OBSERVATIONS ON THE POST-FLEDGING DEPENDENCE PERIOD OF CAPE VULTURES

Robertson, A. S. 1985. Observations on the post-fledging dependence period of Cape Vultures. Ostrich 56: 58–66.

Cape Vultures were observed during their post-fledging dependence period at a colony in the Cape Province, South Africa. Information is presented on the length of the period, behaviour of juveniles and of parents at the nest, survival of juveniles, aggressive interactions between parents and juveniles and retention of the nest site following breeding. At the colony, juveniles initiate contact with their parents, which supply food to their own offspring at the natal site only. Parental aggression was observed over an average period of five months after juveniles had left the nest (range 32–218 days); at two nest sites, the period overlapped with the next season's incubation period, although no transfer of food was observed during this period-of overlap.     

Differential Movement Patterns of Juvenile Tengmalms Owls (Aegolius funereus) during the Post-Fledging Dependence Period in Two Years with Contrasting Prey Abundance

Fledgling behaviour and movement patterns throughout the post-fledging dependence period (PFDP), especially in relation to changing environmental conditions, have been rarely studied, despite the fact that this period is recognized as of crucial significance in terms of high mortality of juveniles. The PFDP can extend over quite a protracted period, particularly in birds of prey, and a knowledge of the movement patterns of individuals is fundamental for understanding mechanisms underlying survival, habitat use and dispersion. We radiotracked 39 fledglings of the Tengmalm’s owl (Aegolius funereus) in two years with different availability of prey: 2010 (n = 29) and 2011 (n = 10) and obtained 1455 daily locations. Fledglings reached independence on average in 45 days after fledging in 2010 (n = 22) and 57 days in 2011 (n = 6). Within years, the most important measures influencing the distance moved from the nest box were age of fledglings and number of surviving siblings present. Individual home range size and duration of PFDP in particular were dependent on maximal number of siblings seen outside the nest box. In the season with low prey availability fledglings were observed at greater distances from the nest box than in the year with higher prey availability (mean distance: 350 m in 2010 and 650 m in 2011) and occupied larger home ranges (mean: 30.3 ha in 2010 and 57.7 ha in 2011). The main factor causing these differences between years was probably the different availability of prey in these two years, affecting breeding success and post-fledging survivorship of the Tengmalm’s owls.     

Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA

We assessed phylogenetic relationships for birds of prey in the family Accipitridae using molecular sequence from two mitochondrial genes (1047 bases ND2 and 1041 bases cyt-b) and one nuclear intron (1074 bases beta-fibrinogen intron 7). We sampled representatives of all 14 Accipitridae subfamilies, focusing on four subfamilies of eagles (booted eagles, sea eagles, harpy eagles, and snake eagles) and two subfamilies of Old World vultures (Gypaetinae and Aegypiinae) with nearly all known species represented. Multiple well-supported relationships among accipitrids identified with DNA differ from those traditionally recognized based on morphology or life history traits. Monophyly of sea eagles (Haliaeetinae) and booted eagles (Aquilinae) was supported; however, harpy eagles (Harpiinae), snake eagles (Circaetinae), and Old World vultures were found to be non-monophyletic. The Gymnogene (Polyboroides typus) and the Crane Hawk (Geranospiza caerulescens) were not found to be close relatives, presenting an example of convergent evolution for specialized limb morphology enabling predation on cavity nesting species. Investigation of named subspecies within Hieraaetus fasciatus and H. morphnoides revealed significant genetic differentiation or non-monophyly supporting recognition of H. spilogaster and H. weiskei as distinctive species.     

NOTICES

Steyn, P. 1975. Observations on the African Hawk-Eagle. Ostrich 46:87-105.

Observations extending over 12 years were made on two pairs of African Hawk-Eagles Hieraaetus spilogaster at Essexvale, Rhodesia. Details on various aspects of adult behaviour are given, particularly on hunting methods and calls. Nest repair usually took about 4–5 weeks. and limited observations indicated that the male does most of the work. Incubation is done mostly by the female, the male relieving her when he brings prey. The incubation period is 43 ± 1 day. Details are given of parental behaviour during the fedging period; time on the nest showed a progressive decline although both adults still perched in the. nest tree a great deal. The male provided most of the prey. The growth and behaviour of the eaglet Is described; usually the eaglet becomes a “brancher” before its first flight which, in four cases, occurred between 61–71 days. Post-of edping attachment to the nest lasted about three weeks in one case. Frief mention is made on the development of adult plumage. Birds made up 74%. mammals 25% and reptiles 1% of 104 prey items recorded at Essexvale. Gamebirds are preferred. The two nests had completely different breeding histories. One pair reared no young while the replacement rate of the other pair was 0,83 voung/pair/year. The combined replacement rate of the two pairs was 0,48 young/pair/year. There appear to be no records of two eaglets being reared together in southern Africa.     

Development of chicks and predispersal behaviour of young in the Eagle Owl Bubo bubo

Little quantitative information on the development and behaviour of chicks and young is available for many species, despite the crucial importance of such data and the sensitivity of this stage in a bird's life. For Eagle Owls Bubo bubo , despite the large amount of scientific literature on this species, much basic information is lacking. This study provides a photographic and morphometric guide for age estimation of nestlings and fledglings, as well as data on the call behaviour of young, and patterns of movements during the post-fledging dependence period. The most remarkable event in chick development is the rapid increase in mass, and size gain, during the first 30 and 40–45 days, respectively. Because after this time morphometric differences become less evident, young-feather development is more useful for ageing. Patterns of chick call behaviour showed that the time spent calling increased with age and, from 110 days of age, chick vocalizations were usually uniformly distributed through the whole night and most synchronized at sunset and sunrise (the maximum recorded number of vocalizations per chick and per night was 1106 calls). During the post-fledging dependence period, radiotagged Owls moved widely, up to 1500 m from the nest after the age of 80–90 days. During such movements, the mean distance among siblings increased with age, from 168 m on average for juveniles less than 100 days old, to 489 m for those older than 100 days. Definitive dispersal started when young were about 150–160 days old. Information on chick call behaviour and movements is crucial for unbiased census and nest checking, as well as for the definition of young post-fledging areas. Knowledge of the latter is very important in terms of conservation and management (especially for those species that move largely around their nest before dispersal) owing to the high mortality that can occur during this period.     

A multi-gene phylogeny of aquiline eagles (Aves: Accipitriformes) reveals extensive paraphyly at the genus level

The phylogeny of the tribe Aquilini (eagles with fully feathered tarsi) was investigated using 4.2 kb of DNA sequence of one mitochondrial (cyt b) and three nuclear loci (RAG-1 coding region, LDH intron 3, and adenylate-kinase intron 5). Phylogenetic signal was highly congruent and complementary between mtDNA and nuclear genes. In addition to single-nucleotide variation, shared deletions in nuclear introns supported one basal and two peripheral clades within the Aquilini. Monophyly of the Aquilini relative to other birds of prey was confirmed. However, all polytypic genera within the tribe, Spizaetus, Aquila, Hieraaetus, turned out to be non-monophyletic. Old World Spizaetus and Stephanoaetus together appear to be the sister group of the rest of the Aquilini. Spizastur melanoleucus and Oroaetus isidori are nested among the New World Spizaetus species and should be merged with that genus. The Old World 'Spizaetus' species should be assigned to the genus Nisaetus (Hodgson, 1836). The sister species of the two spotted eagles (Aquila clanga and Aquila pomarina) is the African Long-crested Eagle (Lophaetus occipitalis). Hieraaetus fasciatus/spilogaster are closest to Aquila verreauxii and should be merged with that genus. Wahlberg's Eagle H. wahlbergi, formerly placed in Aquila, is part of a clade including three small Hieraaetus species (pennatus, ayresii, and morphnoides). The Martial Eagle (Polemaetus bellicosus) is the sister species of the Aquila/Hieraaetus/Lophaetus clade. Basal relationships within this clade remained unresolved. Parsimony reconstruction of the evolution of plumage pattern within Aquilini suggests that: (1) transverse barring of parts of the body plumage was lost in the Palearctic Aquila-Hieraaetus clade, (2) pale underparts in adult plumage evolved three times independently, and (3) dimorphic adult plumage is a derived character of the small-bodied Hieraaetus clade.     

Availability of optimal‐sized prey affects global distribution patterns of the golden eagle Aquila chrysaetos

Climate and landscape change are expected to significantly affect trophic interactions, which will especially harm top predators such as the golden eagle Aquila chrysaetos. Availability of optimal prey is recognized to influence reproductive success of raptors on a regional scale. For the golden eagle, medium‐sized prey species between 0.5 and 5 kg are widely considered to be optimal prey during the breeding season, whereas smaller and larger species are deemed as energetically sub‐optimal. However, knowledge about the effects of optimal prey availability is still scarce on larger scales. To decrease this apparent knowledge gap, we combined biogeographical information on range margins with information about the foraging behaviour and reproductive success of golden eagles from 67 studies spanning the Northern Hemisphere. We hypothesized that availability of optimal prey will affect foraging behaviour and breeding success and, thus, distribution patterns of the golden eagle not only on a local but also on a continental scale. We correlated the diet breadth quantifying foraging generalism, breeding success and proportions of small (< 0.5 kg), medium (0.5–5 kg) and large‐sized (> 5 kg) prey species within the diet with the minimum distance of the examined eagles to the actual species distribution boundary. Closer to the range edge, we observed decreased proportions of medium‐sized prey species and decreasing breeding success of golden eagles. Diet breadth as well as proportions of small and large‐sized prey species increased, however, towards the range edge. Thus, availability of optimal‐sized prey species seems to be a crucial driver of foraging behaviour, breeding success and distribution of golden eagles on a continental scale. However, underlying effects of landscape characteristics and human influence on optimal prey availability has to be investigated in further large‐scale studies to fully understand the major threats facing the golden eagle and possibly other large terrestrial birds of prey.     

Factors Affecting Vocalization in Tengmalm’s Owl (Aegolius funereus) Fledglings during Post-Fledging Dependence Period: Scramble Competition or Honest Signalling of Need?

Begging behaviour of nestlings has been intensively studied for several decades as a key component of parent-offspring conflict. There are essentially two main theories to account for intensity of food solicitation among offspring: that intensity of begging is related to some form of scramble competition between nest mates or that it offers honest signalling of need to parents. The vast majority of studies which have addressed begging behaviour have been based on observations of, and experiments on, nestlings and have not considered begging behaviour, during the post-fledging period. Begging vocalizations in this post-fledging phase of dependence have rarely been studied, despite the importance of vocalizations as a communication method between offspring and parents, particularly for nocturnal species. We radiotracked 39 fledglings of the Tengmalm’s owl (Aegolius funereus) in two years with different availability of prey: 2010 (n = 29 fledglings) and 2011 (n = 10 fledglings) and made 1320 nightly localizations in which we recorded presence or absence of begging calls. Within years, the most important measures related to the probability of vocalization were body condition at fledging, time of night, number of surviving siblings, age and weather conditions. Begging intensity increased with age in both years; however, in the year with low prey availability fledglings vocalized significantly more often. The main factor causing these differences between years was probably the different availability of prey, affecting breeding success, post-fledging behaviour, and thus also both short- and long-term needs of offspring. We believe that our results suggest honest signalling of their fledgling’s need.     

OBSERVATIONS ON THE BREEDING OF THE WOOLLYNECKED STORK

Scott, J. A. 1975. Observations on the breeding of the Woollynecked Stork. Ostrich 46: 201–207.

Little is known about the breeding of the Woollynecked Stork Ciconia episcopus in Africa. This paper discusses breeding, adult and nestling behaviour, nests and sites. Seasonal movements are discussed briefly. Eight nests were studied during 1970 to 1974. At one nest incubation was established at 30 to 31 days and the fledging period 55 to 65 days. No feeding of the young was observed at any time, though one eight hour observation period was undertaken. Few mating displays were seen and none away from the nest.     

Life-history of two African Sylvia warblers: low annual fecundity and long post-fledging care

The investigation of factors that cause differences in life-history traits between temperate and tropical birds is often hampered by a lack of knowledge about tropical species. Even within the well-known warblers of the genus Sylvia , which include resident species from temperate and tropical regions as well as migrants, there are few data from tropical species. We investigated the breeding biology of the tropical species Sylvia lugens and S. boehmi in a 2-year study in Kenya. Both species had a clutch size of 2.0 and laid c.  3.7 clutches per year. Breeding was characterized by long incubation periods ( S. lugens 14.5 days, S. boehmi 15.0 days), long nestling periods (16.0 and 12.9 days, respectively) and high predation rates (Mayfield nest success S. lugens 33.2%, S. boehmi 19.4%). Annual fecundity was 2.3 fledglings in S. lugens and 1.4 fledglings in S. boehmi . After fledging, the young birds were fed for 37.5 days ( S. lugens ) and 58.5 days ( S. boehmi ) (time to independence) and they stayed in their parents' territory for days or weeks, even after feeding had stopped. Fledgling survival until independence was 55.4% in S. lugens and 69.2% in S. boehmi . In general, S. lugens and S. boehmi have smaller but more numerous clutches, longer developmental periods, higher nest predation rates, lower annual fecundity and longer post-fledging care than their temperate congenerics.     

PREY TAKEN BY TAWNY OWLS DURING THE BREEDING SEASON

The diet of Tawny Owls during the breeding seasons 1949-52 in Wytham Woods, near Oxford, was determined (a) from analysis of pellets collected, (b) from observation at night, by the use of a red floodlight, of prey brought to the nest and (c) from records of prey left in the nest made during daily visits to weigh the young.
Analysis of pellets showed an increase in the proportion of moles and beetles (mainly cockchafen) in the diet after the first week of May (the time when, on average, the young owls are about half grown) and a decrease in the proportion of mice and voles.
These changes were confirmed in a more emphatic way from observations of food being brought to the nest and from records of prey left in the nest.
This greater emphasis suggests that tho food brought to the young may differ from that which the adults eat themselves.
The fact that no moles were observed being brought to nests at night, wherean many were recorded as surplus prey in the nest, showed that diurnal hunting is regular during the breeding reaaon.
A true assessment of prey taken by Tawny Owls during the breeding season should be based both on analyeis of pellets cast by the adults and on records of food brought to the nest throughout 24 hours. Such records could best be obtained with an automatic camera and flash and a design of nest-box which is described.     

4. UNUSUAL EXPERIENCES WITH BIRDS

Earlé, R. A. 1989. Breeding biology of the Redbreasted Swallow Hirundo semirufa. Ostrich 60: 13–21.

The two races of the Redbreasted Swallow Hirundo semirufa seem to have separate breeding seasons with the northern race H. s. gordoni breeding April-July, while most records for the nominate race fall in October-February. All nests studied were in concrete culverts less than 1 m high. Eggs laid in second clutches by individual females weighed significantly less than eggs laid in first clutches. Eggs hatched on average 16,2 days after incubation started or 18–21 days after the eggs were laid. Only females incubated. Chicks fledged 23–25 days after hatching and reached a maximum body mass of about 31,5 g on day 18 before a steady decline in mass until fledging. Most nesting failures resulted from infertile eggs or starvation of young in the nest (16,2% of all young starved). Overall breeding success was 60,6%. In all, 81,8% of first clutches produced fledglings but only 44,4% of second clutches. Over a three year period 4,9 young were produced per pair breeding in the area (1,6 young/pair/breeding season).     

The effect of parent sex on prey deliveries to fledgling Eurasian Sparrowhawks Accipiter nisus

The relative contribution of each parent when providing for the fledglings has been recorded in only a few raptor species. We studied prey deliveries by Eurasian Sparrowhawk Accipiter nisus parents to fledglings at seven nests in southern Norway. Parents and young were fitted with radio-transmitters. Males delivered a larger number of prey to the young than did females throughout the post-fledging period (on average c.  80% of the deliveries). Two females were never observed to deliver food to the offspring, and their mates apparently raised the young to independence alone. The duration of the post-fledging period was positively related to per-capita delivery rate in the late stage.     

BREEDING BIOLOGY OF THE BEARDED VULTURE IN SOUTHERN AFRICA,PART III: THE POST-NESTLING DEPENDENCE PERIOD

Brown, C. J. 1990. Breeding biology of the Bearded Vulture in southern Africa, Part III: The post-nestling dependence period. Ostrich 6l: 43–49.

The post-nestling dependence period of the Bearded Vulture Gypaetus barbatus in southern Africa begins with the first flight of the young bird at 126 ± 2 days after latching (November-January) and ends during the pre-laying nod or the parent birds' next breeding attempt (April-June), a nod of about five months. For the first two weeks after first flit young bid remaine6 within about 200m of the nest, moving up to 800 m by the third week. By a month out of the nest young birds spent about 40% of the day in flight, moved up to 3 km from the nest, began bone-dropping and interacting with young birds from neighbouring nests. At six weeks they began to accompany their parents for part of some of their foraging trips, but returned to the nest alone, and by eight weeks they completed foraging forays with parents Pasting up to 3 h. At 2–3 months out of the nest young birds covered an area of about 42 km², excluding the foraging trips with parents, by 3–4 months, 78km² and 4–6 months, 168 km². Parent birds delivered food for at least five months after the young bird's first flight. Young birds left their natal areas of their own accord, usually during the first month of their parents' next breeding attempt.     

Fecal sex steroids and reproductive behaviors in harpy eagles (Harpia harpyja)

Aiming to improve our reproductive knowledge of large birds of prey, behavioral data and fecal steroids were assessed in captive pairs of Harpy eagles, a keystone species that is monogamous and resides in the Neotropics year-round. Adult individuals exhibited different reproductive outcomes and a breeding season extending beyond summer solstice (5–9 months) suggests that harpy eagles may not be absolutely photorefractory. Comparisons among breeding stages in males revealed that mean androgen levels in courtship were higher than in copulation and incubation, but no differences were detected in fecal progestagens or estrogens. Females had higher mean estrogen concentrations in courtship and copulation, whereas mean progestagen levels peaked during egg laying. Mean androgen concentrations were not significantly different among breeding stages in females. Assessment of six egg-lay cycles from three females demonstrated that fecal estrogens peaked predominantly between 31 and 18 days before oviposition (–31 to –18 days), and then remained low until 45 days after laying the first egg (+45 days). In contrast, fecal progestagens raised mostly between –20 and +1 day, lowering to baseline concentrations by +3 days. To our knowledge, this is the first study to describe in detail endocrine and behavioral data regarding reproduction in tropical eagles, which may serve in the future as a reference to developing breeding programs.     

The breeding of the Wedge-tailed Eagle Aquila audax in relation to its food supply in arid Western Australia

The breeding of the Wedge-tailed Eagle Aquila audax was investigated in four areas of the arid zone of Western Australia from 1968 to 1976, with some supporting data from the adjacent Mediterranean zone. Breeding was dependent on, and geared to, the occurrence of a minimum level of available prey. In the arid zone the seasonally most regular occurrence of the low rainfall, combined with greatest diversity of vegetation and prey, was associated with the most regular breeding and the greatest annual productivity of young per pair. At the other extreme, where an identical mean annual rainfall was distributed more erratically between seasons and years and was combined with a less diverse flora, the prey available to eagles was restricted to virtually one species–the introduced European rabbit Oryctolagus cuniculus . In this situation there were gaps of up to 4 years between the breeding of eagles, because of major fluctuations in the size of the population of its rabbit prey. Their density was actually greatest in those areas where the widely fluctuating food supply occasionally allowed them to breed with considerable success; however, this did not compensate fully for the irregularity of breeding. Where the prey available was thus restricted to a single species and was least stable, the area may have been unable to support a population which could maintain itself without recruitment from outside.
Breeding success in the Mediterranean zone was higher than in the arid zone. The Wedge-tailed Eagle's breeding strategy is conservative (with 'k-selected' characteristics), but this study shows that it is ecologically successful in both zones, although least so where the climate is extremely erratic.     

4. GAME RESERVES IN SOUTHERN AFRICA

Steyn, P. &; Grobler, J. H. 1981. Breeding biology of the Booted Eagle in South Africa. Ostrich 52:108-118.

The Booted Eagle Hieraaetus pennatus is a breeding visitor to the Cape Province of South Africa, wintering mostly in Namibia on present knowledge. Palaearctic birds probably also reach the Cape but arrive later. Two nests in different localities in the Cape were studied. The birds breed soon after arrival. Both sexes build the nest on a cliff ledge. Incubation, which lasts 40 days, is done mostly by the female. The female spends most of her time on the nest during the first four weeks of the nestling period, but considerably less time thereafter. The male provides nearly all the prey until near the end of the nestling period, and helps to feed the young. Details of nestling growth and behaviour and of parental care are given. The nestling period was 50 and 54 days in two cases. Post-nestling dependence is about two months. Prey preferences in the two study areas were very similar: 54% birds, 33% lizards and 13% rodents. Breeding biology in South Africa is basically the same as that of Palaearctic populations, with the main differences being the habitat and cliff nest site.     

Mercury in bald eagle nestlings from South Carolina,USA

Bald eagles (Haliaeetus leucocephalus) may be at risk from contaminants in their diet and young birds may be particularly sensitive to contaminant exposure. To evaluate potential risks from dietary mercury exposure to eagle nestlings in South Carolina (USA), we surveyed mercury concentrations in 34 nestlings over two breeding seasons (1998 and 1999). Samples were also obtained from several post-fledging eagles in the region. Nestling feather mercury ranged from 0.61-6.67 micrograms Hg/g dry weight, nestling down mercury from 0.50-5.05 micrograms Hg/g dry weight, and nestling blood mercury from 0.02-0.25 microgram Hg/g wet weight. We did not detect significant differences in tissue mercury between nestlings from coastal and inland regions in contrast to some other studies of piscivorous birds. Mercury concentrations were much higher in the post fledging birds we sampled. Our data show that nestling eagles in South Carolina are accumulating mercury, and that concentrations in older birds may exceed regulatory guidelines.     

Parental care and the transition to independence of Spanish Imperial Eagles Aquila heliaca in Doñana National Park, southwest Spain

The behaviour of five broods of radio-tagged Spanish Imperial Eagles Aquila heliaca adalberti was studied in Doñana National Park, Spain during the post-fledging period. The distance between perching sites and nest, the mean flight duration and distance, the percentage of time spent flying and the home range all increased exponentially with age. As the young got older, the parents spent less time in their vicinity. Young were not seen hunting, but depended on their parents for food. They begged and chased their parents throughout the post-fledging period, with higher intensity at the end. Nevertheless, the adults became progressively more reluctant to feed them, as reflected in the decrease in feeding frequency and in the number of approaching flights towards the young. At the end of the post-fledging period, adults often performed aerial displays and frequently chased their offspring. The age of independence of the different young studied varied between 123 and 145 days. The correlations between individual independence and the dates when the young were last fed by their parents, and when the highest intensity of parental aggressive behaviour occurred, were higher than correlations with the variables related to the maturation of flying. Therefore, it is suggested that parental 'meanness' and aggressive behaviour may be the factors determining the date of juvenile independence and dispersal from the home territory.     

Spatio-temporal segregation of facultative avian scavengers at ungulate carcasses

Spatial and/or temporal segregation of resource use are mechanisms that may allow coexistence between potential competitors. Spatial and temporal patterns of carrion use were studied in the main avian scavengers of Sierra Espuña Natural Park (SE, Spain). We monitored the use of ungulate carcasses provided by hunting during winter and summer of 2005–2006. Non-breeding ravens exploited aggregated carcasses and depleted the resource in a few days while golden eagles used scattered carcasses over a longer consumption period. Moreover, non-breeding ravens exploited carcasses when golden eagles were less active. Almost all available hunter kills were exploited by golden eagles and/or ravens during winter whereas a high number of carcasses were not used during the breeding season, suggesting strong competition in a period of low food availability. Thus carrion arrangement, seasonal behaviour and competitive interactions could be affecting the foraging patterns of these two species. Interestingly, intraspecific aggregation of the smaller species and dominance of the larger one may act on the use of shared resources and trigger segregation mechanisms. Our results support that differences in the spatial and temporal patterns of resource use may allow resource partitioning between two species, thus facilitating their coexistence in sympatric areas.