Flocking behaviour has been studied for decades around the world, but there is little knowledge of this subject in desert bird communities. We investigate winter flock structure in open woodlands of the central Monte desert, Argentina, during two consecutive years. Of the 22 bird species that were recorded in flocks, most were granivorous. There were differences in flock density between years, probably due to fluctuation in seed abundance. More than half of the observed flocks were composed of different species (i.e. mixed-species flocks). We detected only two regular species (found in more than 75% of flocks): Rufous-collared Sparrow Zonotrichia capensis and Ringed Warbling Finch Poospiza torquata, both granivorous birds. Ringed Warbling Finch and Cinnamon Warbling Finch Poospiza ornata co-occurred at a higher frequency than expected by chance, and formed subgroups within flocks. Many-colored Chaco Finch Saltatricula multicolor, Greater Wagtail-tyrant Stigmatura budytoides, Brown Cacholote Pseudoseisura lophotes and Short-billed Canastero Asthenes baeri were found to form family groups, which may be related to delayed natal dispersal. The observed flocking propensity of granivorous birds and the small number of species per flock were similar to that found in other desert bird communities. We discuss some differences and similarities between granivorous and insectivorous flocking patterns, and propose hypotheses on the plausible causes. Our results provide a basis for a better understanding of the flocking behaviour patterns of birds in arid environments.

The diet of Eurasian Kestrels Falco tinnunculus during the breeding season is well documented in continental populations, but not in their island-dwelling counterparts. The subspecies F. tinnunculus canariensis is a habitat-generalist on the oceanic island of Tenerife, one of its southernmost breeding sites in the Western Palaearctic. We analysed trophic diversity and diet in its main five habitat-types by identifying 5284 prey items in regurgitated pellets from nest sites and roosting sites collected during two consecutive breeding seasons. Secondly, we analysed 2585 prey remains collected from nest sites during 19 breeding seasons. In terms of numbers, insects (mainly Orthoptera and Coleoptera) predominated in pellets: 71% in chicks and 89% in adults, with variation in taxa according to habitat. This reflects opportunistic predation of insects, with grasshoppers being the staple diet in subalpine scrub (above 2000 m a.s.l). The endemic Gallot's Lizard Gallotia galloti provided the greatest biomass in pellets (58% in chicks, 55% in adults) and comprised the most abundant source of prey remains found at nest sites (92% in terms of numbers). Chick diet showed broader trophic diversity than adults. We found high overlap in diet composition between habitats in Tenerife (71% chicks; 66% adults). Kestrels inhabiting anthropogenic environments and northern scrub showed broader trophic diversity; those inhabiting subalpine scrub showed the lowest values. Kestrels inhabiting different habitats in Tenerife showed broad trophic diversity which suggests opportunistic and flexible foraging strategies, as expected of a generalist species. Regardless of habitat, trophic diversity showed high overlap in adult diet composition not only between the Canary Islands (87%), but also between insular and continental reference populations, especially the Iberian Peninsula (81%). Thus, the generalist habits of the Eurasian Kestrel seem to predominate over any expected ecological adaptations associated with island populations.

It has been suggested that in most colony-breeding birds, food availability in the feeding areas surrounding the colonies limits, and thereby regulates, population size. However, population size is also determined by adult survival, which will additionally be influenced by circumstances outside the breeding season. Most Eurasian Spoonbills Platalea leucorodia leucorodia in The Netherlands breed on the Wadden Sea barrier islands. After 30 years of exponential growth, the breeding population in the Dutch Wadden Sea area is now levelling off towards a maximum of nearly 2000 nests. For these Spoonbills, density-dependent effects on survival by the different age-classes and in the different seasons have already been demonstrated. However, the mechanisms underlying the densitydependent survival of juveniles before and after fledging remain unclear. To examine whether these density-dependent effects reflect limitations at the colony level, we compared colony growth, chick condition and reproductive success among the Wadden Sea colonies. Population growth rates from 1988 to 2015 varied widely between the 10 existing colonies, and so did the statistically predicted maximum colony sizes. Chick condition, measured for 781 chicks in six different colonies between 2011 and 2015, was lower in stable colonies than in growing colonies, although not for the very late chicks, and reproductive success tended to be lower as well. Over the longer period of 1991 to 2011, reproductive success showed a strong negative relationship with colony size. We propose that the levelling off of colony sizes in the Wadden Sea is caused by local food limitations, and suggest further research in this direction. The continuing growth of the Dutch population is now being fuelled by exponentially increasing numbers of Spoonbills breeding in the Delta area.

Persistent plumage colour polymorphism occurs in around 3.5% of bird species, with raptors showing a disproportionately high frequency of such polymorphisms. The genus Buteo has more polymorphic species than any other raptor genus (15 polymorphic species out of 25). These polymorphisms are interesting from an evolutionary perspective, because they are heritable and hence a good model for understanding mechanisms preserving genetic variation. For evolutionary models, it is important to assess whether discrete morphs exist or whether variation is more continuous. Using image analysis, we show that in Common Buzzards Buteo buteo variation is continuous and unimodal, ranging from very dark to very light individuals. Previous studies on Common Buzzards have used a classification with three discrete morphs. We compared this classification with a seven-scale morph classification used in our study. We used photographs of the same individuals taken at different ages. Even though the plumage gets somewhat darker from juvenile to adult age, morph type did not change substantially.

In this paper, we provide for the first time a detailed description of the breeding ecology of the Masked Laughingthrush Garrulax perspicillatus. Our findings indicate that this species is a cooperative breeder with retained offspring. Flocks of Masked Laughingthrushes occurred in winter; these split into smaller breeding groups during the spring. The size of breeding groups varied from three to six individuals (mean = 3.8 individuals, n = 26). Clutches were initiated between early March and early August. Clutch size averaged 3.3 eggs and ranged from two to five (n = 18). The incubation period lasted on average 13.2 days (n = 9) and chicks left the nest after 12 days (n = 23). Breeding groups produce 2–3 broods per year (n = 2). 82.8% of 58 breeding attempts resulted in fledged offspring. Helpers were observed participating in nest-building, incubation and provisioning. The size of breeding groups was significantly related to both the overall frequency of feeding trips to the nest and brood size at fledging, with a higher frequency of feeding trips and more fledglings for larger groups. Hence, both breeders and helpers may potentially derive fitness benefits from helping at the nest.

Two methods are commonly used to study the diet of nestling passerines: the neck collar method and faecal sampling. Most studies apply either method, however, few methodological studies comparing both methods exist and are mainly limited to farmland birds. Furthermore, existing methodological studies only include high-level taxonomic diet categories. Here, we compared both methods using two wetland species, the Reed Bunting Emberiza schoeniclus and the Sedge Warbler Acrocephalus schoenobaenus, and included family level as a lower taxonomic prey level. We found no differences between the two methods in the dietary composition of high-level taxonomic categories (mainly orders) and only small differences in some orders at the family level. Hence, we recommend using the less invasive and easily accessible faecal sampling method rather than the use of neck collars in diet composition studies.

Earthworms (Lumbricidae) are important prey for many birds. Based on their own feeding ecology, earthworms can be separated into two ecotypes: the detritivores that feed on organic material and the geophages that feed on soil particles and organic matter. Detritivores collect their food on the surface during the night when they are exposed to nocturnal predators. Hungry animals tend to show more risk-prone behaviour and may therefore be more vulnerable to bird predation, so we expect well-fed detritivorous earthworms to visit the surface less frequently. In this study, we tested this hypothesis in dairy farmland in the province of Fryslân, The Netherlands. Two uniform grasslands were split, with each half receiving either an early (1 February 2014) or a late (14 March 2014) farmyard manure application. Every two weeks, nocturnal surface activity of earthworms was measured by counting surfacing earthworms from a slowly pushed cart. Furthermore, soil samples were taken for total abundances and to measure individual body conditions of earthworms. As predicted, the density of surfacing earthworms was on average 2.5 times higher in the fields before farmyard manure was applied. Immature detritivores had significantly lower body masses in fields not yet manured, suggesting that these growing earthworms were hungry. Differences in surfacing behaviour and body mass disappeared after all fields had been given farmyard manure. We conclude that hunger forces detritivorous earthworms to the surface. After manure application, they appear satisfied and avoid the risk of depredation by birds by staying away from the soil surface. To promote earthworm availability for meadow birds, spreading farmyard manure on the surface should occur as late in spring as possible. In this way, hungry earthworms are forced to the surface and are available as meadow bird prey for longer periods.

We studied the diet of four avian scavenger species, the Griffon Vulture Gyps fulvus, Black Vulture Aegypius monachus, Egyptian Vulture Neophron percnopterus and Bearded Vulture Gypaetus barbatus in Azerbaijan, in the South Caucasus region, from 2008–2012. During these years, a total of 1861 remains were collected between May and July at nests of each of the four vulture species. The collected food remains belonged to 45 different animal species, including at least 24 species of wild mammals and eight species of domestic mammals. Diet composition of Griffon and Black Vultures differed greatly between years, consisting mainly of Domestic Sheep Ovis aries in 2008 and 2009, carnivores such as Grey Wolf Canis lupus, Golden Jackal Canis aureus and Red Fox Vulpes vulpes in 2010, and Domestic Horses Equus ferus caballus in 2011 and 2012. The diet of Egyptian Vultures was less variable across years, but generally consisted of a larger variety of wild animals, including Red Fox, Brown Hare Lepus europaeus caucasicus, reptiles and several species of birds, and only a small fraction of domestic mammals (<5%). The diet of Bearded Vultures consisted mostly of Daghestan Tur Capra cylindricornis, a wild goat species. The variation in diet between years observed in Griffon and Black Vultures coincided with changes in the availability of carcasses in the environment.