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Tuesday, 6 January 2015

Ibis (British Ornithologists' Union). January 2015, Volume 157, Issue 1. TOC and Abstracts

Ibis
British Ornithologists' Union

Image of International Journal of Avian Science cover ad

January 2015, Volume 157, Issue 1

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Review Article


A review of the impacts of corvids on bird productivity and abundance

Christine F. Madden 1, Beatriz Arroyo 2,3 andArjun Amar 1,*
Author Information
1 Percy FitzPatrick Institute of African Ornithology, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch, South Africa
2 Instituto de Investigación en Recursos Cinegéticos, IREC (CSIC-UCLM-JCCM), Ciudad Real, Spain
3 Centre d′Etudes Biologiques de Chizé (CEBC-CNRS), Villiers en Bois, France
* Corresponding author.
Email: arjun.amar@uct.ac.za
Article first published online: 15 DEC 2014 | DOI: 10.1111/ibi.12223

Abstract

Corvids are often viewed as efficient predators capable of limiting prey species populations. Despite this widely held belief, a comprehensive review quantifying the effect of corvids on the demography of prey species is lacking. We examine the impacts of crows, ravens Corvus spp. and Eurasian Magpies Pica pica on the population parameters of other bird species. We summarize results from 42 studies, which included 326 explicit evaluations of relationships between a corvid and a potential prey species. Population parameters of studied prey species were categorized as abundance-related (numbers, nest density) or productivity-related (nest success, brood size). Information from both experimental removal studies and correlative studies was examined. Combining all studies, no negative influence of corvids on either abundance or productivity of prey species was found in 81% of cases. Negative impacts were significantly more likely in cases examining productivity rather than abundance (46 vs. 10%). Experimental studies that removed only corvid species were significantly less likely to show a positive impact on productivity than those removing corvids alongside other predators (16 vs. 60%). This suggests that the impact of corvids is smaller than that of other predators, or that compensatory predation occurs. The impact of corvids was similar between diverse avian groups (such as gamebirds, passerines and waders; or ground-nesting and other species). Crows were found to be significantly more likely to have a negative impact on prey species productivity than were Magpies (62 vs. 12%), but no differences were found in relation to prey abundance. We conclude that while corvids can have a negative impact on bird species, their impact is small overall, and nearly five times more frequent for productivity than for abundance. These results suggest that in most cases bird populations are unlikely to be limited by corvid predation and that conservation measures may generally be better targeted at other limiting factors. However, negative impacts were found in a minority of cases, and those may require further investigation to develop management tools to mitigate such impacts where they are of economic or conservation concern.

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ORIGINAL ARTICLES

PRODUCTIVITY

Factors influencing double brooding in Eurasian Hoopoes Upupa epops

(pages 17–30)
Jael Hoffmann, Erik Postma and Michael Schaub
Article first published online: 11 AUG 2014 | DOI: 10.1111/ibi.12188

Abstract

Double brooding may be a good strategy for short-lived species to maximize annual and lifetime reproductive success (ARS and LRS, respectively). Nevertheless, there is typically individual variation in the probability of producing a second clutch. Here we evaluate factors that influence the decision to double brood in the Eurasian Hoopoe Upupa epops. Analyses of an 11-year dataset showed that 36% of the females and 21% of the males produced a second clutch after successfully raising a first clutch. Double-brooded females had higher ARS (9.1 ± 1.9 fledglings; mean ± se) and LRS (0.93 ± 0.08 recruits) than single-brooded females (ARS: 4.5 ± 2.1 fledglings; LRS: 0.36 ± 0.03 recruits). This suggests that double brooding is adaptive in Hoopoes, and raises the question of why most individuals only produce one clutch per season. The probability of double brooding varied only slightly between years, suggesting that it is influenced by individual characteristics rather than by external, population-level environmental factors. In both sexes, the probability of double brooding increased with earlier timing of the first clutch, and the timing of reproduction was the most important factor influencing reproductive success. The latter is likely to be mediated by changes in resources during the season. The probability of double brooding also increased slightly with female age, due to differences in intrinsic quality among females rather than to a gain in experience. In contrast to many other studies, the probability of double brooding increased with an increasing number of fledglings from the first clutch, suggesting that it is a strategy of individuals of high quality. Taken together, we show that the individual quality of the breeder and the timing of their first clutches are key factors influencing the decision to double brood, and thereby that they are important determinants of reproductive performance in Eurasian Hoopoes.
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Low incubation investment in the burrow-nesting Crab Plover Dromas ardeola permits extended foraging on a tidal food resource 

(pages 31–43)
Giuseppe De Marchi, Giorgio Chiozzi, Giacomo Dell'Omo and Mauro Fasola
Article first published online: 23 SEP 2014 | DOI: 10.1111/ibi.12208

Abstract

We used GPS data-loggers, video-recordings and dummy eggs to assess whether foraging needs may force the low incubation attentiveness (< 55%) of the Crab Plover Dromas ardeola, a crab-eating wader of the Indian Ocean that nests colonially in burrows. The tidal cycle was the major determinant of the time budget and some foraging trips were more distant from the colony than previously known (up to 26 km away and lasting up to 45 h). The longest trips were mostly made by off-duty parents, but on-duty parents also frequently left the nest unattended while foraging for 1–7 h. However, the time spent at the colony area (47%) and the time spent roosting on the foraging grounds (16%) would have allowed almost continuous incubation, as in other species with shared incubation. Therefore, the low incubation attentiveness is not explained by the need for long foraging trips but is largely dependent on a high intermittent rhythm of incubation with many short recesses (5.8 ± 2.6 recesses/h) that were not spent foraging but just outside the burrow or thermoregulating at the seashore. As a result, the eggs were warmed on average only 1.7 °C above burrow temperature, slightly more during high tide periods and when burrow temperature was lower between 20:00 and 10:00 h, only partly counteracting the temperature fluctuations of the incubation chamber. These results suggest that low incubation attentiveness is due to the favourable thermal conditions provided by safe nesting burrows and by the hot tropical breeding season, a combination that allows simultaneous foraging by parents and the exploitation of distant foraging grounds. Why Crab Plovers engage in many short recesses from incubation still remains to be clarified but the need to thermoregulate at the seashore and to watch for predators may play a role.
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Predictors of incubation costs in seabirds: an evolutionary perspective 

(pages 44–53)
Akiko Shoji, Kyle H. Elliott, Stéphane Aris-Brosou, Rory P. Wilson and Anthony J. Gaston
Article first published online: 3 NOV 2014 | DOI: 10.1111/ibi.12219


Abstract
Energy costs during breeding play an important role in the evolution of life history traits. Seabirds show substantial variation in both incubation shift length (ISL) and metabolic rates. However, it is still unclear how variation in life history traits relates to incubation metabolic rates (IMR). Here, we examine the relationship between IMR and life history traits, including ISL, fledging strategy (precocial to altricial), incubation period, nest location (surface vs. underground) and clutch mass relative to adult body mass for 30 species of seabirds collated from the literature. Using both conventional non-phylogenetic and phylogenetic generalized least-squares approaches, we show that IMR is negatively associated with ISL, relative clutch mass and with underground nesting, while fledging strategy and incubation period have no impact on IMR once phylogeny is accounted for. Maximum likelihood reconstructions further suggest than ancestral seabirds had average ISL and relative clutch mass, and were surface nesters. We conclude that lower metabolic rates during incubation are associated with both an increased incubation shift length that allows animals to travel farther, as well as the evolutionary emergence of underground nesting that requires less social interaction.
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FOSSIL BIRDS


New remains of the Eocene Prophaethon and the early evolution of tropicbirds (Phaethontiformes) 

(pages 54–67)
Gerald Mayr
Article first published online: 18 OCT 2014 | DOI: 10.1111/ibi.12214

Abstract

A partial skeleton of the early Eocene tropicbird Prophaethon shrubsolei (Prophaethontidae) from the London Clay of Walton-on-the-Naze (UK) is described. Most of the bones preserved in this fossil have not been described previously for Prophaethon or prophaethontids in general. The pelvis and leg bones of Prophaethon, including the previously unknown tarsometatarsus, are very different from modern tropicbirds and show a strong similarity to procellariiform birds, especially albatrosses. Rather than employing plunge-diving like their extant relatives, prophaethontids therefore probably used foraging strategies similar to those of modern albatrosses, which seize food on the sea surface. Prophaethontids also appear to have been less pelagic than extant tropicbirds, and these different life modes, as well as the disappearance of Phaethontiformes from northern latitudes, attest to major changes in Northern Hemispheric marine avifaunas during the Cenozoic, which also affected other pelagic birds. The reasons for the profound changes in the historical biogeography and way of living of tropicbirds are unknown, but ecological competition and predation at breeding sites are likely to have played a role.
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A Plains-wanderer (Pedionomidae) that did not wander plains: a new species from the Oligocene of South Australia 

(pages 68–74)
Vanesa L. De Pietri, Aaron B. Camens and Trevor H. Worthy
Article first published online: 3 NOV 2014 | DOI: 10.1111/ibi.12215

Abstract

The remarkable fauna of Australia evolved in isolation from other landmasses for millions of years, yet understanding the evolutionary history of endemic avian lineages on the continent is confounded by the ability of birds to disperse over geographical barriers even after vicariance events. The Plains-wanderer Pedionomus torquatus (Charadriiformes) is an enigmatic, predominantly sedentary, quail-like bird that occurs exclusively in sparse native grasslands of southeastern Australia. It is the only known species of its family (Pedionomidae), and its closest relatives are the South American seedsnipes (Thinocoridae). Here we describe a further representative of this lineage, Oligonomus milleri gen. et sp. nov., from the Late Oligocene of South Australia (26–24 Ma), which pre-dates the earliest record of P. torquatus by c. 22 Ma and attests to the presence of this lineage during Australia's period of isolation (50–15 Ma). Based on the morphology of the coracoid and the palynological record, we propose that O. milleri and P. torquatus were ecologically disparate taxa and that, similar to coeval marsupials, O. milleri inhabited well-wooded habitats, suggesting that the preference for grassland in the extant P. torquatus and thinocorids is likely to be convergent and not ancestral. The speciation event leading to the evolution of the extant Plains-wanderer was probably triggered by the spread of grasslands across Australia in the Late Miocene–Pliocene, which this record pre-dates. The presence of a pedionomid in the Late Oligocene of Australia strengthens the hypothesis of a Gondwanan divergence of the lineages giving rise to Thinocoridae and Pedionomidae.
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BIOGEOGRAPHY AND SPATIAL ECOLOGY


Niche shift in four non-native estrildid finches and implications for species distribution models 

(pages 75–90)
Darius Stiels, Bianca Gaißer, Kathrin Schidelko, Jan O. Engler and Dennis Rödder
Article first published online: 20 AUG 2014 | DOI: 10.1111/ibi.12194

Abstract

Non-native species can have severe impacts on ecosystems. Therefore, predictions of potentially suitable areas that are at risk of the establishment of non-native populations are desirable. In recent years, species distribution models (SDMs) have been widely applied for this purpose. However, the appropriate selection of species records, whether from the native area alone or also from the introduced range, is still a matter of debate. We combined analyses of native and non-native realized climate niches to understand differences between models based on all locations, as well as on locations from the native range only. Our approach was applied to four estrildid finch species that have been introduced to many regions around the world. Our results showed that SDMs based on location data from native areas alone may underestimate the potential distribution of a given species. The climatic niches of species in their native ranges differed from those of their non-native ranges. Niche comparisons resulted in low overlap values, indicating considerable niche shifts, at least in the realized niches of these species. All four species have high potential to spread over many tropical and subtropical areas. However, transferring these results to temperate areas has a high degree of uncertainty, and we urge caution when assessing the potential spread of tropical species that have been introduced to higher latitudes.
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Site-specific dynamics in remnant populations of Northern Wheatears Oenanthe oenanthe in the Netherlands 

(pages 91–102)
H. Herman van Oosten, Chris Van Turnhout, Caspar A. Hallmann, Frank Majoor, Maja Roodbergen, Hans Schekkerman, Remco Versluijs, Stef Waasdorp and Henk Siepel
Article first published online: 19 SEP 2014 | DOI: 10.1111/ibi.12205

Abstract

Dynamics of populations may be synchronized at large spatial scales, indicating driving forces acting beyond local scales, but may also vary locally as a result of site-specific conditions. Conservation measures for fragmented and declining populations may need to address such local effects to avoid local extinction before measures at large spatial scales become effective. To assess differences in local population dynamics, we aimed to determine the demographic drivers controlling population trends in three remaining populations of the Northern Wheatear Oenanthe oenanthe in the Netherlands, as a basis for conservation actions. An integrated population model (IPM) was fitted to field data collected in each site in 2007–2011 to estimate fecundity, survival and immigration. Sites were 40–120 km apart, yet first-year recruits were observed to move between some of the sites, albeit rarely. All three populations were equally sensitive to changes in fecundity and first-year survival. One population was less sensitive to adult survival but more sensitive to immigration. A life table response experiment suggested that differences in immigration were important determinants of differences in population growth between sites. Given the importance of immigration for local dynamics along with high philopatry, resulting in low exchange between sites, creating a metapopulation structure by improving connectivity and the protection of local populations are important for the conservation of these populations. Site-specific conservation actions will therefore be efficient and, for the short term, we propose different site-specific conservation actions.
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ORNITHOLOGICAL METHODS


Exposing hidden endemism in a Neotropical forest raptor using citizen science 

(pages 103–114)
Alexander C. Lees and Robert W. Martin
Article first published online: 20 SEP 2014 | DOI: 10.1111/ibi.12207

Abstract

Gaps in our knowledge of the geographical distribution of species represent a fundamental challenge to biogeographers and conservation biologists alike, and are particularly pervasive in the tropics. Here we highlight the case of the Rufous-thighed Kite Harpagus diodon, a South American raptor commonly mapped as resident across half the continent. Recent observations at migration watch points have indicated it may be partially migratory in the southernmost parts of its range. To investigate this possibility, we collated contemporary and historical specimen records, published sight records and ‘digital vouchers’ – photographs and sound-recordings archived online (from citizen science initiatives) – and explored the spatiotemporal distribution of records. We were unable to trace any documented records of this species from Amazonia during the austral summer (October–March), or records from the Atlantic Forest biome during the peak of the Austral winter (June–August), and all proven breeding records stem from the Atlantic Forest region. We compared this pattern with that of a ‘control’ species, the congeneric Double-toothed Kite H. bidentatus, again using specimens and digital vouchers. For this species we found no evidence of seasonality between biomes and can disregard spatiotemporal variation in observer effort as a cause of seasonal biases. We consider that all populations of Rufous-thighed Kites are fully migratory, wintering in Equatorial forests in the Amazonian basin. We provide evidence that this pattern was previously obscured by erroneous undocumented records and poor or erroneous specimen metadata, and its discovery was primarily facilitated by digital vouchers. This discovery requires a reassessment of the species’ global conservation status as an Atlantic Forest breeding endemic, threatened by habitat loss and degradation, as it was previously considered to be resident across large swathes of undisturbed Amazonian Forest on the Guiana Shield. The bulk of the digital voucher data used to elucidate this pattern were extracted from a Brazilian citizen science initiative WikiAves, which may serve as a model for collating biodiversity data in megadiverse countries and help catalyse environmental awareness.
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Assessing the short-term effects of capture, handling and tagging of sandgrouse 

(pages 115–124)
Fabián Casas, Ana Benítez-López, Jesús T. García, Carlos A. Martín, Javier Viñuela and Francois Mougeot
Article first published online: 18 NOV 2014 | DOI: 10.1111/ibi.12222

Abstract

Capturing and marking free-living birds permits the study of important aspects of their biology but may have undesirable effects. Bird welfare should be a primary concern, so it is necessary to evaluate and minimize any adverse effects of procedures used. We assess short-term effects associated with the capture, handling and tagging with backpack-mounted transmitters of Pin-tailed Pterocles alchata and Black-bellied Pterocles orientalis Sandgrouse, steppe birds of conservation concern. There was a significantly higher mortality (15%) during the first week after capture than during the following weeks (< 2.5%) in Pin-tailed Sandgrouse, but no significant temporal mortality pattern in Black-bellied Sandgrouse. In Pin-tailed Sandgrouse, mortality rate during the first week increased with increasing relative transmitter and harness weight regardless of season, and with increasing handling time during the breeding season. There were no significant differences in mortality rate between study areas, type of tag, sex or age or an effect of restraint time. These results suggest the use of lighter transmitters (< 3% of the bird's weight) and a reduction of handling time (< 20 min), particularly during the breeding season, as essential improvements in procedure to reduce the mortality risk associated with the capture, handling and tagging of these vulnerable species.
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DISPERSAL AND MIGRATION


Wind conditions experienced during the day predict nocturnal restlessness in a migratory songbird 

(pages 125–132)
Cas Eikenaar and Heiko Schmaljohann
Article first published online: 3 OCT 2014 | DOI: 10.1111/ibi.12210

Abstract

A variety of methods have been used to study the relationship between wind conditions and departure decisions of migrant birds at stopover sites. These methods are either costly or suffer from inaccuracy in determining whether or not an individual has resumed migration. Here we present a novel and simple approach to studying the relationship between wind conditions and departure likelihood. Northern Wheatears Oenanthe oenanthe caught during stopover were temporarily caged to measure their nocturnal migratory restlessness, which is an accurate proxy for their individual departure likelihood. We then related the degree of nocturnal restlessness to wind conditions prevailing at the time of capture. Confirming the general pattern from previous studies of departure, the intensity of nocturnal migratory restlessness, and hence departure likelihood, increased with increasing wind support towards the migratory goal. This suggests that approximating the propensity to depart by measuring nocturnal migratory restlessness is a reliable way to study the effect that wind conditions experienced during stopover has on the departure decision of migrants. Our study also shows that nocturnal migrants possess the ability to use information gathered during the day for their departure decisions at night. Because measuring migratory restlessness is straightforward and inexpensive, our approach is ideally suited to test hypotheses regarding spatio-temporal variation in wind selectivity in migrating birds.
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Dispersal, movements and site fidelity of post-fledging King Eiders Somateria spectabilis and their attendant females 

(pages 133–146)
Rebecca L. Bentzen and Abby N. Powell
Article first published online: 11 NOV 2014 | DOI: 10.1111/ibi.12217

Abstract

Post-fledging dispersal and site fidelity are poorly understood, particularly for sea ducks that spend the majority of their annual cycle at sea. This is the first description of movements and their timing for first-year (juvenile) and second-year (subadult) King Eiders Somateria spectabilis in relation to their attendant females. We fitted satellite transmitters that operated for 2 years to 63 hatch-year birds and 17 attendant females at breeding areas in northern Alaska in 2006–2009. Our goals were to describe the spatio-temporal distribution of pre-breeding individuals and adult females that had been successful breeders. We also examined fidelity to wing moulting and wintering areas as well as natal philopatry. Juveniles did not appear to follow attendant adults, although they did winter in the same three general wintering areas, suggesting that genetic inheritance and social factors may have roles in the initial migration from the breeding area. Additionally, juveniles were more variable in the timing and duration of migration, moved longer distances during the winter, and were less faithful to moulting and wintering areas than adults, indicating that individual exploration and acquired navigational memory played a role in subsequent migrations. Most (75%) subadult females returned to natal areas, probably prospecting for future nesting sites, whereas subadult males were widely dispersed at sea. Timing and duration of moult migration and wing moult of adult females that were presumed to be successful breeders differed from those of unsuccessful breeders due to the extended time that the former spent on the breeding grounds. Temporal and spatial segregation of post-fledging King Eiders from adults has direct management implications in terms of resource development and population dynamics.
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SHORT COMMUNICATIONS


Body mass and latitude both correlate with primary moult duration in shorebirds 

(pages 147–153)
Maurine W. Dietz, Ken G. Rogers, Jorge S. Gutiérrez and Theunis Piersma
Article first published online: 1 AUG 2014 | DOI: 10.1111/ibi.12185

Abstract

We investigated the effects of body mass and latitude on primary moult duration from published data of migrating shorebirds that moult exclusively on the wintering grounds. Non-phylogenetic and phylogenetic models demonstrated that body mass and latitude correlate with moult duration in a non-additive way: the models predict different latitudinal relationships for smaller and larger shorebirds, and in the northern hemisphere, primary moult duration increased allometrically with body mass (exponent = 0.17), whereas in the southern hemisphere, primary moult duration was not correlated with body mass. If birds optimize feather quality and if slower moult yields sturdier feathers, the fast primary moult of northerly wintering shorebirds indicates additional selection pressures at work.
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Migrating ducks in inland North America ignore major rivers as leading lines 

(pages 154–161)
Benjamin J. O'Neal, Joshua D. Stafford and Ronald P. Larkin
Article first published online: 20 AUG 2014 | DOI: 10.1111/ibi.12193

Abstract

A recently developed radar-based technique permitted empirical re-evaluation of the established but poorly supported theory that migrating North American waterfowl (Anatidae) use landscape features such as rivers as leading lines. Ducks departing the Illinois River Valley in the autumn of each of 15 years travelled SSE with a mean track that was 68° different from the 220° course of the Illinois River (P ≤ 0.001). We conclude that leading lines were unimportant navigation aids for ducks leaving this major stopover site in autumn and suggest that rivers have less effect on the spatial course of duck migration than previously thought. Timing of departures was examined in a representative subset of 8 years and found to be consistent, with a mean start time of 44 min after civil sunset.
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Reduced genetic diversity in Bearded Vultures Gypaetus barbatus in Southern Africa 

(pages 162–166)
Sonja C. Krüger, Philipp L. Wesche and Bettine Jansen van Vuuren
Article first published online: 23 SEP 2014 | DOI: 10.1111/ibi.12200

Abstract

The Bearded Vulture Gypaetus barbatus occurs throughout its range in small and dwindling population fragments with limited genetic differentiation between populations, suggesting that the species might be managed as a single entity. The numbers of East and Southern African Bearded Vultures included in previous studies were small, so we determine the genetic variation within, evolutionary placement of and connectivity among sub-Saharan African populations. Mitochondrial DNA fragment analyses detected little or no differentiation between populations in Ethiopia and Southern Africa, with reduced haplotype diversity in Southern Africa compared with populations in the Northern Hemisphere. The results inform conservation management of this species globally and locally, and offer guidelines for translocations should populations continue to decline.
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Cavity use throughout the annual cycle of a migratory woodpecker revealed by geolocators 

(pages 167–170)
Elizabeth A. Gow, Karen L. Wiebe and James W. Fox
Article first published online: 20 SEP 2014 | DOI: 10.1111/ibi.12206

Abstract

The importance of cavities as roost sites in migratory species is often unknown because it is challenging to monitor cavity use during the non-breeding period. We documented cavity use throughout the annual cycle of a woodpecker using light-level geolocators. Northern Flickers Colaptes auratus spent 63–90% of nights roosting in a cavity throughout the year, including during migration. The high frequency of year-round cavity use by Flickers suggests that cavities provide benefits beyond nest-sites. Our work highlights the potential use of geolocators to examine cavity use.
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Population genetics and demographic inferences in a recovering shorebird, the African Black Oystercatcher Haematopus moquini 

(pages 171–176)
Timothy C. Bray and Phil A. R. Hockey
Article first published online: 19 SEP 2014 | DOI: 10.1111/ibi.12209

Abstract

The extensive literature on the African Black Oystercatcher is a testament to what is now a conservation success story. Here we provide the first genetic insight into the population dynamics of this recovering shorebird and an assessment of genetic variation within the species using microsatellite markers. Although behavioural studies suggest strong natal philopatry, we found a single genetic cluster across all of the locations sampled and a significant signal of isolation by distance suggesting some geographical structuring. The microsatellite markers used in this study are useful at a population level, and the limited genetic variation detected is likely to be due to a low historical population size.
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Naturally high heavy metal concentrations in feathers of the flightless Kagu Rhynochetos jubatus 

(pages 177–180)
Jörn Theuerkauf, Tokushi Haneda, Nozomu J. Sato, Keisuke Ueda, Ralph Kuehn, Roman Gula and Izumi Watanabe
Article first published online: 3 NOV 2014 | DOI: 10.1111/ibi.12216

Abstract

We assessed heavy metal concentrations in feathers of 38 Kagus Rhynochetos jubatus living on ultramafic soils in New Caledonia. Concentrations of heavy metals in down feathers were similar to concentrations in shafts of primary or secondary feathers, whereas the concentrations in vanes were much higher, indicating that concentrations in down feathers were not due to external contamination but rather to ingestion. Although there was no anthropogenic pollution in our study area, concentrations of iron (Fe), zinc (Zn), manganese (Mn), chromium (Cr), selenium (Se), strontium (Sr) and cobalt (Co) in feathers were 1.2–21 times higher in Kagu than the average in other bird species studied, the majority of those from polluted environments. Kagus may have specific adaptations that enable them to live in environments with naturally high heavy metal concentrations.
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Supplementary feeding increases Common Buzzard Buteo buteo productivity but only in poor-quality habitat 

(pages 181–185)
Eimear Rooney, Neil Reid and W. Ian Montgomery
Article first published online: 24 NOV 2014 | DOI: 10.1111/ibi.12218


Abstract
Temporal heterogeneity in the effects of food supply during the breeding season on the productivity of the Common Buzzard Buteo buteo was investigated in a supplementary feeding experiment. Pairs were fed artificially (1) before egg-laying, (2) after chicks hatched and (3) continuously throughout the season, and compared with (4) unfed controls. Pairs fed before egg-laying had marginally larger clutches than those not fed, but lay date, egg volume and weight, brood size and hatching success were unaffected. Territorial quality had far greater effects, with pairs nesting in low-quality habitats (bog, scrub and semi-natural grassland) laying later and having lower hatching success, smaller broods and fewer fledglings than those in more productive agricultural landscapes. Supplementary feeding after egg hatching neutralized the negative effect of poor habitat, resulting in fed birds having significantly more fledglings. This study emphasizes the importance of food availability when provisioning chicks in suboptimal habitats and has implications for the success of diversionary feeding in reducing game losses to Buzzards.
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