The conservation of critically endangered flightless birds in New Zealand

The current status of Kakapo Strigops habroptilus and Takahe Porphyrio mantelli is described along with recent developments in programmes for their conservation. Both species were (at different times) thought to be effectively extinct, and both have been temporarily reprieved by the discovery of new populations. Population declines have continued, with Kakapo now reduced to less than 50 individuals and Takahe to about 150. Kakapo are especially at risk; 87% of the remaining birds are over 14 years old and only 17 females are known. Research on relict populations of both species has identified predation and competition from introduced mammals as major threats. Both species have high rates of egg infertility and low survival of young. Increasingly intensive management of both Kakapo and Takahe over recent years has included translocation to predator-free island refuges, supplementary feeding to encourage breeding, clutch manipulation, captive rearing and predator control. All known Kakapo have now been transferred to three island refuges, where the overall rate of population decline has slowed and supplementary feeding has apparently encouraged more frequent breeding attempts. Takahe conservation has concentrated largely on attempts to increase the population in Fiordland, New Zealand, through clutch manipulation and release of captive-reared young, but birds have also been released on four islands, which now hold 19% of the total population. The relict Fiordland populations of both Kakapo and Takahe were confined to apparently suboptimal habitat. Both species have successfully adapted to novel environments and foods when translocated, and the populations which now exist present improved opportunities for intensive management using a range of conservation techniques to enhance productivity and survival. Recent population trends of Kakapo and Takahe are reconstructed, and the contribution of research to their conservation is reviewed.     

Daughters on request: about helpers and egg sexes in the Seychelles warbler

The Seychelles warbler (Acrocephalus sechellensis) was an endangered endemic of the Seychelles islands where, until 1988, the entire population of ca. 320 birds was restricted to the one island of Cousin Island (29 ha). Additional breeding populations were successfully established on the islands of Aride (68 ha, 1988) and Cousine (26 ha, 1990) and now with the existence of ca. 2000 warblers on three islands the conservation status of the warbler has improved from endangered to vulnerable. Emigration from the island is extremely rare, so birds that disappeared were known to have died. Almost every bird on Cousin Island has been individually colour ringed and monitored throughout all breeding attempts during a 17-year period (1985-2002; total ca. 2400 birds). These birds were also blood sampled for molecular parentage and sex analyses. Therefore the lifetime reproductive success of many birds is known. Although warblers can breed independently in their first year, some individuals remain in their natal territory as subordinates, and often help by providing nourishment to non-descendant offspring. The frequency of 'helping' is affected by habitat saturation and variation in territory quality (insect prey availability). The long-term benefits of helping are higher for daughters than for sons, and it is therefore no wonder that most helpers are daughters from previous broods. Furthermore, on low-quality territories breeding pairs raising sons gain higher fitness benefits than by raising daughters, and vice versa on high-quality territories. Female breeders adaptively modify the sex of their single-egg clutches according to territory quality: male eggs on low quality and female eggs on high quality. The Seychelles warbler is a beautiful example of behavioural and life-history adaptations to restricted circumstances.     

Demography of takahe (

The last remaining natural population of the critically endangered takahe (Porphyrio hochstetteri) is confined to the Murchison Mountains in Fiordland, New Zealand. This mainland population contains about half of the c.?300 remaining takahe and benefits from one of the costliest recovery programmes in the country. Management activities include deer culling, stoat trapping, nest manipulation (e.g. removal of infertile eggs) and captive rearing of chicks. To determine what effect this intensive management has had on the recovery of the Fiordland takahe population, we modelled 25 years of survival and breeding success data as a function of environmental factors (e.g. precipitation, temperature, beech seedfall, tussock flowering) and specific management activities (egg manipulation, captive rearing, stoat control). Annual adult survival, estimated at 78% (credibility interval (CI) = 75?81%), is significantly increased to 85% (76?92% CI) in presence of stoat trapping, but is still low relative to introduced takahe populations on offshore islands and other large New Zealand bird species in predator-free environments. This suggests that the harsh environment of Fiordland may be suboptimal habitat in terms of survival for takahe. On the other hand, reproductive output in Fiordland is similar to that for introduced island populations, and is improved even further by management. Number of chicks per pair fledged with nest manipulation and captive rearing is estimated at 0.66 compared with 0.43 in the absence of nest management. The difference is explained mainly by low fledging success in the wild, especially for double clutches, which justifies the practice of removing one of two viable eggs and transferring it to a captive-rearing facility. The results of this study indicate that current management activities such as stoat trapping and captive rearing have a strong positive effect on population growth of the Murchison Mountains takahe population.     

Variation in breeding success among reintroduced island populations of South Island Saddlebacks Philesturnus carunculatus carunculatus

South Island Saddlebacks Philesturnus carunculatus carunculatus were once found throughout the South Island of New Zealand, but by the early 1960s were confined to the island of Big South Cape, in the extreme south of the country. All subsequent reintroduced populations of South Island Saddlebacks are derived from 36 surviving birds from this relict population. The aim of this study was to compare the breeding success of three recently reintroduced populations of Saddlebacks relative to their distance from, and habitat similarity to, the relict population. The three study islands show a latitudinal cline with Ulva, Breaksea and Motuara Islands located 60, 190 and 810 km north of Big South Cape, respectively. Saddlebacks on Ulva and Breaksea appeared to prefer to establish breeding territories in coastal scrub, the dominant habitat feature of Big South Cape. The area of coastal scrub habitat was much smaller on Motuara, where breeding territories were instead scattered through broadleaf forest habitat. Nesting success, calculated using Mayfield's method, was significantly greater on Ulva (73%) than on Breaksea (32%) or Motuara (19%) owing primarily to higher egg fertility and hatching success. Although egg failure rates were highest on Motuara, the island least similar to Big South Cape, they were also relatively high on Breaksea where the habitat was similar to Ulva and Big South Cape. Therefore, the results only partially support the hypothesis that nesting success should decrease with increasing habitat difference associated with increasing latitudinal distance from the source population. The data from this 1-year study lay the groundwork for examining further hypotheses on the effects of reintroducing endangered species outside their contemporary range, but within their historical range.     

Spatial distribution and settlement strategies in willow ptarmigan

In heterogeneous landscapes individuals select among several habitat patches. The fitness rewards of these choices are assumed to play an important role in the distribution of individuals across landscapes. Individuals can either use environmental cues to directly assess the quality of breeding sites, or rely on social cues to guide the settlement decision. We estimated the density of adult birds and per capita reproductive success of willow ptarmigan over 5–15 years in 42 survey areas, nested within 5 spatially separated populations in south-central Norway. Our aims were to (1) examine spatial and temporal patterns of variation in densities of adult birds (i.e., the breeding densities) and reproductive success (juveniles/pair) measured in autumn and (2) evaluate which habitat distribution model best described the distribution of willow ptarmigan across heterogeneous mountain landscapes. Variation in density of adult birds was primarily attributable to variation between survey areas which could arise from spatial heterogeneity in adult survival or as a consequence of spacing behavior of juveniles during the settlement stage. In contrast, reproductive success was more variable between years and did not vary consistently between survey areas once year effects were accounted for. The lack of any relationship between the density of adult birds and reproductive success supported the predictions of an ideal free distribution (IFD), implying that within years, the mean reproductive success was approximately equal across survey areas. However, analysis based on Taylor's power law (i.e., the relationship between logarithms of spatial variance and mean density of adult birds) suggested that aggregation was stronger than expected under IFD. This implies that the relative change in density of adult birds was larger in areas with high mean densities than in areas with low densities. The exact mechanisms causing this statistical pattern are unclear, but based on the breeding biology of willow ptarmigan we suggest that yearlings are attracted to areas of high densities during the settlement period in spring. Our study was conducted during a period of low overall density and we suggest that this pattern might be particular to such situations. This implies that the presence of conspecifics might represent a cue signaling high adult survival and thus high habitat quality.     

Assessing the reproductive consequences of mate retention and pair bond duration in Thorn-tailed Rayadito (Aphrastura spinicauda), a short-lived,socially monogamous neotropical bird

The adaptive value of mate retention has been studied in several socially monogamous birds but evidence of reproductive benefits for short-lived species is inconclusive. Most studies come from northern latitudes but more research on tropical birds is needed, as these species typically show higher survival rates and longer pair bonds than those from temperate regions. We gathered data on the reproductive biology of a subtropical, isolated population of Thorn-tailed Rayadito Aphrastura spinicaudaduring 2008–2017 to evaluate the reproductive consequences of mate retention. We examined data from 243 breeding attempts made by 159 breeding pairs. We found that ~30% of all breeding pairs bred together during at least two consecutive years, and some were mated for 6 years. The main cause of pair dissolution was mate loss, not divorce. Mixed-effects models provided moderate evidence for positive effects of mate retention and successive remating on reproductive success. Newly formed pairs laid eggs later and had slightly smaller clutches than remated pairs. Furthermore, clutch size seemed to increase with successive remating. Overall, our results suggest that newly formed pairs are less efficient in reproduction and that minor yearly reproductive benefits of mate retention might accumulate for birds that are able to breed with the same partner over many years. Because breeding habitat is limited in our study population, Thorn-tailed Rayaditos could benefit from remating if the number of individuals that can breed exceeds the number of available breeding positions. Profitable long-term pair bonds might be more frequent in tropical birds and therefore more studies are needed to assess the prevalence of remating-mediated effects on reproduction in relatively short-lived monogamous species breeding in tropical regions.     

A cross-fostering experiment between the endangered takahe (

New Zealand's avifauna is characterised by a variety of endemic, often flightless, birds most of which are critically endangered. One of these, the takahe, is a large flightless rail which has been reduced to one population of 115 birds in its natural alpine habitat plus 52 others introduced on four small offshore islands. By contrast the takahe's closest extant relative, the pukeko, has been highly successful since its invasion of New Zealand within the past 800 years. This paper summarises results of a pilot study in which takahe eggs were cross-fostered to pukeko nests on Mana Island in order to increase the number of juveniles produced by each pair of takahe. Over two seasons, 67% (8/12) of the cross-fostered eggs hatched successfully with 25% (2/8) of the resulting young surviving to one year of age. These results were not significantly different from 42% (5/12) and 40% (2/5) hatching and fledging success of takahe-reared eggs from the same clutches. Low fledging success of cross-fostered chicks may reflect poor quality of takahe eggs per chicks rather than poor parental care by the pukeko foster parents, as hatching success of all parent-reared takahe eggs on Mana Island was only 22% (5/23) over the course of this research.     

Quantifying and managing the loss of genetic variation in a free-ranging population of takahe through the use of pedigrees

Pedigree analysis has clear benefits for the genetic management of threatened populations through the evaluation of inbreeding, population structure and genetic diversity. The use of pedigrees is usually restricted to captive populations and few examples exist of their exclusive use in managing free-ranging populations. One such example is the management of the takahe (Porphyrio hochstetteri), a highly endangered, flightless New Zealand rail at risk from introduced mammalian predators and habitat loss. During the 1980’s and 90’s, as part of the takahe recovery programme, birds were translocated from the sole remnant population in Fiordland to four offshore islands from which introduced predators had been eradicated. The subsequent “island” population, now numbering 83 and thought to be at carrying capacity, has been closely monitored since founding. Detailed breeding records allow us to analyse the island pedigree, which is up to 7 generations deep. Gene-drop analysis indicated that 7.5% of genetic diversity has been lost over the relatively short timeframe since founding (2.1 generations on average; total genetic founders = 31) due to both a failure to equalise founder representation early on and subsequent disproportionate breeding success (founder equivalents = 12.5; founder genome equivalents = 6.6). A high prevalence of close inbreeding will have also impacted on genetic diversity. Predictions from pedigree modelling suggest that 90% genetic diversity will be maintained for only 12 years, but by introducing a low level of immigration from the Fiordland population and permitting the population to grow, 90% GD could be maintained over the next 100 years. More generally, the results demonstrate the value of maintaining pedigrees for wild populations, especially in the years immediately after a translocation event.     

Agonistic display and spacing in the black-headed gull, Larus ridibundus

Black-headed gulls nesting on islands in a marsh habitat had a higher breeding success than those nesting on the periphery of the colony. Island birds maintained close inter-nest distances whereas peripheral nests were spaced further apart as predation of eggs increased. These changes in spacing corresponded with changes in the response distances of agonistic displays. There was no change during incubation for island birds but peripheral birds displayed to intruders at much greater distances than during pair formation. Island birds were more likely to attack and display more frequently to intruders than peripheral birds. However, in one season the peripheral birds were more aggressive during pair formation because of an increase in intrusions by unpaired females.     

THE POPULATION,ECOLOGY AND CONSERVATION OF THE BLACK OYSTERCATCHER HAEMATOPUS MOQUINI

Summers, R. W. & Cooper, J. 1977. The population, ecology and conservation of the Black Oystercatcher Haematopus moquini. Ostrich 48:28-40.

The population of Black Oystercatchers Haematopus moquini in the southwestern Cape, South Africa, was estimated to be 2 942 birds. Birds occurred most abundantly on coastal islands and were also abundant on mixed (sandy and rocky) shores of the mainland. Sandy shores and coastal wetlands supported few birds. Black Oystercatchers bred mainly from December to February with the number of clutches present reaching a peak in the first half of January. The most frequent clutch size was two eggs, the mean clutch size was 1,81. No significant differences were found in either linear dimensions or mass between the first and second eggs. The mean proportion of juveniles in groups of birds in July was 3,6 % suggesting a low recruitment to the adult population. The breeding population at Marcus Island is apparently sedentary throughout the year. The primary moult season for adults extends from March to October (eight months). Introduced mammalian predators should be controlled on islands and important mainland breeding sites should be protected by the creation of nature reserves and restricting human access during the breeding season.     

Determining productivity of Maui Parrotbills,an endangered Hawaiian honeycreeper

ABSTRACT Maui Parrotbills (Pseudonestor xanthophrys), critically endangered Hawaiian honeycreepers endemic to the island of Maui, are restricted to a single population of ～500 individuals located in remote, mountainous terrain. From January to June 2006–2011, we located nests and fledglings in the Hanawi Natural Area Reserve (NAR) in east Maui, Hawaii, to document nest success and annual reproductive success. Nest success is a commonly used measure of productivity and is a central component of many demographic studies. Annual reproductive success is less frequently documented because greater effort is required to monitor the reproductive success of breeding pairs through time. However, for species whose nests are difficult to locate or access, such as Maui Parrotbills, the presence or absence of fledged young may provide a more accurate measure of breeding success than monitoring nests. During our study, we located and determined the outcome of 30 nests to document nest success, and monitored 106 territories for the presence or absence of fledglings to calculate annual reproductive success. Nest success probability was 19% (N= 30) and seasonal nest success was 46%. During our monitoring efforts, 49 of 106 breeding pairs produced a single fledged young. Because parrotbills typically have single egg clutches and only re‐nest after nests fail, the presence or absence of a fledgling is an indication of a pair's overall reproductive success for a breeding season. Based on the number of fledglings per pair, our estimate of annual reproductive success was 46%, confirming our initial productivity estimate from nests. Thus, our results indicate that the two methods, determining annual reproductive success by monitoring fledglings and calculating nest success, provide similar estimates of annual productivity for Maui Parrotbills. Based on our estimates, the parrotbill population appears to be demographically stable. However, our productivity estimate was based only on the population at Hanawi, an area representing just 3% of the total range of parrotbills. Thus, our results may not accurately reflect the status of parrotbills over their entire range.     

Intraspecific variation in size and density of Avocet colonies: effects of nest-distances on hatching and breeding success

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).     

Increased survival and breeding performance of double breeders in little penguins Eudyptula minor,New Zealand: evidence for individual bird quality?

The little penguin Eudyptula minor is unique among penguin species in being able to fledge chicks from two clutches in one breeding season. Pairs laying two clutches in a given season make a higher reproductive investment, and may be rewarded by a higher reproductive success as they may raise twice as many chicks as pairs laying one clutch. The higher effort made by pairs laying two clutches could correlate negatively with survival, future reproductive performance or offspring survival, indicating a cost of reproduction. Conversely, a positive relationship between the number of clutches produced in a given breeding season and survival, future reproductive performance or offspring survival would indicate that birds laying two clutches belonged to a category of birds with higher fitness, compared to birds laying only one clutch in the season. In this study we used a long‐term data set taken from an increasing population of little penguins in Otago, SE New Zealand. We modelled the relationship between the number of clutches laid in a breeding season and survival probability, reproductive performance in the next breeding season and first year survival of offspring using capture‐recapture modelling.
Birds laying two clutches produced 1.7 times more fledglings during a breeding season than pairs laying one clutch. We found that birds laying two clutches had a higher probability of breeding in the following breeding season, a higher probability of laying two clutches in the following breeding season and a higher survival probability. There was no overall difference in post‐fledging survival between the young of birds producing one clutch and the young of birds producing two clutches. However, the survival of young of single clutch breeders declined with laying date, whereas the young of double clutch breeders had the same survival rate irrespective of laying date. For a subset of data with birds of known age, we found evidence that the probability of laying two clutches increased with age. However, there were also indications for differences among birds in the tendency to lay two clutches that could not be attributed to age. We tentatively interpret our results as evidence of quality difference among little penguin breeders.     

Roosting of Yellow-naped Parrots in Costa Rica: estimating the size and recruitment of threatened populations

ABSTRACT.   Many parrot populations are threatened with extinction due to habitat loss and collection for the pet trade. The loss of nest trees and chick poaching can drastically reduce reproductive success. However, due to the long life span of many parrots, populations are unlikely to become extinct rapidly even with complete reproductive failure. For parrots that travel in family groups, rapid estimates of reproductive success can be obtained by recording group sizes in areas where they congregate. We used roost counts over an 18-month period to estimate the size and productivity of a population of Yellow-naped Parrots ( Amazona auropalliata auropalliata ) in Costa Rica. Up to 300 birds were observed flying to roost on offshore islands near Curú National Wildlife Refuge. Roost counts were lowest during the breeding period (December–March), increased after fledging (April–July), and peaked during the late wet season (September–October). Increased food availability on the islands during the breeding season allowed the parrots to become seasonal island residents, and lowered roost counts during that period. We calculated reproductive parameters by assuming that groups of >2 birds were adults traveling with young. The percentage of young in the population was 12.5% and did not differ between years. Studies of group size in birds that form stable family groups, such as psittacines in the genera Amazona and Ara , are an inexpensive way to obtain estimates of the reproductive output of some parrot populations and determine if further study or intensive management are warranted.     

A comprehensive demographic assessment of the endangered Fiordland crested penguin Eudyptes pachyrhynchus

ABSTRACT

Many species of Eudyptes penguin have shown substantial population declines and in response, there have been efforts to identify the key demographic parameters. Here, we present the demographic parameters of one of the least well known and the least abundant species of crested penguin, the endangered Fiordland crested penguin Eudyptes pachyrhynchus. A population study incorporating mark–recapture, nest occupancy and breeding success was conducted over 16 years at several sites in the northern half of the range of the species. Survival probabilities were calculated using standard Cormack–Jolly–Seber models and the Burnham Live and Dead model. The annual probability of true survival for banded birds and apparent survival for birds with transponders were both estimated at 89% during their adult years, which is similar to that reported for Eudyptes penguin species inhabiting more southerly latitudes. Annual juvenile survival was assessed for Fiordland crested penguins until their first return at 77%. The mean breeding success (0.61?±?0.02 chicks/pair) was higher than is observed for other crested penguin species, except the southern rockhopper penguin, which may be due to having lower A-egg ejection rates and higher rates of fledging two chicks per pair. Breeding success was related to the niche of predators present.     

Low genetic diversity and small population size of Takahe Porphyrio hochstetteri on European arrival in New Zealand

The rediscovery of the Takahe Porphyrio hochstetteri in 1948 in the remote mountains of Fiordland, New Zealand, has been described as one of the greatest moments in ornithological history. The subsequent management of the population has become a model for avian recovery programmes, yet questions still remain regarding the population size at the time of, and prior to, its rediscovery. We used 20 microsatellite markers to genotype samples of the three surviving museum specimens (1849–1898) collected prior to the initial declaration of extinction to estimate levels of genetic diversity and effective population size. These estimates were compared with equivalent estimates from DNA samples of three specimens preserved at the time of rediscovery (1949) and with 20 contemporary samples. Using rarefaction simulations to account for the limited sample sizes, the results suggest that only slightly more genetic diversity (allelic diversity and numbers of polymorphic loci) existed in the earliest Takahe sampled and that levels of genetic diversity at the time of rediscovery were very similar to those today. Effective population size estimates showed a similar pattern. Contemporary samples from a widespread congener to Takahe, the Pukeko Porphyrio porphyrio, showed consistently higher levels of genetic diversity and greater effective population size, even after equivalent rarefaction to the same small sample sizes available for Takahe. It is likely that the population size of Takahe in Fiordland at the time of European arrivals in the 1800s was similar to its current size. These results provide molecular support for the hypothesis that Takahe were common throughout most coastal and eastern parts of the South Island of New Zealand before being hunted to extinction in these regions by early Maori, and persisted as a relatively small and isolated population in Fiordland where they may never have been very common. This is in marked contrast to other New Zealand endemic birds found in Fiordland, such as the Kakapo Strigops habroptilus and several forest passerines, which remained relatively numerous until the time of European arrival before undergoing rapid declines thereafter.     

Modelling the occurrence and abundance of a colonial species,the arctic tern Sterna paradisaea in the archipelago of SW Finland

Knowledge of the habitat requirements and suitable breeding areas of sea birds is crucial for their management and conservation. However, there are still few studies that have modelled the breeding distribution and abundance of colonial sea birds. In this study, we created predictive distribution models for a colonial species, the arctic tern Sterna paradisaea, using 14 environmental variables calculated for 525 islands in the Archipelago Sea in SW Finland. We modelled the occurrence (presence‐absence) using generalised additive models (GAMs) and abundance (pair numbers/colony size) using hurdle models fitted with GAM. We tested for spatial autocorrelation in model residuals and evaluated the models on independent data. Critical factors influencing the occurrence of the arctic tern were the proportions of boulder or gravel and forest of island area, as well as island maximum elevation and area, such that the species seemed to prefer large and low islands with sparse vegetation. Abundance was influenced by the proportions of boulder or gravel and bare rock of island area, as well as exposure and island area. To some extent, different factors influenced the occurrence and the abundance. The evaluation results of the models were good, with an AUC value of 0.91 for the most accurate presence‐absence model and a Pearson's correlation coefficient of 0.60 for the most accurate hurdle model. The predictive ability of the models increased when we removed islands with single or few breeding pairs from the data set. Although the hurdle models did not produce accurate pair number estimates, they indicated which islands are suitable for larger colonies. Abundance is a crucial factor for colonial species. This modelling technique can therefore be of great value for the conservation and management of the arctic tern and similar colonial species.     

Estimating the home range and carrying capacity for takahe (

Predator-free offshore islands play an important role in the conservation of many of New Zealand's endemic species. Takahe (Porphyrio mantelli) have small populations established on four offshore islands and although hatching success is lower than that of the wild mainland population in Fiordland, juvenile and adult survival is high and populations are growing exponentially. Accurate estimates of home range size and potential carrying capacities are therefore essential for the future management of the population as a whole. The mean home range size of takahe pairs in one study population on Mana Island (217 ha) was 2.8 ± 1.9 ha. The island was assessed for current and maximum available area for takahe and the potential carrying capacity was estimated at 22—53 pairs. Current and maximum available areas were also used to calculate carrying capacities on each of three other islands using two different estimates of mean home range size for Maud Island (7—34 pairs) and Kapiti Island (5—33 pairs) and one estimate of home range size for Tiritiri Matangi Island (25 pairs). A model of the population growth of takahe on islands predicted that estimated carrying capacities would be reached between 1997 and 2009. The urgency of planning to make use of the considerable potential of island populations of takahe is stressed.     

Are salinas a suitable alternative breeding habitat for Little Terns Sterna albifrons?

This paper describes the breeding population, breeding habitats and reproductive variables of Little Terns Sterna albifrons in natural (sandy beaches) and alternative (salinas) habitats. Studies of nesting success conducted between 1998 and 2002 in these two types of habitat were combined with a literature review of census work from the past 30 years in order to assess whether salinas are suitable alternative breeding habitat for Little Terns. Most of the Portuguese Little Tern population now breeds in salinas. Census data from the last 30 years show that this is a recent breeding behaviour, because until the 1990s most colonies were located on sandy beaches. Destruction and disturbance of the natural habitat has caused this habitat shift. Despite this shift, the Portuguese Little Tern breeding population did not decline during this period and no significant differences were found in nesting success between natural and alternative habitats. This might indicate that salinas are a suitable alternative breeding habitat for Little Terns, but differences in laying period, clutch size and egg size were recorded between birds nesting on sandy beaches and in salinas in the same area. Birds nested earlier on sandy beaches and laid larger clutches and eggs than in salinas. These data suggest that, when both habitats are available, older and/or higher quality birds prefer sandy beaches for breeding, presumably trying to re-nest in salinas when first breeding attempts failed. We discuss conservation priorities and management actions for both habitats.     

Environmental and genetic determinants of reproduction in the house sparrow: a transplant experiment

A transplant experiment was carried out to examine whether genetic differentiation can explain geographical variation in the reproductive strategies of house sparrows Passer domesticus. Individuals from an inland and a coastal population in Central Norway were released on a small island, near the coastal area. No directional selection was found on any of the morphological characters from the release to the onset of breeding, but the proportion of the inland males that remained to start breeding on the island was smaller than that of the coastal males. The new environment influenced the time of egg laying which was, relative to the source populations, more delayed among the introduced inland females than among the coastal females. In 1992, chicks raised by inland females grew faster and were fed more frequently than chicks raised by coastal females. No difference was found between birds of inland and coastal origins in their breeding success and their relative number of surviving recruits. Transplanted parents from the inland fed their offspring more frequently than transplanted parents from the coastal area. This experiment shows that the plasticity of reproductive traits in combination with stochastic factors in the environment may lead to an establishment of introduced genes in small populations.