Steen R., Løw L.M., Sonerud G.A., Selås V. & Slagsvold T. 2011. Prey delivery rates as estimates of prey consumption by Eurasian Kestrel Falco tinnunculus nestlings. Ardea 99: 1–8.

In altricial birds the type of prey selected by parents for their nestlings may affect the allocation of time and energy spent on hunting, preparing prey and feeding the nestlings, which in turn may affect the rate of provisioning. Raptors take relatively large prey items, which facilitates the quantification of rates of prey items and prey mass delivered to nestlings. Estimates of rates of prey delivery in raptors are nevertheless few and have been based on direct observations from a hide in combination with analyses of prey remnants and regurgitated pellets. To obtain better estimates we video monitored prey deliveries at 55 nests of Eurasian Kestrels Falco tinnunculus. Of the 2282 prey items recorded, voles were most abundant by number, followed by birds, shrews and lizards, while insects and frogs were rare. An average brood of 4.3 nestlings was estimated to consume 18.3 g/h, hence a nestling consumed on average 4.2 g/h. This is equivalent to 67.8 g/d, given an average daily activity period of 16.1 h. The estimated delivery rate of prey items required to feed an average brood in our study was 91 per h if the kestrels had provided only insects, and 3.4, 1.9, 0.83 and 0.52 if they had provided only lizards, shrews, voles or birds, - respectively. This corresponds to one prey delivery per 40 s if feeding solely on insects and one per 18, 32, 75 and 120 min if feeding solely on lizards, shrews, voles or birds, respectively. We argue that kestrels in the boreal forest would be unable to raise an average brood solely on insects or lizards, unlikely to do so solely on shrews, but able to do so solely on voles in a vole peak year.

Probst R., Nemeschkal H.L., McGrady M., Tucakov M. & Szép T. 2011. Aerial hunting techniques and predation success of Hobbies Falco subbuteo on Sand Martin Riparia riparia at breeding colonies. Ardea 99: 9–16.

We analysed 291 attacks by 15 male Hobbies Falco subbuteo at 13 different Sand Martin Riparia riparia colonies in Austria, Hungary, and Serbia in 2004 and 2005. We predicted that the choice of escape strategy would be contextdependent and related to the condition and age of swallows and relative position and flight characteristics of both predator and prey. We predicted that swallows would be unable to escape falcons in a level chase and would not seek cover. We predicted that falcons would be more successful when juveniles were present. Hunting success rates were higher during the swallows' post-fledging period, probably because of the weaker flight performance of juveniles. Invariably, adult swallows tried to outclimb falcons, while probable juveniles also tried to escape to cover. Hobbies most often attacked adult swallows by a fast approach from great heights and distances. In contrast, in the post-fledging period, when juveniles were available, low horizontal attacks and long climbing chases were common. In doing so, Hobbies at times prevented juvenile swallows from taking cover and were, in turn, sometimes able to outclimb and capture them. Significantly more attacks were abandoned during the post-fledging period. Sand Martins were unable to escape Hobbies in a level chase. Individual male Hobbies showed no difference in hunting success, maybe because all were experienced. The number of Sand Martins present at the time of attack did not influence hunting success. The results are discussed in the light of the anti-predator strategies of animals living in groups.

Tomé R., Dias M.P., Chumbinho A.C. & Bloise C. 2011. Influence of perch height and vegetation structure on the foraging behaviour of Little Owls Athene noctua: how to achieve the same success in two distinct habitats. Ardea 99: 17–26.

We compared the diurnal hunting behaviour of a mainly perch-hunting species, the Little Owl Athene noctua, in two structurally different habitats: a treeless pseudo-steppe and a Holm Oak Ouercus ilex rotundifolia woodland in Portugal. While the overall prey availability was similar, perch and vegetation characteristics differed between habitats. Using focal sampling in 29 territories, we measured the type and height of utilized perches, time spent on perches and attack and giving-up distances involved in insect hunting. Moreover, we analysed the interrelationships between behaviour and habitat-specific vegetation characteristics. Little Owls adapted their hunting strategies to habitat features, achieving similar prey detection rates and the same hunting success in the two habitats. In the pseudo-steppe, where only low stone piles were available as perches, owls selected the highest spots (average 0.77 m). In this area, a positive correlation was found between perch height and distance to prey attacked, indicating that perching higher resulted in increased prey detectability. In the woodland, owls selected perches that were lower than maximally available (averages 2.67 m vs. 4.99 m, respectively). Attack distance did not differ between habitats, despite the use of higher perches in the woodland. These results indicate that the more developed ground vegetation in the woodland possibly hampered detection of prey, counterbalancing the possible advantages for prey detection due to the use of higher perches. In such situations, Little Owls seemed to select an intermediate foraging height to maximize prey detectability.

Czyz B. 2011. Do female Penduline Tits Remiz pendulinus adjust parental decisions to their mates' behaviour? Ardea 99: 27–32.

In contrast to older models of parental care, recent theoretical models assume that parents do not make their decisions independently of one another, but respond to the behaviour of their mates. Studies involving mate removal have mostly been conducted in biparental species and such experiments in uniparental species are scarce. I studied the Penduline Tit Remiz pendulinus, a small passerine bird with uniparental care provided either by a female (45% in the studied population) or a male (17%). During the egg-laying period, one parent (or both; 38% in the studied population) deserts the clutch and starts a new breeding attempt. The aim of this study was to find out whether the parental care decision of female Penduline Tits is affected by their mate's decision to desert or not. In the control group (nests where males were caught, ringed and released), almost 50% of the females deserted the nest. By contrast, most females from the manipulated group did not desert their nests after I had removed their mates. In the following days 12 experimental females (60%) mated with replacement males at their nests; this behaviour was not observed in the control group, and is very rare in the study population (3.7%). These results may suggest that female behaviour is affected by the male decision to desert or stay. However, after attracting a replacement male, some females deserted their nests. As a result, only 11 experimental females (55%) stayed and started incubation, which represents a proportion similar to that found in the control group. This study shows that Penduline Tit females respond in real time to the behaviour of their mates and that their reproductive tactics are flexible.

Cecere J.G., Cornara L., Mezzetta S., Ferri A., Spina F. & Boitani L. 2011. Pollen couriers across the Mediterranean: the case of migrating warblers. Ardea 99: 33–42.

At stopovers sites in the Sahara and on Mediterranean islands, European warblers may feed on nectar. As a consequence of this behaviour the pollen of exploited plants often sticks on the birds' bill or plumage. We analyzed pollen samples carried by migrating warblers staging at Ventotene Island (Italy), a stopover site located in the Central Mediterranean and reached by large numbers of birds after a direct flight from North Africa. We discuss the possible role of migrants as pollen vectors. A total of 38 plant taxa were recorded in the pollen samples collected on 147 migrants. Pollen of Brassica sp., Ferula communis, Citrus sp. and Eucalyptus sp. were most commonly found. The nectar of the first two plants is largely exploited by warblers on Ventotene and the presence of their pollen on plumage is principally due to nectar feeding in situ. On the contrary, Citrus sp. and Eucalyptus sp., which are scarce and absent on the island respectively, were mainly collected on dried and agglutinated samples and their presence is likely to be due to nectar feeding at other sites than Ventotene. The other 34 plant taxa were recorded with low frequencies. Overall, the data suggest that nectar feeding migrants could play a role as pollen vectors only for Citrus sp., Eucalyptus sp., F. communis and Brassica sp. However, the other less common plant taxa could also be useful markers of migration routes. We found species-specific relationships between bird species and the plants used for nectar feeding: short-distance migrants (mainly Eurasian Blackcap Sylvia atricapilla and Subalpine Warbler S. cantillans) land on Ventotene when Brassica sp. flowers are more abundant and they mainly carry the pollen of this species. On the contrary, long-distance migrants (Garden Warbler S. borin and Common Whitethroat S. communis) principally transport the pollen of F. communis, whose flowering period takes place at the same time as their staging period on the island. The study underlines the tendency of warblers towards nectar feeding during migration.

Barshep Y., Minton C., Underhill L.G. & Remisiewicz M. 2011. The primary moult of Curlew Sandpipers Calidris ferruginea in North-western Australia shifts according to breeding success. Ardea 99: 43–51.

The population moult parameters, yearly onset of moult and sex-specific schedule of moult in relation to breeding success, and pattern of feather mass growth were examined in a population of Curlew Sandpipers Calidris ferruginea that migrate to northwest Australia. The mean start date of moult was 18 September, and it lasted on average 129 days. No significant variation in duration of moult was detected and feather mass was deposited at a constant rate. The yearly onset of moult was positively correlated with the proportion of first year (juvenile) birds: the mean start date of moult in good breeding years was 25 September, ten days later than mean start date of moult in poor breeding years, being 15 September. Males generally started moult five days earlier than females. The mean moult start date of males was five days earlier in poor breeding years compared to good breeding years, while the moult of females was 11 days earlier in poor breeding years compared to good breeding years. In Curlew Sandpipers the timing of post-breeding migration is advanced in bad breeding seasons, which explains the observed correlation between breeding success and the timing of moult in non-breeding areas.

Vágási C.I., Pap P.L., Tökölyi J., Székely E. & Barta Z. 2011. Correlates of variation in flight feather quality in the Great Tit Parus major. Ardea 99: 53–60.

The most important function of moult in birds is the renewal of deteriorated feathers. Worn and holey remiges may incur fitness costs, yet little is known about the factors responsible for the degree of feather wear and sources of variation in feather hole incidence. Here, we report results on variation in feather quality based on a study of three consecutive annual cycles of a Great Tit Parus major population. We found that month, age, sex, weight and the presence of feather holes are the main sources of variation in degree of wear. Juveniles and individuals with lower feather quality (measured through rachis diameter) and with fault bars present had higher feather hole loads. Feather abrasion peaked in the breeding season and was higher in females probably due to higher workload. The lower feather quality of juveniles compared to adults probably arises because of fast ontogeny in contrast to adults' prolonged moult. Our results indicate that feather deformities are positively interrelated and can be used as proxies of feather quality. Our findings on the correlates of feather holes seem partially contradictory with the widespread view that holes are feeding marks of chewing lice. We propose that feather holes are instead minor feather handicaps, at least in Great Tits.

Castillo-Guerrero J.A., Guevara-Medina M.A. & Mellink E. 2011. Breeding ecology of the Red-billed Tropicbird Phaethon aethereus under contrasting environmental conditions in the Gulf of California. Ardea 99: 61–71.

We studied the breeding ecology of Red-billed Tropicbirds Phaethon aethereus at Farallón de San Ignacio, Sinaloa, in the south-central part of the Gulf of California, during two years with different oceanographic conditions: 2004, a neutral year, and 2007, a moderate El Niño year. We characterized oceanic changes by sea surface temperature and chlorophyll a concentration (150 km around the colony) from monthly satellite images. During two 5-day visits every month from January to May of each year we recorded timing of breeding, parental attendance, chick diet, and maximum diving depth of adults. We analyzed hatching and fledging success, chick growth and body condition. In agreement with oceanographic differences, we expected differences in timing of breeding, diet and foraging behaviour and lower breeding success and chick growth in the El Niño year. Sea surface temperature was higher, and chlorophyll concentration lower during early 2007 than in 2004. Average laying date and peak of laying occurred later in 2004 than in 2007. In 2007 adults dived deeper (2.09 ± 0.96 vs. 0.96 ± 0.66 m), had a different and more varied diet, and spent more time at sea at the expense of nest attendance than in 2004, suggesting that less food was available for this species in 2007. In agreement, hatching success was lower (35 vs. 75%), and chicks were lighter (641 vs. 739 g) and in worse body condition in 2007. Overall, despite the lower body condition of the chicks, the species seemed to exhibit some capacity to cope with the different conditions derived from warmer waters during the mild El Niño of 2006–2007.

Zozaya E.L., Brotons L. & Vallecillo S. 2011. Bird community responses to vegetation heterogeneity following non-direct regeneration of Mediterranean forests after fire. Ardea 99: 73–84.

Mediterranean forests are highly resilient to fires, showing a rapid recovery after disturbance. However, in some cases direct tree regeneration fails leading to radical changes in landscape composition. In this study, we evaluated the impact of landscape changes on the conservation value of bird species using the new landscape mosaic arising from non-direct regeneration after a fire. We used data from a large fire that occurred in central Catalonia (NE Spain) in 1998. The fire affected about 26,000 ha of a land mosaic mainly covered by Black Pine Pinus nigra forests and farmland dominated by cereal crops. We used line transects to estimate bird abundance and gathered information on dominant vegetation covers and landscape variables. Redundancy analysis (RDA) and generalized linear models were used to explore how the measured environmental variables explain bird species abundance and to analyze how post-fire heterogeneity in vegetation affected the conservation value of the bird community. Factors describing the main patterns in the post-fire landscape explained up to 31.2% of the total variability in bird community composition and described three main groups of bird species sharing similar ecological requirements. Additionally, 71% of the studied species significantly responded to one of the first three vegetation gradients distinguished in the study area. Finally, the conservation value of the bird community significantly decreased in areas dominated by Q. humilis resprouters and significantly increased in shrubland areas. Overall, our results suggest that large fires affecting non-direct regenerating forest types lead to a new and radically different mosaic landscape offering new opportunities to species with unfavourable European conservation status.

Konter A. 2011. Seasonal patterns of aggressiveness in colonial Great Crested Grebes Podiceps cristatus. Ardea 99: 85–92.

In birds, coloniality is considered to be evolutionary more advanced than solitary breeding. Territorial Great Crested Grebes Podiceps cristatus may engage in opportunistic colonial breeding. The present study focuses on behavioural aspects associated with clumped nesting. Based on the assumption that different agonistic interactions may trigger different costs, aggressiveness during colony establishment and subsequent nesting in the Great Crested Grebe was measured. Upon platform initiation, focal pairs claimed a territory by performing intense platform courtship. With agonistic behaviour they tried to prevent additional conspecifics from settling in their direct vicinity. As a consequence, early levels of aggression in the entire colony increased with the numbers of settled pairs. Quite quickly however, aggressiveness declined despite additional pairs settling and long before the maximum number of platforms for a particular year was reached. Two main phenomena may have contributed to the decline in aggression. First, colonial Great Crested Grebes could have been conducting behaviour consistent with the ‘dear-enemy-effect’. Second, habituation to or accommodation with new neighbours could have been helped by behavioural adaptations. Focal pairs provided evidence for a relationship between aggression and egg-laying. The aggressive behaviour that was observed after clutch initiation could have been an effort to reduce the risk of intraspecific brood parasitism. Thereafter, fighting was uncommon and aggression was greatly limited to ritualized threatening. Aggression levels were higher in areas of high nesting density prior to and during egg-laying, but no longer so after clutch completion. It is concluded that colony establishment in the Great Crested Grebe is not an index of the species' sociability, but rather expresses its phenotypic plasticity to adapt to close neighbours and to contain its aggressiveness.

Albano N., Masero J.A., Sánchez-Guzmán J.M., Villegas A. & Santiago-Quesada F. 2011. Effects of diet on growth-related patterns of energy and macronutrient assimilation efficiency in a semi-precocial bird, the Gull-billed Tern Gelochelidon nilotica. Ardea 99: 93–101.

Despite the extensive literature on energy assimilation efficiency in birds, only a few studies have dealt specifically with offspring, and to our knowledge there is no information on macronutrient assimilation efficiencies during the growth period of chicks. We studied growth-related energy and macronutrient assimilation efficiencies of semi-precocial chicks of Gull-billed Terns Gelochelidon nilotica as a function of their diet. We experimentally evaluated several digestive parameters in chicks fed different diets — fish vs. insects — when 10, 15 and 22 days old. Gross daily energy intake was similar in the two groups throughout the growth period, but fish-fed chicks showed consistently higher energy and macronutrient assimilation efficiencies than chicks fed insects. Energy and macronutrient assimilation efficiencies varied with age, peaking at 15 days old. The only digestive parameter that did not decrease during the last phase of growth was the lipid assimilation efficiency. Fish-fed chicks grew significantly faster than those fed on insects, which showed delayed growth. We suggest that semi-precocial chicks could modulate energy and macronutrient assimilation efficiency according to their growth requirements and that such digestive parameters can help us to understand differences in chick growth rates and breeding success in a natural environment.

Ruokonen M. & Aarvak T. 2011. Typology revisited: historical taxa of the bean goose — pink-footed goose complex. Ardea 99: 103–112.

Taxonomic practices change over time and this affects the number of taxonomical units recognized. In late 19th and early 20th centuries the number of species increased as a consequence of typological thinking, i.e. classifying all aberrant individuals to a separate species. During this period, several species or subspecies of the bean goose complex were described, and currently their status is either considered not valid or is not agreed upon. We studied individuals from five of the historical taxa, Anser neglectus, A. mentalis, A. oatesi, A. fabalis johanseni and A. fabalis curtus, by using mitochondrial DNA and morphological measurements to clarify their taxonomical status. Overall, we did not find support for additional taxa other than those currently recognized.

Onrubia A., Muñoz A.-R., Arroyo G.M., Ramírez J., de la Cruz A., Barrios L., Meyburg B.-U., Meyburg C. & Langgemach T. 2011. Autumn migration of Lesser Spotted Eagle Aquila pomarina in the Strait of Gibraltar: accidental or regular? Ardea 99: 113–116.

The Lesser Spotted Eagle (LSE) migrates to its winter quarters via the eastern Mediterranean corridor. During 1998 to 2009, 47 LSEs have been registered in the Strait of Gibraltar during a monitoring program of bird migration. All observations were made between 6 August to 12 October (mean 16 September, median 12 September). Of thirteen age-identified LSEs, ten birds were nonjuveniles. Six out of 86 LSEs fitted with a satellite transmitter at the western limit of its distribution followed the western route. Three of those birds reached Africa via the Strait of Gibraltar. The presence of LSE in our study area, albeit in small numbers, indicates the existence of a minor migration route across the Iberian Peninsula.

Hegemann A. & Voesten R. 2011. Can Skylarks Alauda arvensis discriminate a parasite nestling? Possible case of nestling Cuckoo Cuculus canorus ejection by its host parents. Ardea 99: 117–120.

The Common Cuckoo Cuculus canorus is an obligate brood parasite and many studies have dealt with egg rejection by host species. However, evidence for ejection of Cuckoo nestlings by host parents has not been reported. Here we describe an observation of a Skylark Alauda arvensis pair that probably ejected a young Cuckoo and subsequently raised their own offspring. This was the only case we detected Cuckoo parasitism among 348 Skylark nests in our study area in the northern Netherlands, while we found about 21% of 43 Meadow Pipit Anthus pratensis nests being parasitized by Cuckoos.