The Colombian Horned Lark Eremophila alpestris peregrina is an endemic bird of the Colombian Andean Plateau that is endangered due to habitat loss. Information on the population status, habitat use and reproductive biology of this species is therefore vital. We studied these aspects in the La Copa reservoir, where the largest population of this species is found. First, we determined at which locations around the reservoir it was present. At these locations, we used fixed-width transects to estimate its abundance and densities in different habitats for eight months. We monitored its reproductive biology, through behavioural observations and nest tracing during 12 months. The species was only present in plain areas with sparse short vegetation, using grassland, cropland or a mix of the two. Population densities varied significantly between habitats, being high (5.7 birds/ha) in extensive grasslands and medium to low in mixed cropland-grassland (1.1 birds/ha) and cropland (0.41 birds/ha). These differences may be related to the presence of grazing, flooding dynamics, the density of perennial forbs, the size of the grassland fields and the detrimental effect of toxic pesticides used for crop production. We estimated that 133 to 230 (95% CI) individuals (mostly adults), inhabit the entire reservoir. This is a significant number since it may represent 13–23% of the Colombian Horned Lark population. Finally, we present our data on the reproductive cycle of these larks.

Survival is a major life history trait known to be age- and/or sex-specific in many bird species. Regardless of age and sex, the survival of resident birds can be reduced by high mortality during harsh winters. In this study, we used mark-recapture data collected during 2014–2018 to assess return rates and apparent survival in relation to age, sex and winter severity in two Common Kingfisher Alcedo atthis populations from Slovakia and the Czech Republic. During five seasons, we ringed a total of 2261 Kingfishers, 353 adults and 1908 nestlings, which yielded 85 recaptures. In total, we recaptured 13.0% of birds ringed as adults (17.5% males, 8.2% females) and 0.8% of those ringed as nestlings (0.7% males, 0.1% females). Surviving adults returned to the previously used nesting hole in 87.0% of cases. Young birds never returned to the hole where they hatched. Breeding dispersal was significantly shorter than natal dispersal. Returned birds started to breed significantly earlier in the year of their return than in the previous year, but breeding success did not vary between these years. Estimated values of apparent survival were quite low, varied annually, and were negatively affected by winter severity. Males did not differ in apparent survival from females, but adults survived better than juveniles. We discuss the difference in apparent survival between the age categories by varying degrees of site fidelity/philopatry and different mortality rates.

Altricial birds face the challenge of defending their offspring against potential threats in a fixed location: their nest. In species with biparental care, both parents have an equal interest in defending their nest, although the sexes may differ in their investment in anti-predatory behaviours. We conducted a field experiment to investigate sex-asymmetry in anti-predatory behaviours in a breeding population of Lined Seedeaters Sporophila lineola, a small passerine that exhibits sexual dimorphism in adult plumage colour, in south-eastern Brazil. In Lined Seedeaters females are known to be solely responsible for nest building and incubation. Males help to feed the nestlings and are expected to assume the main role in performing anti-predatory behaviours. We presented stuffed models of nest predators (toucans Ramphastidae) and non-predators (pigeons Columbidae) at active nests and measured the number of alarm calls per minute, number of visits during the trial and latency to resume nest visits after the trial. Our results show that birds emitted alarm calls at higher rates when facing a predator than a control stimulus. Moreover, males generally emitted more alarm calls than females, irrespective of the treatment. Both parents did not visit the nest during the predator trials and they took longer to return to the nest after the model had been concealed than during the control trials. Although males seem to take the main role when it comes to responding to intruders (predator and non-predator), further studies, testing a bigger array of predatory stimuli, are needed to better test and understand sex asymmetry in risk-taking behaviours.

The ‘wintering strategy hypothesis’ predicts that the body mass of long-distance migratory dabbling ducks is low in early winter, after autumn migration, increases in mid-winter and decreases again in late winter because of the high energetic demands of the pairing period. However, this hypothesis is assumed rather than demonstrated, since very few studies have examined these predictions. Here, we tested the theory by examining changes in size-corrected body mass (Scaled Mass Index, SMI) in Northern Pintails Anas acuta wintering at rice fields of Extremadura, a key site in Southern Europe. In both females and males, SMI increased with rainfall and deceased with fasting time, peaking in midwinter and decreasing in late winter. Northern Pintails leaving Extremadura cover between 2600 and 5600 km to reach their breeding grounds and use a number of stopover sites during their northward migration. Together, our findings support the wintering strategy hypothesis and suggest that Northern Pintails wintering in Southern Europe follow an energy-minimizing migration strategy (i.e. taking advantage of the food stock found along the route and adaptively varying fat reserves in relation to the distance to cover). We discuss that this may enable them to spend more energy and time on activities such as moulting and pairing.

The Javan Pied Starling Gracupica jalla, a recent taxonomic split from Asian Pied Starling G. contra, has disappeared almost entirely unnoticed from its native range in Java and Bali, Indonesia; in a circumstance unique in bird conservation, the only known populations are held in bird shops. To provide an evidence base for any future endeavour to re-establish a population in the wild, we reviewed all published information on the species relevant to its conservation, supplemented by specimen label data, unpublished field notes, diaries and manuscripts. A population in eastern Sumatra (nine localities reported, including Bangka) had obscure origins. The species was widespread in Java (168 localities) and Bali (13 localities), and was described as one of the commonest birds in open, i.e. non-forest, lowland country (records up to 1600 m), having a high tolerance of disturbed habitats, especially agricultural areas, with often large roosts inside city limits. It fed mainly on terrestrial invertebrates and fruits, often consuming plant pests and frequently probing dung. It bred all year but chiefly in response to rains, with apparent peaks in January and May in West Java and April in East Java, building conspicuous untidy nests high in trees and laying mostly 3 (2–4) eggs. The cagebird trade is blamed for the massive decline that abruptly became apparent in the late 1990s and early 2000s, but the use of pesticides in Java and Bali's agricultural environment seems likely to have played an unseen role. Searches are needed to find any remnant populations, along with the creation of a programme of captive breeding and research to identify potential areas for reintroduction.

The relative number of adult males to females in a population, the adult sex ratio (ASR), is an important demographic variable in populations, which plays a role in, for instance, mating systems and viability of populations. The origins of variation in ASR between populations are often unclear. A skewed ASR in a local population may result from a skewed sex ratio among fledglings, sex differences in survival or dispersal or a combination of these. Meta-analyses show that ASRs across bird species are mostly male-biased and that male-biased survival is the main contributor to this bias. Here, we examine the origins of a female-biased ASR in a small population (3–24 breeding females in 2007–2017) of a passerine, the Northern Wheatear Oenanthe oenanthe. Because 95% of all fledglings were sexed, 88% of the individuals were colour-banded and because this species is highly philopatric, we could accurately examine: (1) fledgling sex ratio, (2) sex-specific first year and adult apparent survival and (3) sex-specific dispersal. It appeared that survival was not sex-biased for either age cohort but that fledgling sex ratio was male-biased, especially so among late broods. In addition, natal dispersal out of the breeding population was likely male-biased, in contrast to the general pattern of female-bias in avian dispersal. So, perhaps females are more common in our relict population solely because more males disperse from the population than females, without being compensated by male-biased fledgling sex ratio or survival and without compensation from immigrating males. Likely, the population sex ratio (including both adults and young) at the end of the breeding season is male-biased, because of a pronounced male-biased sex ratio among fledglings from late nests. Perhaps this male-bias induces prospecting young males to settle elsewhere to avoid competition next year, but at the same time convinces prospecting females to settle particularly in this area.

Nesospiza finches are endemic to two small islands in the Tristan da Cunha Archipelago in the South Atlantic Ocean. The finches have radiated into two ecologically distinct forms at both islands: an abundant, small-billed dietary generalist, and a scarce, large-billed specialist. On Nightingale Island (area 2.6 km²), the endangered large-billed Wilkins' Finches N. wilkinsi use their strong bills to crack open the hard, nut-like fruits of Island Cape Myrtle Phylica arborea trees to access the seeds. Although Phylica fruits are available year-round, the finch population is constrained by the limited area of fruit bearing Phylica trees (c. 12 ha), which makes Wilkins' Finch one of the world's naturally rarest bird species. Prior to this study, rough estimates ranged from 30–85 pairs, but there has been no dedicated survey of the population size. Over the austral summers of 2012, 2016 and 2017 we systematically caught and colour ringed birds to better estimate the population size. Pairs were present wherever there are Phylica trees across the island, utilising even small, isolated Phylica copses. Mean territory size for 117 pairs in 2017 was 0.215 ± 0.094 ha (±SD, range 0.043–0.718) with a mean density of 9.8 pairs/ha in Phylica woodland. The total population was estimated to be 120 breeding pairs (c. 280–300 mature birds). The most pressing threat to the Wilkins' Finch population is the recent arrival of an invasive insect, the Brown Soft Scale Coccus hesperidum, and its associated sooty mould Seiridium phylicae, which reduces Phylica fruit loads and kills large trees. The potential use of a biological agent to control Brown Soft Scale infestations is being investigated, since without swift and effective mitigation, we predict the health of these woodlands will rapidly degrade with serious implications for the persistence of Wilkins' Finch. Until effective mitigation is taken, we recommend up-listing the species to Critically Endangered based on IUCN Red List Criterion B2.

The European Shag Phalacrocorax aristotelis is a threatened seabird species in Portugal. Knowledge about this population is limited, and currently there is no information about dietary needs and threats posed by fisheries. We studied the diet composition of Shags in the Berlengas archipelago, the largest breeding colony in the country, through the analysis of 124 regurgitated pellets, and estimated trophic overlap with local fisheries, during the breeding and winter seasons of 2016–2017. A total of 32 fish species were identified in their diet, while their major prey consisted of sand eels (Ammodytidae) and species from the Labridae, Gadidae and Sparidae families. Diet composition varied seasonally and was more specialized during the breeding season, with sand eels comprising 70% of all prey consumed and 45% of total biomass. During winter, the consumption of heavier predatory fish increased, particularly fish from the Gadidae and Sparidae families. Shags consumed 17 species also targeted by commercial fisheries, and fish were in the same size range, highlighting the potential for resource competition. Fish species that contributed the most to prey overlap were the Pouting Trisopterus luscus, White Seabream Diplodus sargus, Common Two-banded Seabream Diplodus vulgaris, Bogue Boops boops and Black Seabream Spondyliosoma cantharus. Among different types of fishery, trophic overlap with Shags was more pronounced with polyvalent gear (longlines and gillnets), especially during winter, than with purse seine and trawling. Competition between Shags and local commercial fisheries may represent an additional pressure on foraging Shags, as well as increasing their conflict with fishing activity.

Classic explanations for polygyny consider habitat, genetic makeup and paternal care, but little attention has been paid to social inertia. We studied facultative social polygyny in a population of Blue Tits Cyanistes caeruleus with a low rate of polygyny (3% of males across 12 years). Occurrence of polygyny was best predicted by social turnover after the disappearance of one or more individuals; habitat quality and individual phenotypic traits were unimportant. Females settled as secondary females with a male and in an area they had previously associated with, indicating a role of familiarity in the formation of polygyny. Females mated to polygynous males received less help feeding nestlings. Reduced paternal care is potentially costly, because these females survived less well than females mated to monogamous males. Reduction in care occurred at both primary and secondary nests although polygynous males rarely divided their care between nests. On any given day during the nestling period, polygynous males were more likely than monogamous males to not feed nestlings at all and – as a consequence – polygynous males provided less care in total than monogamous males. Polygynous males rarely intermingled visits at both nests, suggesting a cost of switching between feeding locations. Both primary and secondary nests had reduced fledging success, even after controlling for variation in habitat quality and paternal care, due to a higher rate of nest failure. Paternity loss was higher at secondary nests, presumably because the secondary female copulated with a previous mate that disappeared. Due to increased paternity loss and reduced fledging success polygynous males did not sire more fledglings than monogamous males in a given season. Thus, the benefit of social polygyny for males seems limited. Social polygyny in our population probably arises as a by-product of widowed females settling as secondary mates with a familiar male or in a familiar area, thereby making the best of a bad situation.