Burrow limitations and group living in the communally rearing rodent, Octodon degus

Group living is thought to evolve whenever individuals attain a net fitness advantage due to reduced predation risk or enhanced foraging efficiency, but also when individuals are forced to remain in groups, which often occurs during high-density conditions due to limitations of critical resources for independent breeding. The influence of ecological limitations on sociality has been studied little in species in which reproduction is more evenly shared among group members. Previous studies in the caviomorph rodent Octodon degus (a New World hystricognath) revealed no evidence that group living confers an advantage and suggest that burrow limitations influence formation of social groups. Our objective was to examine the relevance of ecological limitations on sociality in these rodents. Our 4-year study revealed no association between degu density and use of burrow systems. The frequency with which burrow systems were used by degus was not related to the quality of these structures; only in 1 of the 4 years did the frequency of burrow use decrease with decreasing abundance of food. Neither the number of females per group nor total group size (related measures of degu sociality) changed with yearly density of degus. Although the number of males within social groups was lower in 2008, this variation was not related clearly to varying density. The percentage of females in social groups that bred was close to 99% and did not change across years of varying density. Our results suggest that sociality in degus is not the consequence of burrow limitations during breeding. Whether habitat limitations contribute to variation in vertebrate social systems is discussed.     

Foraging areas of breeding blue-footed boobies Sula nebouxii in northern Peru, as determined by direction recorders

The association between the distribution of blue-footed boobies Sula nebouxii (BFB) and marine productivity around their breeding grounds is unclear. In Peru, they breed in a region seasonally influenced by the cold, nutrient rich Humboldt Current, and by warm, nutrient poor oceanic waters. The foraging range of BFB in Peru is unknown, although some evidence suggest that they may feed in warm offshore waters. During the austral winter 2002 and summer 2003, we tracked 26 BFBs breeding on Isla Lobos de Tierra, Peru (located approximately 15 km west of the mainland), during 59 feeding trips using small direction recorders to determine their marine habitat use. BFBs preferentially moved to the east of the island and foraged over the continental shelf in cold water masses where marine productivity and the abundance of the main prey, the Peruvian anchovy Engraulis ringens , are usually higher than in other areas. Overall, the median maximum foraging distance from the colony was 39 km (range 3–109 km), with 90% of all trips located within 30 km from the mainland, and enclosed in an area of 13,113 km². These results reveal that BFBs exploit the productive waters of the Peruvian Coastal Upwelling System, rather than open oceanic waters as previously suggested. BFBs travelled a greater distance, dispersed in a broader area, and visited more offshore waters during the winter 2002, than during the summer 2003, following the typical seasonal horizontal dispersion of the Peruvian anchovy.     

Effects of seasonal migration on the latitudinal distribution of west Palaearctic bird species

This paper examines seasonal changes in the latitudinal distribution of birds (excluding seabirds) that breed in the western Palaearctic. Some resident species occupy ranges that span less than 5° of latitude year-round, while some migrant species range over more than 120° of latitude during the course of a year. Among migrant species of land and freshwater habitats, the latitudinal spans of breeding and wintering ranges are correlated. In general, species that breed over a narrow span of latitude also winter over a narrow span of latitude, and vice versa. Among both groups, for any given span of breeding range, species that winter partly in Eurasia and partly in Africa winter over a wider latitudinal span than those that winter entirely within Eurasia or entirely within Africa. Among coastal birds, there is no correlation between the latitudinal spans of breeding and winter areas; most shorebird species breed over a narrow span of (northern) latitude and winter over a wide span distributed linearly along coastlines. Several migration patterns can be distinguished, from complete overlap of breeding and wintering ranges in year-round residents, through partial separation of summer and winter ranges, to complete separation of summer and winter ranges in different geographical regions. In some such species, the gap between breeding and wintering ranges spans up to 55° of latitude (6000 km).     

Optimal moult strategies in migratory birds

Avian migration, which involves billions of birds flying vast distances, is known to influence all aspects of avian life. Here we investigate how birds fit moult into an annual cycle determined by the need to migrate. Large variation exists in moulting patterns in relation to migration: for instance, moult can occur after breeding in the summer or after arrival in the wintering quarters. Here we use an optimal annual routine model to investigate why this variation exists. The modelled bird's decisions depend on the time of year, its energy reserves, breeding status, experience, flight feather quality and location. Our results suggest that the temporal and spatial variations in food are an important influence on a migratory bird's annual cycle. Summer moult occurs when food has a high peak on the breeding site in the summer, but it is less seasonal elsewhere. Winter moult occurs if there is a short period of high food availability in summer and a strong winter peak at different locations (i.e. the food is very seasonal but in opposite phase on these areas). This finding might explain why only long-distance migrants have a winter moult.     

Annual variation in the timing of reproduction in Antarctic fur seals, Arctocephalus gazella, at Bird Island, South Georgia

The arrival of Antarctic fur seals at a breeding beach on Bird Island, South Georgia, was studied over five consecutive breeding seasons, 1983 to 1987. Experienced bulls arrived first and established breeding territories on the beaches in anticipation of the arrival of the cows. Male arrival, which is less synchronous within years than female arrival, was significantly later in 1987 than in any other year. Female arrival, estimated by pup birth date where necessary, was highly synchronous; it usually started when 80% or more of potential territory sites were occupied by males. Cows arrived significantly later in 1984 and 1987 than in 1983, 1985 or 1986. The late arrival of both males and females in 1987 is attributed to unusually severe climatic conditions during the preceding winter. The late arrival and reduced fecundity of females in 1984 is attributed to markedly reduced food availability during the austral winter and summer of 1983. Males were not affected in 1984 because they could move away from the area of reduced food availability earlier than females and because they have a more varied diet. Factors influencing the winter distribution, the timing and pattern of arrival and the breeding of male and female Antarctic fur seals are discussed.     

Predator–prey interactions: why do larger albatrosses eat bigger squid?

The relationship between predator sizes and prey sizes is well documented for terrestrial but rarely for marine ecosystems. We show that wandering albatrosses, the biggest albatross species, feed on larger cephalopod prey than those consumed by smaller albatrosses (grey-headed and black-browed albatrosses). This reflects differences in timing of breeding, foraging ecology and their feeding methods. Wandering albatrosses breed later in the year, during the austral winter, than smaller albatrosses (therefore catching older squid) and forage most of the year in Antarctic open waters, sub-Antarctic, subtropical and tropical waters, overlapping minimally with the smaller albatrosses' foraging range while breeding. Also, wandering albatrosses mostly scavenge whereas smaller albatrosses feed more on live prey. Prey ecology may also play a key role because many squid species might experience post-spawning mortality during the austral winter, becoming easily available to wandering albatrosses. Spawning in winter can be linked to predator avoidance (i.e. reduction in mortality in winter by avoiding pelagic predators) and would allow squid larvae to develop and take advantage of the high productivity (i.e. Antarctic phytoplankton bloom) in spring and at the beginning of summer. Thus, aspects of prey and predator ecology may combine to generate observed differences in prey size.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre‐breeding food conditions and winter severity on between‐year variations in population size and reproductive performance. To estimate pre‐breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.     

Population regulation and dispersion of the smoky mouse,Pseudomys fumeus II. Spring decline,breeding success and habitat heterogeneity

The smoky mouse (Pseudomys fumeus) undergoes large annual fluctuations in abundance, characterized by a dramatic decline in numbers just before the summer breeding season. The population on Mount William has two components which are differentially affected by this decline. The first, consisting of animals living in preferred microhabitat, have high breeding success and are unaffected by the decline. Females normally breed in two seasons, and in the second season breed earlier than first year females. The second component lives in non-preferred microhabitat, is severely affected by the decline and shows high levels of fighting during the decline period. This difference may result from the lack of high quality food resources in non-preferred microhabitat following the seasonal cessation of production of fungal sporocarps. The role of spatial and temporal heterogeneity in the availability of food resources in the population processes of small mammals is discussed.     

Waterfowl of a subtropical African floodplain

Many water bodies in arid southern Africa are seasonal and waterfowl habitats become restricted during the dry winters. Nevertheless, some tropical species, such as the white-faced duck, are expanding their ranges into more temperate regions where summer habitats are available, thus increasing pressure on overwintering habitats. The subtropical Pongolo River floodplain is an important overwintering area for a diverse water-fowl community that includes 13 of the 16 species that breed in South Africa and one of the few regular migrants. Historical evidence suggests that numbers of white-faced duck, which represent over 70% of the floodplain community, have increased 10-fold over the last two decades. An abundant, nutritious food (Potamogeton crispus turions) attracts waterfowl to the Pongolo floodplain during winter and an increase in bird fat reserves suggests that they leave for summer breeding grounds in good condition. Unseasonal flood releases from an upstream reservoir may cause low food supplies in late spring before the onset of the summer rainy season when breeding habitats become available. This study emphasizes the need for a better understanding of the role of winter habitats in maintaining waterfowl populations.     

The feeding ecology of mink (Mustela vison) in coastal habitat

The diet of a coast-living population of mink was investigated from the scats collected over a three-year period, and compared with information on the availability of principal prey species. Lagomorphs were the single most important prey, and predation upon them matched the abundance of rabbits as determined by monthly counts. Aquatic foraging was particularly important, with rockpool-inhabiting fish accounting for 29–1% occurrence of food items. Fish predation was more pronounced during winter months when lagomorph prey was less available. Crustacean prey, particularly the shore crab, Carcinus maenas , occurred frequently in the diet. Seabirds figured regularly in the diet; these were either taken as carrion from the strand-line or through predation on breeding colonies during the summer months.     

Ranging behaviour and activity of red foxes (Vulpes vulpes: Mammalia) in relation to environmental variables, in a Mediterranean mixed pinewood

The relationships between the main abiotic environmental variables, food availability, dict, activity and home range size of the fox in a Mediterranean mixed pinewood were assessed. Food habits were determined by faecal analysis on a weekly basis. Food availability was measured by weekly censuses. Radio-tracking allowed the detection of fox movements and activity. Individual differences shown by a sample of four radio-tagged foxes were analysed. Juniper berries (Juniperus oxycedrus) were the staple of the diet during the year, except in summer. Insects, mainly nocturnal Orthoptera and cicada larvae (Cicada orni), were the main prey in the warm season. Large vertebrates, mostly wild boars (Sus scrofa), were scavenged in winter. In the warm season foxes' activity depended largely on the pattern of activity of prey. Food habits tended to depend on food availability, which, in turn was mainly influenced by temperature. In spite of habitat similarity, individual differences in food habits were detected within the same season. Home ranges were larger in pinewood than in neighbouring heterogeneous habitats. Individual home range sizes were: (i) directly correlated to Orthoptera abundance and distribution; (ii) inversely correlated to the abundance of cicada larvae in diet. Resident males may exist in fox society, exploiting other males' territories when good clumped food resources are available.     

The nature of migration in the red admiral butterfly Vanessa atalanta: evidence from the population ecology in its southern range

1. The migrant Vanessa atalanta (L.) occurs throughout Europe and North Africa. In autumn, populations emigrate from northern and central Europe to the Mediterranean region to overwinter. In the spring, the northern range is recolonised by migrants from the south. The dynamics of the species in the winter range is poorly known. 2. From 1994 to 1999, adults and immatures of V. atalanta were monitored all year round in Mediterranean habitats in north‐east Spain. 3. Data showed that the Catalonia lowlands is an area to which V. atalanta migrates to breed during the winter. Migrants arrive in October and early November and initiate a period of intensive breeding. Larval development occurs throughout the winter until a first annual generation of adults appears in early spring. 4. Most of the butterflies emerging in the spring emigrate and leave the area without breeding. The data suggest strongly that recolonisation of the northern range is by these butterflies not by wintering adults. Altitudinal migration also seems to be a common phenomenon, allowing a further summer generation of adults to occur at high elevations within the Mediterranean region. 5. The complex phenology of V. atalanta in its southern range has evolved as a strategy to track larval resources through space and time. Autumn migration coincides with the greatest availability of the main food plant, Urtica dioica L. Late spring migration occurs by the time food quality is decreasing.     

A theoretical investigation of the effect of latitude on avian life histories

Tropical birds lay smaller clutches than birds breeding in temperate regions and care for their young for longer. We develop a model in which birds choose when and how often to breed and their clutch size, depending on their foraging ability and the food availability. The food supply is density dependent. Seasonal environments necessarily have a high food peak in summer; in winter, food levels drop below those characteristic of constant environments. A bird that cannot balance its energy needs during a week dies of starvation. If adult predation is negligible, birds in low seasonal environments are constrained by low food during breeding seasons, whereas birds in high seasonal environments die during the winter. Low food seasonality selects for small clutch sizes, long parental care times, greater age at first breeding, and high juvenile survival. The inclusion of adult predation has no major effect on any life-history variables. However, increased nest predation reduces clutch size. The same trends with seasonality are also found in a version of the model that includes a condition variable. Our results show that seasonal changes in food supply are sufficient to explain the observed trends in clutch size, care times, and age at first breeding.     

The population ecology of Rattus exulans on Tiritiri Matangi Island,and a model of comparative population dynamics in New Zealand

Abstract

On Tiritiri, a small predator-free island in northern New Zealand, kiore (Rattus exulans) were live and snap trapped in grassland and forest. In both habitats, kiore abundance peaked in late summer/autumn. The increase followed a 3 month breeding season during which females produced two to three litters, each averaging 7 young. During the population decline in autumn and winter, animals lost weight. Few bred in the breeding season of their birth and none lived to breed in a second breeding season, so the population consisted of distinct age cohorts. These patterns may relate to a highly seasonal food supply.

Kiore elsewhere in New Zealand show seasonal breeding, but the length of breeding, sexual maturation, and litter size vary. Other studies of kiore in the Pacific show less marked seasonal fluctuations, longer breeding seasons, and smaller litters. We propose a model to explain the variation in rodent demography in New Zealand. The model is based on the seasonal availability of food, along with the modifying influences of predation and dispersal.     

Testing agri‐environment delivery for farmland birds at the farm scale: the Hillesden experiment

The Hillesden experiment, established in 2005/2006 to test the delivery of biodiversity benefits under Environmental Stewardship, covers c. 1000 ha of arable farmland in central lowland England. It is a randomized block experiment with five replicates of three treatments: (1) CC: cross compliance, the control; (2) ELS: 1% of land removed from production for wildlife habitat provision; and (3) ELS‐X: 5% of land used for wildlife habitat, each treatment being applied to contiguous areas of 70–80 ha. Bird usage of winter food patches, comprising three different seed mixes, was monitored through the winter and was also related to seed yield. Winter and breeding season bird/territory abundance was recorded before and after the provision of the winter food patches. Bird use of the patches differed between seed mixes. There was large variation between individual patches in both seed yield and bird numbers and between individual bird species in their use of different seed mixes, suggesting that the availability of a range of patch types would be beneficial. Use of all patch types declined sharply in late January to February, indicating depletion and/or inability of birds to access shed seed. Winter bird abundance at a farm scale for all species combined, granivorous species and nine individual species increased for all monitored species when seed patches were available. At a treatment level, the increases tended to be greater in ELS‐X, where most of the patches were located. In the breeding season at a farm scale, the numbers of territories for all species combined and granivorous species increased significantly when seed patches had been available in the previous winter. There was little evidence of a treatment‐scale response. The provision of winter food appeared to increase winter bird abundance and to follow on into an overall increase in the breeding population, but if the latter effect is to be reflected elsewhere, this requires that sufficient breeding habitat is available to accommodate an increase.     

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.     

Resource partitioning by ungulates on the Isle of Rhum

Summary This paper describes the seasonal changes in vegetation community use by red deer, cattle, goats and ponies on the Isle of Rhum, Scotland. During the winter, when food resources were of low abundance and digestibility, the ungulates showed extensive resource partitioning. During the summer, when resource availability and digestibility was high, the grazing species, red deer, cattle and ponies congregated on the vegetation communities which contained high biomasses of a high quality resource, mesotrophic graminoids and forbs. Goats, with a digestive system adapted to dealing with browse, foraged primarily on the communities dominated by dwarf shrubs. The patterns of resource use in this group of ungulates are discussed in relation to competition; species had relatively exclusive esource use during periods of low food availability during tye winter and had a high degree of resource use overlap when food was abundant during the summer. This suggests that there was little competition for food during the summer and that exploitative competition for the high quality foods led to resource partitioning during the winter. Senarios are described which predict the pattern of resource use between two species (one competitively superior to the other on the preferred resource) utilizing mutually or exclusively preferred resources. A model developed by Illius and Gordon (1987), based on the allometry of metabolic requirements and bite size, is used to provide a mechanistic explanation for the observation that the red deer were able to exploit the high quality plant communities during the winter, whereas the cattle moved off to feed on poorer quality communities at this time.     

Elevational range and timing of breeding in the birds of Ladakh: the effects of body mass, status and diet

We studied the effects of body mass, status (resident or migratory) and diet on the breeding elevation range and timing of reproduction of the birds in the Trans-Himalayan region of Ladakh, northwestern India. Most of breeding birds of Ladakh are Palearctic or breed at high elevations in the mountains. There is a small proportion of Oriental species, and no bird is endemic to this region. We found that heavier birds tended to start their egg-laying earlier than lighter ones. Since body mass is related to the length of incubation and nesting periods, it would appear that one result of this phenomenon is that the time of peak demand for food for most birds coincides with peak food abundance in summer. Status affected the elevation of the breeding range, with resident birds tending to breed at higher elevations than summer visitors. Residents and summer breeders also differed significantly in their diet composition, with the former feeding mainly on plants and seeds, and the latter feeding on molluscs, insects and worms.     

Spatial and Temporal Variability in Territoriality of a Tropical Benthic Damselfish on a Coral Reef (Réunion Island)

The relationship between length of individual Stegastes nigricans and size of the territory that they defend, and both the spatial and temporal variation in territoriality were investigated monthly on a fringing coral reef of Réunion Island over the course of one year. Length of individual S. nigricans was correlated positively with size of the territory. Most small individuals were found separate from adults, in areas with low algal turf cover. This is probably due to strong intra-specific competition for access to algal food resources and shelter availability, and/or differences in habitat preference. Both abundance of individuals and surface defended showed seasonal fluctuations. Densities were slightly higher in austral summer than in winter, and the surface defended by individuals larger than 8cm increased in winter. A permanent redistribution of territories also occured between individuals over time.     

Reproductive biology of Río Negro tuco-tuco,Ctenomys rionegrensis (Rodentia: Octodontidae)

Reproductive success depends on a precise synchronization of organisms’ activities with the environment, determining the evolution of mechanisms controlling reproductive behaviour. In temperate zones mammals exhibit pronounced seasonal reproduction because of thermoregulation costs imposed by low winter temperatures and limited food availability. Even occupying burrows that buffer external ambient conditions, these restrictions also affect subterranean rodents inhabiting these latitudes. Tuco-tucos (genus Ctenomys) are subterranean herbivorous rodents that have a Neotropical distribution between 17 and 54° of latitude S. Ctenomys rionegrensis is one of the three species occurring in Uruguay and generated interest due to chromatic polymorphism in a restricted area (50×60 km). Here we describe the timing of breeding in C. rionegrensis based on the reproductive status of free-living females and the proportion of juveniles in the population, and describe the characteristics of the estrous cycle of the species using cytological techniques. As expected, the data showed a clear seasonality in female breeding and provided evidence of the occurrence of post-partum estrous. The reproductive activity began in late austral autumn and the highest proportion of pregnant females was observed in winter. At the beginning of the austral spring, the prevalence of lactating females increased as a consequence of the first births and remained high until early summer. This pattern of breeding seasonality was clearly correlated with the annual temperature variation. The estrous cycle showed four phases characterized by both different cellular types and the abundance and appearance of mucus, which allows a clear determination of female's reproductive status.