BREEDING OF THE GREY WARBLER GERYGONE IGATA AT KAIKOURA, NEW ZEALAND

I studied the breeding of Grey Warblers Gerygone igata (Muscicapidae: Acanthizinae) in forest near Kaikoura, New Zealand, between 1976 and 1979. Only males sang and singing occurred all year. From late July to January pairs defended self-contained territories of 0·25–1·73 ha but they occupied larger home ranges when not breeding. Territorial adults were strictly sedentary all year. The average annual mortality of breeding adults was 18·5% and the predicted life-expectancy 4·9 years, which is remarkable in a bird weighing 6–7 g. The breeding season from first building to last fledging was six months long and it began early. Exceptionally, Grey Warblers may build and lay before the shortest day. As the season progressed warblers nested lower on average, both in absolute terms and relative to the tree nested in and canopy at the site. Warblers built in 7–27 days then delayed up to eight days before laying. Only females built and at no stage of breeding did males feed their mates. Both sexes fed the young. Grey Warblers laid for 15–16 weeks of the year and first clutches were laid asynchronously during 5–6 weeks. Eggs of a clutch appeared at two-day intervals and each egg weighed 1·5 g when fresh (23% of mean adult weight). Clutch size was nearly constant (mean 3·9, mode 4, range 3–5). The incubation period was 17–21 days (mean 19·5 days) and the nestling period 15–19 days (mean 17·2 days). On average the clutch hatched over 1·4 days, even though incubation commenced with the laying of the last egg. Nestlings reached maximum weight on Days 13–14 on average and then receded in weight by 4%, apparently through loss of water. All healthy nestlings exceeded mean adult weight during development by up to 39%. Nestlings from broods of two were at first lighter on average than those from larger broods, but in the second half of the nestling period twins were significantly the heaviest. Grey Warblers were fed for 28–35 days after fledging and they survived well while dependent on parents. Fledglings dispersed up to 3 km or more at independence and only 5% per annum joined the breeding population. Of nests that received eggs, 42% produced at least one fledgling. On average each breeding adult raised 2·0 fledglings per season. Of 265 eggs in 73 nests 70% hatched and 38% produced fledglings. Of 185 nestlings 54% fledged. Probably the main cause of mortality of eggs and nestlings was predation by introduced rodents and mustelids. Grey Warblers raise two small broods slowly during a long breeding season, rather than investing in one large quickly-reared brood. In New Zealand's mild climate the warbler's food supply may not decline severely in winter, and the population of warblers may remain so close to the limit set by food that extra for breeding is hard to obtain. Thus the breeding strategy may be adapted to a restricted food supply.     

Breeding success of New Zealand pigeons (

A 55 ha remnant of coastal native forest at Wenderholm Regional Park (near Auckland) was selected as the site for a pilot experiment to test if rat control could yield measurable benefits in increased productivity of New Zealand pigeons. Talon 50WB poison baits were used to reduce rat numbers over the summer of 1992-93. Pigeon breeding success was significantly higher (5 fledglings from 11 nests) than in preceding summers without rat control (no fledglings from 27 nests).     

Brood-parasitism by the Shining Cuckoo Chrysococcyx lucidus at Kaikoura, New Zealand

For three seasons starting in 1976 I studied the breeding of Shining Cuckoos Chrysococcyx lucidus in forest near Kaikoura, New Zealand. There is no evidence that the cuckoo parasitizes any host on mainland New Zealand other than the Grey Warbler Gerygone igata. A nestling cuckoo returned to within 1 km of its natal site in a subsequent breeding season, presumably after migrating beyond New Zealand. Empirical and theoretical estimates of the area occupied by Shining Cuckoos while breeding are given. Cuckoos near Kaikoura laid during ten weeks, the modal week of laying following seven weeks after the presumed peak of arrival of birds in New Zealand. First clutches of the host escaped parasitism because they were laid before most cuckoos arrived. Parasitized clutches received one cuckoo egg which replaced a host's egg. It was laid before, just after or long after the host began incubating, and mimicry was lacking. Cuckoo eggs, which were about 8% of the adult cuckoo's weight, hatched in 14–17 days. The frequency of parasitism near Kaikoura was 55% of late clutches (n = 40).
At 3–7 days old, nestling Shining Cuckoos evicted from the nest all other contents. The nestling period was at least 19 days. Growth in weight followed a logistic curve and the equation is given. Just over half the cuckoo eggs produced fledglings. The effect of brood-parasitism on the Grey Warbler's productivity was small. Only 17% of late warbler eggs, and late eggs only, were prevented by parasitism from yielding fledglings. Late laying by some Shining Cuckoos (relative to the host's incubational cycle), and late eviction, often led to brief inter-specific competition among nestlings for food. The brief coexistence of young Warblers and Cuckoos in the nest may explain the apparent mimicry by newly-hatched Shining Cuckoos of the host's young.     

Nesting densities,productivity and survival of breeding Whimbrel Numenius phaeopus in Shetland

Between 1986 and 1988 data on the nesting densities, productivity, and survival of breeding Whimbrel Numenius phaeopus were collected from 5 study sites in the Northern Isles of Shetland. Nesting densities on sites varied between 11 and 21 pairs per 100 ha. Few studies elsewhere have recorded such high densities of nesting Whimbrel as those on certain sites used in the present study. Each breeding pair produced an average of between 0.75 and 0.91 fledglings per year. Productivity varied considerably between different study sites however, primarily because of differences in the survival rate of chicks between hatching and fledging (ranging from 3% to 55% in one year). The annual survival rate of breeding adults was at least 89%. Considering adult survival in relation to overall productivity, it appears likely that the production of fledglings from study sites is in excess of that required to balance adult mortality. This result is consistent with the current increase of the Whimbrel population in Shetland.     

Breeding success and chronology of Wood Storks Mycteria americana in northern and central Florida, U.S.A.

The breeding success and chronology of Wood Storks Mycteria americana were studied at eight colonies in northern and central Florida during 1981–1985. Mean ± s.d. clutch size for all colony-years was 3.07 ± 0.56 (n = 2694 nests), with three-egg clutches (72%) most frequent. Mean clutch size among all colonies and years ranged from 2.73 ± 0.55 to 3.41 ± 0.61. Many colonies exhibited significant negative trends in clutch size with, hatching date because of a proportional decrease in four-egg clutches later in the season. Mean colony clutch size was not correlated with nest numbers, nesting density or mean hatching date within most years. Mean ± s.d. number of fledglings for all colonies and years was 1.29 ± 1.16 fledglings per nest (n = 2812 nests). Mean annual fledging rates in colonies ranged from 0 (colony failed) to 2.66 fledglings per nest. Most breeding failure occurred prior to egg hatching, and the second highest mortality occurred between hatching and 2 weeks of age. Four-egg clutches fledged more storks than three-egg clutches, which in turn were more successful than two-egg clutches. However, all clutch sizes showed similar fledgling per egg rates. The seasonal decline in productivity was associated proportionally with smaller clutch sizes later in the breeding season. An increase in mean hatching date was correlated with an increase in latitude. There was greater within-year breeding synchrony among colonies than interyear breeding synchrony within each colony. Breeding synchrony was not correlated with mean hatching date, latitude, longitude, nest numbers or nesting density.     

Influence of climate on Bonelli's eagle's (Hieraaetus fasciatus V. 1822) breeding success through the Western Mediterranean

Aim To assess the impact of certain climatic variables on the breeding success of some populations of Bonelli's eagle (Hieraaetus fasciatus V. 1822) throughout its latitudinal distribution range, in order to account for recent and differential declines in populations. Location Western Mediterranean, from southern Morocco to southern France. Methods Seven populations were considered for the latitudinal distribution range of the species. Data from 1052 breeding attempts were taken from the literature and, for each population, breeding success was measured as the mean number of fledglings per pair per year. Breeding success, as a dependent variable, was related to five geographical and climatic variables (latitude, mean annual temperature, mean minimum temperature of the coldest month, mean maximum temperature of the hottest month and mean annual precipitation) as independent variables, through some regression models, which take into account the multicolinearity of the variables. Results All the analyses agreed that average annual temperature was an important factor associated with the breeding success of the species in each region, and accounted for up to 97% of the variance of the breeding success throughout a latitudinal gradient in the study area. Main conclusions The low breeding success of the northern populations (probably because of climatic constraints) and the tendency of juveniles to disperse southwards, diminishes recruitment in those populations. Therefore, as human pressure and habitat destruction causes high adult and pre‐adult mortality of the species throughout its entire latitudinal range, disturbances in the northern populations have more profound effects, thereby explaining observed population declines.     

Can predation by invasive mice drive seabird extinctions?

The house mouse, Mus musculus, is one of the most widespread and well-studied invasive mammals on islands. It was thought to pose little risk to seabirds, but video evidence from Gough Island, South Atlantic Ocean shows house mice killing chicks of two IUCN-listed seabird species. Mouse-induced mortality in 2004 was a significant cause of extremely poor breeding success for Tristan albatrosses, Diomedea dabbenena (0.27 fledglings/pair), and Atlantic petrels, Pterodroma incerta (0.33). Population models show that these levels of predation are sufficient to cause population decreases. Unlike many other islands, mice are the only introduced mammals on Gough Island. However, restoration programmes to eradicate rats and other introduced mammals from islands are increasing the number of islands where mice are the sole alien mammals. If these mouse populations are released from the ecological effects of predators and competitors, they too may become predatory on seabird chicks.     

Demography of the Seychelles Black Paradise-flycatcher: considerations for conservation and reintroduction

The Seychelles Black Paradise-flycatcher Terpsiphone corvina is currently listed as Critically Endangered, on the basis of small population and restricted range. Currently, there is only one self-sustaining population comprising c. 150–200 individuals on the 10km² island of La Digue (Republic of Seychelles, western Indian Ocean), and consequently the creation of additional island populations has been identified as essential to improve its conservation status. We quantified the annual breeding success, adult mortality and juvenile recruitment of the flycatcher on La Digue, monitored tri-weekly over a two-year period (June 1999–June 2001), to determine factors affecting population demographics and assess the implications for the reintroduction of populations to other islands. A total of 267 breeding attempts were recorded with c. 45% of the documented world population of pairs systematically monitored each year. On average, pairs attempted to breed three times in a 12-month period (range 0–6), although not all attempts were successful. Breeding success was consistently low between years: 62% of nests (controlling for observation time) and 17–19% of study territories failed to produce any fledglings in each respective 12-month period. Daily failure rates were generally higher during incubation than in the nestling period. Nests close to the forest edge were more likely to fail. The majority (143) of the 152 failed nesting attempts were consistent with depredation and were characterised by the disappearance of nest contents and sometimes by egg and chick remains and the disappearance of the adult female. Predators were identified at 13 nests: five (3.3%) were depredated by birds, and eight (5.2%) were depredated by mammals and/or reptiles: Rattus sp. were confirmed as predators. Video monitoring conducted at 14 nests also confirmed the endemic Seychelles bulbul Hypsipetes crassirostris as a nest predator. Adult mortality was c. 21% and alien predators (Rattus sp. and Felis cattus) were identified in causing adult mortality. However, in the majority of cases, reasons for adult mortality were unknown. Of the 52 marked fledglings that could have been recruited to the plateau population, 45% (23) were observed away from their natal territory c. 9–10 months after fledging, 25% (13) of which were confirmed as territory-holding individuals. We present a simple model to predict population growth using the above data, and discuss implications for the creation of additional self-sustaining populations on suitable islands.     

A comparative study of nerve healing in adult, neonatal, and fetal rabbits.

This experiment quantitatively compared the human equivalent of a nerve repair following surgical division in the fetal, adult, and early childhood period of development using a rabbit as an experimental animal model. Twelve time-dated pregnant New Zealand White rabbits at 24 days' gestation (term = 31 days) underwent hysterotomy; one hind limb was delivered through the uterine opening. The sciatic nerve was divided and repaired by primary neurorrhaphy using two 11-0 epineural sutures. Sciatic nerve repair was also performed in 10 neonatal and 10 adult New Zealand White rabbits. Following repair, each group was assessed using electromyography examination, measuring distal motor latency and amplitude at 1, 2, 3, and 4 months postrepair. There was no difference in any of the groups in distal motor latency. The amplitude rose incrementally in all groups, and the fetal group had significantly higher amplitudes (p < 0.02) at 1, 2, 3, and 4 months in comparison with the adult group. There was no statistically significant difference between fetal and neonatal nerve repairs at any of the time periods. At the completion of the study, the nerve repair sites were harvested for histologic estimation of mean myelinated fiber density and fiber diameter distribution distal and proximal to the repair site. A greater percentage of myelinated axons crossed the repair site in the fetal group (83 percent) in comparison with the adult group (63 percent) (p < 0.03). Our study also demonstrated significant increases in the number of larger myelinated fibers crossing the repair site in comparison with the neonatal and adult groups (p < 0.04). This study found that fetal nerve healing following surgical repair is superior to that found in adult animals and results in a higher number of larger myelinated fibers crossing the repair site in comparison with adult and neonatal repairs.     

Breeding success of the Great Bustard Otis tarda in Zamora Province, Spain, in 1984

Great Bustards are still fairly abundant (5-2 nests/1000 ha) in Zamora. Overall fecundity was high (92% of adult females attempt to nest; 2–47 eggs/clutch; 89% egg fertility), but pre- and post-hatching mortality were also high (50% of eggs laid; 57% of nestlings hatched), due mainly to agricultural machinery but also to natural predators. Calculated annual yields per 100 adult females were: 227 eggs, 102 hatchlings, 44 fledglings. Production of 44 fledglings/y could sustain a stable adult population (mortality approx. 8%/y) if mortality of immatures is not more than 18–22%/y.     

Neonatal mortality in New Zealand sea lions (Phocarctos hookeri) at Sandy Bay, Enderby Island, Auckland Islands from 1998 to 2005

As part of a health survey of New Zealand sea lions (Phocarctos hookeri) on Enderby Island, Auckland Islands (50 degrees 30'S, 166 degrees 17'E), neonatal mortality was closely monitored at the Sandy Bay colony for seven consecutive years. Throughout the breeding seasons 1998-99 to 2004-05, more than 400 postmortem examinations were performed on pups found dead at this site. The primary causes of death were categorized as trauma (35%), bacterial infections (24%), hookworm infection (13%), starvation (13%), and stillbirth (4%). For most pups, more than one diagnosis was recorded. Every year, two distinct peaks of trauma were observed: the first associated with mature bulls fighting within the harem and the second with subadult males abducting pups. In 2001-02 and 2002-03, epidemics caused by Klebsiella pneumoniae increased mortality by three times the mean in nonepidemic years (10.2%). The increased mortality was attributed directly to acute suppurative infection due to the bacterium and also to an increase in traumatic deaths of debilitated pups. Parasitic infection with the hookworm Uncinaria spp. was a common finding in all pups older than three weeks of age and debilitation by the parasite may have contributed to increased susceptibility to other pathogens such as Klebsiella sp. or Salmonella sp. This study provides valuable quantitative data on the natural causes of neonatal mortality in New Zealand sea lions that can be used in demographic models for management of threatened species.     

Using miniaturized radiotelemetry to discover the breeding grounds of the endangered New Zealand Storm Petrel Fregetta maoriana

Identification of breeding sites remains a critical step in species conservation, particularly in procellariiform seabirds whose threat status is of global concern. We designed and conducted an integrative radiotelemetry approach to uncover the breeding grounds of the critically endangered New Zealand Storm Petrel Fregetta maoriana (NZSP), a species considered extinct before its rediscovery in 2003. Solar‐powered automated radio receivers and hand‐held telemetry were used to detect the presence of birds on three island groups in the Hauraki Gulf near Auckland, New Zealand. At least 11 NZSP captured and radiotagged at sea were detected at night near Te Hauturu‐o‐Toi/Little Barrier Island with the detection of an incubating bird leading to the discovery of the first known breeding site for this species. In total, four NZSP breeding burrows were detected under mature forest canopy and three adult NZSP and two NZSP chicks were ringed. Telemetry data indicated NZSP showed strong moonlight avoidance behaviour over the breeding site, had incubation shifts of approximately 5 days and had a breeding season extending from February to June/July, a different season from other Procellariiformes in the region. Radiotelemetry, in combination with rigorously collected field data on species distribution, offers a valuable technique for locating breeding grounds of procellariiform seabirds and gaining insights into breeding biology while minimizing disturbance to sensitive species or damage to fragile habitat. Our study suggests an avenue for other breeding ground searches in one of the most threatened avian Orders, and highlights the general need for information on the location of breeding sites and understanding the breeding biology in data‐deficient birds.     

Life history traits contribute to decline of critically endangered lizards at Macraes Flat, Otago

To measure the costs and benefits of an aerial 1080 possum control operation to kereru and kaka in Whirinaki Forest Park, individuals of both species were radio-tagged from October 1998 to June 2002. We monitored birds in one treatment and one non-treatment study area to compare toxin-related mortality, nesting success and survival. The poison operation involved the spreading of non-toxic carrot baits on 1 May 2000, and the toxic baits on 17/18 May 2000. Possums and rats were moderately abundant in both study areas prior to the poison operation, but afterwards few possums and rats remained in the treatment area. All radio-tagged kaka and kereru in the treatment area survived the poison operation. No radio-tagged kereru and too few radio-tagged kaka bred in either study area during the 2000/01 nesting season to show whether reduced possum and rat populations would enable the birds to nest more successfully. A reduction in possum and rat densities in the non-treatment area (and an increase in densities in the treatment area) during 2001/02 meant that during the second nesting season after the poison operation, possum and rat densities were similar in the two study areas. The nesting effort and success of kaka and kereru is described for each of four nesting seasons, with the main cause of nesting failure for both species being predation. While no radio-tagged adult male kaka died during the study, 6 females did, giving them a mean life expectancy of 9.5 years. In contrast, radio-tagged adult kereru suffered high mortality, resulting in a mean life expectancy of just 1.5 years. Predation by introduced mammalian predators was the main cause of mortality of kaka eggs, chicks, fledglings and adult females, and of kereru eggs, chicks, fledglings and adults. Effective control of introduced mammalian predators, including control by aerial 1080 operations, just before mast fruiting events that invariably promote prolific kaka and kereru breeding, should benefit these bird populations.     

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.     

Targeting efforts in rescue programmes mitigating light-induced seabird mortality: First the fat,then the skinny

Oceanic conditions determine food availability to seabirds and affect seabird reproductive parameters, such as breeding success, chick growth, and survival rates. In seabirds, juvenile survival at sea is positively correlated with body condition at fledging. In addition, in several seabird species, especially petrels and shearwaters (Order Procellariiformes), fledglings are disoriented by artificial lights during their maiden flights from their nests to the sea, and many of them fall on the ground and are rescued by volunteers to mitigate light-induced mortality. We studied variations in body condition and body mass in Cory’s Shearwater (Calonectris borealis) fledglings on Faial Island (Azores), using data from rescue campaigns conducted over 15 consecutive years. We checked if body condition was related to oceanic conditions. Late fledglings were in poorer body condition than early ones. Significant inter-annual variations in fledging body condition were observed. These were not related to North Atlantic Oscillation fluctuations. However, annual mean fledgling body condition was positively correlated with sea surface temperatures measured in the autumn of the previous year in a northern feeding area used by adults throughout the breeding season. This study broadens our knowledge of the factors affecting fledgling body condition in Procellariiformes and provides advice to better manage the rescue campaigns. Optimal management of rescue campaigns is essential given the limited economic or human resources allocated to such an aim.     

Evaluating Habitat Quality for the Dusky Flycatcher

Abstract: We studied the dusky flycatcher (Empidonax oberholseri) at 8 sites in central Idaho, USA, in 2002 and 2003 to examine relationships among vegetation cover, density of breeding conspecifics, and indicators of habitat quality. Number of breeding territories and number of fledglings per hectare were positively associated, suggesting that the dusky flycatcher experienced increased reproductive success where it bred at the highest densities. However, the relationships between nesting success, annual reproductive success, number of fledglings per hectare, and amount of understory cover showed substantial annual variation. Nesting success did not differ significantly across sites or between years. Both reproductive success, expressed as young produced per hectare (range: 0.34–3.09 in 2002 and 0.79–3.82 in 2003) and young produced per nesting attempt (range: 0.71–2.78 in 2002 and 1.11–3.10 in 2003), differed across study sites in each year. Mean clutch size did not differ significantly among sites or years. Mean egg weight showed significant variation across some sites within years and was associated negatively with the 3 measures of reproductive success in 2002, although small sample sizes prevented reliable inference about the appropriateness of this measure as an indicator of habitat quality. Mean clutch size and mean egg weight were not associated with vegetation cover variables. Thus, dusky flycatcher reproductive success showed inconsistencies with individual vegetation measurements at the site scale. Forest managers who use vegetation treatments to increase amounts of understory shrub cover (e.g., by removing portions of the overstory conifer canopy) should increase densities of this species and, in turn, increase number of fledglings produced, but these responses appear to be better measured at the territory or nest scales than at the stand or site scales.     

Predation and other factors currently limiting New Zealand forest birds

Holdaway (1989) described three phases of historical extinctions and declines in New Zealand avifauna, the last of which (Group III, declining 1780?1986) was associated with European hunting, habitat clearance, and predation and competition from introduced European mammals. Some forest bird species have continued to decline since 1986, while others have increased, usually after intensive species-specific research and management programmes. In this paper, we review what is known about major causes of current declines or population limitation, including predation, competition for food or another resource, disease, forest loss, and genetic problems such as inbreeding depression and reduced genetic variation. Much experimental and circumstantial evidence suggests or demonstrates that predation by introduced mammals remains the primary cause of declines and limitation in remaining large native forest tracts. Predation alone is generally sufficient to explain the observed declines, but complex interactions between factors that vary between species and sites are likely to be the norm and are difficult to study. Currently, the rather limited evidence for food shortage is mostly circumstantial and may be obscured by interactions with predation. Climate and food supply determine the number of breeding attempts made by herbivorous species, but predation by introduced mammals ultimately determines the outcome of those attempts. After removal of pest mammals, populations are apparently limited by other factors, including habitat area, food supply, disease or avian predators. Management of these, and of inbreeding depression in bottlenecked populations, is likely to assist the effectiveness and resilience of management programmes. At the local or regional scale, however, forest area itself may be limiting in deforested parts of New Zealand. Without predator management, the number of native forest birds on the New Zealand mainland is predicted to continue to decline.     

Attraction of petrels to artificial lights in the Canary Islands: effects of the moon phase and age class

The extent and intensity of artificial night lighting has increased with urban development worldwide. The resulting light pollution is responsible for mortality among many Procellariiformes species which show nocturnal activity on their breeding grounds. Here, we report light‐induced mortality of Procellariiformes during a 9‐year study (1998–2006) on Tenerife, the largest island of the Canary archipelago. A total of 9880 birds from nine species were found grounded, the majority being Cory’s Shearwaters Calonectris diomedea (93.4%). For this species the majority of grounded birds were fledglings (96.4%), which fall apparently while leaving their nesting colony for the first time; for the smaller species (storm‐petrels) adult birds were more often grounded than fledglings. For almost all species, grounding showed a seasonal pattern linked with their breeding cycle. Certain phases of the moon influenced grounding of Cory’s Shearwater, with the extent of grounding being reduced during phases of full moon. The percentage of fledglings attracted to lights in relation to the fledglings produced annually varied between species and years (0–1.3% for the Madeiran Storm‐petrel Oceanodroma castro; 41–71% for Cory’s Shearwater). Mean adult mortality rates also varied between species (from 0.4% for the European Storm‐petrel Hydrobates pelagicus and the Cory’s Shearwater, to 2.3% for the Manx Shearwater Puffinus puffinus). Here we show that light‐induced mortality rates are of concern, at least for petrels and small shearwaters. Thanks to efforts involving civil cooperation, 95% of grounded birds have been returned to the wild. To minimize the impact of artificial lights on petrels we recommend several conservation measures: continuing rescue campaigns, alteration of light signatures and reduction of light emissions during the fledging peaks. Furthermore, we recommend that a monitoring program for petrel populations be implemented, as well as further studies to assess the fate of released fledglings and continued research to address why petrels are attracted to lights.     

Allometric scaling and Bayesian priors for annual survival of birds and mammals

Allometric theory predicts that instantaneous mortality rates scale with body mass with a negative quarter power. Such a relationship would mean that the survival rate of one species is partly predictable from the survival rate of other species. We develop allometric regression models for annual adult survival of birds and mammals, using data collected from the literature. These models conform to the predictions of the allometric theory; the value of negative one-quarter for the scaling parameter is within the 95% credible interval, which is [-0.31, -0.10] for birds and [-0.35, -0.15] for mammals. The predictions are very well supported when evaluated using an independent set of data. The regression models can be used to provide objective and informative Bayesian priors for annual adult survival rates of birds and mammals or to act as a point of comparison in new studies.     

Multi-species territoriality and dynamic of neotropical forest understorey bird flocks

1. Eleven contiguous mixed-species bird flocks, with colour-banded individuals, were monitored continuously during 3 years in a 132-ha study area of primary rainforest in French Guiana.
2. Flock members were divided into six categories according to their flocking propensity and occurrence: 10 core or permanent species and 56 regular, occasional or incidental species. Each core species was represented by a single breeding pair with their fledglings and extra 'floaters' (unmated subadults and adults).
3. Flock home ranges overlapped slightly, but were communally defended by all core species in areas of overlap. Their size varied from 3·2 to 14·3 ha and was inversely correlated with vegetation density, but not flock size or species composition.
4. Flock number, size and composition, as well as boundaries were highly stable between seasons and years. Each flock had a single permanent gathering site and bathing site in late afternoon, the latter sometimes shared by 2–3 flocks.
5. Core species produced 0·18–0·73 fledglings per pair per year, which stayed in their natal flock for 200 to over 421 days. Then, these individuals usually moved between two and six different flocks, sometimes for up to 3 years, before finding a mate and a flock where they could settle and breed. Once breeding, they probably remained for life in the same flock. The mean annual survival rate was at least 0·75.
6. This highly evolved and stable organization, associated with a low breeding success and high survival rate was a critical factor maintaining low species density, delayed reproduction and a proportion of floating individuals buffering population fluctuations.
7. These social groups with their multi-species territoriality and co-evolved roles of flock members were similar to those described elsewhere in South America. They seem to be a general phenomenon in neotropical lowland rainforests.