Black Robin Research Articles

Genomic trajectories of a near-extinction event in the Chatham Island black robin

BackgroundUnderstanding the micro-­evolutionary response of populations to demographic declines is a major goal in evolutionary and conservation biology. In small populations, genetic drift can lead to an accumulation of deleterious mutations, which will increase the risk of extinction. However, demographic recovery can still occur after extreme declines, suggesting that natural selection may purge deleterious mutations, even in extremely small populations. The Chatham Island black robin (Petroica traversi) is arguably the most inbred bird species in the world. It avoided imminent extinction in the early 1980s and after a remarkable recovery from a single pair, a second population was established and the two extant populations have evolved in complete isolation since then. Here, we analysed 52 modern and historical genomes to examine the genomic consequences of this extreme bottleneck and the subsequent translocation.ResultsWe found evidence for two-fold decline in heterozygosity and three- to four-fold increase in inbreeding in modern genomes. Moreover, there was partial support for temporal reduction in total load for detrimental variation. In contrast, compared to historical genomes, modern genomes showed a significantly higher realised load, reflecting the temporal increase in inbreeding. Furthermore, the translocation induced only small changes in the frequency of deleterious alleles, with the majority of detrimental variation being shared between the two populations.ConclusionOur results highlight the dynamics of mutational load in a species that recovered from the brink of extinction, and show rather limited temporal changes in mutational load. We hypothesise that ancestral purging may have been facilitated by population fragmentation and isolation on several islands for thousands of generations and may have already reduced much of the highly deleterious load well before human arrival and introduction of pests to the archipelago. The majority of fixed deleterious variation was shared between the modern populations, but translocation of individuals with low mutational load could possibly mitigate further fixation of high-frequency deleterious variation.

Breeding and Territorial Behaviour of Indian Black Robin (Copsychus fulicata leucoptera) in Mihintale, Sri Lanka

Indian Black Robin (Copsychus fulicata leucoptera) ( Lesson, 1840) is one of the territorial birds often found in all climatic zones in Sri Lanka. Territory size of this birds species is vary according to the breeding season and habitats that they occupy. The present study was carried out to understand the breeding ecology and territorial behavior of Indian Black robin both in breeding and non-breeding periods. The study was carried out at the Mihintale sanctuary and the Faculty premises of Rajarata university of Sri Lanka. Eleven breeding pairs of Black robins were observed to collect using scan and focal animal sampling methods from 2014 to 2017. Territory mapping was done using ArcGIS 10.3 and % behavioral act was calculated using Microsoft excel. Two breeding seasons were identified during March to September. The average nest building period was13.25±0.96 days. Total of 10 nests were recorded, seven were successful nests but chicks were observed from only three of them while in other four of them were damaged due to several reasons. Three nests were abandon by the female bird with eggs which may considered as pseudo nests. The eggs were whitish in colour with small brownish blotches. The clutch size ranged from 2-4. The average incubation period was 11± 3.4 days. The identified foraging sites are nearby roads, human settlements and live foliage. Fifteen territories were recorded during the study period in the open land areas, sparse grasslands or scrublands. The territory sizes of non-breeding season ranged from 617 to 5504 m2 while territories of breeding season ranged from 1335 to 8736 m2.

Fitting Markovian binary trees using global and individual demographic data

We consider a class of continuous-time branching processes called Markovian binary trees (MBTs), in which the individuals lifetime and reproduction epochs are modelled using a transient Markovian arrival process (TMAP). We develop methods for estimating the parameters of the TMAP by using either age-specific averages of reproduction and mortality rates, or age-specific individual demographic data. Depending on the degree of detail of the available information, we follow a weighted non-linear regression or a maximum likelihood approach. We discuss several criteria to determine the optimal number of states in the underlying TMAP. Our results improve the fit of an existing MBT model for human demography, and provide insights for the future conservation management of the threatened Chatham Island black robin population.

Importance of Breeding Ecology and Territorial Behaviour of Indian Black Robin (Saxicoloides fulicata leucoptera) for its Conservation

Indian Black Robin (Saxicoloides fulicata leucoptera) is one of the territorial bird found in scrub forest, rocky areas, open grasslands and near human residence and distributed throughout the country in all climatic zones. Breeding success of birds can be depended on the size of the territory. Territory size can be varying according to breeding season and different locations they occupied. Present study attempted to understand the breeding ecology and territorial behavior of black robin in both breeding and non-breeding seasons. The data were collected using scan sampling and focal animal sampling from 2014 to 2017 in adjacent to the Mihintale sanctuary. The behavioral and territory variations were checked by using a dummy of black robin. ArcGIS v10.3 and Minitab v17 were used for data analysis. The breeding season of black robin lasted nearly three months twice a year from March to June and July to September. Courtship behaviour was started beginning of April and nest building was performed by both male and female. The nest building period averaged 13.25±0.96 days. Ten nests were recorded within the study period whilst 4 of them were successful and 6 were pseudo nests. Nests were observed at different places such as rocky areas, rock fragments and joisters of resident places. The clutch size was 2-4 and eggs were whitish in background with small brownish blotches. Average incubation period was 11±3.4 days. Both male and female fed the chicks after hatching. Foraging sites were mostly nearby roads, human associated places and live foliage. As a percentage, male used to feed chicks 69.23% and female 30.77% within the observed period. There were 12 territories recorded within the study period. The territorial areas were changed according to the members of the group and the breeding season. Territory size ranged from 617 m2 to 5,050 m2 and smaller territories were recorded during the non breeding period while sizes were larger during the breeding period. Results suggest that this species require sufficient habitats to demarcate their territory and nesting. Hence maintain the gardens and shady areas are recommended to conserve this species in domestic areas. Keywords: Black Robin, Territory, Nests, Conservation

Post‐reintroduction distribution and habitat preferences of a spatially limited island bird species

AbstractInvestigating habitat use and preferences of a threatened species can be challenging, especially if wild populations have decreased to such low numbers that they occupy only fractions of their former natural range. Hence, assessing habitat suitability of a potential release site for a threatened species before a reintroduction attempt can be difficult because frequently no comparable baseline data are available. In these instances, post‐release monitoring data can inform about habitat use and preferences of a reintroduced species. Here, we use monitoring data of an endangered endemic island bird, the Chatham Island black robin Petroica traversi, to investigate habitat preferences and the temporal change in distribution patterns across 26 years following a reintroduction. We show that densities and distribution of black robin pairs at the reintroduction site have changed significantly over the years. Spatial distribution of pairs is clustered, and this clustering has intensified as the population increased. We used the maximum entropy method MaxEnt to model habitat suitability on the island, showing that black robins clearly prefer forested areas inland that are within 70 m to the forest edge at lower elevations (<40 m a.s.l.) and on slopes that have a N‐NE aspect. The model also identified one area on the island that comprises suitable habitat, but is currently uninhabited. Applying maximum observed densities to the available area of each suitability class, carrying capacity is estimated as 170 nesting pairs across the island, highlighting the need to find further appropriate habitat urgently. Overall, these topographical and habitat preferences considerably restrict this species' potential distribution, a constraint that has serious conservation implications for future population growth of current populations and (re)introductions to new locations. This study demonstrates that post‐release data can reveal relevant limitations to habitat use of highly threatened species.

Black Scholars Matter: #BlkTwitterstorians Building a Digital Community

In his visionary work, Freedom Dreams: The Black Radical Imagination, historian and scholar-activist Robin D.G. Kelley writes, “Revolutionary dreams erupt out of political engagement; collective so...

How old is this bird? The age distribution under some phase sampling schemes

In this paper, we use a finite-state continuous-time Markov chain with one absorbing state to model an individual's lifetime. Under this model, the time of death follows a phase-type distribution, and the transient states of the Markov chain are known as phases. We then attempt to provide an answer to the simple question "What is the conditional age distribution of the individual, given its current phase"? We show that the answer depends on how we interpret the question, and in particular, on the phase observation scheme under consideration. We then apply our results to the computation of the age pyramid for the endangered Chatham Island black robin Petroica traversi during the monitoring period 2007-2014.

When the neighbourhood goes bad: can endangered black robins adjust nest‐site selection in response to the risk of an invasive predator?

AbstractThe introduction of exotic predators into new areas has had significant impacts on naïve prey species, which initially lack behavioural mechanisms to avoid predation. Understanding a species’ ability to respond appropriately to novel threats may inform in situ management options for threatened island populations. In the presence of nest predators, physical characteristics of the nest site can influence the likelihood that eggs or chicks are lost to predation. Some birds that evolved under high nest predation pressure show predictable changes in nest‐site selection following nest predation, but the ability of naïve island birds to alter nest‐site decisions based on experience with novel nest predators has not been well studied. We examined nest‐site choices of re‐nesting Chatham Island black robins Petroica traversi following nest predation by invasive European starlings Sturnus vulgaris. Robins whose first nests were depredated re‐nested in a new location that was significantly lower to the ground than pairs whose first nests were lost through other causes. As predation risk increases with nest height, the lower placement of re‐nests is consistent with a movement towards safer nest sites. The cause of nest failure did not influence the choice of substrate for a replacement nest, nor did individual pairs re‐nest further away from depredated nests. Changes in nest‐site selection did not carry over into subsequent nesting seasons. Our results suggest that some evolutionarily naïve species may be capable of assessing immediate risk through individual experience with novel predators, and modifying their nest‐site decisions accordingly.

Genetic diversity and population differentiation within and between island populations of two sympatric Petroica robins, the Chatham Island black robin and tomtit

Small island populations are particularly prone to extinction due to the effects of genetic drift and inbreeding reducing genetic variation and fitness of such populations. Furthermore, isolated island populations may experience population divergence due to drift or divergent selection. Reciprocal translocations of individuals between populations may be used to stimulate gene flow between such isolated populations. To determine whether populations of the endangered Chatham Island black robin Petroica traversi may benefit from such translocations, we compared levels of genetic diversity and differentiation within and among populations of the black robin and its sympatric sister-species, the Chatham Island tomtit Petroica macrocephala chathamensis. Although the black robin has recovered following a severe population bottleneck, the bottleneck and subsequent intense inbreeding experienced by the black robin have likely had long-term consequences affecting the viability of this endangered species. We analysed the genetic diversity and population structure of the black robin at 15 polymorphic microsatellite loci, and compared this to the level and pattern of genetic diversity from 17 polymorphic loci for the tomtit, which comprises three larger island populations. The black robin displayed a lower number of alleles and expected heterozygosity than the Chatham Island tomtit. We also found that island populations of both species have differentiated from one another, likely due to strong genetic drift acting independently on these populations over a period of isolation. Reciprocal translocations of black robins between islands are recommended to prevent further loss of diversity through drift, and so to improve the probability of species persistence.

Female-biased dispersal in a spatially restricted endemic island bird

Dispersal of individuals before their first breeding attempt or between subsequent attempts facilitates spatial and temporal gene flow within and among populations. However, in species on oceanic islands, dispersal is often restricted to a single island, and thus, the risk of inbreeding is particularly high in those small, closed, and isolated populations. One of the mechanisms that may prevent inbreeding within island populations is sex-biased dispersal, which results in close kin of the opposite sex not being in the same area for breeding. In this study, we investigated dispersal patterns, and their costs and benefits, in the Chatham Island black robin, a small passerine confined to two small islands. We found that black robins practice a resource defense mating system as male black robins were more likely to divorce than change territory between breeding seasons. Natal dispersal was female-biased in both the proportion of birds dispersing and the distance dispersed. Bird density in the natal year increased the proportion of birds dispersing in both sexes. Breeding success was reduced for females after natal dispersal. Breeding dispersal was rare and female-biased in proportion only. Regardless of sex, black robins were more likely to disperse after losing a mate, but females dispersed further than males. This study suggests that in closed populations of island species with limited habitat, sex-biased density-dependent dispersal may be a mechanism that minimizes inbreeding. Dispersal of individuals facilitates gene flow within and among populations. However, in species on oceanic islands, dispersal is often restricted to movement within a single island. Few studies have investigated dispersal and its costs and benefits in spatially restricted species. Here, we studied the endangered Chatham Island black robin, a songbird confined to two small islands. We found that on an island, where habitat is extremely limited, males are highly territorial and they are more likely to change partners than territories. Bird density in the natal year forces both young males and females to move, but females are more likely to disperse and move further than males. Sex-biased density-dependent dispersal may be a mechanism that minimizes inbreeding. This is particularly important for threatened island endemic species where maintaining high genetic diversity ensures the population’s long-term viability.

Unexpected positive and negative effects of continuing inbreeding in one of the world's most inbred wild animals.

Inbreeding depression, the reduced fitness of offspring of related individuals, is a central theme in evolutionary biology. Inbreeding effects are influenced by the genetic makeup of a population, which is driven by any history of genetic bottlenecks and genetic drift. The Chatham Island black robin represents a case of extreme inbreeding following two severe population bottlenecks. We tested whether inbreeding measured by a 20-year pedigree predicted variation in fitness among individuals, despite the high mean level of inbreeding and low genetic diversity in this species. We found that paternal and maternal inbreeding reduced fledgling survival and individual inbreeding reduced juvenile survival, indicating that inbreeding depression affects even this highly inbred population. Close inbreeding also reduced survival for fledglings with less-inbred mothers, but unexpectedly improved survival for fledglings with highly inbred mothers. This counterintuitive interaction could not be explained by various potentially confounding variables. We propose a genetic mechanism, whereby a highly inbred chick with a highly inbred parent inherits a "proven" genotype and thus experiences a fitness advantage, which could explain the interaction. The positive and negative effects we found emphasize that continuing inbreeding can have important effects on individual fitness, even in populations that are already highly inbred.

Biodiversity, Historic Importance and Threats of Garanduwa Lagoon Situated in Mirissa Tourist Zone A Case Study

Out of 89 lagoons, Garanduwa is the only lagoon located nearly 3 km away from the sea that comes under atoll lagoon. The extent is approximately 65 km2. It is located in association with unexplored southern coast and belongs to five Gramaseva divisions; Udupila, Thanhagoda, Garanduwa, Henwala, and Thalaramba in Matara district. It is intermittently connected to ocean by two restricted inlets; Mirissa, Udupila and Thalaramba. A case study was conducted to investigate the biodiversity, historic background and the threats in association with the tourist industry. A reconnaissance survey was carried out in the morning and evening by a catamaran boat to identify fauna and flora. Thirty five villages were interviewed by a questionnaire to gather information on the history and prevailing threats. Garanduwa lagoon hosts rich assemblages of different species. Variation of muddy and sandy sediments is home to a rich biodiversity. Different variety of trees, many insects, reptiles, amphibians, birds, mammals thrive in the habitat. More than 20 bird species were recorded. Wooly-necked storks, Indian pond heron, Ceylon blue magpies, common babler, Ceylon hill mynah, crimpson backed wood peckers, little egret, larger egret, spot billed pelican, Ceylon green pigeon, purple coot, black robin, Southern common babler, scimitors, paradise fly catchers, orioles, chaffinchs and bats were prominent. Breadfruit and its wild species, Kirala, Kadol, Jak fruit, Cashew nut, Hog plum, Grosse sapota, Kekuna, Bael fruit were the prominent tree species. Variety of crab species were found among the roots, on the trunks and within the canopy. The name “Garanduwa” derived from a Sanscrit term because of the presence of many crocodiles in the past. At present crocodiles became extinct. Ancient prince named “Keerthi” (10th century), later became as the King 1 Wijayabahu built his palace in the island within the lagoon. The king was adorned with the sword to the battle against Solli at the palace was called as “Siribandala Palace” and still the ruins are remaining. Because o f close proximity to many tourist hotels, there is a potential to build tourist hotels by destructing the nature and will be a potential site for sewage accumulation. Therefore, it is timely important to save this wetland for a sustainable utilization and thereby encourage ecotourism. Keywords: Atoll lagoon, Biodiversity, Garanduwa, History, Threats

Cattle Egrets (Bubulcus ibis) Control the Population of House Flies (Musca domestica) in Garbage Dumping Sites: A Comparison between Two Garbage Dumping Sites, Kandy, Sri Lanka

House flies spread many communicable diseases such as cholera, dysentery and spread parasitic infections. Therefore, it is important to control house flies at garbage dumping sites as they are a rich source of disease agents. Cattle Egret (Bubulcus ibis) is one of the common wetland birds in Sri Lanka, often seen foraging on flies at garbage dumping sites. Referring to the preliminary observations reported before, two garbage dumping sites were selected from Kandy district. Digana garbage dumping site (7.260 N 80.740 E) was selected as a Cattle Egret occupied site and Panvila garbage dumping site (7.220 N 80.430 E) was selected as the control site where no Cattle Egrets were recorded. The adult house flies (Musca domestica) were counted which random quadrate sampling twice a month for 5 min. Birds were counted from 08:00 to 10:00 hrs by point count method with a binocular. Cattle Egrets, Crows, Common Mynahs, Spotted Doves, Green bee-eaters, House Sparrows, Black Robins, Indian Pond Herons and Asian Palm Swifts were identified as bird species in Digana garbage dumping site and only Common Mynas, Spotted Doves and Asian Palm Swifts were observed in Panvila site. A strong correlation between populations of Cattle Egrets and house flies was observed in the Digana garbage dumping site (<0.05). Since major food item of Cattle Egret is insects, they are attracted to waste dumping site, which provides abundant dipterans maggots at low energy expenditure. However, the house fly population was significantly high in Panvila site than Digana site as Cattle Egrets were not observed in Panvila site. Also In both sites, no correlation was observed between populations of other bird species and population of house flies (0.05<). During breeding season, the Cattle Egrets were observed to be migrating away from the Digana site and were not recorded in late June. No Cattle Egrets in July to September were observed in this site. The number of house flies was clearly increased during this period and with the return of Cattle Egrets after breeding season the numbers of house flies decrease dramatically. The present study shows that there is a strong relationship between population of house flies and Cattle Egret abundance. Keywords: Cattle Egrets, Garbage dumping sites, House flies

Assessment of hybridisation between the endangered Chatham Island black robin (Petroica traversi) and the Chatham Island tomtit (Petroica macrocephala chathamensis)

Hybridisation between an endangered species and a more common species can facilitate population decline and extinction of the endangered species due to wasted reproductive effort, outbreeding depression and/or swamping of alleles due to widespread or complete admixture. The Chatham Island black robin (Petroica traversi) is an endangered songbird species, which was reduced to only five individuals in 1980. Intensive cross-fostering, whereby black robin offspring were placed into nests of the closely related Chatham Island tomtit (Petroica macrocephala chathamensis) to increase reproductive output, contributed to the rapid recovery of the species within 10 years. Several hybridisation events occurred and although those hybrids were successfully eliminated from the population, concerns remained for the possibility of introgression between the two species that may have gone unnoticed. In this study, we genotyped seven microsatellite loci in both species from the two islands where they coexist, to assess the level of hybridisation and the extent of introgression between the two species. The two species shared no alleles at five of the seven loci genotyped, and cluster analysis, AMOVA and admixture analysis of a total of 174 black robins and 78 Chatham Island tomtits showed no evidence of hybridisation or introgression on either of the two islands where they co-exist. As a result, there is no evidence that black robins are currently in any danger of population decline or extinction through hybridisation with tomtits, although small population size and skewed sex ratio, particularly in the smaller of the two populations, may facilitate future hybridisation events.

Killing with kindness: the hidden perils of conservation

What looked like an iconic conservation success story so nearly ended in disaster. The Chatham Island black robin, offers a cautionary tale for would-be species savers

Human-Assisted Spread of a Maladaptive Behavior in a Critically Endangered Bird

Conservation management often focuses on counteracting the adverse effects of human activities on threatened populations. However, conservation measures may unintentionally relax selection by allowing the ‘survival of the not-so-fit’, increasing the risk of fixation of maladaptive traits. Here, we report such a case in the critically-endangered Chatham Island black robin (Petroica traversi) which, in 1980, was reduced to a single breeding pair. Following this bottleneck, some females were observed to lay eggs on the rims of their nests. Rim eggs left in place always failed to hatch. To expedite population recovery, rim eggs were repositioned inside nests, yielding viable hatchlings. Repositioning resulted in rapid growth of the black robin population, but by 1989 over 50% of all females were laying rim eggs. We used an exceptional, species-wide pedigree to consider both recessive and dominant models of inheritance over all plausible founder genotype combinations at a biallelic and possibly sex-linked locus. The pattern of rim laying is best fitted as an autosomal dominant Mendelian trait. Using a phenotype permutation test we could also reject the null hypothesis of non-heritability for this trait in favour of our best-fitting model of heritability. Data collected after intervention ceased shows that the frequency of rim laying has strongly declined, and that this trait is maladaptive. This episode yields an important lesson for conservation biology: fixation of maladaptive traits could render small threatened populations completely dependent on humans for reproduction, irreversibly compromising the long term viability of populations humanity seeks to conserve.

SEVERE INBREEDING DEPRESSION AND NO EVIDENCE OF PURGING IN AN EXTREMELY INBRED WILD SPECIES-THE CHATHAM ISLAND BLACK ROBIN

Although evidence of inbreeding depression in wild populations is well established, the impact of genetic purging in the wild remains controversial. The contrasting effects of inbreeding depression, fixation of deleterious alleles by genetic drift, and the purging of deleterious alleles via natural selection mean that predicting fitness outcomes in populations subjected to prolonged bottlenecks is not straightforward. We report results from a long-term pedigree study of arguably the world's most inbred wild species of bird: the Chatham Island black robin Petroica traversi, in which conditions were ideal for purging to occur. Contrary to expectations, black robins showed a strong, negative relationship between inbreeding and juvenile survival, yielding lethal equivalents (2B) of 6.85. We also determined that the negative relationship between inbreeding and survival did not appear to be mediated by levels of ancestral inbreeding and may be attributed in part to unpurged lethal recessives. Although the black robin demographic history provided ideal conditions for genetic purging, our results show no clear evidence of purging in the major life-history trait of juvenile survival. Our results also show no evidence of fixation of deleterious alleles in juvenile survival, but do confirm that continued high levels of contemporary inbreeding in a historically inbred population could lead to additional severe inbreeding depression.

Nest site selection by the endangered black robin increases vulnerability to predation by an invasive bird

AbstractFew studies have investigated the impacts of established invasive birds on the native threatened avifauna. However, measuring the levels of mortality in native birds from exotic birds can help with management decisions on whether or not such introduced species need to be controlled. The black robin Petroica traversi is an endangered bird endemic to the Chatham Islands of New Zealand. Black robins build cup‐like nests either within tree cavities (‘cavity’ nests) or in the sub‐canopy vegetation (‘open’ nests). Nest predation, most likely by the invasive European starling Sturnus vulgaris, was the largest cause of nest failure in the main population of the black robin on Rangatira Island. Nest predation rate over five breeding seasons was 20.6% in comparison with 7.74% of nests failing because of severe weather events (the second largest cause for nest failure). Cavity nests experienced a significantly higher rate of predation (36.33%) than open nests (10.82%). The greater frequency of open nests (63.5% out of 244 nests monitored) may be a result of higher selection pressure by starlings on cavity nests. Nest height also influenced predation, with predation risk increasing from 4.88% for nests below 1 m to 31.89% for nests above 3 m. Overall, predation on black robin nests decreased chick production in the population by 15.6% annually. For a population of only 220–240 birds, this loss may be limiting continued population growth and we recommend that efforts be made to reduce predation through either the culling of starlings or the installation of nest boxes at the low heights avoided by starlings.

The Art and Science of Restoration

The Art and Science of Restoration

The phylogenetic analysis of avipoxvirus in New Zealand

Avipoxvirus is known to be endemic in New Zealand and it is a cause of ongoing mortalities in the endangered black robin and shore plover populations. There is no information on the strains of avipoxvirus occurring in New Zealand and their likely origin or pathogenicity. This study was designed to identify the phylogenetic relationships of pathogenic avipoxvirus strains infecting introduced, native, and endemic bird species in New Zealand. Avipoxvirus 4b core protein gene was detected in tissue samples from 25/48 birds (52.1%) from 15 different species in New Zealand. Bootstrap analysis of avipoxvirus 4b core protein gene revealed that the New Zealand avipoxvirus isolates comprised of three different subclades. The majority of New Zealand avipoxvirus isolates (74%) belonged to A1 subclade which shared 100% genetic similarity with the fowlpox HPB strain. An isolate from a wood-pigeon (kereru) belonged to subclade A3, displaying 100% sequence homology to albatrosspox virus. An additional group, isolated from two shore plovers and one South Island saddleback, grouped within subclade B1 and presented 99% sequence homology to European PM33/2007 and Hawaiian HAAM 22.10H8 isolates. The results suggest that a variety of New Zealand bird species are susceptible to avipoxvirus infection, that there are more than two distinctive avipoxvirus subclades in New Zealand, and that the most prevalent A1 strain may have been introduced to New Zealand through introduced avian hosts such as passerines or poultry.