource allocation strategy in this high‐arctic breeding shorebird.     

Finding the right home: distribution of food resources and terrain characteristics influence selection of denning sites and reproductive dens in arctic foxes

We examined 83 arctic fox (Alopex lagopus) dens on Bylot Island (Canada) during the summers of 2003–2005, to determine how arctic foxes select a denning site among potential sites, and a breeding den among existing dens. We compared denning sites to random locations in a 425 km² study area (landscape scale) and to other potential denning sites in a 100 m radius (local scale). Dens were located on mounds or in slopes and were closer to streams than expected. Sites with low snow cover in spring, high ground temperature, high depth to permafrost, and steep and southerly exposed slopes were preferred. Of the 83 dens, 27 were used at least once for reproduction from 2003 to 2005. We show with a resource selection function analysis that an attractive force (distribution of food resources) and an apparently repulsive one (presence of other dens in the vicinity) affected selection of dens for reproduction. We generate testable hypotheses regarding the influence of food and social factors on the denning ecology of arctic foxes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

Abwesenheit von Haematozoa bei einer Brutpopulation des SeeregenpfeifersCharadrius alexandrinus in Nordspanien

A low presence of haematophagus parasites has been reported in arctic waders. Three hypotheses try to explain these low levels: higher inherent resistance to parasites in the Charadrii, lower presence of parasites in the breeding grounds of waders in the arctic, and influence of the vegetation structure in the habitat of these birds. To test these hypotheses, we took blood samples from 87 alive-trapped Kentish PloversCharadrius alexandrinus nesting in Northeast Spain. None of the samples had haematophagus parasites. Therefore, very low infection rates occur also in a non-arctic species. These data support the hypotheses that Charadrii have a higher resistance or a lower probability of being infected by blood parasites than other taxa, independently of their breeding distribution.     

Phenological advancement in arctic bird species: relative importance of snow melt and ecological factors

Previous studies have documented advancement in clutch initiation dates (CIDs) in response to climate change, most notably for temperate-breeding passerines. Despite accelerated climate change in the Arctic, few studies have examined nest phenology shifts in arctic breeding species. We investigated whether CIDs have advanced for the most abundant breeding shorebird and passerine species at a long-term monitoring site in arctic Alaska. We pooled data from three additional nearby sites to determine the explanatory power of snow melt and ecological variables (predator abundance, green-up) on changes in breeding phenology. As predicted, all species (semipalmated sandpiper, Calidris pusilla, pectoral sandpiper, Calidris melanotos, red-necked phalarope, Phalaropus lobatus, red phalarope, Phalaropus fulicarius, Lapland longspur, Calcarius lapponicus) exhibited advanced CIDs ranging from 0.40 to 0.80 days/year over 9 years. Timing of snow melt was the most important variable in explaining clutch initiation advancement (“climate/snow hypothesis”) for four of the five species, while green-up was a much less important explanatory factor. We found no evidence that high predator abundances led to earlier laying dates (“predator/re-nest hypothesis”). Our results support previous arctic studies in that climate change in the cryosphere will have a strong impact on nesting phenology although factors explaining changes in nest phenology are not necessarily uniform across the entire Arctic. Our results suggest some arctic-breeding shorebird and passerine species are altering their breeding phenology to initiate nesting earlier enabling them to, at least temporarily, avoid the negative consequences of a trophic mismatch.     

Are antarctic zooplankton metabolically more cold-adapted than arctic zooplankton? An intra-generic comparison of oxygen consumption rates

Because of the greater age of the antarctic ecosystem in relationto the arctic ecosystem, an elevated metabolic rate and moreobligate stenothermy of antarctic zooplankton compared withtheir arctic counterparts are predicted from the concept ofmetabolic cold adaptation. When oxygen consumption rates werestandardized to 1 mg body nitrogen and 0°C and comparedbetween the species belonging to the same genus, the antarcticrates were greater than arctic rates in Clione (pteropods) andCalanus (copepods), while the reverse was true in Parathemisto(amphipods), Thysanoessa (euphausiids) and Sagitta (chaetognaths).No significant differences were seen in Limacina (pteropods)and Metridia (copepods). These inconsistent results do not supportthe hypothesis of metabolic cold adaptation in the zooplanktonof polar seas.     

Public information and conspecific nest parasitism in goldeneyes: targeting safe nests by parasites

Conspecific nest parasitism (CNP) is a widespread alternativereproductive tactic in birds. Several hypotheses have been putforward to explain the evolution and occurrence of CNP, butno generally applicable hypothesis exists. Recent experimentalresults from the common goldeneye (Bucephala clangula), a cavity-nestingduck, have revealed that parasitic females preferentially layeggs in safe nest-sites, implying that nest predation risk isan important ecological determinant of CNP. The present studyfocuses on the mechanisms by which parasites identify safe nest-sites.Predation risk of a given nest-site was predictable betweensuccessive breeding seasons. At the end of the nesting season,females prospected active nest-sites more frequently than nest-sitesthat did not have a nest in the current season. Nest-sites thathad been prospected more frequently by females in year t hada higher probability to be parasitized in year t + 1. The resultssuggest that the use of public information, derived throughnest-site prospecting, enabled parasites to target safe nests.These findings provide a new and potentially generally applicableperspective to understand the evolution and occurrence of CNP.     

Coexistence and segregation of congeneric pelagic copepods: spatial distribution of the Acartia complex in the r?a of Vigo (NW of Spain)

Four congeneric species of pelagic copepods (Acartia margalefi,A. clausi, A. discaudata and A. grani) coexist in the r?a ofVigo, an estuary located on the NW Spanish coast. There is apartial segregation of the species along the axis of the r?a,their respective abundances decreasing exponentially from thezones of maximum densities. A. margalefi and A. grani have beenfound exclusively in the inner part of the r?a, while A. clausiis more abundant in the external zones, and A. discaudata occupiesan intermediate area. Temperature and salinity gradients seemto have less importance than the spatial differences in stability(in the sense of persistence of environmental factors) as determiningthe species segregation.     

Bioenergetic prediction of climate change impacts on northern mammals

Climate change will likely alter the distribution and abundanceof northern mammals through a combination of direct, abioticeffects (e.g., changes in temperature and precipitation) andindirect, biotic effects (e.g., changes in the abundance ofresources, competitors, and predators). Bioenergetic approachesare ideally suited to predicting the impacts of climate changebecause individual energy budgets integrate biotic and abioticinfluences, and translate individual function into populationand community outcomes. In this review, we illustrate how bioenergeticscan be used to predict the regional biodiversity, species rangelimits, and community trophic organization of mammals underfuture climate scenarios. Although reliable prediction of climatechange impacts for particular species requires better data andtheory on the physiological ecology of northern mammals, tworobust hypotheses emerge from the bioenergetic approaches presentedhere. First, the impacts of climate change in northern regionswill be shaped by the appearance of new species at least asmuch as by the disappearance of current species. Second, seasonallyinactive mammal species (e.g., hibernators), which are largelyabsent from the Canadian arctic at present, should undergo substantialincreases in abundance and distribution in response to climatechange, probably at the expense of continuously active mammalsalready present in the arctic.     

Midsummer succession of rotifer plankton in a shallow eutrophic pond

Temporal changes in the density of rotifer plankton were examinedin a shallow eutrophic pond during July to September 1990, whenabiotic environmental variables were relatively stable. In earlyJuly when Daphnia similis was abundant, rotifer populationsremained at a low density. This is probably due to interferenceby the large cladoceran, because possible food was abundantand the rotifers showed high egg ratio. After late July, whenthe large cladoceran disappeared, a striking succession wasfound in the rotifer plankton. In late July, when Filinia longisetaand Conochilus dossuarius dominated, and in mid- to late Septemberwhen F.opoliensis and Brachionus falcatus dominated, there wasa causal relationship between the density and egg ratio, suggestingthat temporal changes in rotifer density were regulated mainlyby food abundance. However, in August, changes in the densityof most rotifers were not necessarily related with those inthe egg ratio. Brachionus angularis, B.forficula and Keratellaspp. decreased or remained at a low density regardless of theegg ratio, when the population of Asplanchna brightwelli wasdeveloped. However, Polyarthra vulgaris, B.calyciflorus andH.intermedia increased or maintained a high density at thistime. Stomach contents of A.brightwelli revealed that B.angularis,B.forficula and Keratella spp. were the preferred prey, whereasP.vulgaris, B.calyciflorus and H.intermedia were not. Theseresults provide strong evidence that the structure of rotiferplankton can change strikingly within a season due to species-specificdifferences not only in diet, but also in the ability to escapepredation, even if abiotic environmental variables are stable.     

Aggregation of avian predators and zooplankton prey in Otago shelf waters, New Zealand

In Otago shelf waters surface swarms of krill (Nyctiphanes australis),hyperiid amphipods (Parathemisto spp.) and galatheid crab larvae(Munida gregaria) provide an abundant summer food source forplanktivores. We tested the hypothesis that aggregation of avianplanktivores depends upon the spatial distribution of theirprey. Gulls (Larus scopulinus, L.bulleri, L.dominicanus), sootyshearwaters (Puffinus griseus) and white-fronted terns (Sternastriata) showed significantly aggregated distributions. Thedistribution of birds sitting on the sea surface was correlatedwith the abundance pattern of krill but was not correlated withthe distribution of smaller hyperiid amphipods. The distributionof flying red-billed gulls (L.scopulinus), black-billed gulls(L.bulleri) and sooty shearwaters was correlated with the krilldistribution but black-backed gulls (L.dominicanus) were not.Stomach contents of black-billed gulls were dominated by krill,in contrast to sooty shearwaters, which ate a higher proportionof Minida, and black-backed gulls, which contained Munida andfish. No amphipods were found in bird stomachs. There was nosignificant correlation between bird distributions and the hydrographicregime, water depth or distance offshore. The distribution ofprey rather than hydrographic regime was a more important determinantof bird distributions at this spatial scale (2.6–12 km)and location.