Relative forelimb–hindlimb investment is associated with flight style, foraging strategy, and nestling period, but not nest type

We investigated Dial’s 2003 hypothesis that birds that rely more heavily on flight as their primary mode of locomotion and thus invest more in their forelimbs than hindlimbs will experience selection for smaller body sizes, greater altriciality, and more complex nests. To test this hypothesis, we examined the skeletons of over 2,000 individuals from 313 species representing the majority of avian families and all major branches of the avian tree. We used the lengths of the sternal keel and long bones of the wing relative to the lengths of the leg long bones as an index of relative locomotor investment. We found that locomotor investment was predicted by flight style, foraging method, and length of nestling period, supporting Dial’s hypothesis. Soaring birds and birds with more acrobatic flight styles, birds whose foraging methods were heavily reliant upon flight, and birds whose young spent more time in the nest tended to invest more in their forelimbs relative to hindlimbs. Nest type and body size were not significant predictors of relative forelimb–hindlimb investment, however, suggesting that the relationships among flight style, locomotor investment, and life history are not as tightly intertwined as Dial originally hypothesized.

Temporal patterns in prey size between sexes in a raptor with extreme size dimorphism: testing the intersexual competition hypothesis using web-sourced photographs

In most vertebrates, males are larger than females. For raptors, sexual size dimorphism is reversed, with females being larger. Reversed sexual dimorphism (RSD) in raptors is strongly linked to diet, with species feeding on the most agile prey, for example bird-eating raptors, showing the greatest size differences between the sexes. Hypotheses for reversed sexual dimorphism (RSD) include the ‘intersexual competition’ hypothesis, which proposes that RSD evolved to enable pairs to expand their dietary niche (taking a wider range of prey sizes) during the nestling period when both sexes occupy and hunt within the same territory, and thereby reduce competition between the sexes. If intersexual competition is responsible for the evolution of RSD, we predict that sex-related differences in prey size and dietary niche breadth will be particularly pronounced during the nestling period (cf. the non-nestling period). We explore this prediction in the highly dimorphic Eurasian Sparrowhawk (Accipiter nisus), which displays the largest degree of RSD of all raptors, using web-sourced photographs to identify diet throughout the entire year. We analysed 666 photographs of sparrowhawks on their prey over time. In contrast to our predictions, sex-specific prey sizes were most similar during the nestling period compared to any other time of the year. Both males and females reduced the size of their prey during the nestling period which may be a result of the ‘ingestion rate’ hypothesis, or a strategy employed to prevent hunting-related injuries during this critical period of the year.

New Nesting Records and Breeding Ecology Observations of Rufous-legged Owls in the Mediterranean Temperate Forest of Central Chile

ABSTRACT The Rufous-legged Owl (Strix rufipes) is the southernmost Strix owl species and its breeding ecology remains little known. We report new observations on the species' breeding ecology, including clutch size, egg size, duration of the incubation and nestling periods, and nestling diet. We conducted our observations on nests found during the summers of 1999 through 2004 in a forestry landscape of central Chile, dominated by Monterey pine (Pinus radiata) plantations with intermixed fragments of native southern beech (Nothofagus) forests. Clutch size was two eggs (n = 2 nests), with one egg larger than the other (mean = 48.8 × 40.1 mm). The incubation period was 30 d and the nestling period 34 d. We analyzed 10 pellets from nestling owls and identified 45 prey items, mostly dominated by large beetles, grasshoppers, and rodents (native and exotic). This information, though based on a limited number of nests, provides baseline ecological data that can inform future studies.

Male Barn Swallows Tolerate Nestling-Like Courtship Calls of Rival Males

Animals often exhibit conspicuous, and sometimes curious, courtship traits, such as nestling-like courtship display in birds, though modern studies of nestling-like courtship display (and calls) are virtually lacking. An exception is previous experiments on the barn swallow Hirundo rustica, demonstrating that females are equally attracted to playback of two structurally similar calls, nestling-like male courtship calls and nestling food-begging calls. The experiments support the sensory trap hypothesis, i.e., that male signals mimic nestling stimuli to exploit female parental care for nestlings. However, female attraction might not be the sole function of nestling-like traits, and males might also have a sensory bias toward nestling-like traits, in which males would be less aggressive toward characteristics typical of immature individuals. Here, I conducted playback experiments to study the function of nestling-like male courtship calls in the context of male–male interactions. Playback of male courtship songs induced frequent approaches by neighbouring males, while nestling-like male courtship calls or nestling food-begging calls induced fewer approaches, though male responses to the latter two vocalisations increased when approaching the nestling period. The observed pattern indicates that, by mimicking immature individuals, males attract intended signal receivers (i.e., females) while avoiding interference from eavesdroppers (i.e., neighbouring males). This unique function can explain why species with parental care exhibit immature-like behaviour.

Quantitative analysis of the orientation of white stork nestlings’ parents from video monitoring

Video-monitoring has become in the last decades common practice for animal observation and conservation purposes. In Ornithology, it is mostly used for tracking predators and nest surveillance, but, with the rapid development and spreading of webcams on nests for educational purposes, new opportunities arise for behavioral investigation, through citizen science for instance. In this article, we use video-monitoring from a public webcam on a White stork (Ciconia ciconia) nest and perform systematic image analysis to record the positioning and orientation of the guarding parent on the nest, during the nestling period over 60 days. From this data of 450 orientation samples, correlations with weather parameters are drawn. Our results suggest that the sun is responsible for most of the orientation with an hourly dependence, while the wind has prevalence during rainy days. A change in the parent behavior is also observed around the time the nestlings are known to attain their maximal weight. These preliminary findings provide new insights on weather influence on parental care behavior likely linked with the parent’s sensing. The versatility of the proposed method allows for behavioral studies on a wide variety of species.

Breeding records of Leptotila rufaxilla (Aves: Columbidae) in southwestern Brazilian Amazon with notes on nesting in some regions of occurrence

We present new aspects of breeding biology of Gray-fronted Dove Leptotila rufaxilla, from five nests found between 2012 and 2014 in a lowland forest fragment in southwestern Brazil. The nests simple/platform shape were built at a mean height of 1.90 m above ground. The clutch size was two eggs white and elliptic, incubated for 15 days (based on three nests). We recorded predation in two nests still in incubation phase. Minimum hatch weight of nestlings was 10 g and young fledged with a mean mass of 56 g. The constant growth rate (K) of nestlings was 0.40 with a growth asymptote of 60.7 g. Daily survival rate, Mayfield and apparent nesting success in the incubation period was 90, 20 and 56%, respectively, while in the nestling period were all 100%. Our data and the contribution of citizen science showed that L. rufaxilla breeds over the year, mainly in the rainy season, both in southwestern Amazonia and in other regions of occurrence.

Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Nestling ejection is a rare type of host defence against brood parasitism compared to egg ejection. Theoretically, host defences at both egg and nestling stages could be based on similar underlying discrimination mechanisms but, due to the rarity of nestling ejector hosts, few studies have actually tested this hypothesis. We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis, a host that seemingly accepts non-mimetic eggs of its parasite, the shining bronze-cuckoo Chalcites lucidus, but ejects mimetic parasite nestlings. We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings. We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs. Ejection of artificial nestlings did not depend on whether their colour matched that of the brood. The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host. Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood, but only occasionally when they did not match the colour of the foster brood. Begging calls differed significantly between parasite and host nestlings throughout the nestling period. Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone or cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin colour. This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.

Imperfect mimicry of host begging calls by a brood parasitic cuckoo: a cue for nestling rejection by hosts?

Coevolutionary interactions between avian brood parasites and their hosts often lead to the evolution of discrimination and rejection of parasite eggs or chicks by hosts based on visual cues, and the evolution of visual mimicry of host eggs or chicks by brood parasites. Hosts may also base rejection of brood parasite nestlings on vocal cues, which would in turn select for mimicry of host begging calls in brood parasite chicks. In cuckoos that exploit multiple hosts with different begging calls, call structure may be plastic, allowing nestlings to modify their calls to match those of their various hosts, or fixed, in which case we would predict either imperfect mimicry or divergence of the species into host-specific lineages. In our study of the little bronze-cuckoo Chalcites minutillus and its primary host, the large-billed gerygone Gerygone magnirostris, we tested whether: (a) hosts use nestling vocalisations as a cue to discriminate cuckoo chicks; (b) cuckoo nestlings mimic the host begging calls throughout the nestling period; and (c) the cuckoo begging calls are plastic, thereby facilitating mimicry of the calls of different hosts. We found that the begging calls of little bronze-cuckoos are most similar to their gerygone hosts shortly after hatching (when rejection by hosts typically occurs) but become less similar as cuckoo chicks get older. Begging call structure may be used as a cue for rejection by hosts, and these results are consistent with gerygone defences selecting for age-specific vocal mimicry in cuckoo chicks. We found no evidence that little bronze-cuckoo begging calls were plastic.

Spatio-temporal patterns of the Red-footed Falcon’s hunting behavior during the nestling period suggest ad hoc conservation policies

The Red-footed Falcon (Falco vespertinus) is a species of high international conservation interest. We analyzed its hunting behavior at the two largest colonies in Italy during the nestling period. Using accurate data-loggers, we tracked three adult Red-footed Falcons in June and July, 2019 and collected 4703 GPS points. We detected clear patterns of hovering and perching activity (HPA) in both time and space. HPA occupied one-third of the Red-footed Falcons’ day, and showed two peaks just after sunrise (between 35 and 40% of the monitoring time) and just before sunset (50‒60%) in both June and July, and minimum (20‒30%) at night and during the hottest time interval (10:00 a.m.‒4:00 p.m.). Almost 40% of HPA occurred within 50 m from nests. Our findings, although preliminary, have important implications for the conservation of these two colonies that are located within two Natura 2000 sites. The detected spatio-temporal patterns of Red-footed Falcons’ hunting behavior suggests the creation of two nested protection belts: the inner one is a narrow belt (up to 50 m from the two rows of trees that host the two colonies) with integral conservation, and hopefully increase the alfalfa crops and fallow land, and the outer belt (50 m‒2 km) with optimized agricultural activities.

Predation and prey-caching of Eastern Water Skinks Eulamprus quoyii by nesting Nankeen Kestrels Falco cenchroides in eastern New South Wales

The breeding diet of a pair of Nankeen Kestrels Falco cenchroides nesting in Beresfield, eastern New South Wales, in 2020 was investigated. By individual prey species, the diet comprised 61.3% reptiles (including two prey species not previously recorded in the Nankeen Kestrel diet—Eastern Water Skink Eulamprus quoyii and most likely Southern Rainbow Skink Carlia tetradactyla), 9.7% birds (including a new prey species—Superb Fairy-wren Malurus cyaneus), 6.4% invertebrates (two crickets: Grylloidea), 3.2% mammals (one House Mouse Mus musculus) and 19.4% unidentified prey items (percentages by number). During 31.5 h of observations, the male delivered 22/31 prey items (71%) and the female delivered 9/31 prey items (29%) to the nest tree. The average delivery rate over the entire nestling period was one prey item per hour. Prey-caching, whereby the female stored lizards in the fork of a tree and later retrieved them and fed them tothe single nestling, was observed. Further studies are needed to obtain well-documented accounts of prey-caching by Australian falcons.