Magpie Nests Research Articles

Do birds select the plastics debris used for nest construction? A case study in a Mediterranean agricultural landscape

Plastic pollution is becoming a global problem due to its ubiquitous occurrence and the impacts detected for many species. However, the research about plastics in nests of terrestrial bird species has remained relatively overlooked in comparison to those devoted to marine ecosystems. Here we study the occurrence and patterns of use of anthropogenic material in nests of two passerine birds, the Eurasian magpie (Pica pica) and the European serin (Serinus serinus), breeding in an orange tree cultivation in Mediterranean Spain. Our results show that both species use extensively plastic debris as nest material; almost 71% of the European serin nests and 96% of nests of Eurasian magpies contained plastic debris. Furthermore, by analyzing the plastic debris availability in the agricultural landscape surveyed we confirmed a selection pattern in the two species. Thus, both species preferably select plastic filaments over other plastic debris. The Eurasian magpie does not select plastic based on size or color but the European serin avoid black plastics prefer smaller fragments in comparison to the average size available. Moreover, we suggest the apparent similarity of plastic filaments with the natural materials typically used by these species, as well as how they use the plastic in their nests could influence their selection behavior. More studies focused on terrestrial birds inhabiting human modified habitats could offer a deeper approach to how plastic debris interacts with wildlife in different ways.

Landscape factors influencing bird nest site selection in urban green spaces

IntroductionUnderstanding the birds’ breeding strategies in urban habitats is vital for ensuring their continued existence. Therefore, more research must be conducted on bird breeding and urban adaptation strategies in urban green spaces. This study aimed to address this gap by investigating the influence of landscape factors on the selection of bird nest sites. MethodsData on the presence and absence of magpie (Pica pica) and gray magpie (Cyanopica cyana) nests were collected through field surveys conducted in the campus of Nanjing Forestry University during the 2023 breeding season. Generalized additive models (GAMs) incorporating landscape variables were employed to assess the effects of these predictors on nest occurrence. The model with the lowest Akaike’s information criterion value was selected among the candidate GAMs.ResultsBelow is a summary of the main results. Nest tree height (TH), distance from the central lawn (D), and tree coverage (TC) within the sampled area were identified as the primary landscape factors influencing nest site choice. Conversely, factors such as the shortest distance to the water source, herb coverage, shrub coverage, percentage of buildings, and percentage of hard pavement did not significantly impact on nest site selection. Furthermore, the nesting potential of magpies and grey magpies initially increased with tree height, reaching a maximum at ca. TH=25 meters after which it began to decline. The nesting occurrence rate showed an initial decrease tendency with increasing distance from the central lawn, reaching a minimum at D=400 meters, and then increased with further distance. Additionally, nesting potential decreased initially with increasing of TC in the range of 0–20%, fluctuated evenly between 20–60% TC, and decreased rapidly when TC exceeded 60%.DiscussionThis study provides valuable insights into the selection of nest sites by birds in urban habitats, specifically with respect to landscape factors. The understanding of the impact of urban green spaces on urban birds and the underlying mechanisms of their behavior contributes to the conservation of wild birds and promotes the harmonious development of urban areas.

Multiparasitism and repeated parasitism by the great spotted cuckoo Clamator glandarius on its main host, the magpie Pica pica: effects on reproductive success, nest desertion and nest predation

Brood parasites are expected to lay only one egg per parasitized nest, as the existence of several parasitic nestlings in a brood increases competition and can lead the starvation of some of them. However, multiparasitism (laying of two or more eggs by one or more parasitic females in a single host nest) is surprisingly frequent. Here, we study multiparasitism by different females or by the same female (repeated parasitism) in the great spotted cuckoo Clamator glandarius, a non‐evictor brood parasite that mainly parasitizes the magpie Pica pica, and whose chicks may be raised together with host nestlings in the same nest. We used a total of 262 magpie nests found during four breeding seasons. Multiparasitism and repeated parasitism are very frequent because this brood parasite is less virulent than other cuckoo species and magpie hosts can successfully raise more than one parasitic nestling per nest. The total number of cuckoo chicks fledged was higher in multiparasitized nests than in single‐ or double‐parasitized magpie nests. Magpie breeding success (i.e. the proportion of eggs that produce young that leave the nest) did not differ between single‐, double‐, and multiparasitized magpie nests. These results suggest that multiparasitism is an adaptation in the great spotted cuckoo. The intensity of parasitism (number of cuckoo eggs per nest), after controlling for the potential effect of year, did not affect nest desertion or nest predation rate, neither during the incubation nor the nestling periods. This implies that nest concealment does not affect the susceptibility of one nest being parasitized and predated, as nest predation rate was similar regardless of the intensity of parasitism. Predation rate during the nestling phase did not vary according to intensity of parasitism, which does not support either the ‘mutualism' hypothesis or the ‘predation cost of begging' hypothesis.

HABITAT STRUCTURE AND HETEROGENEITY DETERMINE A SUCCESSFUL BREEDING PROBABILITY OF THE LONG-EARED OWL (<i>ASIO OTUS</i>, STRIGIDAE, STRIGIFORMES)

In 2001 to 2020, for each Long-eared owl nest in the Crane Homeland Nature Reserve territory with an area of 48 km2, the following microhabitat parameters were determined using standard field methods: the nest type built by different bird species, the presence of a nest roof, the nesting tree species, and the nest height above the ground. In most cases, for nesting the Long-eared owl reused magpie nests (Pica pica) (77%), and half of the nests were found on willow trees (family Salicaceae) (50%). The nest height above the ground varied from 1.5 to 22 m. Vegetation on the nesting area with a radius of 500 m was determined using the “Semi-Automatic Classification Plugin” automatic vegetation classifier of QGIS software. Five habitat types were so classified: forests, shrubs, meadows, arable land, and satellite image mistakes. Village areas were allocated separately. The average shares of the largest habitat types for over 20 years on the nesting sites included meadows (51.1%) and shrubs (16%). From 2001 to 2020, a habitat change in the breeding area was observed: forest and shrub areas decreased, while the meadow, village and arable land areas increased. An analysis of the effect of habitat types on the nesting success was evaluated by means of the “gbm” and “dismo” modules in the R program using the Boosted Tree classifier algorithm. The presence of such habitat types in the nesting area as villages (24.2%), shrubs (19.3%), meadows (11.8%), and habitat heterogeneity (11.6%) most strongly affected the probability of owl successful nesting. That owls tend to use anthropogenic and agricultural territories is associated with the diversity, easy foraging and more effective protection from predators during the breeding season.

Nest characteristics and composition of the colonial nesting Azure-winged magpie Cyanopica cyanus in South Korea.

Bird nests are crucial for reproductive success since they serve as structures to hold the eggs and nestlings safely. Therefore, the structural characteristics of bird nests have optimally evolved to maximize reproductive success, which are known to be affected by various factors. We gathered information on the nest characteristics such as nest structure and constituent materials in the colonial breeding Azure-winged magpie (Cyanopica cyanus) and investigated the relationship between ecologically relevant factors and the size and mass of the nests. The Azure-winged magpie nest can be deconstructed into an outer nest and an inner cup, and the type and mass of materials used for the construction of each part varies. Compared to the inner cup, the outer nest, which constitutes the overall shape of the nest, is composed of relatively harder materials, such as branches and soil. In contrast, the inner cup, which is the part where birds directly incubate eggs and raise nestlings, is composed of more flexible and softer materials, such as fiber and moss. We found that there was no relationship between nest characteristics and ecologically relevant factors. However, as the breeding season progressed, the volume of the inner cup decreased with increasing ambient temperatures. Our results show that Azure-winged magpies use differing materials for structurally distinct parts of the nests during construction. The results also indirectly suggest that the choice regarding the amount of insulating materials relative to changing temperatures during the breeding season may be one of the more significant adaptive strategies in the nest-building behaviors of Azure-winged magpies.

New Data on Breeding Strategies and Reproductive Success of the Globally Threatened Turtle Dove Co-Occurring with the “Competitive” Collared Dove and the “Predatory” Maghreb Magpie in Olive Orchards

Interactions between co-occurring species, including competition and predation, comprise critical processes regulating local community structure, habitat use, and diversity. We monitored nesting habitats, breeding chronology, and reproductive success rates to describe the patterns of spatiotemporal organization of three co-habiting species: the “native” turtle dove, the “invasive” collared dove, and the “predatory” Maghreb magpie. We defined nesting site parameters, breeding chronology dates, and success rates to explain how these species are dispersed in space and time. Similarly, predation attacks were evaluated. Patterns of habitat use were best explained by fear of predation and competition. Both doves selected nesting sites far away from the predatory Magpie to protect their nests. Equally, sympatric Columbidae turtle dove and collared dove were segregated horizontally and vertically only in space to reduce competition inside olive orchards. On the other side, Maghreb magpie started the breeding activity first, most probably to benefit from food abundance targeted in doves’ nests (eggs and nestlings). Further, breeding success was higher in both doves, despite predation pressure exercised by the Magpie and other reptiles. Magpie nests were colonized by the great spotted cuckoo (Clamator glandarius). Finally, this study provides the first and only detailed data on nest-niche of the turtle dove co-occurring with competitor and predator species, in the entire Northwest Africa range. Additionally, our data provide an opportunity of large-scale comparative studies of the nesting niche and breeding performances of the turtle dove, collared dove, and Maghreb magpie complex.

Selection of Urbanized Areas by Magpie Pica pica in a Medium Size City in Poland.

Simple SummaryThe aim of this study was to estimate the Magpie population and to give a detailed characterization of nest site selection in a medium size city in Poland (Gorzów Wlkp.) in the XXI century. We also focused on the analysis of nest site selection along an urban gradient. The average density of Magpies was 5.5 pairs/km2 (min = 0, max = 22 nests/square). The Magpie density in those study squares situated completely within the city boundaries of Gorzów Wlkp. was 6.9 p/km2, in the non-urbanized habitat type—3.7 p/km2, and in the urbanized habitat type—13.5 p/km2. The increasing proportion of the number of nests along the urbanization gradient shows that in Gorzów Wlkp., the Magpie population has undergone the synurbanization process and is currently in the “spread” phase. The study shows that Magpies can adapt to changing urbanization factors, and changes in the choice of conifers help the species to adapt to highly anthropogenic habitats.The Magpie Pica pica occurs all over open agricultural areas in Poland, especially near human settlements (particularly in western Poland). The aim of this study was to estimate the size of the local Magpie population and characterize, in detail, nest site selection in a medium size city Górzów Wlkp. in the XXI century. For this study, the whole city was divided into a total of 114 squares of 1 × 1 km. Data were collected in spring 2014. A total of 474 Magpie pairs were recorded. The average density was 5.5 pairs/km2 (min = 0, max = 22 nests/square), in the non-urbanized habitat type—3.7 p/km2, and in the urbanized habitat type—13.5 p/km2. Magpie nests were found most often on Spruces Picea sp. and Poplars Populus sp. The mean height of the nest site was 11.5 m, while the mean height of trees used for nesting was 13.4 m. The type of tree arrangement most frequently used for nesting was tree rows (26.3%), followed by single trees (24.6%) and clusters of 4–10 trees (20.1%). The results for the Magpie’s environmental preferences do not differ from the general patterns described earlier. The study shows that magpies can adapt to changing urbanization factors, and changes in the choice of conifers help the species to adapt to highly anthropogenic habitats.

Impact of Enzootic Plague on a Population of Mexican Woodrats

Photo 1: Our controlled study of plague utilized capture–recapture to estimate survival rates of Mexican woodrats (Neotoma mexicana) in four groups comprising all combinations of vaccination, vector control, and no treatment. Photo credit: D. Biggins. Photo 2: Our study area in the Colorado foothills had many woodrat nests in shrub patches (especially three-leaf sumac, Rhus trilobata, whose leaves turned orange in fall (foreground and right side of photograph). A few nests were in cavities of cottonwoods (Populus deltoides; center). Photo credit : D. Biggins. Photo 3: Mexican woodrats are industrious nest-builders. Panel A shows a large stick nest (~ 1 m high, estimated volume 510 liters, ranked 11th largest of 139 stick nests measured) in a hawthorn (Crataegus succulenta) and sumac shrub patch. Some nests were in rock crevices (B). Photo credit : D. Biggins (A) and S. Ramakrishnan (B). Photo 4: Woodrats also constructed nests by modifying abandoned magpie (Pica hudsonia) nests (panels A and B). We infused woodrat nests on treated plots with deltamethrin dust to control vector fleas. Photo credit: D. Biggins. Photo 5: We trapped woodrats in wire mesh traps (A) and handled them under isoflurane anesthesia to collect blood samples (B), comb fleas, and take measurements, and to vaccinate a subsample of them with an experimental plague vaccine. We combed one or more fleas from 51% of the woodrats on non-dusted plots compared to a flea prevalence of 5% on dusted plots. Photo credit: S. Ramakrishnan. These photographs illustrate the article “Enzootic plague reduces survival of Mexican woodrats (Neotoma mexicana) in Colorado” by Biggins, D. E. S. Ramakrishnan, T. E. Rocke, J. L. Williamson, and J. Wimsatt published in Ecosphere. https://doi.org/10.1002/ecs2.3371.

Effects of wind farms on the nest distribution of magpie (Pica pica) in agroforestry systems of Chongming Island, China

The use of wind turbines for energy generation has complex impacts on ecosystems, especially for flying wildlife. Given the importance of birds in many ecosystems and food webs, they are often used as ecological indicators to evaluate the direct (e.g., collision mortality) and indirect (e.g., habitat degradation and loss, low food available) impact of wind farms. To test the effect of wind farms on the nest distribution of magpie (Pica pica), a common bird species in agroforestry systems on Chongming Island, China, the differences in magpie nest density variables and character variables were compared between quadrats inside and outside a wind farm. The relationship between magpie nest character variables and density variables in each quadrat was also examined and the impacts of landscape variables on magpie nest density variables were clarified in each quadrat. From March to December 2019, nest density variables (including total and in-use nest density) were recorded in quadrats inside and outside a wind farm in an agroforestry system on Chongming Island, Shanghai. Three nest character variables and five landscape variables were also recorded in each quadrat. The total nest density and nesting height in the quadrats outside were significantly higher than those inside the wind farm. There was a significant negative correlation between the average nest size in the quadrats and the total nest density, and a significant positive correlation between the average nesting height in the quadrats and both nest density variables. Moreover, farmland shelterbelt network cover and the distance to the nearest wind turbine were significantly positively related to the total nest density, whereas the farmland shelterbelt network cover was significantly positively related to the in-use nest density. These results indicate a negative effect of wind turbines on the nest density of magpies, which could be addressed by the provision of more farmland shelterbelt networks inside the wind farms located in agroforestry systems on Chongming Island, China.

Nest-site selection of an avian urban exploiter, the Eurasian magpie Pica pica, across the urban-rural gradient

Although rapid growth in the extent of urbanized habitats across the globe represents a major threat to biodiversity, there is growing evidence that urban ecosystems can represent suitable habitats for many taxa, including birds. Exploring aspects of bird ecology across the urban-rural gradient, including determinants of habitat associations, are crucial to understanding responses to urbanisation. Here, we examined factors affecting nest-site selection of Eurasian magpies across an urban-rural gradient, contrasting urban and non-urban habitats. The presence and density of Eurasian magpie nests was positively associated with the proportion of green urban areas, and negatively with forests, arable land and buildings, despite habitat associations differing across the urban-rural gradient. We also found a negative relationship between nest height and distance from city edge. The highest nests were found in city centre residential areas, whereas the lowest nests were in the new residential areas. We conclude that Eurasian magpies can successfully exploit urban environments, partially due to adaptation of their nesting behaviour. In particular, they construct their nests higher in urban areas to avoid the negative impacts of human disturbance and predation.

Parental dependence on the nest's spatial cues in offspring recognition decreases with nestling growth in the azure-winged magpie.

In altricial birds, to address which cues are used by parents to recognize their offspring, and when they switch between cues during reproduction, it has not been well determined. In this study, we address this question in a Tibetan population of the azure-winged magpie Cyanopica cyanus, by examining the dependence of parents on a nest’s spatial position in offspring recognition. During the egg and nestling phases, azure-winged magpie nests were translocated to new positions across various distances from their original site, and parental responses to the translocated nests were investigated. Our findings show that a nest’s spatial position is not connected with the survival of its young, but might be used as a cue in parental offspring recognition. When nests are translocated to a new position within a certain distance, parents could recognize their nests and returned to resume their parenting behaviors. Parental dependence on the nest’s spatial position in offspring recognition is higher during the egg phase than during the nestling phase, and it decreases with the growth of nestlings. After nestlings reach a certain age, the nest’ s spatial position was no longer used by parents as the single cue for offspring recognition. These findings suggest that azure-winged magpies switch their cues in offspring recognition during the different stages of reproduction. After parent–offspring communication has been established, the offspring’s phenotypic traits may become a more reliable cue than the nest’s spatial position in offspring recognition.

Great spotted cuckoos show dynamic patterns of host selection during the breeding season. The importance of laying stage and parasitism status of magpie nests

AbstractAvian brood parasites depend entirely on their hosts to raise their nestlings until independence. Thus, parasite females should select suitable host nests for egg laying according to traits that enhance offspring survival. The availability of nests of certain characteristics influencing the survival of parasitic offspring is, however, temporally dynamic and, thus, patterns of host selection should be evaluated considering characteristics of available host nests the day of parasitism. This allows detecting possible seasonal changes and, therefore, a more realistic picture of host selection by brood parasites. In this paper, we adopt such a new approach and consider daily availability of magpie (Pica pica) host nests at different breeding stage that were or were not parasitized by the great spotted cuckoo (Clamator glandarius). Theory predicts that cuckoos should select host nests at the laying stage. Accordingly, we detected that cuckoos preferred to parasitize magpie nests at the laying stage but, mainly, those that already harbored one or two cuckoo eggs, which may seem counterintuitive. We also showed that patterns of host selection by cuckoos varied during the breeding season, which implies that brood parasite–host interaction is dynamic depending on phenology. These patterns are hidden when not considering the temporally dynamic nature of the availability of host nests of characteristics of interest. We discuss the importance of such patterns and considering diary hosts nests availability for detecting them.

Breeding habitat and nest-site selection by an obligatory "nest-cleptoparasite", the Amur Falcon Falco amurensis.

The selection of a nest site is crucial for successful reproduction of birds. Animals which re‐use or occupy nest sites constructed by other species often have limited choice. Little is known about the criteria of nest‐stealing species to choose suitable nesting sites and habitats. Here, we analyze breeding‐site selection of an obligatory “nest‐cleptoparasite”, the Amur Falcon Falco amurensis. We collected data on nest sites at Muraviovka Park in the Russian Far East, where the species breeds exclusively in nests of the Eurasian Magpie Pica pica. We sampled 117 Eurasian Magpie nests, 38 of which were occupied by Amur Falcons. Nest‐specific variables were assessed, and a recently developed habitat classification map was used to derive landscape metrics. We found that Amur Falcons chose a wide range of nesting sites, but significantly preferred nests with a domed roof. Breeding pairs of Eurasian Hobby Falco subbuteo and Eurasian Magpie were often found to breed near the nest in about the same distance as neighboring Amur Falcon pairs. Additionally, the occurrence of the species was positively associated with bare soil cover, forest cover, and shrub patches within their home range and negatively with the distance to wetlands. Areas of wetlands and fallow land might be used for foraging since Amur Falcons mostly depend on an insect diet. Additionally, we found that rarely burned habitats were preferred. Overall, the effect of landscape variables on the choice of actual nest sites appeared to be rather small. We used different classification methods to predict the probability of occurrence, of which the Random forest method showed the highest accuracy. The areas determined as suitable habitat showed a high concordance with the actual nest locations. We conclude that Amur Falcons prefer to occupy newly built (domed) nests to ensure high nest quality, as well as nests surrounded by available feeding habitats.

Habitat and Nest Site Selection of the European Rollers in the Northern Anatolia

In this study, habitat preferences of the European Rollers (Coracias garrulus) in the Northern Anatolia was investigated, in 2014 breeding season. Total of 31 breeding pairs in 4 certain roller sites were located. The average distance between the breeding territories was 1.2 km in one of the roller sites with 17 pairs. Both solitary and colonial breeding pairs were recorded. Overall, 8, 2 and 2 nests (total of 12 nests) were located on sand quarries, concrete buildings and abandoned magpie nests on electrical poles, respectively. The habitat preferences were determined within a radius of 300 m and 1000 m around the nest site for the breeding and foraging habitats, respectively. We conducted the spatial analysis in ArcGIS 10.5 using Corine Land Cover 2012 database. Agricultural areas were the major land cover types where the European Rollers breed in our study. Use of unfavorable habitats and other nest sites including magpie nests necessitated a conservation program for the European Rollers in the study area.

Use of corvids’ nests by other bird species in Baikal Siberia and Mongolia

The paper presents the species composition of corvids in Baikal Siberia and Mongolia. More than 700 nests of 8 species of corvids in Transbaikalia, Baikal and Mongolia were examined. 133 cases of using nests of 5 species of corvids (Magpies, Eastern Carrion Crow, Rooks and Daurian Jackdaws) by other species of birds were noted. Nests of small corvids do not attract other birds. Nests of magpies are most commonly used; they are characterized by a specific structure. Of the 8 species that use corvid nests for nesting, Amur red-footed Falcon and long-eared owl are obligate tenants. Then goes Kestrel that prefers magpie nests. The number of these types in many places is determined by the abundance of magpies and crows. In recent years, due to the high number of magpies, the number of Amur falcons in the region is growing. They began following magpies to penetrate the outskirts of Ulan-Ude. Three species (Mallard, hobby, tree sparrows) are considered optional to be the tenants and three other species (Ruddy Shelduck, Long-eared Owl and House Sparrow) are considered to be random. Tree sparrows often nest in the magpie nests in natural habitats. Almost all types of tenants use old nests of the owners. Regional features in the use of corvid nests are revealed. Some species in different regions do not prefer the same nests of different types of corvids.

Aggregation of Eurasian Scops Owls Otus scops Breeding in Magpie Pica pica Nests

The Eurasian Scops Owl, a small nocturnal raptor living in continental and southern Europe, is often solitary and territorial but sometimes forms local groups, of which little is known. In this study, I examined a group of territorial Scops Owls in a habitat with limited nest site availability in Southern Italy in July of 2016 and 2017. Male Scops Owls were identified through spectrographic analysis of their vocalizations, and their location was recorded. Male Scops Owls clustered around a human-inhabited area with significant noise and light pollution and avoided the undisturbed forest, which apparently was only used for foraging. The location of territories was relatively consistent in two subsequent years. Scops Owls tended to sing where conspecifics occurred, not necessarily near their own nests. Sometimes neighbouring males occupied the same area and sang simultaneously, even when close to each other. The results are in contrast with the concept of an all-purpose, exclusive territory described for this species as the norm, and suggest that the social and spatial organization of this population is more flexible than previously thought. Scops Owls bred exclusively in abandoned Eurasian Magpie Pica pica nests, which is unusual for this typically cavity-nesting species and was presumably caused by the lack of alternative sites. The distribution of Magpie nests might thus be the main driver of nest spacing and territorial behaviour of Scops Owls in this presumably nesting site limited population. However, the underlying cause of aggregation is unknown.

Nest-site selection by Common Green Magpie (Cissa chinensis) in a tropical dry evergreen forest, northeast Thailand

ABSTRACT The Common Green Magpie (Cissa chinensis) is a nest predator in tropical evergreen forests of Indomalaya and is likely impacting the reproductive success of other birds nesting in areas where it occurs. We studied the Common Green Magpie's nest-site selection in northeastern Thailand between March and July 2015. We actively searched for Common Green Magpie nests, recorded and compared vegetation variables such as vegetation cover and stem density at 32 nest sites with 64 randomly selected non-nest sites, and modeled nest-site selection using generalized linear models. The results indicated that vegetation cover (at heights 1–3 m, >3–5 m, and >5–7 m) and stem density (at heights >3–5 m and >5–7 m) were significantly greater at nest sites than at random sites. The GLM analysis indicated that vegetation cover at >5–7 m and stem density at >7 m were the most important vegetation variables influencing nest site selection by these magpies. Choice of sites with greater vegetation cover and stem density ...

Complex feeding behaviour by magpies in nests with great spotted cuckoo nestlings

Parent decisions about food allocation are usually based on simple time‐saving rules that optimize their own fitness; however, they can sometimes vary depending on the prevailing ecological conditions both outside and inside the nest. Parent–offspring interactions also become more complex when parents suffer from brood parasitism, which implies that they care for the parasite's eggs and unrelated young. The great spotted cuckoo Clamator glandarius is a specialist brood parasite that uses the magpie Pica pica as its primary host. Here, by filming food allocation by magpie parents in natural non‐parasitized and experimentally parasitized and non‐parasitized magpie nests, we have found that magpie provisioning behaviour is highly complex including two types of feedings apart from normal ones. First, false feedings, when the parent touched the chick's beak but did not leave any food, occurred more frequently when feeding a cuckoo than when feeding magpie nestlings. Second, two types of what we have called coax feedings: 2a) when magpie parents induce a nestling to beg by waking it up by touching it softly with the beak, and 2b) when parents disregard begging signals (always from brood parasitic great spotted cuckoos) while coaxing one non‐begging nestling (always one of their own) to feed it. We suggest that brood parasitism, involving selfish excessively begging nestlings, could have acted as a selective pressure for both false and coax feedings to evolve, as both imply ignoring nestlings that beg too much. We also discuss that these parental responses could have evolved either by a discrimination without recognition mechanism, or, more probably, by a recognition‐based discrimination mechanism.

Formal comment to Soler et al.: Great spotted cuckoo nestlings have no antipredatory effect on magpie or carrion crow host nests in southern Spain.

Formal comment to Soler et al.: Great spotted cuckoo nestlings have no antipredatory effect on magpie or carrion crow host nests in southern Spain.

Criteria for host selection in a brood parasite vary depending on parasitism rate

Avian brood parasites leave parental care of their offspring to unrelated foster parents; therefore, their fitness will closely relate to their efficiency in selecting the best host. Empirical studies have shown that parasitism is not random, although it is yet unclear if this results from strategic choices of better quality hosts by brood parasites or can be a consequence of hosts and/or nests characteristics that make them more exposed to parasitism. Here, we hypothesize that the optimal strategy of host use for a brood parasite may switch depending on fluctuations in the relative abundance of parasites with respect to hosts and predict that parasites should more likely select phenotypic traits indicating host quality when this is relatively low (i.e., many available host nests for each parasite at a given time). In an 8-year study of magpie Pica pica hosts parasitized by great spotted cuckoos Clamator glandarius, we have found that in years with lower than average parasitism bigger magpie nests were more likely parasitized than smaller ones, whereas in years with higher than average parasitism big and small magpie nests had a similar chance of being parasitized. Because nest size is a postmating sexually selected signal revealing parental abilities in magpies that can be used as a target to choose profitable hosts by cuckoos, our findings support the hypothesis that active selection will become a more prevalent great spotted cuckoo laying strategy when cuckoos have a larger availability of host nests to choose among.