8. SHORT NOTES

Stutterheim, C. J. 1980. Moult cycle of the Redbilled Oxpecker in the Kruger National Park. Ostrich 51:107-112.

This paper describes the pattern and rate of the complete moult cycle in the Redbilled Oxpecker Buphagus er ythrorhynchus. The average duration of primary moult in adult birds was 340 days and the mean time to replace a primary feather was calculated as 34 days. The moult of the secondaries is initiated at two points, at the first secondary and at the innermost secondary. Secondary moult takes seven months. The differentiated inner secondaries moult in the normal middle/inner/outer passeriform fashion. The rectrices moulted only once annually. The two body moult cycles correspond with the moult of the differentiated inner secondaries. First-year birds undergo a partial postjuvenile feather replacement at three months of age.     

Supplemental food alters nest defence and incubation behaviour of an open‐nesting wetland songbird

Climate‐driven increases in spring temperatures are expected to result in higher prey availability earlier in the breeding season for insectivorous birds breeding in wetland habitats. Predation during the incubation phase is a major cause of nesting failure in open‐nesting altricial birds such as the Eurasian reed warbler. The nest predation rate in this species has recently been shown to be substantially reduced under conditions of experimentally elevated invertebrate prey availability. Food availability near the nest may be an important determinant of adult incubation and nest defence behaviours during the incubation period. We used two experimental studies to compare incubation behaviour and nest defence in food‐supplemented and unsupplemented adult Eurasian reed warblers during the incubation phase. In the first study we measured nest defence behavioural responses to a taxidermic mount of a native predator (stoat Mustela erminea). In the second study we used temperature loggers installed in nests to measure breaks in incubation as a measure of nest vulnerability. Food‐supplemented birds responded aggressively to the presence of a predator more quickly than those in the unsupplemented group, suggesting they are closer to their nest and can more quickly detect a predator in the vicinity. Food‐supplemented birds also had shorter breaks in incubation (both in terms of maximum and mean off‐bout durations), presumably because they were foraging for shorter periods or over shorter distances from the nest. This study therefore identifies the behavioural mechanisms by which changes in food availability may lead to changes in nest survival and thus breeding productivity, in open‐nesting insectivorous birds.     

Dark tree cavities – a challenge for hole nesting birds?

Holes provide the safest nest sites for birds, but they are an underutilized resource; in natural forests there are usually more holes than birds that could use them. Some bird species could be prevented from nesting in holes because of their inability to operate in the low light conditions which occur in cavities. As no visual system can operate in complete darkness some nest cavities could be too dark to be useable even by hole‐nesters. Thus, the light conditions within tree cavities could constrain both the evolution of the hole nesting habit, and the nest site choice of the hole‐nesting birds. These ideas cannot be tested because little is known about the light conditions in cavities. We took an opportunity provided by ongoing studies of marsh tits Poecile palustris and great tits Parus major breeding in a primeval forest (Bia?owie?a National Park, Poland) to measure illumination inside their nest cavities. We measured illuminance in cavities at daybreak, which is just after the parents commenced feeding nestlings. Only ca 1% of incoming light reached the level of the nest. Illuminance at nests of both species (median = 0.1–0.2 lx) fell within mesopic‐scotopic range, where colour vision is impaired. Measurements in model cavities showed strong declines in illumination with distance from the entrance, with light levels typically as low as 0.01 lx at 40 cm from the cavity entrance. Thus cavities can be very dark, often too dark for the use of colour vision, and we suggest that ‘lighting’ requirements can affect the adoption of specific nest sites by hole nesting birds. We discuss implications of the findings for understanding the adaptations for hole‐breeding in birds.     

Floaters as intraspecific brood parasites in the grey starling Sturnus cineraceus

The breeding season of the grey starling Sturnus cineraceus is divided into two periods: the early and late breeding season. The birds that breed in each season are referred to as early and late breeders, respectively. In this study, the late breeders mainly consisted of new immigrants that did not breed in the early season. This suggested that these new immigrants were probably floaters in the early breeding season. Because intraspecific brood parasitism occurred frequently, it is possible that the parasites were floaters without nesting boxes. To check for the presence of floaters, two field experiments were conducted and floaters were captured with traps. With additional nesting boxes provided during the breeding season, all new boxes were quickly occupied by floaters from the period of incubation to hatching in the early breeding season, but were not occupied by floaters during the egg laying period of the late breeding season. The addition of boxes before the start of the breeding season significantly decreased the parasitic rate and number of parasitic eggs per nest. There was a positive correlation between the relative occupancy of nesting boxes and the parasitic rate. The removal of boxes again increased the parasitic rate. As for the capture of floaters with traps, the number of trapped birds per day was also related to the relative occupancy of nesting boxes. The floaters trapped between incubation and nesting periods of early breeders became the late breeders. Judging from these results, many floaters were present from the incubation to hatching periods of early breeders, and were probably intraspecific brood parasites.     

The advertising display of double-crested cormorants varies with microhabitat and time of the season in a tree-nesting colony

Male double-crested cormorants (Phalacrocorax auritus) perform advertising displays at potential nest locations at spring breeding grounds to attract females. Yet, there is no research on how the frequency of this behaviour changes over time or its association with habitat features. Studies of this behavioural display may provide insight into how birds choose areas for nesting, an important issue given the environmental and societal impacts of dense colonies of cormorants. Advertising behaviour was observed in trees throughout the 2014 nesting season, at six different sampling stations, using both scan sampling (for temporal changes in display frequency) and focal sampling (for temporal changes in four microhabitat variables: tree health, height in tree, nest density and presence of a nest). Advertising data (scans N = 484 birds; focal samples N = 827 birds) were divided into pre-incubation, incubation and chicks-present categories using a breeding chronology dataset. The number of cormorants advertising varied temporally and spatially. Using scan data in a marginal model, we found that the number of cormorants advertising was highest at the beginning of the season (peaking at week 3) and lowest once chicks were present. The GLM (focal data) showed that most cormorants advertised without nests especially past the second week of the season. The model also indicated that cormorants advertised in low nest density trees from pre- to mid-incubation. Contrary to our predictions based on colony expansion over the season, we did not observe an interaction of tree health*time or station*time, which suggests that the advertising display revealed a nest site selection process that was not visible at the population level.     

Nest position,breeding success and diet of the Black-crowned Night Heron,Nycticorax nycticorax in the Anzali Wetland,Northern Iran (Aves: Ardeidae)

Breeding ecology of the Black-crowned Night Heron (Nycticorax nycticorax) was studied in a mono-specific colony in the Anzali wetland, Northern Iran during the breeding season of 2016. The breeding period lasted from mid-May to late July. The average clutch size was 3.1±0.6 eggs and the breeding success 77.6%. No significant differences were found between nests built on trunks and those built on branches of trees. The clutch size and breeding success appeared to be independent of the structural variables of the nesting site (diameter of trees, height from the ground, height of nests from the canopy, nest number per tree, location of nests on trunks and branches). No significant difference was found between the timing of the start of incubation and the height of nests above the ground. The average vertical and horizontal distances between nests was one metre. Fish, particularly Carassius gibelio, dominated the diet of the nestlings.     

Issue Information

The population of Yellow‐naped Amazons (Amazona auropalliata) declined by an estimated 50% between 1980 and 2000, and the current population is estimated to be between 10,000 and 50,000. Poaching of young has been a persistent problem, but the species is also threatened by habitat loss and degradation. Because most aspects of their life history, behavior, and ecology have not been examined in wild populations, we studied Yellow‐naped Amazons with the following objectives: (1) identify the species of trees used for nesting, (2) determine the size and potential function of breeding territories, (3) determine nesting success, and (4) examine their duetting behavior. We located nests at 16 sites on the Pacific Slope of Costa Rica from 1999 to 2008. We searched for nests from January to May. Every nest was visited at least once and some nests were visited every 2–3 weeks throughout the breeding season. We also collected territory and duetting data at one site (Ahogados). The breeding season of Yellow‐naped Amazons was during the dry season (January–May). Yellow‐naped Amazons nested in 21 species of trees, but 68% of nests were located in only five species, and cavities in dead coyols (Acrocomia aculeata) were used most often. We found no association between breeding success and the species of tree in which birds nested. Mean territory size was 25,578 m², and these small areas generally consisted of several trees surrounding a nest tree. Pairs continued to duet throughout the breeding season, suggesting that duetting is important for territory defense. The nest failure rate in our study was 89%, and most nest failures (64%) were due to poaching for the pet trade. We recommend immediate population management and conservation actions, including increased law enforcement to reduce nest poaching, protection of key nesting areas, educational programs, and habitat conservation.     

Diet of the Silvery-cheeked Hornbill Bycanistes brevis during the breeding season in the East Usambara Mountains,Tanzania

The breeding season diet and nesting characteristics of the Silvery-cheeked Hornbill Bycanistes brevis are poorly known. To further understand these aspects of the breeding biology of this hornbill species, 14 nests were studied in and around Amani Nature Reserve located in the East Usambara Mountains, Tanzania. Nesting tree species were identified and the diet composition of nesting hornbills was evaluated between July and November 2001. The ejecta from each nest were collected, inventoried, identified (as completely as possible) and enumerated. Food items were categorised as plant, vertebrate or invertebrate. Plants, represented largely by fruits, were the dominant food type (n = 861), followed by invertebrates (n = 306; mainly millipedes and beetles), and vertebrates (n = 15; mainly smaller birds and chameleons). A comparison of results from the current study to other nesting observations made approximately seven decades earlier in the same area suggest that (1) the invasive tree species Maesopsis eminii, which was the most common food type consumed (n = 4 539 seeds), has become a favoured new food source in the breeding season, and (2) the breeding season appears to have shifted to an earlier period, potentially due to the fruiting phenology and abundance of Maesopsis eminii.     

Risk-taking by incubating rufous bush robins Cercotrichas galactotes: season-dependent incubation stage effect

Risk-taking by incubating birds is commonly assumed to increase with reproductive stage due to increased nest value, and also with time of the breeding season due to decreased renesting opportunity. Nonetheless, the potential for these two factors to interact has not been given much importance. However, the extent to which risk-taking may increase with reproductive stage could be expected to vary with season. We investigated this issue using data on rufous bush robins (Cercotrichas galactotes) that we experimentally flushed from their nests at different stages of incubation and at different dates in the breeding season. We found that flushing distance of incubating birds decreased significantly with both incubation stage and season. More interestingly, we also found that incubation stage and season interact in shaping risk-taking the behaviour of incubating birds. As the breeding season progresses, and renesting opportunity declines, the effect of incubation stage on incubating parent risk-taking decreases. Overall, our work once again underlines the great complexity of behavioural and ecological factors and processes that affect risk-taking by nesting birds. In particular, it stresses the need to consider the interaction between reproductive stage and season when dealing with nest-defence behaviour in birds.     

Breeding ecology of Kori Bustard Ardeotis kori strunthiunculus in the Serengeti National Park

The breeding ecology of the Kori Bustard Ardeotis kori strunthiunculus was studied in the plains of the Serengeti National Park, Tanzania in 2014 and 2015. Random transects were used to search for male courtship displays, nests, chicks and subadults. GPS satellite collars were used to locate nesting females. Linear regression analyses and post hoc tests were used to determine the predictors that contributed most to the variation of the dependent variables (courtship display, nest, chicks and subadults). The results indicate that courtship behaviour peaks during the short dry and short rainy season before the peaks in nests and chicks. The highest nest frequency was found in short grass habitats. Female Kori Bustard may undergo repeated nestings within a single breeding season. The adult sex ratio was female skewed during the breeding season. The Kori Bustard breeding season in the Serengeti plains is relatively long, lasting for almost nine months, and taking place during all seasons except for the long dry season. We recommend that management authorities conduct assessments of Kori Bustard recruitment as well as habitat suitability in the Serengeti ecosystem to develop future conservation strategies.     

DIET,HOME RANGE,HUNTING AND REPRODUCTIVE BEHAVIOUR OF A PAIR OF DICKINSON'S KESTREL FALCO DZCKZNSONZ IN THE KRUGER NATIONAL PARK,SOUTH AFRICA

Summary

BENN, G.A. &; KEMP, A.C. 1995. Diet, home range, hunting and reproductive behaviour of a pair of Dickinson's Kestrel Falco dickinsoni in the Kruger National Park, South Africa. Ostrich 66: 81–91.

During July-December 1992, the diet, home range, hunting and reproductive behaviour of a pair of Dickinson's Kestrel Falco dickinsoni was recorded in the Kruger National Park, South Africa. Numerically, for both sexes combined, invertebrates formed the majority (56%) of the diet, while separately the female caught 75% and the male 49% invertebrate prey. During courtship and incubation the male supplied the female with primarily vertebrate prey and both provisioned mainly vertebrates to the nestlings (male = 80%; female = 57%). The non-breeding home range of the female was 27.8 km², and the breeding home range of the male was 26.3 km2. Both utilised their home ranges differentially, the area within a 2 km radius of the nest (12.6 km²) being used proportionally more than the remaining area. The home range of the female was compared to that of other Falco spp. and was larger than would be expected based on body weight. Perch-hunting was the only technique utilised by both sexes, with 79–80% of observed strike attempts from dead trees. During the day, the 9.emale spent 87% and the male 77% of the time perch-hunting, with respective hunting success rates of 69% and 58%. During courtship, the female spent much of her time (94%) close to the nest, where the male supplied her with prey. During incubation, the male spent 95% of his time within 2 km of the nest tree, where he hunted to supply the female with prey at a rate of 0.3 items.hr^?1 and assisted in nest defence. On occasion the male entered the nest to relieve the female, and remained in the cavity on average for 134 min (n = 5). As the young got older, the female spent less time at the nest and provisioned more items to the nestlings. Overall, there was an increase in the rate of prey provisioning to the nestlings from 0.45 items.hr^?1 (10 days old) to 0.85 items.hr^?1 (21 days old). The male initially passed prey to the female but provisioned directly to older nestlings.     

Productivity and mortality of mohua (Mohoua ochrocephala)

Abstract

Mohua (Mohoua oehrocephala) breeding and mortality were studied in the Eglinton Valley, Fiordland National Park, New Zealand. Mohua on the valley floor (380 m a.s.l.) bred from early October until March, though birds at higher altitude in the Eglinton and elsewhere started later. In low altitude areas, most pairs raised two broods a year, but elsewhere they seemed to raise only one. Eggs were laid daily, and incubation began with the laying of the last egg and lasted about 20 days. The nestling period was about 23 days. Clutches contained 1–5 eggs, most often three. During three breeding seasons there was no significant nest predation by introduced mammals, but in 1990/91, when stoat (Muslela erminea) numbers were high, 67% of nests and 50% of nesting females were destroyed by stoats. When stoat numbers were low, the productivity and mortality of double‐brooded mohua were well within the ranges recorded for other forest‐dwelling bird species, and the productivity of single‐brooded mohua was lower than that of most other forest‐dwelling passerines. During years when stoat numbers were high, the productivity and mortality of even the double‐brooded mohua were lower than for most other forest‐dwelling passerines. There is some evidence that there were density dependent mechanisms influencing the productivity and survival of chicks.     

BREEDING BEHAVIOUR OF OSPREYS PANDION HALIAETUS IN SCOTLAND

Ospreys Pandion haliaetus nested at a site near Loch Garten, Inverness-shire continuously from 1959 to 1973. Each year the Royal Society for the Protection of Birds has organized a continuous watch on the eyrie in the breeding season. The detailed records kept of the activities of Ospreys at the nest by those participating in the watch were analysed and the results presented here. Ospreys are migratory and arrived in the breeding area in early April. Nesting material was usually added to an existing eyrie platform. The male collected more material than the female. The female lined the nest cup. The extent of nest building activity and the frequencies of mating and other activities prior to laying varied markedly from year to year. These differences may have been related to changes in the identity of the nesting female, but the birds were not individually marked. Both sexes incubated but the female took the greater share and normally incubated at night. When the young hatched they were brooded by the female. The female stayed in the vicinity of the nest for most of the time until the young fledged at about 53 days old. The male Osprey caught almost all the fish eaten by his mate and young during the breeding season. The number of fish caught per day increased markedly after the young hatched. Pike Esox lucius and Trout Salmo trutta were the main species taken, and some Rainbow Trout Salmo gairdnerii were identified. There were seasonal and diurnal changes in the size and the species composition of the catch. The effects of weather conditions on hunting are examined. The occurrence of Ospreys other than the resident birds at the nest site is described. The behaviour of another pair of Ospreys which repeatedly failed to hatch eggs is described. There was an instance of egg eating in this pair, and some differences in behaviour were found between these birds and those at Loch Garten whose breeding success was good. The breeding biology of Ospreys is compared with that of other British diurnal birds of prey. In other species the female leaves the young unguarded at some stage in the nestling period and hunts food for them, whereas female Ospreys do not usually hunt in the nesting period.     

SOCIAL ORGANIZATION AND NEST-BUILDING IN THE FOREST WEAVER BIRDS OF THE GENUS MALIMBUS (PLOCEINAE)

A comparative study was made of social organization during breeding among the genus Malimbus. In M. nitens, the male chooses the nest site, builds the nest alone, guards the nest during incubation, and feeds the young; the female incubates, broods alone and with the male feeds the young. In M. malimbicus, the male chooses the nest site, builds the nest with the female and guards the nest; the female builds the nest with the male, but incubates alone. In M. racheliae and M. cassini, the nest is built by one female and a multi-male party of two or three. One male drives off the other males when the nest is completed. One male and one female incubate alternately. The female seems to be the leader of the building group, and works like a male. In M. coronatus, the nest is built by a mixed party of males and females (3–6 birds), all working together without any overt leadership. Only one male and one female however, incubate, brood and feed the young. In their morphology and behaviour, Malimbus spp. are close to the weaver birds of the genus Ploceus. M. nitens seems the least evolved species while M. cassini and M. coronatus are behaviourally the most evolved. In the last species, which has a very elaborate nest, the pair of breeding birds is helped by one to four other birds. These helpers are birds in full adult plumage, and are probably capable of breeding and may do so at another period in the long breeding season of at least six months.     

Nest site competition between cavity nesting passerines and golden paper wasps Polistes fuscatus

Nest boxes provide sheltered nesting sites for both passerines and paper wasps. Although neither wasps nor birds appear to evict the other once one is fully established, it is unclear which is the dominant competitor at the onset of the breeding season. Using wire mesh, we excluded birds but not golden paper wasps Polistesfuscatus from alternating boxes along a transect through edge habitat in North Carolina from 2006 – 2008. If wasps dominate Carolina chickadees Poecile carolinensis and eastern bluebirds Sialia sialis during the early spring (all have similar nest initiation dates), we would expect wasps to settle in both box types at equal frequencies. However, if birds dominate wasps, we would expect wasp nests to be concentrated in “bird‐proof” boxes. We found wasps in bird‐proof boxes significantly more often than in bird‐accessible boxes, indicating that secondary‐cavity nesting birds are able to exclude wasps from available nest sites. Additionally, we found that during the period of nest initiation, birds usurp wasps more often than vice versa.     

THE BIOLOGY OF THE WAVED ALBATROSS DIOMEDEA IRRORATA OF HOOD ISLAND, GALAPAGOS

As a nesting species, the Waved Albatross Diomedea irrorata is restricted to Hood Island in the Galapagos archipelago where 12,000 pairs bred in 1971. Outside the islands the species occurs over the northern parts of the Humboldt Current. Two colonies were studied in detail (1970–1971). At the start of a season, males returned first to the colonies and defended a small territory. Copulation occurred without any elaborate ceremony and the female spent little time on land before laying. There was no fixed nest-site, even within a season, and birds moved their eggs considerable distances. This resulted in heavy egg losses. Younger birds bred later than older birds and laid longer but narrower eggs. The average incubation spell varied from four to five days at the extremes of the incubation period to 19 days in the middle. The average incubation and fledging periods were 60 and 167 days respectively. Pairs which lost an egg sometimes adopted the abandoned egg of another bird and successfully reared the chick. Most pairs nested in both seasons. Nesting success was extremely variable, both between years and between colonies. Between 1961 and 1971 at Punta Suarez, virtually no young were reared in four seasons. Even in 1970–71, where nesting success was good, some groups of birds deserted their eggs en masse whereas in neighbouring areas up to 80% of the pairs reared young. The main foods of the young were squid and fish. Birds did not moult wing and tail feathers at the breeding colonies, and about 50% retained some primaries for more than one season, suggesting that successful pairs had difficulty in fitting in a complete moult between breeding attempts. Old feathers were normally found among the inner primaries and at the next moult were preferentially replaced, though adjacent newer feathers were sometimes retained for another season. Some birds bred in their fourth years, but most not until a year or two older. Immatures were present at the colonies late in the breeding cycle, the youngest returning latest and remaining until the last young fledged. Survival of adults and young averaged at least 95% and 93% per annum over many years. Adults and young ringed in 1961 survived equally well. The significance of the timing of the return of immatures and of the large-scale desertion of eggs, apparently not due to food shortage or disturbance, is discussed.     

Nesting success and within-season breeding dispersal in the Orange-breasted Sunbird Anthobaphes violacea

Nest predation is a primary cause of nesting mortality for many bird species, particularly passerines. Nest location can affect predation, and it has also been demonstrated that predation risk can alter nest site selection. Birds can limit predation risk by selecting specific habitat characteristics; by changing nest site characteristics between attempts; and by dispersing between nesting events. Here we report breeding data from a population of Orange-breasted Sunbirds Anthobaphes violacea (L.), for a single breeding season in the Jonkershoek Nature Reserve, South Africa. Neither shrub type nor nest height was found to affect the outcome of a nest. For subsequent breeding attempts, birds were not more likely to change the type of shrub in which they nested after a predation event than when the attempt was successful, nor did they change the height of their nest. However, we found that the distance between a nest and the subsequent one was significantly shorter after a successful nest than after an unsuccessful one. We interpret this as an adaptive strategy to avoid predation.     

BREEDING OF SACRED IBIS THRESKIORNIS AETHIOPICA AT LAKE SHALA, ETHIOPIA

Data are based on more than 200 h of observation at Ethiopia's Lake Shala from 1966 to 1972. Except for differences in size of bill, there are no useful field characters separating male and female Sacred Ibis. The breeding plumage is described; vivid blood-red colour underneath the wings and the ornamental plumes are especially obvious when nesting commences. Physical and biological features of Lake Shala, Ethiopia, and its nesting islands are described; the species of birds nesting on the Shala islands are given. Ibises nest at Shah from March to August; no nesting has been recorded from September to February during the last months of the ‘big’ rains through the main dry season. Nesting normally begins in the ‘small’ rains (between 14 March-24 April), although instances were recorded as early as 1 March and as late as 20 August. The ibises normally nest once per year, although it is possible that occasionally a second nesting may occur after an unsuccessful first attempt. The ibises at Shala nest in discrete groups; several nesting groups may form on any or all of the islands; the number of groups attempting to nest varied from year to year. Nesting activity begins when males arrive and establish pairing territories, usually in a small tree but sometimes on the ground. When females and other males arrive at the pairing territories, pair formation ensues. At this time males perform forward threat, modified forward threat, pursuit flight, supplanting attack and modified snap displays, while both sexes perform stretch and bow displays. Once established, the pair abandons the pairing territory and moves to the nesting area, usually near but always distinct from the pairing territory, and establishes a nest-site territory. Most members of the nesting group move to the nesting area on the same day. Copulation then takes place, and is followed by collection of nest material, usually by the male. Nests are built close together. The average area of 10 nests measured was 0.09 m². Nests are usually less than 20 cm thick and are made of many small branches and sticks. The average clutch in 34 nests was 2.24 eggs; the average size of 34 eggs was 63.4×43.5 mm. Incubation probably begins when the clutch is complete. Both sexes incubate, and the incubation period probably lasts 28–29 days. The development of the young is described. The young leave the nest-site territory when 14–21 days old. Although they are capable of some flight when 35–40 days old, the young do not leave the colony until they are 44–48 days old. In the colony, both parents care for the young. Usually only one parent at a time is with the young. The parents recognize their own young and are usually recognized by them. The behavioural interactions between young and parents are described. Fledging success in 1968 was 1.06 young per pair. The number of pairs successfully rearing young varied annually from none to 81%, on average over six years (1966–70, 1972) 35%. Predation at the breeding colonies is minimal. The food of one one-month old chick consisted of beetle larvae, lepidopteran larvae and beetles. Feeding areas, although undetermined, must be widespread. Inter-specific competition between Sacred Ibis and other nesting birds at Shala is discussed. Among possible factors stimulating nesting at Shala one, fairly heavy rainfall, seems to be especially important. It is also suggested that especially heavy rain-storms cause ibises to abandon the colonies, and result in poor breeding success.     

Seasonal occurrence and local movements of the grey-headed (brown-necked) parrot Poicephalus fuscicollis suahelicus in southern Africa

Seasonal movements of grey‐headed (brown‐necked) parrots were recorded in parts of its range and are likely a response to breeding and availability of specific food sources. Breeding occurred in the northern Kruger National Park and lowveld near the Mutale–Luvhuvhu river confluence from April to August. Aggregations and movements of birds occurred during the post‐breeding season (August–December) in response to seasonally abundant food sources. In north‐eastern South Africa, grey‐headed parrots occurred at Levubu, following the breeding season and their arrival in the area was correlated with the availability of unripe Mabola Plum, Parinari curatellifolia fruit. Similar regional movements occurred in Zimbabwe, the Caprivi of northern Namibia and Zambia. During these movements, flocks of up to 50 individuals were observed, whilst during breeding months singletons and pairs were more frequently seen. This increased abundance in time and space suggests that seasonal migratory movements occur.     

The role of body size in nest-site selection by secondary cavity-nesting birds in a subtropical Chaco forest

Most bird species that nest in tree cavities globally occur in diverse assemblages in little-studied tropical and subtropical forests which have high rates of habitat loss. Conservation of these communities will require an understanding of how species traits, such as body size, influence nest-site selection. We examined patterns of nest-site selection of secondary cavity-nesting birds at the nest patch, tree and cavity scale, and investigated how these patterns are influenced by body size. Using conditional logistic regression, we compared characteristics of 155 nest tree cavities paired with 155 unused tree cavities in quebracho Schinopsis balansae forests in Chaco National Park, Argentina (2016–2018). The odds of a cavity being used for nesting increased with its depth and height above ground, decreased with entrance size, and were greater for dead trees than live. Small-bodied (13–90 g) species used floor diameters in proportion to availability, but medium- (150–200 g) and large-bodied (400–700 g) species selected cavities with larger floors. Model selection indicated that characteristics at the nest patch scale (canopy cover, tree density) had little effect on nest-site selection when cavity-scale variables were included. Cavity floor diameter, entrance size, cavity height and tree diameter (but not cavity depth) increased with body mass, and larger bird species more often used live trees. Two tree species proved to be key for the community: large and medium-sized birds used almost exclusively large live Schinopsis balansae, whereas small birds used live and dead Prosopis spp. in a proportion greater than its availability. Small birds could be differentiated according to species-specific cavity characteristics, but medium and large species overlapped considerably with one another. Although body mass explained much of the overall variation in tree and cavity characteristics between small and medium/large species, several small-bodied species consistently used cavities outside of the expected characteristics for their body size, suggesting that other natural history traits may play important roles in nest-site selection by small-bodied birds. To retain the full suite of secondary cavity-nesters in species-rich tropical and subtropical forests, it is necessary to conserve a diversity of trees and cavities that meet the full range of nesting requirements of these trait-diverse communities.