XIA, D.-P., LI, J.-H., GARBER, P. A., MATHESON, M. D., SUN, B.-H. and ZHU, Y. (2013), Grooming Reciprocity in Male Tibetan Macaques. Am. J. Primatol.. doi: 10.1002/ajp.22165
In several primate species, adult males are reported to compete for access to reproductive partners as well as forming affiliative and cohesive social bonds based on the exchange of goods or services. We hypothesized that among a broad set of fitness-maximizing strategies, grooming can be used by individual adult males to enhance social relationships through reciprocity and/or through the interchange of grooming for a different but equivalent good or service. We used focal animal sampling and continuously recorded dyadic grooming and agonistic interactions to test a series of predictions regarding male social interactions in a free-ranging group of Tibetan macaques (Macaca thibetana) at Huangshan, China. During the non-mating season or between males of similar rank throughout the year, grooming effort given was matched by grooming effort received. However, lower ranking males groomed higher ranking males at a greater rate and/or for a longer duration during both the mating and non-mating periods. We found that higher ranking males directed less aggression towards males with whom they formed a frequent grooming partnership, indicating that grooming received was interchanged for increased social tolerance. These data suggest that individual male Tibetan macaques employ alternative social strategies associated with grooming reciprocity or interchange depending on dominance rank and rates of aggression, and highlight the importance of both biological markets and grooming reciprocity as behavioral mechanisms used by resident adult males to form and maintain affiliative social bonds.
Only distance matters — non-choosy females in a poison frog population
Meuche I, Brusa O, Linsenmair KE, Keller A, Pröhl H
Frontiers in Zoology 2013, 10:29 (20 May 2013)
Females have often been shown to exhibit preferences for certain male traits. However, little is known about behavioural rules females use when searching for mates in their natural habitat. We investigated mate sampling tactics and related costs in the territorial strawberry poison frog (Oophaga pumilio) possessing a lek-like mating system, where both sequential and simultaneous sampling might occur. We continuously monitored the sampling pattern and behaviour of females during the complete period between two successive matings.
We found no evidence that females compared males by visiting them. Instead females mated with the closest calling male irrespective of his acoustic and physical traits, and territory size. Playback experiments in the natural home ranges of receptive females revealed that tested females preferred the nearest speaker and did not discriminate between low and high call rates or dominant frequencies.
Our results suggest that females of O. pumilio prefer the closest calling male in the studied population. We hypothesize that the sampling tactic in this population is affected by 1) a strongly female biased sex ratio and 2) a low variance.
Zootaxa 3652 (5): 501–518 (21 May 2013)
A new species of the Gekko japonicus group (Squamata: Sauria: Gekkonidae) from the border region between China and Vietnam
TRUONG QUANG NGUYEN, YING-YONG WANG, JIAN-HUAN YANG, TANJA LEHMANN, MINH DUC LE, THOMAS ZIEGLER & MICHAEL BONKOWSKI
We describe a new species of the genus Gekko on the basis of 25 specimens from southern China and northern Vietnam. Gekko adleri sp. nov. is distinguished from the remaining congeners by a combination of the following characters: size moderate (SVL on fourth toe 11–15; finger and toe webbing present at base; tubercles absent on upper surface of fore limbs; tubercles on tibia 0–8; precloacal pores 17–21 in males; postcloacal tubercle single; tubercles present on dorsal surface of tail base; subcaudals enlarged; dorsal surface of body with four or five narrow light bands between shoulder and sacrum.
Zootaxa 3652 (5): 547–561 (21 May 2013)
The rediscovery of Oplurus bibronii Guichenot, 1848 a valid species of the liolaemid genus Phymaturus (Iguania: Liolaemidae)
JAIME TRONCOSO-PALACIOS, FERNANDO LOBO, RICHARD ETHERIDGE, JUAN CARLOS ACOSTA & ALEJANDRO LASPIUR
Oplurus bibronii was a species described more than 160 years ago from the highlands of Ovalle, Chile. The species was earlier synonymized with Phymaturus palluma and since then its taxonomic status has not been re-examined. In February of 2011, we were successful in capturing specimens of Phymaturus in the highlands of Ovalle and additionally we examined high quality digital pictures of the type series of O. bibronii. Our analysis shows that the type series is composed of two different species, one of which overlaps their diagnostic characters with the characters of the specimens collected in the highlands of Ovalle, and therefore they correspond to Phymaturus bibronii (new combination). In addition, our review
of the holotype, and some paratypes and topotypes of the recently described P. paihuanense shows that this is a junior synonym of P. bibronii.
Zootaxa 3652 (5): 562–568 (21 May 2013)
New species of Lebiasina (Ostariophysi: Characiformes: Lebiasinidae) from the upper Mazaruni River drainage, Guyana
ANDRÉ L. NETTO-FERREIRA, HERNÁN LOPEZ-FERNANDEZ, DONALD C. TAPHORN & ELFORD A. LIVERPOOL
Lebiasina ardilai is described from the upper Mazaruni in Guyana. The new species differs from all its congeners by its color pattern consisting of: a narrow, nearly straight primary stripe, extending from posterior to humeral blotch to near the vertical through anal-fin origin, being absent or inconspicuous in females and conspicuously marked in males; the presence of four series of dark blotches at the distal border of the scales of longitudinal series 2–5; the faint secondary stripe running onto scales of second and third longitudinal row of scales; intermediate stripe absent; and the posteriorly displaced
caudal blotch, not reaching the posterior tip of caudal peduncle.
Lexi Journey, Jonathan P. Drury, Michael Haymer, Kate Rose, Daniel T. Blumstein
Vivid birds respond more to acoustic signals of predators
Behavioral Ecology and Sociobiology, May 2013
Because conspicuous morphology such as colorful plumage may increase predation risk, we aimed to see if variation in plumage coloration could explain variation in avian anti-predator behavior. We included several measures of plumage coloration: human perception of vividness from images in field guides, total intensity from reflectance spectra of museum skins, contrasts calculated from physiological models of these spectra parameterized for both raptors and humans, chroma, and spectral saturation. We investigated how well these measurements predicted risk assessment in ten species of birds in St. John, U.S. Virgin Islands. We quantified how each species responded to playbacks of a predator’s calls and compared this response to that elicited by songs from a non-predatory, sympatric bird. We found that human-determined measures of vividness best predicted anti-predator responses of birds—more vividly colored species responded more to predators than duller species. No spectrophotometric variable explained variation in species reactions to a predator call. Our results suggest that vivid birds may compensate for their conspicuousness by being more responsive to the sound of predators and that more work is needed to better evaluate how animal coloration is quantified in comparative studies.
Céline Prévot, Alain Licoppe
Comparing red deer (Cervus elaphus L.) and wild boar (Sus scrofa L.) dispersal patterns in southern Belgium
European Journal of Wildlife Research, May 2013
This study analyses the natal dispersal of red deer and wild boar in order to compare their dispersal capabilities in southern Belgium and to evaluate the relevance of management unit areas (MUA) designed for their monitoring. Dispersal was studied thanks to a mark-recovery method based on 111 red deer fawns and 1,613 piglets. The recovery rate of ear-tagged animals was 68 and 40 %, respectively. In both species, sub-adult males moved on longer distances ( x − red deer = 4.82+/−4.17 km and x − wild boar = 4.90+/−5.65 km) than females and juveniles x − (red deer = 1.84+/−1.46 km and x − wild boar = 2.49+/−3.74 km). Taking into account the age and sex categories, we found no difference between species in dispersal mean distance. But we observed higher maximal dispersal distances in wild boar compared to red deer. The natal home range mean sizes were 5.29 km2 (+/−4.87) for red deer and 6.23 km2 (+/−4.60) for wild boar. Red deer and wild boar showed similar dispersal rates according to age and sex category: 53 and 42 % in sub-adult males and 14 and 16 % in females and juveniles. Our results confirmed the higher proportion of philopatry in females and juveniles of both species compared to sub-adult males more likely to disperse. Wild boar of any sex or age seemed to be less sensitive than red deer to infrastructure (road, rail, river) network on which the management unit area limits are currently based.
Dong, L., Heckel, G., Liang, W. and Zhang, Y. (2013), Phylogeography of Silver Pheasant (Lophura nycthemera L.) across China: aggregate effects of refugia, introgression and riverine barriers. Molecular Ecology. doi: 10.1111/mec.12315
The role of Pleistocene glacial cycles in forming the contemporary genetic structure of organisms has been well studied in China with a particular focus on the Tibetan Plateau. However, China has a complex topography and diversity of local climates, and how glacial cycles may have shaped the subtropical and tropical biota of the region remains mostly unaddressed. To investigate the factors that affected the phylogeography and population history of a widely distributed and nondeciduous forest species, we analysed morphological characters, mitochondrial DNA sequences and nuclear microsatellite loci in the Silver Pheasant (Lophura nycthemera). In a pattern generally consistent with phenotypic clusters, but not nominal subspecies, deeply divergent mitochondrial lineages restricted to different geographic regions were detected. Coalescent simulations indicated that the time of main divergence events corresponded to major glacial periods in the Pleistocene and gene flow was only partially lowered by drainage barriers between some populations. Intraspecific cytonuclear discordance was revealed in mitochondrial lineages from Hainan Island and the Sichuan Basin with evidence of nuclear gene flow from neighbouring populations into the latter. Unexpectedly, hybridization was revealed in Yingjiang between the Silver Pheasant and Kalij Pheasant (Lophura leucomelanos) with wide genetic introgression at both the mtDNA and nuclear levels. Our results highlight a novel phylogeographic pattern in a subtropical area generated from the combined effects of climate oscillation, partial drainage barriers and interspecific hybridization. Cytonuclear discordance combined with morphological differentiation implies that complex historical factors shaped the divergence process in this biodiversity hot spot area of southern China.
Zootaxa 3661 (1): 001–060 (22 May 2013)
Review of the systematics, distribution, biogeography and natural history of Moroccan amphibians
WOUTER BEUKEMA, PHILIP DE POUS, DAVID DONAIRE-BARROSO, SERGÉ BOGAERTS, JOAN GARCIA-PORTA, DANIEL ESCORIZA, OSCAR J. ARRIBAS, EL HASSAN EL MOUDEN & SALVADOR CARRANZA
The amphibian fauna of the Kingdom of Morocco was traditionally regarded as poor and closely related to its European counterpart. However, an increase in research during the last decades revealed a considerable degree of endemism amongst Moroccan amphibians, as well as phenotypic and genotypic inter- and intraspecific divergence. Despite this increase in knowledge, a comprehensible overview is lacking while several systematic issues have remained unresolved. We herein present a contemporary overview of the distribution, taxonomy and biogeography of Moroccan amphibians.
Fourteen fieldtrips were made by the authors and colleagues between 2000 and 2012, which produced a total of 292 new distribution records. Furthermore, based on the results of the present work, we (i) review the systematics of the genus Salamandra in Morocco, including the description of a new subspecies from the Rif- and Middle Atlas Mountains, Salamandra algira splendens ssp. nov.; (ii) present data on intraspecific morphological variability of Pelobates varaldiiand Pleurodeles waltl in Morocco; (iii) attempt to resolve the phylogenetic position of Bufo brongersmai and erect a new genus for this species, Barbarophryne gen. nov.; (iv) summarize and assess the availability of tadpole-specific characteristics and bioacoustical data, and (v) summarize natural history data.
T. M. Scheyer, O. A. Aguilera, M. Delfino, D. C. Fortier, A. A. Carlini, R. Sánchez, J. D. Carrillo-Briceño, L. Quiroz, and M. R. Sánchez-Villagra. Crocodylian diversity peak and extinction in the late Cenozoic of the northern Neotropics. Nature Communications. May 21, 2013. doi:10.1038/ncomms2940I
Northern South America and South East Asia are today’s hotspots of crocodylian diversity with up to six (mainly alligatorid) and four (mainly crocodylid) living species respectively, of which usually no more than two or three occur sympatrically. In contrast, during the late Miocene, 14 species existed in South America. Here we show a diversity peak in sympatric occurrence of at least seven species, based on detailed stratigraphic sequence sampling and correlation, involving four geological formations from the middle Miocene to the Pliocene, and on the discovery of two new species and a new occurrence. This degree of crocodylian sympatry is unique in the world and shows that at least several members of Alligatoroidea and Gavialoidea coexisted. By the Pliocene, all these species became extinct, and their extinction was probably related to hydrographic changes linked to the Andean uplift. The extant fauna is first recorded with the oldest Crocodylus species from South America.
First cytogenetic information for Drymoreomys albimaculatus (Rodentia, Cricetidae), a recently described genus from Brazilian Atlantic Forest
Elkin Suárez-Villota, Camilla Di-Nizo, Carolina Neves, Maria José De Jesus Silva
ZooKeys 303 (2013): 65-76
The recently described taxon Drymoreomys albimaculatus is endemic to the Brazilian Atlantic Forest and its biology and genetics are still poorly known. Herein, we present, for the first time, the karyotype of the species using classical and molecular cytogenetics, which showed 2n=62, FN=62, and interstitial telomeric signals at the sex chromosomes. Nuclear and mitochondrial DNA sequences from the two karyotyped individuals verify the taxonomic identity as the recently described Drymoreomys albimaculatus and confirm the relationship of the species with other Oryzomyini. Additionally, external morphological information is provided.
Tozer, D. C., C. M. Falconer, and D. S. Badzinski. 2013. Common Loon reproductive success in Canada: the west is best but not for long. Avian Conservation and Ecology 8(1): 1.
Reproductive success of Common Loons (Gavia immer) is a powerful indicator of aquatic ecosystem health, especially in relation to mercury and acid precipitation. We examined relationships between Common Loon reproductive success and longitude, year, lake area, and pH across southern Canada using data collected from 1992 to 2010 by participants in Bird Studies Canada’s Canadian Lakes Loon Survey. Our goal was to indirectly describe the health of lakes in southern Canada with respect to mercury and acid precipitation. The overall model-predicted number of six-week-old young per pair per year was 0.59 (95% confidence limits: 0.56–0.62). Six-week-old young per pair per year decreased by 0.19 from west-to-east (−127° to −52° longitude), decreased by 0.14 between 1992 and 2010, increased by 0.22 as lake area increased from 10 to 3000 ha, and increased by 0.43 as acidity decreased from pH 5 to 9. The relationships were likely linked to acid- and temperature-mediated exposure to methylmercury and/or acid-induced reductions in forage fish. The temporal decrease was unexpectedly steeper in southwestern than in southeastern Canada. Projections suggested that reproductive success across southern Canada may not drop below the demographic source-sink threshold until ~2016 (range: 2009-2029). Reproductive success on pH 6.0 lakes, however, may have passed below the source-sink threshold as early as ~2001 (1995-2009), whereas reproductive success on pH 8.0 lakes may not pass below the threshold until ~2034 (2019-2062). There were ~0.1 more six-week-old young per pair per year on 2500 ha lakes than on 20 ha lakes. Reproductive success crossed below the source-sink threshold on 20 ha lakes at pH 6.4 (5.8–7.1) and on 2500 ha lakes at pH 5.5 (4.1–6.6). Our results show that citizen science is powerful for monitoring ecosystem health and indirectly support further action to abate emissions of mercury and the harmful components of acid precipitation throughout North America and globally.
Desrochers, A., J. Tardif, and M. J. Mazerolle. 2012. Use of large clear-cuts by Wilson’s Warbler in an eastern Canadian boreal forest. Avian Conservation and Ecology 7(2): 1.
Wilson’s Warbler (Cardellina pusilla; WIWA) has been declining for several decades, possibly because of habitat loss. We compared occupancy of territorial males in two habitat types of Québec’s boreal forest, alder (Alnus spp.) scrubland and recent clear-cuts. Singing males occurred in clusters, their occupancy was similar in both habitats, but increased with the amount of alder or clear-cut within 400 m of point-count stations. A despotic distribution of males between habitats appeared unlikely, because there were no differences in morphology between males captured in clear-cuts vs. alder. Those results contrast with the prevailing view, mostly based on western populations, that WIWA are wetland or riparian specialists, and provide the first evidence for a preference for large tracts of habitat in this species. Clear-cuts in the boreal forest may benefit WIWA by supplying alternative nesting habitat. However, the role of clear-cuts as source or sink habitats needs to be addressed with data on reproduction.
Morneau, F., B. Gagnon, S. Poliquin, P. Lamothe, N. D’Astous, and J. A. Tremblay. 2012. Breeding status and population trends of Golden Eagles in northeastern Québec, Canada. Avian Conservation and Ecology 7(2): 4.
In North America, it is hypothesized that the Golden Eagle’s (Aquila chrysaetos) eastern population declined during the period 1946-1973 because of organochlorine pesticides and other anthropogenic causes of mortality. Since 1970, upward trends for the species have been observed at most eastern hawkwatches. To determine whether such positive trends can be observed on breeding grounds, Golden Eagle counts were performed to monitor nesting territory occupancy between 1994 and 2007 in the Moisie and Sainte-Marguerite River valleys, northeastern Québec. Aerial surveys were conducted during seven of the 14 years. During this period, the number of known nesting territories in the study area increased from 10 to 20, while the number of pairs rose from six to 14. The increase is attributed mostly to investigators’ improved experience in finding nests and to their greater familiarity with the study area, and possibly to the growth of the regional population. Occupancy of nesting territories by pairs was very stable over the years. Annual mean % of laying pairs (or laying rate) was 48.0 (SD = 19.9), and productivity (mean number of fledglings per pair) was 0.49 (SD = 0.35).
Silvergieter, M. P., and D. B. Lank. 2011. Patch scale nest-site selection by Marbled Murrelets (Brachyramphus marmoratus). Avian Conservation and Ecology 6(2): 6.
The Marbled Murrelet (Brachyramphus marmoratus) is a threatened alcid that nests almost exclusively in old-growth forests along the Pacific coast of North America. Nesting habitat has significant economic importance. Murrelet nests are extremely difficult and costly to find, which adds uncertainty to management and conservation planning. Models based on air photo interpretation of forest cover maps or assessments by low-level helicopter flights are currently used to rank presumed Marbled Murrelet nesting habitat quality in British Columbia. These rankings are assumed to correlate with nest usage and murrelet breeding productivity. Our goal was to find the models that best predict Marbled Murrelet nesting habitat in the ground-accessible portion of the two regions studied. We generated Resource Selection Functions (RSF) using logistic regression models of ground-based forest stand variables gathered at plots around 64 nests, located using radio-telemetry, versus 82 random habitat plots. The RSF scores are proportional to the probability of nests occurring in a forest patch. The best models differed somewhat between the two regions, but include both ground variables at the patch scale (0.2-2.0 ha), such as platform tree density, height and trunk diameter of canopy trees and canopy complexity, and landscape scale variables such as elevation, aspect, and slope. Collecting ground-based habitat selection data would not be cost-effective for widespread use in forestry management; air photo interpretation and low-level aerial surveys are much more efficient methods for ranking habitat suitability on a landscape scale. This study provides one method for ground-truthing the remote methods, an essential step made possible using the numerical RSF scores generated herein.
Arnold, T. W., E. A. Roche, J. H. Devries, and D. W. Howerter. 2012. Costs of reproduction in breeding female Mallards: predation risk during incubation drives annual mortality. Avian Conservation and Ecology 7(1): 1.
The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats.
DesGranges, J., and M. LeBlanc. 2012. The influence of summer climate on avian community composition in the eastern boreal forest of Canada. Avian Conservation and Ecology 7(1): 2.
Understanding the relative influence of environmental variables, especially climate, in driving variation in species diversity is becoming increasingly important for the conservation of biodiversity. The objective of this study was to determine to what extent climate can explain the structure and diversity of forest bird communities by sampling bird abundance in homogenous mature spruce stands in the boreal forest of the Québec-Labrador peninsula using variance partitioning techniques. We also quantified the relationship among two climatic gradients, summer temperature and precipitation, and bird species richness, migratory strategy, and spring arrival phenology. For the bird community, climate factors appear to be most important in explaining species distribution and abundance because nearly 15% of the variation in the distribution of the 44 breeding birds selected for the analysis can be explained by climate. The vegetation variables we selected were responsible for a much smaller amount of the explained variation (4%). Breeding season temperature seems to be more important than precipitation in driving variation in bird species diversity at the scale of our analysis. Partial correlation analysis indicated that bird species richness distribution was determined by the temperature gradient, because the number of species increased with increasing breeding season temperature. Similar results were observed between breeding season temperature and the number of residents, short-distance and long-distance migrants, and early and late spring migrants. Our results suggest that the northern and southern range boundaries of species are not equally sensitive to the temperature gradient across the region.
Shutler, D., D. J. T. Hussell, D. R. Norris, D. W. Winkler, R. J. Robertson, F. Bonier, W. B. Rendell, M. Bélisle, R. G. Clark, R. D. Dawson, N. T. Wheelwright, M. P. Lombardo, P. A. Thorpe, M. A. Truan, R. Walsh, M. L. Leonard, A. G. Horn, C. M. Vleck, D. Vleck, A. P. Rose, L. A. Whittingham, P. O. Dunn, K. A. Hobson and M. T. Stanback. 2012. Spatiotemporal patterns in nest box occupancy by Tree Swallows across North America. Avian Conservation and Ecology 7(1): 3.
Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78° W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78° W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broad-scale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America.
Gaston, A. J., and S. Descamps. 2011. Population change in a marine bird colony is driven by changes in recruitment. Avian Conservation and Ecology 6(2): 5.
The population dynamics of long-lived birds are thought to be very sensitive to changes in adult survival. However, where natal philopatry is low, recruitment from the larger metapopulation may have the strongest effect on population growth rate even in long-lived species. Here, we illustrate such a situation where changes in a seabird colony size appeared to be the consequence of changes in recruitment. We studied the population dynamics of a declining colony of Ancient Murrelets (Synthliboramphus antiquus) at East Limestone Island, British Columbia. During 1990-2010, Ancient Murrelet chicks were trapped at East Limestone Island while departing to sea, using a standard trapping method carried on throughout the departure period. Adult murrelets were trapped while departing from the colony during 1990-2003. Numbers of chicks trapped declined during 1990-1995, probably because of raccoon predation, increased slightly from 1995-2000 and subsequently declined again. Reproductive success was 30% lower during 2000-2003 than in earlier years, mainly because of an increase in desertions. The proportion of nonbreeders among adult birds trapped at night also declined over the study period. Mortality of adult birds, thought to be mainly prebreeders, from predators more than doubled over the same period. Apparent adult survival of breeders remained constant during 1991-2002 once the first year after banding was excluded, but the apparent survival rates in the first year after banding fell and the survival of birds banded as chicks to age three halved over the same period. A matrix model of population dynamics suggested that even during the early part of the study immigration from other breeding areas must have been substantial, supporting earlier observations that natal philopatry in this species is low. The general colony decline after 2000 probably was related to diminished recruitment, as evidenced by the lower proportion of nonbreeders in the trapped sample. Hence the trend is determined by the recruitment decisions of externally reared birds, rather than demographic factors operating on the local breeding population, an unusual situation for a colonial marine bird. Because of the contraction in the colony it may now be subject to a level of predation pressure from which recovery will be impossible without some form of intervention.