Post-fledging Dependence Period Research Articles

Using juvenile movements as a proxy for adult habitat and space use in long‐lived territorial species: a case study on the golden eagle

Effective conservation management of wildlife species depends on understanding their space and habitat use. Telemetry has become the primary source of data for information on how species use space and habitats. However, animals can be difficult to capture, leading to limited sample sizes and thus low quality inferences. As some individuals may be easier to capture than others, it may be tempting to use them to make inferences about the studied population as a whole. Juvenile birds, in contrast to adults, are easy to capture while they are still in the nest. However, there are few studies on when and how they might serve to obtain a representative characterization of the habitat or space use of adults. This study investigated this by using GPS‐tracking data of 35 adult/juvenile dyads of golden eagles Aquila chrysaetos, with the juvenile and adult in a dyad sharing the same home‐range. We assessed juvenile‐to‐adult home‐range overlap and also compared their relative use of habitats within that space. We also analysed how these metrics evolved throughout the post‐fledging dependence period (PFDP). During this period, juvenile‐to‐adult similarity was more than 80% for the entire home‐range, whereas it was lower for the core area (approximately 60%). Habitat‐use similarity was high, at approximately 90% for both the home‐range and core area, both in land‐cover and topography. The similarity increased following the improvement of juvenile flight skills over a period of two months, to the extent that two months after fledging and until the end of the PFDP, habitat and space use of juveniles can be used to infer the home‐range and habitat requirements of adults. It would be valuable to study this ‘adult‐by‐juvenile replacement' approach in other species to determine whether it could be generalized, notably for species with a shorter dependence period or more complex social interactions.

Post-Fledging Movements and Factors that Influence Permanent Departure of Juvenile Crested Caracaras in Florida

ABSTRACT We tracked 48 young Crested Caracaras (Caracara plancus) in south-central Florida from fledging through their first year and sought to define the post-fledging pre-dispersal period and the timing and drivers of permanent departure (PD) from the natal area. By examining Euclidean distances between telemetry locations and the nest for each tagged caracara, we defined the post-fledging dependency period as the first 2 mo after fledging, when fledglings remained mostly within 2.5 km of the nest and were dependent on their parents for food. Before PD, young caracaras explored areas as much as 11 km from their nest but returned to the natal area, resulting in areas used by fledglings up to 6 times the average home range size of an adult breeding pair. Some caracaras remained within their parents’ home range for several months after fledging, even after becoming independent of their parents for food. A fledgling permanently departed its natal area when telemetry indicated it made an abrupt long-distance movement away from its natal area and did not return. We used generalized linear mixed models and a hierarchical modeling approach to test environmental and biological factors that may affect the timing of PD. The most supported model indicated that PD depended on parental reproductive strategy and on the timing of fledging relative to the length of the breeding season. Birds with parents that raised only one brood remained in the natal area for 11.6–21.0 wk longer than birds with parents that raised multiple broods in the same breeding season; fledglings from the first of two broods departed at a younger age, suggesting that the PD decision is partially triggered by the level of parental investment in the first and subsequent brood. Additionally, birds that fledged early in the breeding season departed the natal area 2.8–12.2 wk earlier than those that fledged later in the breeding season, and birds that were exposed to high heat during the nestling stage departed the natal area earlier than those exposed to less heat. The period between fledging and permanent departure from the natal area is important for the conservation of species with delayed dispersal. When developing a conservation strategy for Florida’s caracara population, attention should be paid to protecting areas used by fledglings until PD rather than just focusing on a limited protection zone around the nest.

Home range size of Tengmalm’s owl offspring during the post-fledging dependence period in Central and North Europe

A greater knowledge of the intrinsic and extrinsic factors of animal home range (HR) formation can help us to understand the fundamental biological issues underlying, for instance, movement patterns, habitat selection and survival. However, very little is known about the HRs of birds of prey fledglings, even though the post-fledging phase is recognised as crucial due to the high mortality of juvenile birds. We radio-tracked 138 Tengmalm’s owl (Aegolius funereus) fledglings from 43 broods to determine their HRs during the post-fledging dependence period and to investigate the factors affecting their sizes. The study was conducted during four breeding seasons in Czechia and two seasons in Finland. The mean fledglings’ HR size calculated according to the 95% IID Kernel Density Estimation method was 63.7 ± 43.9 ha (± SD; n = 71) during nocturnal activity and 52.0 ± 46.1 ha (n = 63) during diurnal roosting. The sizes of both nocturnal activity and diurnal roosting HRs increased with the longer individual duration of the post-fledging dependence period and also the higher rank of hatching within a brood. Diurnal roosting HRs were two times smaller in the Czech site, probably because of the very limited number of dense forest patches suitable for roosting as a legacy of the air pollution calamity in the 1970s, during which most coniferous stands died out. There was no difference in the size of nocturnal activity HR between the two study areas, although they differed markedly in terms of night length, altitude, weather, and forest age, structure and composition. This suggests that environmental factors are not decisive in determining the size of nocturnal activity HRs of Tengmalm’s owl fledglings. Since the diurnal HRs always occurred within the area of the nocturnal HRs, we suggest that conservation of the densest and preferably oldest forest stands within the areas of the study species occurrence may offer straightforward conservation tasks for protecting Tengmalm’s owl fledglings and also other species.

Breeding biology and behaviour of the Pacific Baza Aviceda subcristata in subtropical coastal New South Wales

The breeding biology and behaviour of predominantly two pairs of Pacific Bazas Aviceda subcristata were studied in subtropical north-eastern New South Wales from 2007 to 2017, with intensive observations in 2010–2012 (442.5 h). Fifteen breeding attempts were documented: eleven from observed nest sites, and four from observations of dependent juveniles. The pre-laying period occupied late August and September, with nest building taking 6–19 days. The mean incubation period was 31 days, usually from early October to early November. Both male and female shared diurnal incubation (Pair 1: male 42%, female 58%, only the female incubated overnight; Pair 2: male 62%, female 38%, sharing overnight incubation). The mean nestling period was 37.5 days, including a brooding period of 9–14 days. Breeding productivity was 1.87–2.0 fledglings/attempt (n = 15) across all sites combined. Fledging generally occurred in December, but on two occasions occurred in mid–late February. The post-fledging dependence period lasted at least 22 days, with juveniles joining flocks of other broods in the area at c. 40 days, and leaving the study area c. 45–60 days after fledging. Delivered prey was predominantly insects, especially cicadas (Hemiptera: Cicadoidea) and phasmatids (Phasmatodea: Phasmatidae) by number, and tree frogs Litoria spp. by biomass. Bazas brought prey at a mean rate of 1.2 items/h/juvenile (nestling and post-fledging periods combined), with juvenile intake estimated at 7.6 g/h/juvenile. Various behaviours – nest building, vocalisations, inter- and intraspecific interactions and their frequencies and contexts, and changes in juvenile morphology through the post-fledging period – are described for the years 2010–2012.

Similar post-fledging behavior observed in wild and reintroduced juvenile Bonelli’s Eagle in two Mediterranean islands

Abstract Reintroduction projects are gaining popularity; however, their relatively elevated cost and chance of failure make them debatable, hence assessing their effectiveness is essential. Within the early stages of raptors, the post-fledging dependency period (PFDP) is the one in which individuals must face dangers without having completely developed their skills. Thereby, comparing PFDP patterns concerning reintroduced and wild individuals is of major interest as it would help to plan and improve future conservation actions. We analyzed the behavior of 38 juvenile Bonelli’s Eagles (Aquila fasciata) (15 reintroduced and 23 wild) tracked through GPS telemetry, tagged as nestlings in two insular environments. The study period encompassed 9-yr movement data from reintroduced chicks in Mallorca (Spain) and wild chicks from Sicily (Italy). Movement parameters (i.e., age of first flight, age of dispersal, length of the PFDP, revisits to the natal or release area, and residence time in them) were analyzed together with their behavior for reintroduced and wild individuals. Similar movement patterns were obtained for both origins, although wild individuals revisited the natal site more often and dispersed earlier. Behavior was also similar, though it varied throughout the PFDP, observing a more abrupt progress in wild individuals and an earlier development of travelling and hunting behaviors. Observed differences are probably related to food availability, which can improve body condition and thus delay onset of dispersal, together with parental presence, which can prompt an earlier ending of the PFDP by encouraging juvenile independence. In conclusion, our study provides valuable insights into the behavior of reintroduced Bonelli’s Eagles during their PFDP and how it compares to their wild counterparts. Our results suggest that reintroduced individuals can successfully adapt to their environment and behave similarly to wild individuals. These findings can aid in the planning and improvement of future reintroduction projects and conservation actions for this endangered species.

Timing of departure from natal areas by golden eagles is not constrained by acquisition of flight skills

The post‐fledging dependence period (PFDP), which extends from a fledgling's first flight out of the nest to its departure from the parents' territory, is crucial in the lifecycle of birds. During this period, juveniles develop their flight and foraging skills to become fully independent. Despite the importance of this life stage in basic bird ecology and conservation, it remains largely overlooked – notably its link with the acquisition of flight skills. In this study, we modeled the variation in seven proxies describing flight skills of 84 GPS‐tracked golden eagle juveniles in France between 2016 and 2020. Juveniles had a long but highly variable PFDP, averaging 177.9 (± 62.2) days after departure from the nest. This period is divided into two phases: a first phase of rapid increase in flight skills over the first 60 days after departure from the nest, followed by a plateau in which flight skills no longer develop until independence. These results suggest that the full development of flight skills is not a constraining factor during the PFDP and that it is advantageous for juveniles to choose to remain in their natal territory. We posit that parents' tolerance of fledged juveniles is a type of parental care that may maximize their own fitness by improving the survival of their descendants. In future studies, it may be of interest to investigate the factors that may explain the high variability in the duration of this stage between individuals within the same population.

Post-fledging survival of Tengmalm’s owl offspring in boreal forests: Interactive effects of varying dynamics of main prey and habitat composition

The knowledge about the mortality rate of offspring is crucial for estimating bird population dynamics and conserving species with declining populations. Parents of predatory birds provide food for their offspring during the post-fledging dependency period, which is frequently described as essential due to inexpert flying skills. Using radio telemetry, we studied fledglings’ probability of dying by starvation and predation in Tengmalms’ owls (Aegolius funereus). Nestlings (21 and 39) from 10 and 14 broods in 2019 and 2021, respectively, were equipped with leg-mounted tags and monitored throughout the post-fledging dependency period in west-central Finland. In total, 28 out of 60 fledglings did not survive the post-fledging dependency period (12 died due to starvation, and 16 were predated). The fledglings’ probability of dying by starvation and predation was 3.7 and 2.4 times higher, respectively, in the decreasing (2019) than during the increasing (2021) abundance of main foods (voles), showing that prey availability is essential for survival during the post-fledging dependency period. The probability of starvation increased with augmenting agricultural lands in the home range and increasing precipitation after fledging, which indicated that parent owls avoided hunting in open areas and during rainy nights. The predation rate during the post-fledging dependency period increased with augmenting cover of old-growth forests in the home range. This result suggested that coverage of old-growth forests is nowadays so small in the study area that they act as ecological traps for newly-fledged owlets. The reason is that the main avian enemies of Tengmalm’s owls’ (goshawks and Ural owls) also prefer old-growth forests for breeding and hunting.

Hacked kestrels (<em>Falco tinnunculus</em>) show similar patterns of post-fledging food dependency as wild reared birds: implications for best practice in release management of orphaned raptors

One of the challenges of wildlife rehabilitation is ensuring that rehabilitated animals have the required characteristics for survival after release. This is especially the case for orphaned animals that normally develop survival skills during a prolonged period of parental care. For raptors, this is called the post-fledging dependency period (PDP), where parents provide nutritional support to juveniles whilst they develop the physiological and behavioural characteristics required to successfully hunt prey. Orphaned raptors can be rehabilitated and released using a method termed “hacking,” a type of “soft-release” where fledglings are released from a nest box, which they learn to associate with food. This method gives the birds an opportunity to develop prey capture skills, whilst continued nutritional support is provided by rehabilitators at the box. Here, we used a hacking method to rehabilitate and release 15 orphaned kestrels (Falco tinnunculus) and observed the pattern of return to the hacking box. Of the released birds, 80% returned to the hack site for food at least once. The average number of days birds returned to the box was 12.67 ± 8.76, and there was a clear trend towards a gradual decrease in return rate (number of visits to the box per day) over time. Our observations are comparable to patterns of PDP in wild-reared kestrels and we therefore suggest that orphaned kestrels can be successfully rehabilitated in this way.

Surviving the Urban Jungle: Anthropogenic Threats, Wildlife-Conflicts, and Management Recommendations for African Crowned Eagles

Larger carnivores often trigger human-wildlife conflicts that arise from perceived threats to humans and domestic animals’ safety, which generate the need for management and removal strategies. These issues become especially challenging when humans and wildlife coexist close to one another, for example, in urban landscapes. African Crowned Eagles (Stephanoaetus coronatus) are powerful forest raptors that breed within the metropolitan green-space system of Durban and Pietermaritzburg, South Africa. Negative human-wildlife interactions can occur because eagles occasionally predate on pets, such as cats (Felis catus) and small dogs (Canis lupus familiaris), and provisioning domestic stock to nest sites has previously been quantified. Here, wildlife management becomes critical, usually aimed at reducing or eliminating causes of economic or social harm, but have to be balanced against conservation goals regarding threatened species. In this study, we (i) identified causes of harm or loss of Crowned Eagles because of injuries (n = 53 incidents; 31 mortalities); and (ii) describe interactions with negative perceptions to human livelihoods, particularly concerning predation on pets and livestock. Anthropogenic causes of mortality were more likely to be reported than remote natural deaths, which provides important opportunities for mitigation measures. Most avoidable are electrocution on utility poles, persecution via gunshot wounds and poisoning (targeted or secondary), while collisions with anthropogenic structures, such as glass panes, vehicles and fence wires, are more challenging to mitigate. Out of 44 verified Crowned Eagle vs. pets and livestock conflicts, we documented 19 dog attacks (2012–2020), with detrimental impacts on social perception and acceptance of urban eagles. Pet and livestock conflicts were primarily associated with juveniles and immature eagles (83%). Of these, 19% occurred during September alone, which marks the end of the post-fledging dependency period; 70% occurred outside the breeding season. We provide management recommendations regarding various categories of Crowned Eagle human-wildlife interactions. For example, activities such as rehabilitation and falconry can coordinate to achieve a high standard of public support and conservation outcomes for Crowned Eagles. Finally, we discuss using different management intervention strategies, including rehabilitation, falconry, re-wildling processes, and lethal control of specific “problem” individuals toward achieving the goal of sustainable, healthy Crowned Eagle populations that coexist with humans in urban landscapes.

Re-introduction of the Saker Falcon (Falco cherrug) in Bulgaria - preliminary results from the ongoing establishment phase by 2020.

Considered extinct as breeding species in the early 2000s, the Saker Falcon was recovered when the first active nest from the new history of the species in Bulgaria was discovered in 2018, formed of two birds that were re-introduced back in 2015. Currently, there is only one confirmed wild breeding pair in the country - the male from 2015 with a female changed in 2020, released again as a part of the programme, in 2016. This is a report on the preliminary results and analysis of the ongoing establishment phase of the re-introduction of the Saker Falcon (Falco cherrug) in Bulgaria - first ever performed for this species in the country and globally. The period studied is 2015-2020. Following the re-introduction activities started in 2011, the current phase is defined by standardised methodology and a unified approach. Analysed and presented are methods for captive breeding and hacking, the breeding performance of the falcons, the number of released individuals, data from the post-fledging dependence period and a model of population growth.

Post-fledging dependence period, dispersal movements and temporary settlement areas in saker falcons (Falco cherrug)

Abstract Information on mortality rates and their causes in raptors and owls during the post-fledging dependency period (PFDP) and subsequent dispersal is essential for their more effective protection, including more efficient use of funds. Despite the importance of the above data, these data are not yet available for most birds of prey. The study aimed to provide and expand the knowledge in this field for saker falcon. We used satellite telemetry to monitor a total of six young birds since they left the nest boxes. All young birds survived the PFDP, but none survived to adulthood and died during the period of dispersal movements. The PFDP lasted 47 days (median value hereinafter), and the distance of individuals from the nest boxes during this period was 3.2 km (maximum distance 9 km). The area of the home range of the PFDP calculated by the 100% minimum convex polygon (MCP) method was 81 km2. During the period of dispersal movements, the monitored individuals set up five temporary settlement areas with an area of 422 km2 according to 100% MCP, where they stayed for 37 days. All individuals’ mean length of movement routes throughout the monitoring period was 3862 km. The main finding of the present study is the fact that none of the monitored individuals survived the dispersal period. At least half of them died due to human activity (electrocution, hunting), which is probably unbearable in the long term for wild populations of most animal species. This shows the need to start eliminating all types of artificial traps (e.g., electrocution, hunting, poisoning, etc.) without delay, thus helping to prevent the decline of populations of many species in the shorter or longer time horizon.

Breeding behaviour and diet of Rufous Owls Ninox rufa in the Darwin Botanic Gardens

The breeding cycle of a pair of Rufous Owls Ninox rufa was observed over five breeding seasons, 2016–2020, in the Darwin Botanic Gardens, Northern Territory. A pair failed or did not breed in four of those years and raised one fledgling in 2018. The Owls occupied a hollow 2.5 m above ground in the trunk of an exotic Earpod Tree Enterolobium cyclocarpum. In 2018, laying occurred sometime between 11 June and 2 July, hatching between 21 and 25 July, and fledging (first true flight) on 6 September, with branching on 2–5 September, giving a nestling period of 44–48 days. The juvenile remained dependent until mid November, giving an estimated post-fledging dependence period of 10 weeks. For the following 3 weeks, it roosted alone within its natal home range, increasingly far (270–320 m) from the nest tree and roosting adults. Calling behaviour (including duetting by the pre-laying pair), courtship, copulation and parental behaviour and routines are described. From observations and pellet analysis, the Owls’ diet consisted of 78% mammals [Common Brushtail Possums Trichosurus vulpecula arnhemensis, flying-foxes (probably all Black Flying-foxes Pteropus alecto) and rats (probably Black Rats Rattus rattus)] and 22% birds (passerines and non-passerines up to Orange-footed Scrubfowl Megapodius reinwardt in size) by number.

Begging behavior as an honest signal of need and parent-offspring association during the postfledging dependency period.

Honest signaling mechanisms can function to appropriate care to hungry offspring and avoid misdirected care of unrelated offspring. Begging, the behavior by which offspring solicit food and parental care, may be an honest signaling mechanism for need, as well as association of parents and offspring. Roseate terns (Sterna dougallii) exhibit prolonged parental care during the postbreeding staging period, offering an ideal system in which to study begging as an honest signaling mechanism. We conducted focal sampling during two premigratory staging seasons (2014 and 2015) at Cape Cod National Seashore, Massachusetts, USA to determine whether postfledging tern begging behavior was an honest signal for need and parent–offspring association. Based on honest signaling theory, we expected begging behavior to be highest during times of high perceived need, and we expected to see a decrease in begging behavior as young terns became increasingly independent of the care‐giving parent. Also, we predicted that young terns would be more likely to beg at parents than nonparents. We found that young roseate terns begged at their parents more often than nonparents; however, they did not always beg at parents. Model predictions of begging probability showed a linear relationship between begging and time of day and date of season, such that begging increased with time of day and decreased with date of season, respectively. Our results provide evidence for honest parent–offspring interactions and are inconsistent with parent–offspring conflict theory but suggest that begging may play a complex role in postfledging parent–offspring interactions.OPEN RESEARCH BADGES This article has been awarded Open Data, Open materials Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5281/zenodo.2656718.

Spatial behaviour of Spanish Imperial Eagle Aquila adalberti juveniles during the dependence period revealed by high-resolution GPS tracking data

During the post-fledging dependence period, young raptors are particularly vulnerable as they are still developing flying, hunting and social skills, and collecting spatial environmental information required for emancipation. We studied the use of space during this critical period by the highly threatened Spanish Imperial Eagle Aquila adalberti, using high temporal and spatial resolution tracking devices. Ten juveniles from four different nests were tracked throughout their dependence period with GPS/GSM tags. This period lasted until a median age of 137 days (93–153). Juveniles remained within a stable home range with a median of 232 ha, but when 90–100 days old began making exploratory movements that became more frequent and extensive with the approach of emancipation. These movements had a median of 22.2 km and were usually completed within the same day, but this exploratory behaviour proved to be quite plastic, as one movement was 1291 km long and lasted 4.5 days. Moreover, three individuals that were apparently forced to emancipate particularly early seem to have virtually skipped the exploratory phase. The length of the movements varied among years within the same nest, and those of females were about twice those of males. Most movements were towards the NW, and the outgoing flight was usually against the wind. This behaviour may keep animals from flying so far from the nest that they are then unable to return. The high spatial and time resolution provided by GPS tracking resulted in data that highlight the conservation importance of the nest site until well after fledging. Measures to minimize nest disturbance should thus be extended until early October. Moreover, data show that so much of the activity of the still inexperienced juveniles is concentrated in the small pre-emancipation range that is critical to protecting its habitats and eliminating all anthropogenic sources of mortality.

Onset of natal dispersal in Peregrine Falcon from Mediterranean islands (Italy)

Abstract Basic information on natal dispersal of Peregrine Falcons is virtually lacking in Europe, despite increased attention on this species, and the sensitivity of this stage in the Peregrines’ life history. In this study, we collected satellite telemetry data during the onset of natal dispersal of 19 Peregrine Falcons tagged in Sicily and the Aeolian archipelago (Italy). We divided the onset of dispersal into the following 3 periods: post-fledging dependence period (PFDP), wandering, and wintering. PFDP lasted on average 47±16 days, during which young peregrines moved very little (0.167 km), and explored small areas (0.226 km2) far from the nest cliff, and showed no sex differences. The wandering phase was highly individualistic, with median net displacements of 23.97 km. Both PFDP and wandering bearings were oriented towards NNE-ESE. Only five individuals went sporadically outside the island borders. During their first winter, Peregrines had a mean home range of 135.65±82.31 km2 spatially scattered across Sicily and mainly composed of open habitats, like cereal steppes, arboreal crops and agri-mosaics. Individuals had a dissimilar assortment in habitat composition, however the urban habitat was the most selected and the woodland the least. At night, during both wandering and wintering phases Peregrines used rocks, cliffs and electricity pylons in frequencies not statistically different between sex, phase and type of roost. Only two individuals had significant use of pylons and one of rocks. The multifaceted framework of Peregrine Falcon’s natal dispersal was described here for the first time in a Mediterranean population.

Providing longer post-fledging periods increases offspring survival at the expense of future fecundity.

The cost of reproduction is a key concept in life-history trade-offs. However, our understanding of the reproductive costs is biased towards measures of reproductive effort obtained before offspring independence. During the post-fledging dependence period (PFDP), it is well known that parents feed and protect their offspring. However, the effort devoted to this reproductive activity has never been considered in the context of of the costs of reproduction. Moreover, the potential fitness benefits and costs for offspring and parents, respectively, of the duration of the PFDP are largely unknown. We estimated the duration of the PFDP over 5 years using wild common kestrels (Falco tinnunculus) and studied its association with survival probability and future parental reproductive performance. Our results show that longer PFDPs increase the survival probability of fledglings, probably due to the benefits obtained from parental care. In addition, we found that providing longer PFDPs was associated with reduced clutch sizes but not the number of fledglings in the subsequent breeding season in males. We suggest that increased parental expenditures on offspring during the PFDP may represent a potential cost of reproduction in breeding males.

Post-fledging movement and spatial ecology of the endangered Cape Vulture (Gyps coprotheres)

The post-fledging dependence period (PFDP) is one of the most critical stages in the life history of some avian species. Birds are particularly sensitive to mortality during this stage as they must learn essential skills, such as efficient locomotion, proficient food location and predator avoidance. Knowledge of the PFDP would provide valuable information for conservation management of endangered species, many of which experience high juvenile fatality rates. Post-fledging movements of five endangered Cape Vultures were recorded using Global Positioning System/Global System for Mobile communication telemetry in South Africa. Home range sizes, distances travelled from the nest and habitat use were determined over 11 months during the PFDP. Fledglings increased their home range progressively for the first 2 months, then exhibited a rapid increase in home range size associated with dispersal from their natal colony. Maximum net daily distance also rapidly increased following the dispersal period. A preference for protected areas and woody vegetation (representing cliff faces used for roosting) in terms of habitat use for foraging was evident. The knowledge of the movement and habitat use of juvenile Cape Vultures can aid in the effective conservation planning for the species. Conservation programs in identified areas can be focused on power line and wind-farm mitigation, areas of supplementary feeding and anti-poisoning events.

A juvenile eagle owl moving in the surrounding of the nest during the post‐fledging dependence period, when movement behaviour seems to be mainly related to the rearing environment (picture: Vincenzo Penteriani).

EthologyVolume 124, Issue 3 p. i-i FRONT COVERFree Access A juvenile eagle owl moving in the surrounding of the nest during the post-fledging dependence period, when movement behaviour seems to be mainly related to the rearing environment (picture: Vincenzo Penteriani). First published: 02 February 2018 https://doi.org/10.1111/eth.12671AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume124, Issue3March 2018Pages i-i RelatedInformation

The contribution of flight capability to the post‐fledging dependence period of golden eagles

The period prior to an individual emigrating from its natal site and initiating dispersal is important for developing the skills that are ultimately required for surviving natal dispersal. Using a novel method to quantify the early movements of 35 juvenile golden eagles fitted with satellite transmitters, we hypothesised that variation in golden eagles’ post‐fledging dependence period (PFDP) was determined by variation in how quickly movement skills were acquired in order to become independent and disperse. Twenty nine young eagles exhibited an initial increase in mobility (‘ontogenic phase’) levelling off after a median of 68 d, followed by a period of maintained mobility (‘maintained phase’) that lasted a median of 99 d (range 24–176). Eagles that developed their mobility more quickly during the ontogenic phase had a correspondingly shorter ontogenic phase. Despite this, most of the inter‐individual variation in the length of the PFDP resulted from variation in the length of the ‘maintained phase’. In general, females (the larger sex) developed more slowly and had a longer ontogenic phase. Males exhibited dispersal strategies around two modes with some dispersing early (mode 1: 89.5 d) and others late (mode 2: 220 d). In contrast females dispersed around a unimodal distribution of timing (mode 167.5 d). Apart from six individuals (mostly males) which dispersed with no discernible maintained phase, most offspring remained in the parental home range after they were fully mobile, even those that developed mobility quickly, suggesting that the PFDP in golden eagles is not simply a function of physical capacity for independence, but also a period when young eagles decide to remain, and are tolerated by parents, in their parental home range before dispersing. We suggest that delaying dispersal may be a beneficial strategy for young raptors facing a competitive environment after PFDP.

Breeding Phenology and Chick Growth in the Brown Booby Sula leucogaster (Sulidae) on Nakanokamishima, Japan

We studied the breeding phenology of the Brown Booby Sula leucogaster on Nakanokamishima, southern Ryukyu Islands, Japan. During the breeding season (April–November) of 1989 we observed the presence and absence of 18 chicks and measured their growth on a total of 17 days. Egg hatching was observed during April and May. The estimated minimum pre-fledging period ranged from 60 to 100 days and the maximum pre-fledging period ranged from 86 to 122 days, whereas the minimum post-fledging dependence period ranged from 24 to 105 days and the maximum post-fledging dependence lasted from 74 to 124 days. All of the monitored fledglings left the colony by early-November, and the total period over which parents cared for their chicks was 119–197 days (minimum) and 146–208 days (maximum). Body weight and culmen length attained 95% of asymptotic values in 65 and 69 days of age and wing length in 91 days. Six out of 18 fledglings were seen again in the colony, three to seven years after initial independence.