Identifying important foraging areas is fundamental to detecting the demographic drivers of a species and ultimately to plan conservation measures. For some species, such as small pelagic seabirds, foraging grounds are difficult to locate and remain largely unknown. We used miniaturised GPS devices (∼0.95g) to study foraging movements of Mediterranean Storm-petrels Hydrobates pelagicus melitensis during the incubation period. A total of 43 individuals at Benidorm colony (southwestern Mediterranean Sea) were tracked during a single foraging trip. We first assessed potential negative effects of the tracking devices. We recorded 22 complete foraging trips and measured home-range, foraging areas and the degree of overlap among individuals. We used first passage time analyses (FPT) to differentiate foraging/resting from flying/travelling activities and to infer potential foraging areas. All tracked birds returned to the colony. On average, individual body weight slightly decreased after foraging trips, suggesting a small immediate negative effect of the device. Tracked birds had high breeding success (0.71). Foraging trips lasted between 1 and 4.5 days with the total distance travelled ranging between 303.14 and 1,726.53km. The visited areas covered the whole south-western part of the Mediterranean Sea. Tracked individuals shared more than 50% of their home-range areas. Foraging areas were located further from the colony than previously thought (from 240 to 469km away) on deep sea areas of the Alboran Sea and Cartagena Canyons. Further studies are needed to locate foraging grounds during other life-cycle periods and to evaluate repeatability yearly, in order to determine the important marine areas for the species.—Rotger, A., Sola, A., Tavecchia, G. & Sanz-Aguilar, A. (2021). Foraging far from home: GPS-tracking of Mediterranean Storm-petrels Hydrobates pelagicus melitensis reveals long-distance foraging movements. Ardeola, 68: 3-16.

This paper explores how environmental traits shape the winter distribution of passerine (O. Passeriformes) richness in the south-western Palearctic, a major wintering ground for the European avifauna. We apply three complementary approaches. First, we assess the way climate, landscape and habitat affect species richness by means of field counts across the study area. Second, we model the spatial distribution of six common passerines using ring recoveries as presence data. Finally, where the resulting models predict the actual distribution of birds, we employ the models to forecast the future distribution of richness according to predictions of climate change, i.e. of increasing temperature and decreasing precipitation. The results support an effect of landscape, habitat structure, temperature and precipitation on bird richness. Distribution models fit the actual distribution of bird richness and their predictions suggest that winter species richness will decrease in lowlands and increase in highlands. This pattern could be related to direct effects of temperature on thermoregulatory costs and indirect effects on winter primary productivity affecting food resources. These results also indicate that, in a context of climate warming, species-rich sectors will shift from lowlands to highlands, suggesting that uplands will have a regulatory role in the future winter distribution of birds.—Tellería, J.L., Fandos, G. & Fernández-López, J. (2021). Winter bird richness distribution in the south-western Palearctic: current patterns and potential changes. Ardeola, 68: 17-32.

Extensive bird monitoring programmes are fundamental for estimating inter-annual population trends using data provided by thousands of observers through standardised fieldwork. Gordo (2018) has proposed that abundance data recorded by common bird monitoring schemes (e.g. SACRE programme) should be used cautiously due to its potential inaccuracy, because two surveys per spring are not enough to record the actual maximum number of individual birds at a sampling location. We carried out numerical simulations and analysed the interspecific pattern of statistical significance of the published population trends of the Spanish common birds census, the SACRE programme (1998-2011), in order to test how the number of repetitions of censuses per year affects the power of tests: (i.e. the probability of detecting significant trends that are in fact true), and the probability of obtaining low false discovery rates: i.e. identifying significant changes that are actually false, when estimating yearly population changes. We agree with Gordo (2018) that two surveys of the same sampling stations per year are unable to detect the maximum number of birds throughout a breeding season. Nevertheless, the goal of monitoring programmes is not to obtain the maximum number of birds at each sampling unit over a long time span but to measure reliable population trends. Our results demonstrate that the average number of birds recorded in two surveys per season provides a highly reliable indication of population trends for abundant and widely distributed bird species, the focal taxa in common birds monitoring schemes, especially of long-term average trends > ±2.5% change annually. The actual population trends for very rare species, such as those with data from fewer than 50 UTM squares and < 5 individual birds per census and UTM cell, are hard to detect unless they show yearly percentage population changes greater than ±5%.—Carrascal, L.M. & del Moral, J.C. (2021). Two surveys per spring are enough to obtain robust population trends of common and widespread birds in yearly monitoring programmes. Ardeola, 68: 33-51.

Mountain ecosystems are subject to many pressures, including changes in land use, rising temperatures and increasing recreational activities. These factors may disrupt food webs, threatening the survival of organisms and, ultimately, ecosystem functioning. However, few studies focus on the trends of different groups joined by trophic links in alpine ecosystems. The Yellow-billed (Alpine) Chough, Pyrrhocorax graculus, a gregarious bird that moves in flocks, is an ideal target species within this framework since it has a grasshopper-based diet during the summer and may attend sites that are heavily developed for recreational activities. We tested therefore whether flock size co-varied with grasshopper abundance along an elevational gradient in two alpine areas subject to different levels of human disturbance. Chough flock size and grasshopper abundance were measured along elevational transects. The median flock size was analysed in relation to grasshopper abundance and biomass, we also conducted negative binomial GLMs to account for effects of period (i.e. from June to mid-August), site and elevation. In both study areas, chough flocks were larger at the elevation where grasshoppers were more abundant. This may indicate the capacity of the species to follow large-scale fluctuations in their key insect prey. On the other hand, the relationship between flock size and grasshopper biomass was positive at a natural site and negative at a tourist site. This suggests that where there is a high level of human influence, other factors, such as the availability of human-provided food, may disturb the natural relationship between choughs and their key prey. Overall, our results indicate that flocking by foraging Yellow-billed Choughs reflects both grasshopper abundance and the degree of anthropogenic influence.—Vallino, C., Caprio, E., Genco, F., Chamberlain, D., Palestrini, C., Roggero, A., Bocca, M. & Rolando, A. (2021). Flocking of foraging Yellow-billed Choughs Pyrrhocorax graculus reflects the availability of grasshoppers and the extent of human influence in high elevation ecosystems. Ardeola, 68: 53-70.

Carcass counts notably underestimate avian collision rates due to three main bias sources: imperfect detection, carcass removal by scavengers and carcass dispersion in unsearched areas. We assessed these sources of bias at electric lines of two Canary Islands, Lanzarote and Fuerteventura, quantifying the factors influencing them. We also carried out a cost-effectiveness assessment of carcass search done perpendicularly to electric line axis. We surveyed 230km of three types of electric lines (high-voltage, medium voltage and telephone lines) during three periods (July 2015, November-December 2015 and March 2016) searching for collision fatalities (N = 431), recording the species, the carcass distance from the electric line, mean cable height, carcass detection distance and decomposition state. In addition, we carried out a disappearance rate experiment to estimate carcass removal by scavengers. A generalised least squares model was used to analyse dispersion distance of carcass from electric lines, in relation to species body mass, mean cable height and line typology. Detection probability functions were fitted to estimate carcass detectability, incorporating body mass, decomposition state and habitat structure as covariates. A Generalised Mixed-Effects model was carried out to analyse carcass disappearance in relation to time elapsed since carcass placement, carcass size, season and island. Dispersion distance decreased with body mass and increased with cable height, being further at high-voltage lines. Overall, detection probability was 0.134, increasing with carcass size, decreasing with decomposition state and being lower in rocky areas which offered a significant challenge when walking through rough terrain. Disappearance rates differed between islands probably due to differences in avian scavenger abundance, increased with time elapsed and decreased with bird size. This study provides correction factors to obtain unbiased estimates of avian mortality rates within sparsely vegetated landscapes. Moreover, it identifies a 27m threshold distance at which the cost-effectiveness of searching for carcasses is optimised.—Gómez-Catasús, J., Carrascal, L.M., Moraleda, V., Colsa, J., Garcés, F. & Schuster, C. (2021). Factors affecting differential underestimates of bird collision fatalities at electric lines: a case study in the Canary Islands. Ardeola, 68: 71-94.

In 2010-2016, we monitored 28 clutches of eight adult Little Bustard Tetrax tetrax females tracked by GPS on the Lleida Plain, in the Ebro Depression (NE Spain), to study nesting and incubation behaviour. In addition to describing these behaviours, we used generalised linear mixed models to identify the factors that determine hatching probability, such as laying date, nesting habitat and incubation behaviour. We found a high capacity (53%) to produce replacement clutches following nest failure. Unsuccessful nests represented 67.9% of clutches, mainly due to the low hatching rate of replacement clutches (16.7%) but also of the first clutches (44%). The main causes of failure were nest abandonment or predation (58%), while farming practices were responsible for 38.9% of failures. We found an increased risk of failure due to desertion or predation towards the end of the incubation. The risk of failure was higher in late clutches, although this seemed to be directly related to cereal mowing and to changes in nesting substrate, from cereal to alfalfa, which occurred throughout the breeding season. Likewise, we found a negative effect of the size of the field where the nest was found and of the surrounding habitat on the hatching probability, which we related to the availability of food for the female in these fields. Measures aimed at improving food provision, by increasing field edge density and fallow availability, would help to maintain hens in good condition prior to and during incubation, as well as providing suitable habitat for replacement clutches. Adaptive irrigation and mowing patterns in alfalfa fields during the nesting season could contribute to increasing the hatching success of replacement clutches.—Cuscó, F., Bota, G., Llovet, A. & Mañosa, S. (2021). Nesting and incubation behaviour of the Little Bustard Tetrax tetrax and its relation to hatching success. Ardeola, 68: 95-122.

Knowledge of natal dispersal and juvenile survival from parental independence until recruitment into breeding populations is an important aspect of population dynamics studies. Dispersal allows genetic connectivity and demographic compensation between neighbouring populations. These issues are particularly significant for species confined to mountaintops, as is the Rock Ptarmigan Lagopus muta in southern Europe. We studied natal dispersal and survival in juvenile Rock Ptarmigan in the French Alps and Pyrenees between 1999 and 2018 by radiotracking 113 young captured in September in two study areas. At both sites natal dispersal occurred in two discrete phases, in autumn (October-November) and in spring (late March-mid-May). Juvenile females dispersed twice as far as males in autumn at both sites but this difference decreased in spring and was not significant. Juveniles of both sexes dispersed further in the Pyrenees than in the Alps (males: 3.5 vs. 1.4km; females: 6.5 vs. 4.4km), a situation we attribute more to genetic differences between the two populations rather than to environmental factors. As to geographical barriers to dispersal, our radiotracking data along with extensive visual observations suggest that Rock Ptarmigan living in the Alps and the Pyrenees rarely fly across valleys 10-12km wide. For sexes and locations combined, the survival rate of juvenile Rock Ptarmigan during a ten-month period (September to June) was 0.636 (95%CI: 0.551-0.734). Long-distance dispersal tended to reduce the survival of birds during their first breeding attempt (April-June), a result that suggests a delayed effect of such dispersal.—Novoa, C., Resseguier, J., Muffat-Joly, B., Blanch Casadesus, J., Arvin-Bérod, M., Gracia Moya, J. & Desmet, J.F. (2021). Natal dispersal and survival of juvenile Rock Ptarmigan Lagopus muta in the French Alps and Pyrenees. Ardeola, 68: 123-141.

Anthropogenic noise is spreading worldwide and can interfere with the acoustic communication of multiple animal groups. Species communicating in low-frequency ranges (having large sound production structures) and with limited vocal learning are expected to be especially vulnerable to human noise-induced masking interference. Yet how such species may confront this emerging impact has scarcely been explored. Here we examined the effect of anthropogenic noise on the calling behaviour of a sizeable non-passerine bird, the Little Bustard Tetrax tetrax, across a gradient of road traffic noise and in relation to male position within the lek. Using directional recordings and noise mapping, we determined inter– and intra-individual variation in call parameters and their relationship with noise level and frequency at both spatial and temporal scales, defined respectively as (i) variation of noise according to the position of the calling sites of each male within the lek (spatial scale) and (ii) fine temporal variation of noise experienced by individual males immediately prior to each call (temporal scale). Little Bustard males increased their call rate at sites exposed to higher average noise levels and at those located further from the nearest neighbour within the lek, whereas temporal changes in noise showed no effect on call rate. In contrast, call duration decreased with relative increases in noise level prior to each call, being unaffected by spatial changes in noise. Peak call frequency showed no significant variation over time and among sites. Our findings reveal that, despite its supposedly limited vocal learning, this species seems to exhibit fine-scale vocal adjustment, which implies some capacity to cope with anthropogenic noise. However, the lack of frequency shift suggests behavioural constraints that may compromise communication as the species uses low-pitched calls. This study provides insights into how some non-passerine birds may adjust their vocal sexual display to anthropogenic noise.—Barrero, A., Llusia, D., Traba, J., Iglesias-Merchan, C. & Morales, M.B. (2021). Vocal response to traffic noise in a non-passerine bird: the Little Bustard Tetrax tetrax. Ardeola, 68: 143-162.

The breeding period, a key stage in animal life histories, incurs high energy expenditure and there is often the possibility that parasite infections may compromise its success. Since defences against parasites are also costly to produce, individuals should optimise the allocation of limited available resources to reproduction activities or self-maintenance, e.g. supporting immune function and sustaining body mass. Here we explored the relationships between haemosporidian infection status, body condition and nestling feeding rate in helpers, female breeders and male breeders of a cooperative breeding corvid, the Iberian (Azure-winged) Magpie Cyanopica cooki. For infection status we differentiated between uninfected birds and, separately, those infected with one or more than one Leucocytozoon parasitic lineage. Our predictions were that both breeder and helper Iberian Magpies harbouring a haemosporidian mixed-infection should show lower body condition and nestling feeding rates than single-infected and uninfected birds. We found that most of the Iberian Magpies studied (78.7%) were infected with Leucocytozoon species, most of them (67.1% of Leucocytozoon-infected individuals) harbouring mixed infections. The scaled body mass index did not differ with respect to infection status in male or female breeders; however, mixed-infected helpers showed lower body condition than single-infected ones. Moreover, we found that mixed-infected males, as well as single and mixed-infected female breeders, but not infected helpers, showed lower nestling feeding rates than uninfected individuals. These findings could indicate a compromise between reproductive and immune functions in the Iberian Magpie, which effect becomes more evident in those individuals with a higher reproductive investment during the breeding period. —Parejo-Pulido, D., Magallanes, S., Vinagre-Izquierdo, C., Valencia, J., de la Cruz, C. & Marzal, A. (2021). Relationships between haemosporidian infection and parental care in a cooperative breeder, the Iberian Magpie Cyanopica cooki. Ardeola, 68: 163-180.

The illegal killing of many threatened species is an ongoing conservation concern, especially in the Mediterranean region. This study provides quantitative data on non-game birds admitted with gunshot injuries to wildlife rehabilitation centres (WRC) of the Valencian Community (eastern Spain), over a 25-year period (1991-2015). A total of 2,076 shot non-game birds of 101 different species were admitted, including 112 individuals belonging to 17 threatened species. Raptors were the most affected group, comprising 74% of the total admissions. The number of yearly admissions was positively related to the number of issued hunting licences, and both declined over the study period. Evidently, illegal hunting occurred throughout the year, although it peaked during the official hunting season. The occurrence of birds admitted with gunshot wounds was higher in more densely populated municipalities and in those closer to WRCs. Our results show that illegal hunting of protected bird species prevails despite legislative efforts, and it could pose a major problem for some endangered species. Accordingly, it is necessary to focus current action to reduce illegal hunting in conflictive areas.—Crespo, J., Solís, I. & Barba, E. (2021). Illegal bird hunting in eastern Spain: a declining trend, but still worrying. Ardeola, 68: 181-192.

In most unisexual species, the numbers of male and female individuals are approximately equal. The adult sex ratio (ASR) is a key demographic parameter for the conservation and management of wild species. However, in the case of monomorphic birds such as the Rock Ptarmigan Lagopus muta, estimating the sex ratio is difficult. To test if the sex ratio is balanced, we analysed the adult sex ratio of this tetraonid with two different methods, using microsatellite individualisation of non-invasive samples (faeces) and the hunting bag data of birds hunted in the French Alps and Pyrenees. The results of our non-invasive study revealed a balanced ASR in spring, whereas hunted specimens had a strongly male-biased ratio for adults but an approximately balanced sex ratio for juveniles (< 1 year old). The sex ratio estimated from hunting data may be biased for the adult population and, as occurs in other species, is not representative of the overall sex ratio. Our results suggest that, assuming our sampling strategy was adequate, non-invasive sampling is a good method to estimate ASR.—Aleix-Mata, G., Pérez, J.M., Adrados, B., Boos, M., Marty, E., Mourieres, P., Lauer, E., Zimmermann, S., Mossoll-Torres, M. & Sánchez, A. (2021). Sex ratio of Alpine and Pyrenean Rock Ptarmigans Lagopus muta estimated by a non-invasive method (faecal DNA analysis) and from hunting bag data. Ardeola, 68: 201-212.

According to the host manipulation hypothesis, parasites modify the hosts' phenotype to maximise their transmission success. Avian malaria parasites and related haemosporidians are vector-borne parasites infecting birds worldwide. Recent studies have reported a greater attraction of mosquitoes to infected birds, supporting the host manipulation hypothesis. Changes in the composition of the uropygial gland secretion of birds associated with infections have been proposed as the potential mechanisms explaining this pattern. Here we critically review the published information on the host manipulation hypothesis in the context of avian malaria infections. We focus this article on the suggested role of the secretions of the uropygial gland and bird odours as mosquito attractants. The role of uropygial gland secretions as attractants of mosquitoes was poorly supported by available literature. In contrast, changes in the odour profile of infected birds or a reduction in the anti-mosquito behaviour of infected individuals may explain the parasite-mediated effects on mosquito attraction and biting rates. Finally, we propose future research approaches to identify the role of parasite infections on the interaction between birds and insect vectors.—Martínez-de la Puente, J., Díez-Fernández, A., Soriguer, R.C., Rambozzi, L., Peano, A., Meneguz, P.G. & Figuerola, J. (2021). Are malaria-infected birds more attractive to mosquito vectors? Ardeola, 68: 251-264.

La Sección Bibliográfica de Ardeola publica reseñas de libros publicados recientemente. Estas reseñas se realizan desinteresadamente por un conjunto de colaboradores. Las reseñas son normalmente solicitadas por los editores a los colaboradores, aunque otras adicionales pueden ser consideradas para su publicación. Las reseñas expresan las opiniones de los revisores, de modo que no reflejan necesariamente la opinión de los editores o de SEO/BirdLife.

En este informe se muestra información sobre 176 especies que se reparten por toda la geografía nacional. Entre ellas, se incluyen 23 especies que aparecen de forma escasa y principalmente durante el invierno para las que se muestra su distribución espacio-temporal para el periodo 2019/2020 mediante mapas y gráficas (véase De Juana y Garcia, 2015; Gil-Velasco et al., 2018; Rouco et al., 2018; Molina et al., 2019a y b y 2020). Para contabilizar el número de citas para cada especie escasa se revisaron las observaciones disponibles en diferentes plataforma de recogidas de datos, especialmente en eBird (eBird, 2020; Observado, 2020; Reservoir Birds, 2020 y Ornitho, 2020), descartando aquellas que aparentemente correspondieran a las mismas citas hechas por diferentes observadores con el objeto de contar con muestras de datos lo suficientemente homogéneas. Se sigue la secuencia taxonómica de acuerdo con la nueva lista patrón de las Aves de España (Rouco et al., 2019).