Behavioural ecology of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus during the breeding season

Two nests of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus were monitored for one breeding season (April-July). The females sealed themselves into the nest cavities and remained there for 70–90 days. Incubation was estimated at 16–19 days, and at both nests two offspring fledged. Tarictic Hornbills are cooperative breeders with up to three helpers at the nest and defend foraging territories of 72–139 ha. Food items delivered to the nest included fruits of 34 species (85% of diet items) and invertebrates. Provisioning by helpers allowed breeding males to reduce investment in parental care and may accelerate the development rates in chicks. Constraints on dispersal probably result from habitat saturation rather than living in an unpredictable environment.     

Breeding and nest site characteristics of the Black-casqued Hornbill Ceratogymna atrata and White-thighed Hornbill Ceratogymna cylindricus in south-central Cameroon

The reproductive biology of two species of African hornbill, the Black-casqued Hornbill, Ceratogymna atrata, and the Whitethighed Hornbill, Ceratogymna cylindricus, was investigated over a four-year period (1994–1997) on a 25km 2 site in lowland rainforest in south-central Cameroon. Nesting attempts varied considerably among years, with the percentage of successful nests highest in 1995, with 64% and 54% of Black-casqued and White-thighed Hornbill fledging offspring, respectively. There were no nesting attempts in 1994, despite the fact that hornbills were present in the study area. Large differences in fruit availability were also noted across years, suggesting that reproductive activity and success are related to fruit availability. Data collected from 38 nests, over four breeding seasons (1994–1997), showed a preference for nest cavities in larger trees within areas of the forest containing larger trees. Hornbills did not show preferences for particular tree species, with the possible exception of Petersianthus macrocarpus, in which nine of the active nest cavities were found. Comparisons showed few significant differences in cavity characteristics between the two species . While cavities may have been a limiting factor in nesting in 1995, the year with the highest fruit availability, cavities were not limiting during other years when fruit availability was lower. Hornbill diets, as determined from seed traps at cavities, showed significant year-to-year variation. Although courtship and exploratory behaviour of cavities by pairs took place in most years, females did not wall themselves into cavities unless fruit was plentiful. Hornbills appear to time reproduction to coincide with peak food supply and successfully reproduce only when food is plentiful, and may curtail or forego nesting in years when fruit availability is low.     

Breeding ecology of the Sulawesi Red-Knobbed Hornbill Aceros cassidix

Data are presented for a four-year study of the breeding biology of the Sulawesi Red-knobbed Hornbill Aceros cassidix. The breeding season normally began in mid-June and lasted 27–30 weeks. Initiation of nesting appeared to be stimulated by the cessation of the rains and timed such that chicks emerged during a period of fruit abundance. Nesting period averaged 139 days and incubation was estimated at 35–40 days. Females remain sealed in the nest for an average of 108 days and nestlings fledged, on average, 28 davs after the female emerged. Nesting densities were up to 10.4/km², nesting success was high (up to 80%) and repeated use of nests between years was common. Males delivered a low-protein diet of ripe fruits (89% of total diet) from 12 families and 52 species; invertebrates composed only 1% of food items. Figs ( Ficus spp.) were the primary diet item, accounting for 81% of fruit biomass. Males increased feeding visits throughout the study, but the biomass of fruit delivered declined shortly after the female emerged. Reduced feeding prior to fledging may entice the nestling to emerge. The long developmental period of Sulawesi Red-knobbed Hornbills may result, in part, from the low protein content of the diet. Despite a 16% annual production, numbers in the study area have remained stable over the past 15 years. It is suggested that high post-fledging mortality or dispersal to degraded areas outside the reserve maintains population numbers. Distinguishing between these mechanisms is important for understanding the dynamics of hornbill populations.     

Activity patterns of parent Great Tits Parus major feeding their young during rainfall

The influence of rainfall on the foraging patterns of Great Tit Parus major parents while feeding chicks at the nest was investigated using automated nest monitoring with electronic balances and photography. Great Tit females significantly reduced their visit rate to the nest during all rain intensities, while male feeding frequency did not significantly change. The female response was probably due to increased brooding requirements of young since the reduction in visit rate was most apparent at early nestling stages. At this time the chicks are incapable of thermoregulation and females significantly increased their nestbox occupancy time during rain. There was no indication that parents were compensating for periods of female inactivity during rainfall: there was no significant increase in visit rate following rainfall and no significant increase in prey size delivered to the nest during periods of rain. An analysis of data from six consecutive years revealed that the proportion of wet hours within the first week of the nestling period significantly influenced fledging weight in this species.     

Do parents play a role in the timing and process of fledging by nestling Mountain Bluebirds?

What causes young birds to leave nests remains unclear for almost all altricial species. For many years, the assumption was that parents often controlled the time of fledging by coaxing young from nests, e.g., by holding food within view, but out of reach, of nestlings. This assumption, though, was based solely on scattered anecdotal reports of such behavior. We used continuous video‐recording of nests to assess the role of parents, if any, in the timing and process of fledging of cavity‐nesting Mountain Bluebirds (Sialis currucoides). We placed perches ~50 cm in front of nest‐box entrances to give parents ample opportunity to display food to nestlings. We found no evidence that parents routinely initiated the fledging process. On the day of fledging, parents did not perch on supplemental perches with food more often, or for longer periods of time, than on the day before fledging. Also, after going to nest‐box entrances, parents never held food away from a nestling reaching for the food. Parents were usually absent (16 of 19 cases) when the first nestling fledged. In the remaining three cases, a parent perched with food in view of a nestling for 8, 15 and 65 s, respectively, just before that nestling fledged. Although these might have appeared to be attempts at coaxing, in each case, the parent was encountering, for the first time, a nestling partially emerging from the nest entrance. Parents may simply have hesitated to approach nests because the nestling's position prevented parents from delivering food in the normal manner. Finally, the rate at which parents fed nestlings on the day of fledging did not differ from the rate the day before, suggesting that parents do not try to use hunger to induce fledging. Our results are consistent with previous research suggesting that, in Mountain Bluebirds, it is a nestling that initiates fledging, typically when it reaches some threshold state of development.     

Offspring desertion and parental care in the Whiskered Tern Chlidonias hybrida

In species with biparental care, a conflict of interest can arise if one mate tries to maximize its own reproductive success at the expense of the other's. One of the mates can desert the brood to accrue a number of benefits to enhance its own fitness, leaving parental care to the remaining parent. This study is the first to describe the desertion pattern in a tern species (Sternidae). We investigated offspring desertion in the Whiskered Tern Chlidonias hybrida, a species with semi‐precocial chicks. Offspring desertion was recorded in 52% of nests prior to fledging (n = 131 nests). Females also deserted during the post‐fledging period. Of the deserters, 97% were females. Desertions started when chicks were 5 days old and no longer required intense brooding. Desertions before fledging did not affect fledging success. Provisioning rates between pair members differed, and females supplied much less food than males. Female provisioning rate affected the chances of nest desertion significantly: daily desertion rates were lower when females supplied more food. After females had deserted, males increased their provisioning rates but compensated for the loss of female care only partly in two‐ and three‐chick broods. Only in small (one‐chick) broods was compensation full. We conclude that male and female Whiskered Terns adopt different reproductive strategies in the population studied here. Females invest much less in parental care than males, providing less food and deserting more frequently. Given the ready availability of food and low predation pressure, benefits appear to accrue to females that desert; selection forces may therefore not be acting against female desertion.     

Females compensate for moult‐associated male nest desertion in Hooded Warblers

Uniparental offspring desertion occurs in a wide variety of avian taxa and usually reflects sexual conflict over parental care. In many species, desertion yields immediate reproductive benefits for deserters if they can re‐mate and breed again during the same nesting season; in such cases desertion may be selectively advantageous even if it significantly reduces the fitness of the current brood. However, in many other species, parents desert late‐season offspring when opportunities to re‐nest are absent. In these cases, any reproductive benefits of desertion are delayed, and desertion is unlikely to be advantageous unless the deserted parent can compensate for the loss of its partner and minimize costs to the current brood. We tested this parental compensation hypothesis in Hooded Warblers Setophaga citrina, a species in which males regularly desert late‐season nestlings and fledglings during moult. Females from deserted nests effectively doubled their provisioning efforts, and nestlings from deserted nests received just as much food, gained mass at the same rate, and were no more likely to die from either complete nest predation or brood reduction as young from biparental nests. The female provisioning response, however, was significantly related to nestling age; females undercompensated for male desertion when the nestlings were young, but overcompensated as nestlings approached fledging age, probably because of time constraints that brooding imposed on females with young nestlings. Overall, our results indicate that female Hooded Warblers completely compensate for male moult‐associated nest desertion, and that deserting males pay no reproductive cost for desertion, at least up to the point of fledging. Along with other studies, our findings support the general conclusion that late‐season offspring desertion is likely to evolve only when parental compensation by the deserted partner can minimize costs to the current brood.     

Parental care and social mating system in the Lesser Spotted Woodpecker Dendrocopos minor

The sexes’ share in parental care and the social mating system in a marked population of the single‐brooded Lesser Spotted Woodpecker Dendrocopos minor were studied in 17 woodpecker territories in southern Sweden during 10 years. The birds showed a very strong mate fidelity between years; the divorce rate was 3.4%. In monogamous pairs, the male provided more parental care than the female. The male did most of the nest building and all incubation and brooding at night. Daytime incubation and brooding were shared equally by the sexes, and biparental care at these early breeding stages is probably necessary for successful breeding. In 42% of the nests, however, though still alive the female deserted the brood the last week of the nestling period, whereas the male invariably fed until fledging and fully compensated for the absent female. Post‐fledging care could not be quantified, but was likely shared by both parents. Females who ceased feeding at the late nestling stage resumed care after fledging. We argue that the high premium on breeding with the same mate for consecutive years and the overall lower survival of females have shaped this male‐biased organisation of parental care. In the six years with best data, most social matings were monogamous, but 8.5% of the females (N=59) exhibited simultaneous multi‐nest (classical) polyandry and 2.9% of the males (N=68) exhibited multi‐nest polygyny. Polyandrous females raised 39% more young than monogamous pairs. These females invested equal amounts of parental care at all their nests, but their investment at each nest was lower than that of monogamous females. The polyandrously mated males fully compensated for this lower female investment. Polygynous males invested mainly in their primary nest and appeared to be less successful than polyandrous females. Polyandry and polygyny occurred only when the population sex ratio was biased, and due to strong intra‐sexual competition this is likely a prerequisite for polygamous mating in Lesser Spotted Woodpeckers.     

Provisioning behaviour at the nest in single-parent versus biparental nests and male versus female parents in the common redstart (<Emphasis Type="Italic">Phoenicurus phoenicurus</Emphasis>)

We analysed video-sequences of undisturbed parental provisioning behaviour on 12 nests of common redstart (Phoenicurus phoenicurus). In 4 of the 12 nests, chicks were fed by a single parent only. We compared provisioning rate of chicks, time spent on the nest and food allocation rules between nests with uniparental and biparental care and between male and female parents in biparental nests. In nests with a single parent, the frequency of feeding visits per parent was higher than in biparental nests. As a result, the rate of food provisioning of chicks was similar in uniparental and biparental nests. The food allocation rules did not differ between uniparental and biparental nests. In biparental nests, male and female provisioning behaviour was similar though with two exceptions: males had a strong preference for feeding chicks in front positions in the nest and females spent a longer time on the nest after feeding. We conclude that single common redstart parents are able to compensate fully for the absence of the other parent through increased provisioning efforts, and that in biparental nests, males and females contribute equally to the provisioning of the young.     

A FIELD STUDY OF THE BEARDED BELLBIRD IN TRINIDAD

The Bearded Bellbird Procnias averano, a medium-sized sexually dimorphic cotingid, was studied for three years in the Northern Range of Trinidad. Its preferred habitat is primary forest at altitudes of 500–1,000 feet and with a rainfall near 100 inches. It is entirely frugivorous, taking mostly drupes. The seeds of the fruits eaten are regurgitated and nearly 2,000 were collected from below the male's calling perch and below nests. Most were from the families Lauraceae and Burseraceae, whose fruits have particularly nutritious pericarps. Adult males own a calling territory from which they call throughout most of the day, and throughout the year except for the period of moult. In each territory there are special saplings where display and mating take place. Only males call; the females are voiceless. The call is loud and far-reaching. In Trinidad P. averano has only two calls, the Venezuelan birds have a third more musical call which appears to have been lost by the Trinidad bellbird during the past 60 years. Both males and females visit the adult male in his calling territory. Here he performs a ritualized display to the visitor, which shows off his black and white plumage, the beard of wattles, and also a bare patch on the thigh. The visit of the female may culminate in mating. All aggressive behaviour observed was between males disputing over calling territories. The female builds the nest, incubates, and rears the chick on her own. The very inconspicious nest is built of twigs that readily interlock. Nearly all the twigs are from two species of tree, and it is suggested that the specialized nest-material may be essential, as the female bellbird builds only with the breast and feet. The clutch consists of a single egg. The incubation and fledging periods are both long, 23 and 33 days respectively. The female's visits to the chick are infrequent, brief, silent and inconspicuous. Many details of breeding behaviour indicate that the inconspicuousness of the nest is of paramount importance. The nestling is fed on fruit which the female regurgitates. The main breeding season is from April to July with a minor one in October and November. It takes two and a half years for the male to attain fully adult plumage, and at least two years to achieve a completely adult call. The relationship between type of nest, clutch-size, feeding habits and sexual bonds in tropical forest birds is discussed. The bellbird is an extreme example of a species in which the need for a very inconspicuous nest and a diet of fruit have combined to promote polygamy, with the emancipation of the male from the nest, and to reduce clutch-size to a minimum. The bellbird's structural adaptations to its method of feeding in flight are discussed and a comparison is made with the birds of paradise. The male's adaptations for its primary function of self-advertising are compared with the parallel adaptations evolved in the related Pipridae.     

Behavior of adult and young grassland songbirds at fledging

The behavior of adults and young at the time of fledging is one of the least understood aspects of the breeding ecology of birds. Current hypotheses propose that fledging occurs either as a result of parent‐offspring conflict or nestling choice. We used video recordings to monitor the behavior of nestling and adult grassland songbirds at the time of fledging. We observed 525 nestlings from 166 nests of 15 bird species nesting in grasslands of Alberta, Canada, and Wisconsin, USA. Overall, 78% of nestlings used terrestrial locomotion for fledging and 22% used wing‐assisted locomotion. Species varied in propensity for using wing‐assisted locomotion when fledging, with nestling Grasshopper Sparrows (Ammodramus savannarum) and Henslow's Sparrows (Centronyx henslowii) often doing so (47% of fledgings) and nestling Song Sparrows (Melospiza melodia), Common Yellowthroats (Geothlypis trichas), and Chestnut‐collared Longspurs (Calcarius ornatus) rarely doing so (3.5% of fledgings). For 390 fledging events at 127 nests, camera placement allowed adults near nests to be observed. Of these, most young fledged (81.5%) when no adult was present at nests. Of 72 fledging events that occurred when an adult was either at or approaching a nest, 49 (68.1%) involved feeding. Of those 49 fledgings, 30 (62.1%) occurred when one or more nestlings jumped or ran from nests to be fed as an adult approached nests. The low probability of nestlings fledging while an adult was at nests, and the tendency of young to jump or run from nests when adults did approach nests with food minimize opportunities for parents to withhold food to motivate nestlings to fledge. These results suggest that the nestling choice hypothesis best explains fledging by nestlings of ground‐nesting grassland songbirds, and fledging results in families shifting from being place‐based to being mobile and spatially dispersed.     

The Process and Causes of Fledging in a Cavity-Nesting Passerine Bird, the House Wren (Troglodytes aedon)

Little is known about the process or causes of fledging or nest‐leaving in passerine birds because researchers can rarely predict when fledging will occur in a given nest. We used continuous videotaping of nests to both document the process of fledging in the house wren, Troglodytes aedon, a small, cavity‐nesting songbird, and test hypotheses as to what might cause fledging to begin. Fledging began any time from 14 to 19 d after hatching commenced. Slower‐developing broods fledged later than faster‐developing broods. Fledging typically began within 5 h of sunrise and over 80% of all nestlings fledged before noon. All nestlings fledged on the same day at 65% of nests and over two consecutive days in most other nests. We found no evidence that fledging was triggered by changes in parental behaviour. Parental rate of food delivery to nestlings did not decline during a 3‐h period leading up to the first fledging, nor was the rate of feeding just prior to the first fledging lower than the rate at the same time the day before. Moreover, parents did not slow the rate of food delivery to nests after part of the brood had fledged. Hatching is asynchronous in our study population which creates a marked age/size hierarchy within broods. At most nests, the first nestling to fledge was the most well‐developed nestling in the brood or nearly so (as measured by feather length). This suggests that fledging typically begins when the most well‐developed nestlings in the brood reach some threshold size. However, at about one‐fifth of nests, the first nestling to fledge was only moderate in size. At these nests, severe competition for food may have caused smaller, less competitive nestlings to fledge first to increase their access to food. We found no strong support for the suggestion that the oldest nestlings delay fledging until their least‐developed nestmate reaches some minimum size, although further experimental work on this question is warranted.     

Female Response to Reduced Male Parental Care in Birds: An Experiment in Tree Swallows

In biparental species, parental-investment theory generally predicts an inverse relationship between the level of parental care provided by each parent and incomplete compensation by one parent in response to reduced parental care by their partner. The factors that influence the magnitude of this compensation have rarely been examined in birds. For example, the level of compensation may differ between a widowed bird that receives no assistance from its partner and a mated bird whose partner is still present but providing less than its normal share of parental care. This study compares the compensatory response of female tree swallows (Tachycineta bicolor) without their mate's parental assistance (when females are widowed) and with reduced male parental care (when males are handicapped by cutting some feathers). When compared with control females, experimental females compensated more in terms of nest visits for the absence than the reduction of male parental care. In addition, widowed females had significantly reduced brood mass and fledging success compared with control females. Although handicapped males reduced their nest-visit rate significantly, females with handicapped mates did not significantly increase their nest-visit rate nor was there reduced brood mass or reduced fledging success at their nests. Total nest-visit rate was similar for all groups, yet widowed females fledged fewer and lighter young, suggesting that they brought less food per nest visit. We suggest that fledging success and measures of offspring quality are probably better indicators of the level of compensatory parental care than nest-visit rate. We suggest that for widowed females the benefits of a relatively large compensatory response outweighed the costs; whereas, for females with a handicapped mate the benefits of higher feeding rates were not greater than the cost. The results of this study help to explain the differences among experimental studies of compensatory parental care and point to a new method of testing models of parental care.     

Effects of habitat fragmentation on provisioning rates, diet and breeding success in two species of tit (great tit and blue tit)

The aim of this study was to examine the effects of forest fragmentation on the ability of parent birds to provide their young with an adequate food supply. To examine whether prey population densities of the great tit (Parus major L.) and the blue tit (P. caeruleus L.) vary between study areas in different forest size classes we compared provisioning rates and chick diet and related these parameters to breeding success. We filmed 217 nests over two breeding seasons and collected data on frass fall as a general estimate of caterpillar availability. Nests which were attended by none or one parent only during filming (n = 46) were excluded from the analyses. In both years and for both species feeding rates were highest in the smallest fragments and lowest in the large forest. There was also a suggestion that differences in feeding rates between areas vary between years. We found no consistent tendency for prey size to change with forest size, although both species brought slightly smaller prey items to the nest in the smallest forest fragments and feeding rates correlated negatively with prey size. Caterpillars were the main item fed to nestlings, in both species. We found no evidence to suggest that either frass fall or the proportion of caterpillars in the diet varied with forest size. There was also no correlation between mean frass fall and the total number of caterpillars brought to the nests, in either species. Breeding success, as measured by clutch size, brood size, fledging weight and fledging success, did not differ between the small fragments and the large forest, in either species. There was also no relationship between provisioning rate (as concerns volume of prey fed to nestlings and the quality of chick diet) and breeding success parameters. In conclusion, this study does not suggest suboptimal foraging or breeding conditions in small fragments compared to a nearby large forest, for either species. Received: 23 June 1997 / Accepted: 29 December 1997     

Testing common assumptions in studies of songbird nest success

We studied Ovenbird Seiurus aurocapilla and Golden‐winged Warbler Vermivora chrysoptera populations in northern Minnesota, USA, to test two common assumptions in studies of songbird nest success: (1) that the condition of an empty nest on or near its expected fledge date is an indicator of nest fate; and (2) that the presence of a fledgling or family group within a territory confirms a successful nest in that territory. We monitored the condition of nests and used radiotelemetry to monitor juveniles through the expected fledging date and early post‐fledging period. Of nests that contained nestlings 1–2 days before the expected fledge date, fates were misidentified using nest condition alone for 9.5% of Ovenbird nests, but those misidentifications were made in both directions (succeeded or failed), yielding only a small bias in estimated nest success. However, 20% of Golden‐winged Warbler nests were misidentified as successful using nest condition during the final visit interval, biasing the nest success estimate upward by 21–28% depending on the treatment of uncertain nest fates. Fledgling Ovenbirds from 58% of nests travelled beyond their natal territory within 24 h, rising to 98% after 5 days, and those fledglings travelled up to 390 m from nests within 10 days of fledging. Fledgling Golden‐winged Warblers from 13% of nests travelled beyond their natal territory within 24 h, rising to 85% after 5 days, and those fledglings travelled up to 510 m from nests within 10 days of fledging. We conclude that nest condition and fledgling presence can be misleading indicators of nest fate, probably commonly biasing nest success estimates upward, and we recommend that these assumptions should be tested in additional species.     

Biases in Studying the Diet of the Bearded Vulture

Abstract: We compared methods of assessing the diet of the bearded vulture (Gypaetus barbatus) during the nestling period in the Pyrenees, northeast Spain. We determined diet from direct observations of food items delivered to the nest, recent prey remains present in the nest, remains collected in the nests after fledging, and remains collected in the ossuaries (bone-breaking sites). Data suggest that direct observation (food items delivered and recent prey remains present in the nest) is the only valid method of assessing the bearded vulture's diet accurately. Remains overestimated the presence of large mammals, such as cows (Bos taurus) and horses (Equus caballus), Suidae, and birds; delivered samples contained a higher proportion of small mammals, medium-sized mammals, micromammals, and reptiles. Ossuaries also differed from delivered samples because remains collected there overestimated large and medium-sized mammals. Concerning the skeletal parts, ossuaries, compared to all other methods, underestimated extremities and overestimated long bones, such as femur, humeri and tibiae, scapulae, vertebrae, and skulls. Remains samples, which overestimated scapulae, also differed from delivered and present samples. Our results suggest that bearded vultures favor extremities of prey (78% of the mammal remains, which make up 95% of the diet). The prevalence of small carcasses (almost 17%) suggests that vultures select small animals for food for the young. Because food quality may influence breeding success, future conservation projects based on the selective provision of food to breeding pairs should add to food stations meat remains and small carcasses consistent with our assessment of the birds’ dietary needs.     

An experimental test of predator–parasite interaction in a passerine bird

Experimental studies incorporating multiple trophic levels are scarce but of increasing interest for understanding ecological communities. Here we investigated interactive effects of perceived predation risk and parasite pressure on life‐history traits in a hole‐nesting bird, and the effects of predation risk on parasite success. In a 3 × 2 experimental design we increased perceived predation risk for breeding great tits Parus major via simulations of either nest‐predators (woodpeckers) or post‐fledging predators (sparrowhawks) close to nests, and used a non‐predatory species (song thrush) as a control. Concurrently, half of the nests in each treatment were either infested with ectoparasites, or kept parasite‐free. Regarding the predation risk – parasite interaction, exposure to nest‐predators tended to lower wing and sternum growth rates of nestlings in the absence, but not the presence, of parasites. In the presence of parasites, exposure to a post‐fledging, but not to a nest‐predator, led to significantly reduced wing growth. Mass and tarsus length were not affected by predator exposure, but ectoparasites had slight positive effects on mass gain. In the last third of the nestling period, overall nestling size was significantly smaller when exposed to a post‐fledging predator than to a nest‐predator, but neither differed from the control. Parental feeding rates were not affected by the treatments, but parents became less selective towards food items under either predation risk. Hen‐flea population sizes (adult or larvae) in nests were not affected by predation risk treatment of hosts. In summary, we found some evidence for an interactive effect of predation risk and parasite pressure on nestling growth. The complexity of the interaction, combined with certain inconsistencies of the effects and potential statistical artifacts, prevent however a straightforward interpretation of the results. The insights from the study are useful for designing additional experiments to further investigate the complexity of predator–parasite interactions in wild populations.     

The process of fledging in the Mountain Bluebird

Fledging is a critical event in the avian breeding cycle, but remains unstudied in almost all species. As a result, little is known about factors that cause nestlings to leave nests. We documented fledging behavior in a box‐nesting population of Mountain Bluebirds (Sialia currucoides) using radio‐frequency identification. We attached a passive integrated transponder (PIT tag) to the leg of each nestling in 40 nests. An antenna checked for the presence of a transponder signal (i.e., a nestling) at nest‐box entrances every 2 s. The time of last detection of a nestling was taken as the time that nestling fledged. We found that fledging began when the oldest nestlings were 15–22 d old. Broods that were ahead in development, as measured by primary feather length, fledged at relatively younger ages. All nestlings fledged on the same day at 33 nests (83%) and over 2 d at remaining nests. When all nestlings fledged on the same day, fledging usually began in the morning and median time between the first and last fledging was 55 min (range = 2.3 min–10.6 h). When young fledged over 2 d, fledging always began >8 h after sunrise and usually just one nestling fledged the first day, suggesting that this fledging may have been accidental. Clutches in our population often hatch asynchronously, which sets up a hierarchy within broods in developmental state, size, and competitive ability. In such situations, fledging may be initiated by one of the most‐developed and hence most‐competitive nestlings in a brood, presumably when it reaches a certain threshold state of development. Alternatively, fledging may begin when a less‐developed, less‐competitive, and probably hungrier nestling leaves the nest, presumably to gain better access to food. We used the proportion of time that a nestling was able to occupy the nest‐box entrance late in the nestling stage, waiting to intercept parents with food, as an index of nestling competitive ability. Assuming that the number of nest entrance detections reliably indicates nestling competitive ability, we found that the most‐competitive nestling fledged first at over half of all nests, supporting the notion that fledging usually begins when oldest nestlings reach a threshold state of development.     

Nest site characteristics of four sympatric species of hornbills in Khao Yai National Park, Thailand

Characteristics of nest sites, nest trees and nest holes were documented for four sympatric species of hornbills in Khao Yai National Park: the Great Buceros bicornis. Wreathed Rhy-ticeros undulatus , Oriental Pied Anthracoceros albirostris and Brown Hornbills Ptilolaemus tickelli. Nearly all hornbills nested in cavities in the trunks of at least 13 different genera of living trees. Sixty percent of the 80 nests found were in two tree genera, Dipterocarpus (34%) and Eugenia (26%), which comprised only 7% and 3%, respectively, of all large trees in 302 sample plots. Hornbills tended to prefer holes high in large, emergent trees for nesting, except for the Brown Hornbills, which preferred nest holes within or below the main forest canopy (15–25 m high). Most nest sites were between 700 and 800 m a.s.l. (79% of the total of 80 nests). Brown Hornbill nests were located in areas with a significantly higher altitude than were those of the Oriental Pied Hornbill. Hornbills tended to select nest entrances according to their body size, and all four hornbill species used oval to elongated nest entrances, with the Great Hornbill preferring the most elongated entrances. Hornbills did not select a specific nest entrance orientation.     

Nesting biology and food habits of the endangered Sakalava Rail Amaurornis olivieri in the Mandrozo Protected Area,western Madagascar§

We studied the nesting biology and food habits of the endangered and endemic Sakalava Rail Amaurornis olivieri from July to November 2015 in the Mandrozo Protected Area, western Madagascar. Three nesting pairs were observed and their nests were constructed in a dense mat of reeds Phragmites mauritianus and averaged 56.7 ± 15.3 cm above the water (n = 3 nests). Nests were built by both adults and it took 3 d on average to complete a nest (n = 2 nests). Thirteen matings were observed and lasted 4.1 s on average (n = 2 pairs). Average clutch size was three eggs (n = 2 nests). Both sexes incubated; the incubation period was 15–17 d (n = 2 nests). Both male and female participated in brooding and feeding the young, which remained for 3 d in the nest and became independent of their parents at 45 d of age. Based on 194 identified food items, the Sakalava Rail’s diet was composed of invertebrates: spiders (53.1%), insects (32%), crustaceans (10.8%) and molluscs (4.1%). The home ranges of two radio-tagged individuals were 0.95 and 1.98 ha.