Predation by cats could lead to the extinction of the Mediterranean endemic Yelkouan Shearwater Puffinus yelkouan at a major breeding site

Feral cats are considered to be one of the main harmful invasive species for island species. Adult shearwaters are highly vulnerable to predation by cats. The population of the Yelkouan Shearwater Puffinus yelkouan, a species endemic to the Mediterranean, is predicted to decline, leaving only a few large breeding colonies, due to the invasion of cats. The impact of cats on the Shearwater population of Le Levant Island, one of the major breeding sites for this species, was evaluated by studying cat diet over a 2‐year period. The predation rate obtained was then included in a Shearwater demographic model. Cats preyed upon rabbits, rats and Shearwaters, with a peak of predation on Shearwaters immediately upon their arrival at the colony. Cat predation was heavy and responsible for the yearly death of about 810–3241 birds. This could lead to the extinction of the Le Levant colony within the next four decades and perhaps within just a few years. Cat predation on prospecting individuals, a parameter essential to assess the real impact of predation, may not have an immediate effect on the Shearwater breeding population but can accelerate population extinction. Cat predation must be reduced or removed to prevent the extinction of one of the most important breeding sites for this species.     

Yelkouan shearwater nest-cavity selection and breeding success

We describe, for the first time, nest-cavities selected by the Mediterranean endemic yelkouan shearwater Puffinus yelkouan on French islands, comparing it with the sympatric Cory's shearwater Calonectris diomedea. By monitoring 179 suitable cavities during four years, we show that yelkouan shearwaters select deeper cavities and with more winding tunnels than those selected by Cory's shearwaters or unoccupied cavities. Logistic regression modelling indicates that cavities with nest-like characteristics are not limited. We show that breeding success is enhanced in deeper cavities, with winding tunnels and higher block covers. We do not find any apparent competition between the two shearwater species.     

Yelkouan shearwater Puffinus yelkouan presence and behaviour at colonies: not only a moonlight question

We describe and test the influence of several environmental and biological factors on the presence and activity patterns of the Mediterranean endemic yelkouan shearwater Puffinus yelkouan at colonies. Bird arrival at breeding sites is highly correlated with nautical dusk for moonless or slightly moonlit nightfalls and correlated with moonset when the moon is visible. Breeding cycle and wind speed affect both the arrival times and presence at colonies. Bird activity also varies throughout the night and sex ratio on colonies throughout the breeding cycle in relation to breeding duties. Breeder and non-breeder behaviour particularly differs in the time spent on the ground outside burrows, without protection. Finally, factors other than moonlight can be essential in determining the presence and behaviour of petrels and shearwaters at breeding sites, and we need to determine how differences in behaviour at colonies could be related to differential predation risk.     

Dramatic increase in the Zembretta Yelkouan shearwater breeding population following ship rat eradication spurs interest in managing a 1500-year old invasion

The ship rat (Rattus rattus) was introduced 1,500 years ago to the Zembra Archipelago (Tunisia) and was eradicated in October–November 2009 on two of its islands, Zembretta and Zembrettina. This eradication was performed 2 years after the discovery of a small colony of Yelkouan shearwaters (Puffinus yelkouan), a species recently up-listed to the vulnerable IUCN extinction risk category. For 2 years before and 3 years after rat eradication, the Zembretta Yelkouan shearwater breeding colony was checked yearly at the end of the breeding season. The number of recorded breeding pairs reaching 176 and 145, respectively, increases of 10.4 and 8.5-fold two and 3 years after rat eradication. This experiment shows that eradication of an ancient introduced ship rat population has dramatically improved the Zembretta Yelkouan shearwater breeding population very quickly. This result suggests that managing even long-introduced populations might well be fruitful.     

Two sibling species sympatrically breeding: a new conservation concern for the critically endangered Balearic shearwater

Two Puffinus shearwater species are endemic to the Mediterranean region: the Yelkouan shearwater P.␣yelkouan breeding in the central and eastern, and the critically endangered Balearic shearwater P.␣mauretanicus in the western, exclusively breeding at the Balearic archipelago. All individuals caught in Minorca, a Balearic breeding site, showed phenotypic traits of Yelkouan shearwaters. Ten birds from that colony were sampled and genetically analysed. A fragment of 857 base pairs of the cytochrome b was sequenced and compared to published sequences of both species obtained from GenBank. A Neighbor-Joining (NJ) reconstruction distinguished two clades with high bootstrap support, showing that both species bred sympatrically in that colony. This result was unexpected since shearwaters do not usually form mixed colonies. New conservation concerns arise also from our study: at first, breeding population of Yelkouan shearwaters is even smaller than previously thought; additionally, other potential threats emerge, such as hybridization and ecological competition.     

Morphological versus acoustic analysis: what is the most efficient method for sexing yelkouan shearwaters Puffinus yelkouan?

Sexing monomorphic seabirds is particularly difficult, and available methods have various disadvantages, such as seasonal non-applicability or stress induction. The yelkouan shearwater Puffinus yelkouan is a poorly studied seabird endemic to the Mediterranean basin. Ecological and biological data are needed for this species, thus necessitating the development of appropriate field methods. Here, we tested two methods for sexing yelkouan shearwaters: the classical morphological method and a new acoustic method. Morphological analysis demonstrated sexual differences in head, leg and feather measurements, with a high degree of overlap resulting in only 87.2% accuracy. In contrast, acoustic analysis showed that the highest value of the fundamental frequency (FC) and duration of the clear note of calls did not overlap between males and females. Yelkouan shearwaters can be sexed with 100% accuracy by measuring FC. If FC < 678.4 Hz, the bird is female, while if FC > 678.4 Hz, the bird is male. Other advantages of this method are its simplicity and non-invasiveness, which are particularly important for a potentially threatened species.     

Longline Fisheries and Foraging Distribution of Flesh-Footed Shearwaters in Eastern Australia

ABSTRACT Incidental seabird mortality associated with bycatch during longline commercial fishing is a conservation concern. An initial step to estimating likelihood of seabird bycatch and conceiving conservation strategies is determining amount of overlap between foraging birds and commercial fishing effort, identifying oceanographic features associated with foraging birds, and quantifying dive characteristics. We tracked 24 adult flesh-footed shearwaters (Puffinus carneipes) breeding on Lord Howe Island located east of Australia during incubation and early and late chick-rearing periods from 6 January to 17 April 2005. At-sea foraging distribution of flesh-footed shearwaters was primarily confined within the jurisdictional Australian Fishing Zone. Foraging was strongly associated with sea-surface temperature >24°C. Spatial and temporal overlap of longline fishing with foraging shearwaters varied throughout the breeding season, but was greatest (63% overlap) during early chick-rearing. Mean maximum distance reached from the breeding colony during a foraging event was 804 km (SD = 280) from Lord Howe Island. Foraging behavior was strongly diurnal, with 91% of dives occurring during daylight, and most dives (77%) were <5 m. Given that longline fishing and flesh-footed shearwaters overlap substantially, the Australian Fisheries Management Authority should consider implementing additional regulations to further reduce bycatch. Conservation strategies such as setting longlines at nights may reduce flesh-footed shearwater bycatch.     

Chick‐provisioning behaviour of two shearwaters breeding in south‐eastern Australia

The chick‐provisioning behaviour of the short‐tailed shearwater Puffinus tenuirostris and the wedge‐tailed shearwater Puffinus pacificus was investigated in a mixed colony on Montague Island, New South Wales, Australia, over two breeding seasons. This colony is located at opposite edges of the breeding distribution of the two species. Frequent weighing techniques were used to determine chick feeding frequency, feed timing, meal size, chick weight loss and indices of food conversion efficiency of the chicks. Short‐tailed shearwater parents fed their chicks larger more infrequent meals than wedge‐tailed shearwater parents. Short‐tailed shearwater chicks demonstrated higher food conversion efficiencies and lower weight loss than wedge‐tailed shearwater chicks, indicating either differences in diet or metabolic rates. The feeding frequency in wedge‐tailed shearwaters also fluctuated more widely than for short‐tailed shearwaters over the two breeding seasons. Despite the fact that the timing of the breeding cycle on Montague Island is almost identical for the two species, these differences in chick provisioning are probably a result of differences in prey type and location, so they may help explain variations in annual breeding success and limits to the distribution of the two species.     

Recruitment processes in long-lived species with delayed maturity: estimating key demographic parameters

Long-lived species show delayed maturity and generally skip breeding sites on a given year, causing difficulties in estimating demographic parameters. A novel multi-state capture – recapture model (model G for general) is proposed to estimate survival and recruitment. Model G considers long and short periods of non-attendance at the breeding site. Model G is compared against a reduced model (model R) to test if pre-breeders skip the studied site a given year, potentially prospecting other breeding habitats.
This model is applied to the vulnerable Cory's shearwaters seabird species. As for many species, natal philopatry, pre-breeding attendance and prospecting play an important role for recruitment into the breeding population. Model G shows that all Cory's shearwaters come back to their natal colony, and attend the colony before recruiting into the breeding population. Moreover, model G is preferred against model R, highlighting that prospecting plays a potentially role in the recruitment processes. Return and recruitment probabilities show similar time variation, suggesting an environmental forcing. The maximum probability of the first breeding is reached at the age of seven years. During the first year the annual survival rate is 0.52 (IC_95%=[0.40, 0.64]) and pre-breeders and adult annual survival rates do not differ, being respectively 0.88, IC_95%=[0.83, 0.92] and 0.89, IC_95%=[0.88, 0.9].
Model G provides an improvement to estimate demographic parameters for long-lived species life cycle and an adequate framework to test the influence of covariates. Model G is structured by age and breeding status categories, allowing easy further population models.     

Intermittent breeding in the short-tailed shearwater Puffinus tenuirostris

1.  At one colony of short-tailed shearwaters in Bass Strait, Australia, all birds breeding have been recorded individually each year for over 50 years. Among individuals known to be alive and to have bred before, 14% of each sex were not present at their breeding colony, on average, in any one year.
2.  A further 15% of males and 13% of females (a significant difference), known to have bred before, were present but not associated with an egg in any one year.
3.  Intermittent breeding was associated with pair bond breakdown and with a reduced ability to raise offspring, even when years of absence were allowed for.
4.  The frequency of attendance, laying and successful rearing of progeny to fledging increased with age in the early years of breeding. However, this was followed by a decrease, except in the case of laying frequency, which continued to increase throughout life.
5.  Our analysis indicated that intermittent breeding in short-tailed shearwaters did not result from individuals implementing trade-offs between the effort required for breeding success and their breeding life span. Rather, we suggest that individuals of higher quality are able to breed more frequently than others without any compensatory reduction in either their annual breeding success or their overall breeding life span.     

Predictive habitat modelling to estimate petrel breeding colony sizes: Sooty shearwaters (Puffinus griseus) and mottled petrels (Pterodroma inexpectata) on Whenua Hou Island

Abstract

Between 2001 and 2006, we systematically sampled the entire coast of Whenua Hou, a rugged offshore island in southern New Zealand, to estimate the population densities of sooty shearwaters (Puffinus griseus) and mottled petrels (Pterodroma inexpectata) by counting the entrances of breeding burrows. A two‐step regression modelling process using binomial errors was used to predict the presence of a colony, and a normal general linear model was used to predict the density of entrances within colonies. Aerial photography, GIS and a Digital Elevation Model were used to extract relevant habitat and location variables, and a combination of both regression models was used to predict the density of breeding burrows within each 5.32 m² pixel on the island. This complex GIS and habitat prediction modelling approach gave population estimates very similar to a more traditional simple area extrapolation method and gave no improvement in precision. However, correction for the slope of the land increased our simple area estimates of population size by 11%. We estimate populations of sooty shearwater and mottled petrel breeding pairs at 173 000 (162 000–190 000) and 160 000 (123 000–197 000) respectively. Based on this number of breeding pairs, we calculate that Whenua Hou supports a total population of 868 000 (554 000–1 270 000) sooty shearwaters. Our estimate of the total mottled petrel population 202 000 pairs (162 000–242 000) is comparable with the only published estimate, but could be an underestimate because mottled petrels are sometimes found in large burrows. More research for robust estimation of population trends is needed to assess the conservation status of mottled petrels.     

The Effect of Moonlight on Scopoli's Shearwater Calonectris diomedea Colony Attendance Patterns and Nocturnal Foraging: A Test of the Foraging Efficiency Hypothesis

Moonlight is known to affect the nocturnal behaviour and activity rhythms of many organisms. For instance, predators active at night may take advantage from increased visibility afforded by the moon, while prey might regulate their activity patterns to become less detectable. Many species of pelagic seabirds attend their colony only at night, in complete darkness, avoiding approaching their nest sites under moonlight. This behaviour has been most often interpreted as an antipredator adaptation (‘predation avoidance’ hypothesis). However, it may also reflect a lower foraging efficiency during moonlit nights (‘foraging efficiency’ hypothesis). Indeed, moonlight may reduce prey availability because preferred seabird prey is known to occur at higher depths in moonlit nights. Using high‐accuracy behavioural information from data loggers, we investigated the effect of moonlight on colony attendance and at‐sea nocturnal foraging in breeding Scopoli's shearwaters Calonectris diomedea. We found that birds departing for self‐feeding trips around the full moon performed longer trips than those departing around the new moon. On nights when the moon was present only partly, nest burrow entrances took place largely in the moonless portion of the night. Moreover, contrary to predictions from the ‘foraging efficiency’ hypothesis, nocturnal foraging activity increased according to moonlight intensity, suggesting that birds increased their foraging activity when prey became more detectable. This study strengthens the idea that colony attendance behaviour is strictly controlled by moonlight in shearwaters, which is possibly related to the perception of a predation risk.     

Sign left by introduced and native predators feeding on Hutton's shearwaters Puffinus huttoni

Abstract

The identification of introduced and native predators is important for many conservation studies within New Zealand. Carcasses of Hutton's shearwaters were collected over three field seasons, and where predation was probable, the bodies were autopsied. Paired bites identified stoats as the principal predator of Hutton's shearwater, but also revealed that a feral cat was present within the colony. Stoats killed their prey with a bite to the back of the neck or head, and commenced feeding on the neck or head. Despite the limited number of cat‐killed birds, cats appeared to feed on Hutton's shearwaters differently from stoats, starting on the breast muscles. Harriers and kea left sign that allowed birds killed or scavenged by these native birds to be distinguished from those killed by stoats or cats.     

Corvids congregate to breeding colonies of a burrow‐nesting seabird

Egg predation is a major cause of reproductive failure among birds, and can compromise the viability of affected populations. Some egg predators aggregate near colonially breeding birds to exploit the seasonal increase of prey resources. We investigated spatial and temporal variations in the abundance of an egg predator (little raven Corvus mellori; Corvidae) to identify whether ravens aggregate spatially or temporally to coincide with any of three potential prey species: burrow‐nesting little penguin (Eudyptula minor; Spheniscidae), short‐tailed shearwater (Ardenna tenuirostris; Procellariidae), and surface‐nesting silver gull (Chroicocephalus novaehollandiae; Laridae). We derived spatially explicit density estimates of little ravens using distance sampling along line transects throughout a calendar year, which encompassed little penguin, short‐tailed shearwater and silver gull breeding and non‐breeding seasons. High raven abundance coincided temporally with penguin and gull egg laying periods but not with that of shearwaters. The spatial distribution of raven density corresponded with the little penguin colony but not with shearwater or gull colonies. Thus, the presence of little penguin eggs in burrows correlated strongly with little raven activity, and this implies that little ravens may have learnt to exploit the plentiful subsurface food resource of little penguin eggs. Corvid management may be required to maintain the viability of this socially and economically important penguin colony.     

Age-dependent prospecting and recruitment to a breeding colony of Short-tailed Shearwaters Puffinus tenuirostris

In a small colony of Short-tailed Shearwaters Puffinus tenuirostris , monitored annually since 1947, many of the young ringed as nestlings returned to their natal colony for one or more years before breeding for the first time. These 'prospectors' were first recorded at 4.1 ± 0.1 (range 2–7) years old; they started breeding at 7.0 ± 0.2 (4–14) years old. Overall, 31% of all prospectors bred on their natal island with no significant annual variation in this proportion. However, 8% of all natal recruits started breeding without having been recorded prospecting and bred first when significantly younger (5.6 ± 0.4 years old) than those first recorded prospecting. Shearwaters which subsequently bred at their natal colony started prospecting when significantly older (4.3 ± 0.1) than those that did not breed at their natal colony (4.0 ± 0.1 years). Non-natal recruits spent significantly less time prospecting (1.0 ± 0.1 years) than prospectors born on the island (1.9 ± 0.1 years). The shearwaters appeared to become progressively more faithful to the colony during their prospecting period.     

How can the Yelkouan shearwater survive feral cat predation? A meta-population structure as a solution?

The Yelkouan shearwater, Puffinus yelkouan, is an endangered Mediterranean endemic species of burrowing petrel threatened by feral cats. The life-history parameters of a small population of Yelkouan shearwaters on the Mediterranean island, Port-Cros, were studied in conjunction with the diet of feral cats, to examine the birds’ vulnerability to introduced cats. Yelkouan shearwaters were the birds most frequently found in cat scats, with 431 ± 72 birds killed per year, and predation highest during the pre-laying period. A demographic model was created using data for P. yelkouan and for closely related shearwater species. Without cat predation, only two of four survival rate scenarios led to a mean growth rate (λ) ≥ 1. The model was constrained to have a stable population growth rate and used to predict predation scenarios compatible with the observed population stability, because the population under study has remained stable at around 180 pairs for at least 20 years despite feral cat predation. The results of assuming that the population is closed were inconsistent with the estimated mortalities due to feral cats, while it was possible to reconcile the observed numbers of breeding pairs with the observed mortalities due to cats by assuming that Port-Cros Island is a sink sustained by immigration. This illustrates that small colonies may need to be sustained by larger ones to avoid being driven to extinction. Unfortunately, the absence of a large geographic-scale ringing program makes the precise identification of the origin of the immigrants impossible in this case.     

Temporal and spatial variation in dispersal in the greater flamingo (Phoenicopterus ruber roseus)

We studied movements of individually marked greater flamingos (Phoenicopterus ruber roseus) born in the Camargue, southern France, between their two most important breeding colonies in the western Mediterranean (Camargue and Fuente de Piedra, Spain) from 1986 to 1992. The two sites differ in the frequency with which they offer suitable conditions for breeding. Flamingos have bred each year in the Camargue since 1974, but in only 12 of the past 22 years at Fuente de Piedra. Higher colony fidelity is thus expected in the less variable environment (Camargue), but if dispersal occurs competition might be an important factor causing this dispersal. Following years during which breeding birds in the Camrgue were disturbed (1988 and 1990) a higher proportion of adults changed colonies between breeding attempts (= breeding dispersal, 12.4%), while only 0.4% of flamingos breeding in the Camargue dispersed in the other years. As expected, flamingos breeding at Fuente de Piedra showed a higher rate of breeding dispersal (8.14%). No differences were observed between males and females. The importance of breeding failure as a factor causing breeding dispersal in flamingos was also confirmed by the movements of individual birds. The proportion of young flamingos that moved from their natal colony to start breeding at Fuente de Piedra (= natal dispersal) was independent of sex and age, but increased when breeding access to the Camargue colony was more difficult. However, natal dispersal was also higher in 1988 and 1990 (40.5%) than in the remaining years (1.2%), as was breeding dispersal. We discuss possible ways in which the increased natal dispersal among inexperienced birds could be linked with the increased breeding dispersal of adults in the same year.     

Genetic and phenotypic differentiation between the critically endangered Balearic shearwater and neighboring colonies of its sibling species

Understanding the demographic and evolutionary processes within and between populations is essential for developing effective management strategies. Thus, for establishing good conservation policies both genetic and phenotypic studies are crucial. We carried out an integrated analysis of genetic and phenotypic characters of the critically endangered Balearic shearwater Puffinus mauretanicus (182 individuals) and compared them with those of 2 nearby colonies of Yelkouan shearwater P. yelkouan (40 individuals), a species for which hybridization has been hypothesized. The results of the microsatellite analyses were compared with previous mitochondrial DNA analyses. Genetic variability was low in the Balearic shearwater and high levels of inbreeding were revealed at local scale. Most dispersal in Balearic shearwaters was to neighboring sites, even though low levels of population structure were found. The admixture between the 2 species was much higher at nuclear than at mitochondrial level, but phenotypic characters would seem to indicate that a lower level of admixture exists. Individual nuclear DNA, mtDNA, and phenotype did not match at individual level, showing that migration alone cannot explain this phenomenon. We suggest that these 2 young shearwater species could have been involved in processes of divergence and admixing. However, due to the longer coalescence times in nuclear markers, incomplete lineage sorting cannot be ruled out.     

Pelagic seabird flight patterns are consistent with a reliance on olfactory maps for oceanic navigation

Homing studies have provided tantalizing evidence that the remarkable ability of shearwaters (Procellariiformes) to pinpoint their breeding colony after crossing vast expanses of featureless open ocean can be attributed to their assembling cognitive maps of wind-borne odours but crucially, it has not been tested whether olfactory cues are actually used as a system for navigation. Obtaining statistically important samples of wild birds for use in experimental approaches is, however, impossible because of invasive sensory manipulation. Using an innovative non-invasive approach, we provide strong evidence that shearwaters rely on olfactory cues for oceanic navigation. We tested for compliance with olfactory-cued navigation in the flight patterns of 210 shearwaters of three species (Cory''s shearwaters, Calonectris borealis, North Atlantic Ocean, Scopoli''s shearwaters, C. diomedea Mediterranean Sea, and Cape Verde shearwaters, C. edwardsii, Central Atlantic Ocean) tagged with high-resolution GPS loggers during both incubation and chick rearing. We found that most (69%) birds displayed exponentially truncated scale-free (Lévy-flight like) displacements, which we show are consistent with olfactory-cued navigation in the presence of atmospheric turbulence. Our analysis provides the strongest evidence yet for cognitive odour map navigation in wild birds. Thus, we may reconcile two highly disputed questions in movement ecology, by mechanistically connecting Lévy displacements and olfactory navigation. Our approach can be applied to any species which can be tracked at sufficient spatial resolution, using a GPS logger.     

Estimating dispersal distributions at multiple scales: within‐colony and among‐colony dispersal rates,distances and directions in European Shags Phalacrocorax aristotelis

Knowledge of the rate, distance and direction of dispersal within and among breeding areas is required to understand and predict demographic and genetic connectivity and resulting population and evolutionary dynamics. However dispersal rates, and the full distributions of dispersal distances and directions, are rarely comprehensively estimated across all spatial scales relevant to wild populations. We used re‐sightings of European Shags Phalacrocorax aristotelis colour‐ringed as chicks on the Isle of May (IoM), UK, to quantify rates, distances and directions of dispersal from natal to subsequent breeding sites both within IoM (within‐colony dispersal) and across 27 other breeding colonies covering 1045 km of coastline (among‐colony dispersal). Additionally, we used non‐breeding season surveys covering 895 km of coastline to estimate breeding season detection probability and hence potential bias in estimated dispersal parameters. Within IoM, 99.6% of individuals dispersed between their natal and observed breeding nest‐site. The distribution of within‐colony dispersal distances was right‐skewed; mean distance was shorter than expected given random settlement within IoM, yet some individuals dispersed long distances within the colony. The distribution of within‐colony dispersal directions was non‐uniform but did not differ from expectation given the spatial arrangement of nest‐sites. However, 10% of all 460 colour‐ringed adults that were located breeding had dispersed to a different colony. The maximum observed dispersal distance (170 km) was much smaller than the maximum distance surveyed (690 km). The distribution of among‐colony dispersal distances was again right‐skewed. Among‐colony dispersal was directional, and differed from random expectation and from the distribution of within‐colony dispersal directions. Non‐breeding season surveys suggested that the probability of detecting a colour‐ringed adult at its breeding location was high in the northeastern UK (98%). Estimated dispersal rates and distributions were therefore robust to incomplete detection. Overall, these data demonstrate skewed and directionally divergent dispersal distributions across small (within‐colony) and large (among‐colony) scales, indicating that dispersal could create genetic and demographic connectivity within the study area.