Extreme natal philopatry in female Antarctic fur seals (Arctocephalus gazella)

Natal philopatry is an important component of mammalian behaviour but is difficult to study in natural vertebrate populations due to the requirement for long-term individual-based spatial observations. Consequently, we quantified fine-scale patterns of natal philopatry in an intensively studied colony of Antarctic fur seals (Arctocephalus gazella), where a scaffold walkway allows individual locations to be measured to the nearest metre. Using subcutaneous PIT tags, we tracked the early life histories of 335 females born within the colony, of which 38 were resighted as breeding adults. We found that individual females returned to as little as one body length (2 m) of their birth locations. Moreover, distances between natal and pupping sites were not correlated with female age, but instead tended to decrease with the number of seasons an individual was sighted ashore. This suggests that breeding experience may be a better predictor than age of the ability of females to occupy preferred sites within fur seal colonies.     

The role of despotism and heritability in determining settlement patterns in the colonial lesser kestrel

Avian colony size variation is an evolutionary puzzle in terms of unequal fitness payoffs. We used a long-term marked lesser kestrel (Falco naumanni) population, where individual fitness increases with colony size, to test whether subordinates are evicted despotically from the largest colonies. Yearlings were smaller and lighter, were more attacked than expected, and lost most disputes over nest holes with older birds. Agonistic interactions increased with colony size; consequently, most first breeders recruited in colonies smaller than those at which they first tried to settle. As expected when subordination is a transient state, birds dispersed to a larger colony as they got older even after breeding successfully. The population consequences of these behavioral processes were that the relative frequency of yearlings and first breeders decreased with colony size. At the same time, breeding colony size was repeatable within individuals, so we estimated the amount of heritable variation in this trait. Estimates of heritability derived from parent-offspring and full-sib analyses were consistently high (h2=0.53) when individuals reached asymptotic morphological values and presumably overcame subordinate transient states. Age-related dominance asymmetries masked resemblance among relatives in colony size, but both phenomena seem to coexist in this population and explain a considerable proportion of colony size variation.     

THE EFFECT OF AGE ON THE BREEDING BIOLOGY OF THE KITTTWAKE RISSA TRIDACTYLA

1. From 1954 to 1956 inclusive, the biology of individual marked Kittiwakes was studied at North Shields, Northumberland.
2. It was concluded that older Kittiwakes reacted to the breeding stimulus earlier, more intensively and with greater success than younger breeding birds.
3. Birds with previous breeding experience returned to the colony before birds breeding for the first time and these before non-breeders.
4. Before breeding started, birds which had bred previously spent more of their time at the colony than those about to breed for the first time.
5. Birds breeding for at least the second time laid the first egg 7·5 days earlier than those breeding for the first time.
6. Breeding started one day later for every four days the return to the colony was postponed.
7. Older breeding birds showed greater nest-site tenacity, laid larger clutches and had greater breeding success than younger birds.
8. The chicks in broods of two (but not of one) increased in weight more rapidly where the parents had previous experience.
9. Breeding Kittiwakes showed strong colony tenacity, but 24% of the marked non-breeding birds were subsequently seen in other colonies.
10. Over half the birds retained the same mate as in the previous year.     

Colony genetic organization and colony fusion in the termite Reticulitermes flavipes as revealed by foraging patterns over time and space

Temporal and spatial analyses are seldom utilized in the study of colony genetic structure, but they are potentially powerful methods which can yield novel insights into the mechanisms underlying variation in breeding systems. Here we present the results of a study which incorporated both of these dimensions in an examination of genetic structure of subterranean termites in the genus Reticulitermes (primarily R. flavipes). Most colonies of this species (70%) were simple families apparently headed by outbred primary reproductives, while most of the remaining (27% of the total) colonies contained low effective numbers of moderately inbred reproductives. Mapping the spatial distribution of colony foraging sites over time revealed that despite the high colony density, the absolute foraging boundaries of most R. flavipes colonies were persistent and exclusive of other conspecific colonies, which suggests that this species is more territorial than has been implied by laboratory studies of intraspecific aggression. Nevertheless, we found a single colony (3% of all colonies) which contained the offspring of more than two unrelated reproductives. Although other studies have also described subterranean termite colonies with a similarly complex genetic composition, we demonstrate here that such colonies can form under natural conditions via the fusion of whole colonies. This study underscores how repeated sampling from individual colonies over time and space can yield information about colony spatial and genetic structure that cannot be obtained from conventional analyses or sampling methods.     

Balancing Energy Budget in a Central-Place Forager: Which Habitat to Select in a Heterogeneous Environment?

Foraging animals are influenced by the distribution of food resources and predation risk that both vary in space and time. These constraints likely shape trade-offs involving time, energy, nutrition, and predator avoidance leading to a sequence of locations visited by individuals. According to the marginal-value theorem (MVT), a central-place forager must either increase load size or energy content when foraging farther from their central place. Although such a decision rule has the potential to shape movement and habitat selection patterns, few studies have addressed the mechanisms underlying habitat use at the landscape scale. Our objective was therefore to determine how Ring-billed gulls (Larus delawarensis) select their foraging habitats while nesting in a colony located in a heterogeneous landscape. Based on locations obtained by fine-scale GPS tracking, we used resource selection functions (RSFs) and residence time analyses to identify habitats selected by gulls for foraging during the incubation and brood rearing periods. We then combined this information to gull survey data, feeding rates, stomach contents, and calorimetric analyses to assess potential trade-offs. Throughout the breeding season, gulls selected landfills and transhipment sites that provided higher mean energy intake than agricultural lands or riparian habitats. They used landfills located farther from the colony where no deterrence program had been implemented but avoided those located closer where deterrence measures took place. On the other hand, gulls selected intensively cultured lands located relatively close to the colony during incubation. The number of gulls was then greater in fields covered by bare soil and peaked during soil preparation and seed sowing, which greatly increase food availability. Breeding Ring-billed gulls thus select habitats according to both their foraging profitability and distance from their nest while accounting for predation risk. This supports the predictions of the MVT for central-place foraging over large spatial scales.     

Estimating colony locations of bumble bees with moving average model

It is very difficult to find natural colonies of bumble bees in the field. In this study, the yearly dynamics of floral resources and foraging bumble bee workers were investigated. The optimal colony locations were estimated from the data using moving average on the assumption that bumble bee queens and workers were omniscient. Fortunately, a colony of Bombus ardens was found, and the true location of the colony was evaluated with the estimated optimal locations. The true location was optimal at the latter half of the breeding season.An erratum to this article can be found at     

Penguins from space: faecal stains reveal the location of emperor penguin colonies

Aim  To map and assess the breeding distribution of emperor penguins ( Aptenodytes forsteri ) using remote sensing.
Location  Pan-Antarctic.
Methods  Using Landsat ETM satellite images downloaded from the Landsat Image Mosaic of Antarctica (LIMA), we detect faecal staining of ice by emperor penguins associated with their colony locations. Emperor penguins breed on sea ice, and their colonies exist in situ between May and December each year. Faecal staining at these colony locations shows on Landsat imagery as brown patches, the only staining of this colour on sea ice. This staining can therefore be used as an analogue for colony locations. The whole continental coastline has been analysed, and each possible signal has been identified visually and checked by spectral analysis. In areas where LIMA data are unsuitable, freely available Landsat imagery has been supplemented.
Results  We have identified colony locations of emperor penguins at a total of 38 sites. Of these, 10 are new locations, and six previously known colony locations have been repositioned (by over 10 km) due to poor geographical information in old records. Six colony locations, all from old or unconfirmed records, were not found or have disappeared.
Main conclusions  We present a new pan-Antarctic species distribution of emperor penguins mapped from space. In one synoptic survey we locate extant emperor penguin colonies, a species previously poorly mapped due to its unique breeding habits, and provide a vital geographical resource for future studies of an iconic species believed to be vulnerable to future climate change.     

Fine-scale study finds limited evidence of kin clustering in a gray seal colony

Microsatellites were used to investigate fine‐scale spatial and temporal genetic structure of a gray seal breeding colony, using samples collected throughout the colony (1997) and more extensive local sampling (2000–2002). Previous behavior of breeding seals on North Rona, including philopatry and high breeding site fidelity, suggested female kin may cluster together. However, low F_ST scores indicated no genetic differentiation between the major breeding aggregations in different regions of the colony. Nevertheless, the pairwise relatedness of mothers within regions was significantly higher than the relatedness of mothers between regions. Evidence of kin clustering occurred within one region in the colony. Within this region, mothers' pairwise relatedness decreased significantly with increasing distance between pupping sites. Pairwise relatedness of neighboring females within this region was also higher than expected. Conversely, in the other regions mothers that were considered likely to have social interactions, based on their spatial and temporal proximity, were not more related to each other than random. Therefore, sustained philopatry appears sufficient to produce differences in relatedness at a within‐colony scale (>500 m), but not at finer scales. This suggests that long‐term associations of mothers on North Rona detected previously are unlikely to be formed solely by close kin.     

Sex differences in Adélie penguin foraging strategies

Consistent sex differences in foraging trip duration, feeding locality and diet of breeding Adélie penguins (Pygoscelis adeliae) were demonstrated at two widely separated locations over several breeding seasons. Differences in foraging behaviour were most pronounced during the guard stage of chick rearing. Female penguins made on average longer foraging trips than males, ranged greater distances more frequently and consumed larger quantities of krill. In contrast, males made shorter journeys to closer foraging grounds during the guard period and fed more extensively on fish throughout chick rearing. Mean guard stage foraging trip durations over four seasons at Béchervaise Island, Eastern Antarctica and over two seasons at Edmonson Point, Ross Sea ranged between 31 and 73 h for females and 25 and 36 h for males. Ninety percent of males tracked from Béchervaise Island by satellite during the first 3 weeks post-hatch foraged within 20 km of the colony, while the majority (60%) of females travelled to the edge of the continental shelf (80–120 km from the colony) to feed during this period. Received: 10 December 1997 / Accepted: 10 April 1998     

Sex, age, experience and condition as factors affecting arrival date in prospecting common terns, Sterna hirundo

Several studies have shown that seabird colonies consist to a large extent of young nonbreeders (prospectors). These individuals appear at the colony later in the season than established breeders. The reasons for this late arrival have remained unclear in most cases, mainly because of technical difficulties in collecting sufficient data from nonbreeding individuals. We used a novel transponder system to identify remotely the members of a common tern colony, including nonbreeders, during eight breeding seasons and we combined the system with automatic balances. Ninety-two per cent of prospectors returned for the first time when 2 years old and 88.9% of recruits to the breeding population had spent at least one previous season at the colony as prospectors. In both sexes, most individuals prospected for one season, but more males than females prospected for more than one season, although a higher proportion of females started breeding without a previous prospecting phase. Terns arrived earlier in the season the older they were and the more experience of the colony they had, but experience proved to be more important than age. Prospectors gained about 3 weeks with a previous prospecting season whereas an additional year of age allowed birds to arrive only about 6 days earlier. Prospectors returning later in the season arrived with lower body masses. Males on average arrived earlier at the colony than females. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Spatial contraction in a large gull colony in relation to the position of arctic fox dens

Many species of colonial ground-nesting birds are known to be sensitive to predation by terrestrial predators. The response of prey under the pressure of predation can either be direct (depletion of prey) or indirect due to prey avoiding the predator. We studied the recolonization of arctic foxes into a large and growing breeding colony of lesser black-backed gulls. The gull colony reached the size of 20,000 pairs during the period of no foxes. The number of breeding gulls continued to increase after the colonization of foxes and reached a maximum of 40,000 pairs about 15 years later. During the same time period, the spatial coverage of the gull colony shrunk from 31.4 down to 18.6 km², and the change in distribution was closely linked with position of fox dens, which ranged in number from one to three annually. In 2005, the number of breeding gulls decreased slightly with an ongoing shrinkage in spatial coverage. Food analyses from fox scats and stomachs showed that birds of the order Charadriiformes, particularly gulls, were the key prey item. Survival rates of gull nests were higher in the middle of the colony than at the colony edge close to a fox den. The colony area lost could be explained solely by the number of eggs removed by foxes but is unlikely, e.g., due to reclutching. We suggest that intraspecific predation contributes additionally to the effects of direct fox predation although to an unknown degree.     

Philopatry and colony fidelity of Shags Phalacrocorax aristotelis on the east coast of Britain

Shag Phalacrocorax aristotelis colonies from the Firth of Forth south to the Fame Islands (SE Scotland and NE England) were surveyed in 1982 and 1983 for nesting Shags ringed as chicks or adults in the previous 20 years. On average, 5% of 863 Shags ringed as chicks were breeding away from their natal colony, and only 1% of 401 marked adults had left their breeding colony. The proportion p of chicks that settled at or beyond distance D from the natal colony followed the relationship p = 0.263D-^0.771, implying that more Shags moved 10 km or beyond to breed than expected from diffusion models or a constant-rate dispersal model; adjusted for birds that settled outside the study area, the relationship was p = 0.314D^-0771. There was no effect of colony size on emigration rate, but females showed a greater tendency to settle away from the natal colony than did males. At the natal colony, more males (69%) than females (47%) nested within 300 m of their birthplace. Two mechanisms appear to determine where a Shag settles to breed: a navigational one governing the return to the natal colony, plus the competitive process of nest-site establishment.     

Topographic spatial characterisation of grey seal Halichoerus grypus breeding habitat at a sub-seal size spatial grain

Expansion within breeding colonies may critically depend upon the availability of suitable breeding habitat. Here we use topographic modelling in a GIS to characterise suitable pupping habitat and accurately predict the pattern of colonisation in an expanding grey seal breeding colony – the Isle of May (Scotland). We use high resolution images from large format aerial photographs of the colony to generate sub‐metre accurate Digital Terrain Models (DTMs). GIS modelling with these DTMs provides topographic measures of elevation, slope and ease of access to sea and freshwater pools at a 2 m grid cell size. Seal locations during the 1994 breeding season, with sex‐age class, were also digitised from the same images. We examine how the physical attributes of cells (locations) with and without pups differ and identify areas suitable for pupping but remaining unoccupied during 1994. We predict patterns of future colonisation by characterising areas differentiated by the densities of pups within 5 m grid cells and identifying areas, both occupied or unoccupied, with a potential for increased future pupping densities. Our predictions were tested by examining pup distributions observed in the 1998 breeding season. Occupied sites were significantly closer to freshwater pools and access to the sea (p<0.001) than unoccupied sites suggesting that proximity to water may restrict colony expansion before all areas of suitably flat terrain are occupied. All pup density classes occurred in sites with similar slope values and distance to pools. However, higher pupping densities occurred closer to access points (p=0.014). Pup densities observed in 1998 revealed that our 1994 predictions were accurate (p<0.0001). Only 12% of 466 grid cells had higher densities in 1998 than predicted, of which 88% differed by only 1 pup. These incorrectly classified cells occurred at the expanding edge of the colony (in a more topographically homogenous area) and at the main access points from the sea (major traffic zones). These results demonstrate the value of the accurate quantification of topographic parameters at the appropriate spatial grain (in this case below the size of the individual) for use in habitat classification and predictions of habitat utilisation.     

Breeding dispersal patterns within a large Sand Martin (Riparia riparia) colony

Colonial birds when returning to breed to a previous location can face different settling options regarding their position in the colony. The decision could be influenced by information gained from the conspecifics’ performance, known as habitat copying. Colonial Sand Martins (Riparia riparia) cannot use evident physical cues when returning to breeding sites, as their nesting substrate is usually renewing completely. We investigated settlement decisions of breeding birds in a unique situation at a large colony along the Tisza River, Hungary, where the nesting substrate was renewed completely in two consecutive years. Breeding birds were ringed at 7-m-long sections of the colony, with totals of 6 sections in 2000 and 20 sections in 2001. Aggregation levels of philopatric birds were estimated by calculating individual distances (expressed in sections) between each recaptured bird. From 1,494 adult birds ringed in the first year, 128 individuals returned to breed in the same colony. The distance to the nearest neighbour in the year 2000 predicted the settlement distance in the next year, indicating a clear preference of breeding closer to the neighbours of the previous year than expected by chance. Age composition had an uneven distribution in the colony, as sections where no clumped resettlement occurred had fewer old individuals than the other sections. Morphological measurements were not clearly different between colony sections. This non-random settlement pattern suggests the existence of breeding groups that could disperse together without being attached to a specific colony site.     

Sociability leads to instability

We present a general stochastic model showing that colonial breeding can lead to complex multi-colony population dynamics when combined with nothing more than (inevitably) imperfect decision-making by individuals. In particular, frequent “switching cascades”—mass movement of individuals between locations from one breeding season to the next—arise naturally from our model, bringing into question the need to invoke a separate, fitness-based explanation for this commonly observed real-world phenomenon. A key component of the model is the development, at the beginning of each breeding season, of a set of colonies, based on sequential choices by individuals about where to breed. Individuals favor the colony they bred in previously, but are also attracted to colonies that are rapidly establishing, and may switch locations. This provides a positive feedback that leads to switching cascades. We examine the effect on the dynamics of individuals’ access to (and ability to act on) information, as well as the overall size of the colony system and of individual colonies. We compare the model’s dynamics to the observed population dynamics of a set of heron and egret breeding colonies in New York Harbor.     

Dispersal and recruitment during population growth in a colonial bird, the great cormorant Phalacrocorax carbo sinensis

While the factors influencing reproduction and survival in colonial populations are relatively well studied, factors involved in dispersal and settlement decisions are not well understood. The present study investigated exchanges of great cormorants Phalacrocorax carbo sinensis among six breeding colonies over a 13‐year period when the breeding population in Denmark increased from 2800 to 36 400 nests. We used a multistate capture‐recapture model that combined multisite resightings and recoveries to examine simultaneously recruitment, natal dispersal, breeding dispersal and annual survival of first‐year, immature and breeding great cormorants. Mean survival of first‐year birds (0.50±0.09, range=0.42–0.66 among colonies) was lower than survival of breeders (0.90±0.06, range=0.81–0.97). Mean survival of immature birds over the study period was 0.87±0.08. Dispersal from a colony increased with decreasing mean brood size in the colony in both first‐time and experienced breeders. The choice of the settlement colony in first‐time breeders was affected by conditions in the natal colony and in the colonies prospected during the pre‐breeding years. In particular, first‐time breeders recruited to colonies where they could expect better breeding success. Experienced breeders relied mainly on cues present early in the season and on their own breeding experience to choose a new breeding colony. Newly established colonies resulted mainly from the immigration of first‐time breeders originating from denser colonies. Dispersal was distance‐dependent and first‐time breeders dispersed longer distances than breeders. We suggest that the prospecting behaviour allows first‐time breeders to recruit in nearby as well as more distant potential breeding colonies. Dispersing breeders preferred to settle in neighbouring colonies likely to benefit from their experience with foraging areas. We discuss the importance of these movements for growth and expansion of the breeding population.     

Individual inter‐annual nest‐site relocation behaviour drives dynamics of a recently established Barnacle Goose Branta leucopsis colony in sub‐arctic Russia

Avian breeding colonies are generally in a continuous state of flux, some parts growing whilst others shrink as individuals move within the colony on the search for better nest‐sites. We examined the role of experience in breeding patch choice by individually marked Barnacle Geese Branta leucopsis in a recently established colony in sub‐arctic Russia. Individuals failing to reproduce successfully tended to shift nest location further the following season than did successful pairs, and they did so towards the most dense nest aggregations within the colony, where reproductive success was higher. We suggest that individual decisions on nest‐site choice shape the spatial dynamics of this colony.     

Population genetics of the black ant Formica lemani (Hymenoptera: Formicidae)

Colony kin structure and spatial population structure were studied in multiple populations of the ant Formica lemani , using allozymes and DNA microsatellites. Average genetic relatedness between nestmate workers varied little between populations ( r  = 0.51–0.76), indicating that the average colony kin structure was relatively simple. Worker genotypes could not be explained with a single breeding pair in all nests, however, and the distribution of relatedness estimates across nests was bimodal, suggesting that single- and multi-queen colonies co-occur. We studied spatial population structure in a successional boreal forest system, which is a mixture of different aged habitats. Newly clear-cut open habitat patches are quickly colonized by F. lemani , where it is able to persist for a limited number of generations. Newly-founded populations showed signs of a founder effect and spatial substructuring, whereas older populations were more homogenous. This suggests that new populations are founded by a limited number of colonizers arriving from more than one source. Genetic differentiation among local populations was minor, indicating strong migration between them. There were, however, indications of both isolation by distance and populations becoming more isolated as habitat patches grew older.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 247–258.     

Spatial Heterogeneity as a Genetic Mixing Mechanism in Highly Philopatric Colonial Seabirds

How genetic diversity is maintained in philopatric colonial systems remains unclear, and understanding the dynamic balance of philopatry and dispersal at all spatial scales is essential to the study of the evolution of coloniality. In the King penguin, Aptenodytes patagonicus, return rates of post-fledging chicks to their natal sub-colony are remarkably high. Empirical studies have shown that adults return year after year to their previous breeding territories within a radius of a few meters. Yet, little reliable data are available on intra- and inter-colonial dispersal in this species. Here, we present the first fine-scale study of the genetic structure in a king penguin colony in the Crozet Archipelago. Samples were collected from individual chicks and analysed at 8 microsatellite loci. Precise geolocation data of hatching sites and selective pressures associated with habitat features were recorded for all sampling locations. We found that despite strong natal and breeding site fidelity, king penguins retain a high degree of panmixia and genetic diversity. Yet, genetic structure appears markedly heterogeneous across the colony, with higher-than-expected inbreeding levels, and local inbreeding and relatedness hotspots that overlap predicted higher-quality nesting locations. This points towards heterogeneous population structure at the sub-colony level, in which fine-scale environmental features drive local philopatric behaviour, while lower-quality patches may act as genetic mixing mechanisms at the colony level. These findings show how a lack of global genetic structuring can emerge from small-scale heterogeneity in ecological parameters, as opposed to the classical model of homogeneous dispersal. Our results also emphasize the importance of sampling design for estimation of population parameters in colonial seabirds, as at high spatial resolution, basic genetic features are shown to be location-dependent. Finally, this study stresses the importance of understanding intra-colonial dispersal and genetic mixing mechanisms in order to better estimate species-wide gene flows and population dynamics.     

FACTORS AFFECTING THE AGE OF FIRST BREEDING OF THE KITTIWAKE RISSA TRIDACTYLA

At a Kittiwake colony in Northumberland, 80% of those birds which returned to their natal colony to breed were males and these supplied 52% of all male recruits. More females breed away from their natal colony than males. There was no differences in the proportions of young fledged from sites in the centre or at the edge of the colony, or by parents of different experience, which returned to breed. Kittiwakes breed for the first time at ages from 3 to 8 years, but most at 4 or S years old. Males arrive back at the colony at an earlier age than females and breed for the first time one year earlier. Males obtaining sites at the centre of the colony first breed at an earlier age than those at the edges. Neither the age nor the area of first breeding appear to be transmitted from parent to offspring. Males breeding first aged 4 years or younger produced more young than those which first bred aged 5 years or older, despite their partners laying smaller clutches. This difference was most marked among those males recruited to sites in the centre of the colony. The advantage of this earlier breeding is counteracted by a lower survival rate among those males which start to breed at the younger ages. In all breeding Kittiwakes, annual reproductive output increases with experience while annual survival rates decrease. Once they had started to breed, many birds failed to breed in one subsequent season. Nearly 60% of these cases of intermittent breeding occurred in the year following first breeding. Intermittent breeding was most frequent among young birds and among females. It is suggested that each breeding involves a cost to the individual in terms of reduced survival, and that deferred and intermittent breeding are means of guarding survival. A model is proposed whereby the age at which a bird starts to breed, the nesting site which it obtains, and its subsequent breeding strategy result in each individual producing an optimal number of reproducing offspring in its lifetime, relative to its quality.