Breeding biology and conservation of the Black-vented Shearwater Puffinus opisthomelas

The Black-vented Shearwater Puffinus opisthomelas is endemic to the Pacific coast of Baja California, Mexico. We studied the breeding biology of this species at Natividad Island in 1997 and 1998. The colony at Natividad Island covers approximately 2.5 km² and we estimated there to be 114 455 (± 27 520 95% CI) burrows in the colony. In 1997 burrow occupancy was 66.9%, providing a population estimate of 76 570 (± 18 411 95% CI) breeding pairs, representing about 95% of the world's population of this species. In 1997 the peak in egg laying occurred in early March and hatching began on 7 May. The incubation period averaged 51 days (± 6 sd) and chick rearing averaged 69 days (± 3 sd). In 1998 burrow occupancy was lower (19.6%) and nest initiation was later (peak egg laying in mid-April), perhaps a result of El Niño conditions that prevailed in the Eastern Pacific at that time. We calculated that the development of the town and roads on Natividad Island have destroyed over 15% (26 532 burrows) of the breeding habitat on the island.     

The diet of Atlantic Yellow-legged Gulls (<Emphasis Type="Italic">Larus michahellis atlantis</Emphasis>) at an oceanic seabird colony: estimating predatory impact upon breeding petrels

The diet and breeding ecology of Yellow-legged Gulls (Larus michahellis atlantis) were studied on Selvagem Grande, North Atlantic in the nesting season of 2007. We collected and analyzed 715 pellets from adults. The most frequent prey were White-faced Storm-petrels (Pelagodroma marina; present on 40.8% of all pellets) and the endemic land snails (Theba macandrewiana; present on 36.5% of all pellets). Other birds, namely Cory’s Shearwaters (Calonectris diomedea), Macaronesian Shearwaters (Puffinus assimilis), Bulwer’s Petrels (Bulweria bulwerii), and Band-rumped Storm-petrels (Oceanodroma castro) were relatively less frequent, but overall, seabirds were present in ca. 50% of all pellets, representing an estimated 60.4% of all mass consumed by gulls. We estimate that the contribution of seabirds to the overall caloric balance accounted for 82.5% of all energy consumed. The number of gull pairs breeding on Selvagem Grande was 12 on 2005 and 2007. Breeding success was low (0.92 and 0.25 juveniles per breeding pair, respectively). Using a simple bioenergetics model, we estimate the breeding gull population to have the potential to consume approximately 4,847 adult/sub-adult seabirds in 3.5 months in order to meet its energetic requirements. The importance of the estimated predation levels is discussed and some management actions are suggested.     

Improving the accuracy of population size estimates for burrow‐nesting seabirds

Seabird numbers can change rapidly as a result of environmental processes, both natural and anthropogenic. Informed management and conservation of seabirds requires accurate and precise monitoring of population size. However, for burrow‐nesting species this is rarely achieved due to spatial and temporal heterogeneity in burrow occupancy. Here, we describe a novel method for deriving more accurate population size estimates that employs mark‐recapture methods to correct for unknown variation in nest occupancy throughout a breeding season. We apply it to estimate breeding numbers of a colonial, burrowing seabird, the Little Penguin Eudyptula minor, on the Summerland Peninsula, Phillip Island, Australia. Estimates of active burrow numbers during the September 2008 to February 2009 breeding season were adjusted to numbers of breeding birds based on burrow occupation and modelled population demographics at six, fortnightly monitored reference sites. The population was estimated to be 26 100 (95% CI: 21 100–31 100) and 28 400 (23 800–33 000) breeding Penguins in two temporally separated surveys within one breeding season. We demonstrate using simulation that the method is robust to variation in burrow occupancy throughout the breeding season, providing consistent and more accurate estimates of population size. The advantage of using the corrected method is that confidence intervals will include the true population size. Confidence limits widened as burrow occupancy declined, reflecting the increased uncertainty as larger adjustments for low burrow occupancy were required. In contrast, the uncorrected method that uses burrow occupancy alone as a measure of breeding numbers was inconsistent and significantly underestimated population size across much of the breeding season. Although requiring considerably more survey effort, the corrected approach provides a more accurate means for monitoring population changes in colonially breeding animals while collecting demographic data that can help diagnose the drivers of population change.     

A long-term study of Short-tailed Shearwaters Puffinus tenuirostris on Fisher Island, Australia

All 100–200 Short-tailed Shearwaters Puffinus tenuirostris breeding on Fisher Island, in Bass Strait, Australia, have been individually marked and their breeding performance monitored in each year since 1947. This long study has revealed that mortality rates are greater in older shearwaters and that reproductive performance varies with age, breeding experience and mate familiarity in complex ways. A single study population proved inadequate, however, for estimating pre-breeding survival rates, recruitment rates, emigration and immigration.     

Estimating the abundance of burrow‐nesting species through the statistical analysis of combined playback and visual surveys

The conservation of elusive species relies on our ability to obtain unbiased estimates of their abundance trends. Many species live or breed in cavities, making it easy to define the search units (the cavity) yet hard to ascertain their occupancy. One such example is that of certain colonial seabirds like petrels and shearwaters, which occupy burrows to breed. In order to increase the chances of detection for these types of species, their sampling can be done using two independent methods to check for cavity occupancy: visual inspection, and acoustic response to a playback call. This double‐detection process allows us to estimate the probability of burrow occupancy by accounting for the probability of detection associated with each method. Here we provide a statistical framework to estimate the occupancy and population size of burrow‐dwelling species. We show how to implement the method using both maximum likelihood and Bayesian approaches, and test its precision and bias using simulated datasets. We subsequently illustrate how to extend the method to situations where two different species may occupy the burrows, and apply it to a dataset on wedge‐tailed shearwaters Puffinus pacificus and tropical shearwaters P. bailloni on Aride Island, Seychelles. The simulations showed that the single‐species model performed well in terms of error and bias except when detection probabilities and occupancies were very low. The two‐species model applied to shearwaters showed that detection probabilities were highly heterogeneous. The population sizes of wedge‐tailed and tropical shearwaters were estimated at 13 716 (95% CI: 12 909–15 874) and 25 550 (23 667–28 777) pairs respectively. The advantages of formulating the call‐playback sampling method statistically is that it provides a framework to calculate uncertainty in the estimates and model assumptions. This method is applicable to a variety of cavity‐dwelling species where two methods can be used to detect cavity occupancy.     

Investigator disturbance reduces reproductive success in Short‐tailed Shearwaters Puffinus tenuirostris

Research procedures can have a detrimental effect on the reproductive success of the study species. In this study, the frequency of investigator disturbance on Short‐tailed Shearwaters Puffinus tenuirostris was examined experimentally throughout the incubation period to assess whether disturbance influences hatching success, pre‐fledging chick survival and chick body size. Handling of incubating birds every day, every 3 days and once a week reduced hatching success by 100, 61 and 39%, respectively, compared with pairs that were not disturbed. Most failures resulted from egg abandonment by the parents, particularly during the early stage of incubation. Chick survival did not differ between treatment groups, but control chicks were significantly heavier and had larger bill depths and longer wings. The difference in chick body mass and size observed between the control and disturbed chicks might be due to physiological or behavioural mechanisms in adults or carry‐over effects from the incubation stage to the next life‐history stage. Reduced offspring quality has the potential to affect post‐fledging survival and recruitment. These findings are significant in broader terms because any investigator disturbance that reduces reproductive success, survival and offspring fitness could interfere with the accurate assessment of demographic parameters and exacerbate population declines.     

Nesting activity,breeding success and colony size for the Wedge-tailed Shearwater Puffinus pacificus on Heron Island

Abstract The Capricorn Group of islands in Australia's Great Barrier Reef Marine Park sustains one of the world's largest breeding populations of the Wedge-tailed Shearwater Puffinus pacificus. Heron Island, a 13.5 ha coral cay which supports tourist and research station leases as well as a national park, is the third largest nesting island in the group. Sample censuses of breeding burrows were conducted each year between 1985 and 1990 and a further survey was completed in 1993. These returned estimates of between 13 264±1387 and 16 337±1545 active burrows (Y±SE). Burrow densities within each of the habitats monitored showed no significant trends between years, although there were large differences in burrow density between habitats. There were roughly the same number of burrows in the developed (west) and national park (east) halves of the cay. A miniature video camera system (burrowscope), which allowed nesting chambers at the ends of burrows to be inspected, was used in 1989, 1990 and 1993. This demonstrated that around half the burrows were occupied by incubating birds. Variations were found in the distribution of incubating birds between habitats, although this did not remain constant between the years. In the 1993 season, breeding activity was traced from the burrow establishment to fledging stage. Fifty-one per cent of burrows were used for breeding (eggs laid), 77% of eggs hatched and 80% of chicks produced a fledgling. Overall breeding success for the island was estimated at 61%. In 1993 the area designated as Buildings was found to have significantly lower hatching success compared with natural habitats. Most mortality occurred at the egg stage; however, in the Fringe habitat, mortality was highest at the chick stage. Previous surveys have estimated the breeding population from burrow counts. It now appears that only about 30% of such burrows produce fledglings.     

Seasonal Sexual Segregation by Monomorphic Sooty Shearwaters Puffinus griseus Reflects Different Reproductive Roles during the Pre-Laying Period

Tracking technology has revolutionized knowledge of seabird movements; yet, few studies have examined sex differences in distribution and behavior of small to medium-sized, sexually-monomorphic seabirds. Application of bird-borne geolocation-immersion loggers revealed seasonal segregation in the sexually-monomorphic Sooty Shearwater Puffinus griseus, mainly in the pre-laying period, when there were clear differences in reproductive roles. Shearwaters first returned to the Falkland Islands on 27 Sept±8 d; males, on average, 8 d earlier than females. Prior to egg-laying, distribution at sea, colony attendance and behaviour depended on sex. Males foraged locally over the southern Patagonian Shelf and Burdwood Bank, spending mainly single days at sea and intervening nights in the burrow. Females, who flew for more of the day during this time, foraged in more distant areas of the northern Patagonian Shelf and Argentine Basin that were deeper, warmer and relatively more productive. Attendance of females at the colony was also more variable than that of males and, overall, males were present for significantly more of the pre-laying period (38 vs. 19% of time). Sex differences were reduced following egg-laying, with males and females using similar foraging areas and making trips of similar mean duration in incubation (7.6±2.7 d) and chick-rearing (1.4±1.3 d). Congruence continued into the non-breeding period, with both sexes showing similar patterns of activity and areas of occupancy in the NW Atlantic. Thus, seasonal changes in reproductive roles influenced patterns of sexual segregation; this occurred only early in the season, when male Sooty Shearwaters foraged locally, returning regularly to the colony to defend (or maintain) the burrow or the mate, while females concentrated on building resources for egg development in distant and relatively more productive waters.     

FOOD AS A FACTOR CONTROLLING THE BREEDING OF PUFFINVS LHERMINIERI

A study of Puffinus Iherminieri on Plaza Island, Galápagos, showed that, although eggs were laid in all months, there were marked peaks and troughs of laying. Intervals between successive layings varied with the success or failure of the first egg, an average of nine months for successful pairs, eight months for pairs which lost a young, and 6–5 months for those which failed to hatch an egg. However the breeding success did not influence the time between the end of one breeding attempt and the next laying. This suggests that birds were breeding as quickly as possible. The critical factor preventing more frequent breeding appeared to be the time required to replace the wing and tail feathers.
Details are given of the breeding biology, all aspects of which were strongly influenced by frequent and unpredictable food shortages. The average incubation period was 49 days but this was prolonged by temporary desertion due to food shortages. Chick growth and fledging periods (62 to 100 days) were variable. There was no well–defined desertion period and birds were experimentally induced to feed young for up to 120 days.
Overall nesting success was low (26%) and adult survival between breeding attempts was high (92–95%).
Food, planktonic fish larvae and Crustacea, appeared to be rarely abundant and details are given of the effect of food shortage on the breeding.
The breeding synchrony was brought about by food shortages. The ultimate factor controlling breeding appeared to be the availability of food for egg formation and there was no possibility of birds timing breeding so that young were being fed at a time of food abundance.
A comparison is made of the breeding of eight Puffinus species.     

Negative population trend for Chapada Flycatchers (Suiriri islerorum) despite high apparent annual survival

ABSTRACT Population size and trends are demographic parameters that can be used to help determine the threat of extirpation or extinction of bird populations and in determining management strategies. Chapada Flycatchers (Suiriri islerorum) are endemic to the Cerrado region of Brazil, dependent on open cerrado habitat, defend large territories, and their populations seem to be declining. From 2003 to 2007, we analyzed demographic parameters of a declining population of Chapada Flycatchers, using the rate at which territories became vacant and the size of the breeding population to ascertain the status of the population, and evaluated the relative contributions of apparent annual survival and recruitment rates to these trends. Territories became vacant at a mean rate of 13% per year, and 32% of all territories were vacated during our study. The current breeding population (20 pairs) was at least seven times smaller than the estimated carrying capacity of the reserve (141 territorial pairs). Estimated apparent annual survival probabilities (0.77 for breeders; 0.67 for nonbreeders) based on model averaging were comparable to those reported for other Neotropical passerines. Survival rates did not differ between the sexes and the estimated recruitment rate was 0.21. In many species, adult survival is the factor that most strongly influences population growth rates. However, the population of Chapada Flycatchers we studied is declining despite high annual survival rates, with low and variable breeding success probably causing the decline. Our results improve our understanding of the possible role of adult survival and breeding success in the decline of populations of small passerines in isolated reserves in the tropics.     

Morphometrics and the breeding biology of the Tahiti Petrel Pseudobulweria rostrata

The genus Pseudobulweria includes four extant species, three being classified as critically endangered, while the fourth (Tahiti Petrel P .  rostrata ) is near threatened. Information on the breeding biology of any species of the genus is scarce, even for the Tahiti Petrel. We monitored two Tahiti Petrel nests in New Caledonia and provide the first data on the breeding biology for the genus. Incubation lasts about 55 days, and young fledge at 110 days. Breeding in the southern lagoon of New Caledonia extends from September to April. Very strong interspecific competition for nest cavities occurs with Wedge-tailed Shearwaters Puffinus pacificus . We also document geographical variation in both biometry and breeding phenology over the Pacific breeding range.     

Intra-population variation in the diet of an avian top predator: generalist and specialist foraging in Great Black-backed Gulls Larus marinus

ABSTRACT

Capsule: Great Black-backed Gulls Larus marinus breeding on Skokholm, UK, fed predominantly on seabirds, rabbits, refuse, and marine prey, with the majority of pairs being dietary generalists, but with some specialist pairs.

Aims: To understand the significance of Great Black-backed Gulls as top predators on a small offshore island with internationally important numbers of breeding seabirds (Skokholm, UK) by quantifying their diet and to determine how this varies within the breeding season, to test for pair-level dietary specialization and to examine the consequences of dietary differences for reproductive performance.

Methods: Regurgitated pellets were collected and analysed from 26 breeding pairs on Skokholm during 2017 and related to breeding success.

Results: Analysis of 1035 pellets revealed that, overall, Great Black-backed Gulls fed on seabirds (48% – mostly Manx Shearwaters Puffinus puffinus), mammals (38% – mostly European Rabbits Oryctolagus cuniculus), anthropogenic waste (7%), and marine prey (7%). Diet varied among pairs with 18 (73%) generalist pairs and 7 (27%) specialist pairs (of which, 5 were bird specialists and 2 were mammal specialists). Diet also varied seasonally, but pair-level dietary diversity was repeatable through the breeding season. Dietary diversity did not covary with breeding success.

Conclusion: Great Black-backed Gulls are top predators on Skokholm. Variation in diet among pairs emphasizes that not all individuals contribute equally in terms of predation. Understanding the incidence of this variation has important ecological implications, particularly where apex predators may exert a strong top-down influence.     

An assessment of the breeding range,colony sizes and population of the Westland petrel (Procellaria westlandica)

Abstract

The Westland petrel (Procellaria westlandica) is an endemic New Zealand species and one of the very few burrowing seabird species still breeding on mainland New Zealand. It nests only on a series of coastal ridgelines near to Punakaiki on the West Coast of the South Island. Between 2002 and 2005, surveys were undertaken at 28 of the 29 known colonies. The area occupied by the colonies was 73 ha; most colonies had fewer than 50 burrows, but six colonies had 201–500 burrows and four colonies had more than 1000 burrows. We find that the current breeding range of Westland petrel and the location of individual colonies are similar to those reported in both the 1950s and 1970s. Based on total burrow counts at 28 colonies and burrow occupancy rates determined by annual monitoring, the annual breeding population is estimated to be between 2954 and 5137 breeding pairs.     

The Biology of a Subtropical Population of Halictus ligatus Say (Hymenoptera; Halictidae)

The ability of Manx shearwaters (Puffinus puffinus) to locate their nesting burrows at night was investigated using observation and experiments. Shearwaters walking to their burrows did so at random with respect to the wind direction, and did not vocalize, suggesting that visual cues are important to successful burrow homing. Experiments to test whether vision, audition or olfaction functioned in guiding birds back to burrows supported this conclusion.     

Trends in numbers of petrels attracted to artificial lights suggest population declines in Tenerife,Canary Islands

The secretive breeding behaviour of petrels makes monitoring their breeding populations challenging. To assess population trends of Cory’s Shearwater Calonectris diomedea, Bulwer’s Petrel Bulweria bulwerii and Macaronesian Shearwater Puffinus baroli in Tenerife from 1990 to 2010, we used data from rescue campaigns that aim to reduce the mortality of fledgling petrels attracted to artificial lights as proxies for trends in breeding population size. Despite increases in human population size and light pollution, the number of rescued fledglings of Cory’s Shearwater and Bulwer’s Petrel increased and remained stable, respectively, whereas numbers of rescued Macaronesian Shearwaters sharply declined. In the absence of more accurate population estimates, these results suggest a worrying decline in the Macaronesian Shearwater’s breeding population.     

Burrow and mate fidelity in the Little Penguin Eudyptula minor at Lion Island, New South Wales, Australia

Although both mate and nest fidelity are thought to exist in Little Penguins Eudyptula minor , few studies have statistically assessed the relationship between both types of fidelity and breeding success. Observations of the breeding biology of the Little Penguin were carried out between 1990 and 1998 at Lion Island, New South Wales, Australia. The existence of fidelity and the effect of breeding success on subsequent fidelity were assessed for this population. Strong evidence for the existence of nest and mate fidelity was found with high rates of return to the same burrow and mate being recorded for both sexes. For all years of the study, the average number of female and male birds faithful to their nest was 76 and 79%, respectively, with only two noted cases of intraseasonal burrow swapping. The rate of divorce varied widely between years, with a range of 0–40%. A marginal association of a log linear model showed a highly significant relationship ( P  < 0.001) between success of a clutch in one year and fidelity to a mate in the following year. Consequently, parents successfully raising a fledgling in one year were more likely to reunite in the following year than were pairs that attempted unsuccessfully to breed. Pairs failing to fledge chicks were much more likely to separate owing to the absence of one parent in the following year. We were unable to detect any association between breeding success in one year and subsequent change of nest in the next.     

Re-Examining Mortality Sources and Population Trends in a Declining Seabird: Using Bayesian Methods to Incorporate Existing Information and New Data

The population of flesh-footed shearwaters (Puffinus carneipes) breeding on Lord Howe Island was shown to be declining from the 1970''s to the early 2000''s. This was attributed to destruction of breeding habitat and fisheries mortality in the Australian Eastern Tuna and Billfish Fishery. Recent evidence suggests these impacts have ceased; presumably leading to population recovery. We used Bayesian statistical methods to combine data from the literature with more recent, but incomplete, field data to estimate population parameters and trends. This approach easily accounts for sources of variation and uncertainty while formally incorporating data and variation from different sources into the estimate. There is a 70% probability that the flesh-footed shearwater population on Lord Howe continued to decline during 2003–2009, and a number of possible reasons for this are suggested. During the breeding season, road-based mortality of adults on Lord Howe Island is likely to result in reduced adult survival and there is evidence that breeding success is negatively impacted by marine debris. Interactions with fisheries on flesh-footed shearwater winter grounds should be further investigated.     

High annual variability in reproductive success and survival of an Antarctic seabird,the snow petrel Pagodroma nivea

Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at Pointe Géologie Archipelago, Adélie Land, Antarctica between 1963 and 1990; 21 years of data on adult survival and 27 years of data on breeding success are available. The average age of first return and first breeding were 8.1 and 9.9 years respectively and there was no signifcant difference between the sexes. The overall breeding success averaged 51.3% and was very variable between years (21–80%). Breeding failure was mostly due to incubation failure and annual breeding success was negatively correlated with average snow falls in October–November and October–March. Breeding frequency was very low, averaging 52% of seasons during a reproductive lifetime. Good quality sites, with high occupancy rate and high breeding success were few in the study plots. Poor years in 1966–1967, 1976–1977 and 1983–1984, with low breeding success, very low proportions of nets with breeding attempts and high numbers of non-breeders, occurred 1 year after large-scale El Niño Southern Oscillation (ENSO) events. Snow petrels exhibited very low philopatry. Only 45 birds have been recovered in the study plots from a total of 1115 banded fledglings giving an estimated rate of return of 12.9% between fledging and 3 years old. Annual survival between 3 and 10 years was 91.4%. Annual adult survival (93.4%), though variable, was low during poor years of 1977–1978 and 1983–1984. Adult survival of males (94.7%) was not significantly different from that of females (93.9%). Over the study period, the population of Pointe Géologie was stable. Using the estimated parameters, a Leslie model gave a growth rate of 0.948%, which was probably compensated by immigration (5.7% per year). Restricted numbers of good-quality sites at the place of birth could have led young birds to prospect other colonies and could have selected low philopatry. High adult survival, strong site tenacity and capacity to spread breeding over a long lifetime are probably part of the adaptive strategy of this small fulmarine petrel facing highly variable environmental conditions.     

Status and structure of the griffon vulture (Gyps fulvus) population in Crete

Griffon vulture (Gyps fulvus) population surveys were conducted during 1996–2002 in the island of Crete (Greece) to document population status and structure. Fieldwork was carried out during the breeding period when birds could be monitored in their colonies. Total population size was estimated at 379 individuals (range = 341–417) with adult birds comprising 63%. The breeding population was estimated at 141 pairs, which were distributed on an average in 23 colonies per year (range = 16–30) while the mean number of breeding pairs that laid eggs was 98 (range= 64–126). Crete thus supports the largest insular population of the species in the world and hosts 70–80% of the breeding population of the species in Greece. Population density was estimated at 6.9 individuals/100 km², 2.6 breeding pairs/100 km² and 1.8 nesting pairs/100 km². The average home range of an occupied colony (i.e., breeding group) was estimated at ca. 204 km² producing a theoretical foraging range of 8 km radius around the breeding cliff. No trends in the total number of individuals and breeding pairs appeared to exist, although significant differences in population size of individual colonies occurred between the years. The majority of the population was concentrated in small-sized colonies, which showed a low occupancy rate. The number of abandoned sites and the colonization of new ones could represent a shift of breeding pairs to alternative colonies provoked by local food abundance and conspesific attraction.     

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.