Nest Territory Research Articles

Nest-site selection and nest predation in a tropical passerine in relation to food, friends, and foes

ABSTRACT Nest-site selection is an important determinant of avian reproductive success, mainly through its effect on predation risk. However, which environmental and social factors affect nest-site selection and predation risk remains less well understood. Optimal nest positioning may depend on the balance of many distinct factors such as nest predation, food availability, extra-pair mating opportunities, presence of helpers, and interactions with neighboring conspecifics. We investigated how these factors affect nest-site selection and nest survival in Acrocephalus sechellensis (Seychelles Warbler), a facultative cooperative-breeding passerine that defends stable territories year-round. We found that daily nest survival increased by ~1% for each meter higher in the canopy that a nest was placed. Nests were more likely to be located in food-rich parts of the territory, especially in territories with low overall densities of arthropods. Further, we found that nests in territories with helpers, which reduce nest predation in A. sechellensis, were built in areas with higher food availability, whereas nests in territories without helpers were built in areas with fewer nest predators. Finally, we found that females build their nests 0.5 m closer to the border for each year the nearest neighboring male was older than their partner. Our results suggest that nest-site selection in A. sechellensis is affected by nest predation, food availability, helper presence, and possibly, the female’s opportunity for extra-pair copulations. Clarifying the relative importance of these different selective factors is key to the understanding of optimal nest-site selection to maximize reproductive success.

Nesting Bald Eagle Population Numbers, Density, Territorial Resources, and Relationship to Human Development in Northern Colorado’s Front Range

To better understand the population of the Bald Eagle (Haliaeetus leucocephalus) nesting along northern Colorado’s Front Range, from 2016 to 2022 we studied 86 occupied nests within an area of 20,586 km2. From 2017 to 2020, 279 juveniles fledged from 237 nesting attempts in a smaller, main nest-study area with 68 nests. The nests’ success over these four years ranged from 52 to 70%, and their productivity varied from 1.1 to 1.3. The average nearest-nest distances for three discrete areas in the Front Range (5.03 to 7.26 km) are at least 2.8 to 4.0 times greater than these distances in four nesting populations in wetter regions but shorter than distances observed between nests in drier Arizona. In our study area the coverage of buildings within 400 m of Bald Eagle nests is relatively low by comparison to the coverage around randomly selected points, averaging 1344 m2; for 63% of the nests this coverage was less than 800 m2. We classified the 86 nest territories into eight categories that describe the dominant resource habitat and predicts the eagles’ reliance on Black-tailed Prairie Dogs (Cynomys ludovicianus) versus fish as prey. Predation on fish was predicted to be dominant at 51% (n = 44) of the nests, predation on prairie dogs at 32% (n = 28).

Sharing habitat: Effects of migratory barnacle geese density on meadow breeding waders

1.Following targeted conservation actions most goose populations have increased. The growing goose populations caused an increase in human-wildlife conflicts and have the potential to affect nature values. As meadow birds, including meadow-breeding waders, were declining throughout Western Europe, the possible negative effect of rising numbers of foraging barnacle geese on their breeding success has been questioned.2.We used GPS-transmitter data to measure the density of foraging barnacle geese during daylight hours. Using dynamic Brownian Bridge Movement Models (dBBMM), we investigated the effect of barnacle goose density on the territory distribution of five wader species, and on nest success of the locally common Northern lapwing. We used model selection methods to identify the importance of barnacle goose density related to other environmental factors.3.Our results showed an insignificant positive association between barnacle goose density and nest territory density of the Northern lapwing and common redshank. Barnacle goose density had no influence on territory selection of godwit, oystercatcher and ringed plover. We did, however, find a negative correlation between barnacle geese density and the nest success of the Northern Lapwing.4.We infer that either barnacle goose foraging leads to improved territory conditions for some wader species, or that both barnacle geese and waders prefer the same type of habitat for foraging and nesting. Higher barnacle goose density was correlated with fewer Northern lapwing nests being successful.5.Synthesis and application: Experimental research is needed to disentangle the causal chain, but based on our observational findings, we suggest to increase water logging that may attract both barnacle geese and wader species. Further investigation on the effects of barnacle geese on wader species is necessary to identify the cause of the negative correlation between barnacle geese density and nest success of lapwings; nest protection experiments could give further insight.

Tall, heterogeneous forests improve prey capture, delivery to nestlings, and reproductive success for Spotted Owls in southern California

Abstract Predator–prey interactions can be profoundly influenced by vegetation conditions, particularly when predator and prey prefer different habitats. Although such interactions have proven challenging to study for small and cryptic predators, recent methodological advances substantially improve opportunities for understanding how vegetation influences prey acquisition and strengthen conservation planning for this group. The California Spotted Owl (Strix occidentalis occidentalis) is well known as an old-forest species of conservation concern, but whose primary prey in many regions—woodrats (Neotoma spp.)—occurs in a broad range of vegetation conditions. Here, we used high-resolution GPS tracking coupled with nest video monitoring to test the hypothesis that prey capture rates vary as a function of vegetation structure and heterogeneity, with emergent, reproductive consequences for Spotted Owls in Southern California. Foraging owls were more successful capturing prey, including woodrats, in taller multilayered forests, in areas with higher heterogeneity in vegetation types, and near forest-chapparal edges. Consistent with these findings, Spotted Owls delivered prey items more frequently to nests in territories with greater heterogeneity in vegetation types and delivered prey biomass at a higher rate in territories with more forest-chaparral edge. Spotted Owls had higher reproductive success in territories with higher mean canopy cover, taller trees, and more shrubby vegetation. Collectively, our results provide additional and compelling evidence that a mosaic of large tree forest with complex canopy and shrubby vegetation increases access to prey with potential reproductive benefits to Spotted Owls in landscapes where woodrats are a primary prey item. We suggest that forest management activities that enhance forest structure and vegetation heterogeneity could help curb declining Spotted Owl populations while promoting resilient ecosystems in some regions.

Golden Eagle Nesting Territory Distribution in Wind Energy Landscapes of the Southern Great Plains

Abstract Deaths of four Golden Eagles (Aquila chrysaetos) due to collision trauma at a new wind energy facility in east-central New Mexico during 2004–2005 prompted concerns about the species' population status in the encompassing Southern Great Plains region, primarily because its breeding distribution there was poorly documented and wind energy development was expanding rapidly. Therefore, we conducted aerial searches for Golden Eagle nests across northeastern New Mexico, northwestern Texas, western Oklahoma, and adjacent portions of Colorado and Kansas during 2006–2009 and 2015–2020. We delineated five Golden Eagle Nest Search Areas (NSAs) with unique physiographic/geological origins. Individual NSAs were searched partially or entirely for up to 8 yr. Collectively, we identified 123 nesting territories (NTs) occupied by Golden Eagles ≥ 1 yr, of which 94 (76%) were in northeastern New Mexico. The most NTs (40) were in the 11,720-km2 Highlands NSA. Greatest NT density (126.6 km2/NT) and shortest NT nearest neighbor distance (7.4 km) were in the 3533-km2 Northern Caprock NSA. Wind turbines existed near (within 3.2 km) eight nests distributed among five of 28 NTs in the Northern Caprock and were planned for sites in two occupied NTs. Elsewhere, only potential turbines were near nests and only within six NTs. The number of nesting territories we found underscores the importance of the Southern Great Plains to Golden Eagles, even though this region lies at the eastern margin of the species' western North American breeding range. Our data provide strong support for protecting breeding habitat from potential threats, particularly those posed by wind energy development, and are also a foundation for long-term population monitoring.

Nest site selection by Loggerhead Shrike (Lanius ludovicianus) in a fragmented landscape

Understanding which factors influence nest site selection can lead to more effective species conservation. The Loggerhead Shrike (Lanius ludovicianus) has experienced severe declines since the 1940s and could potentially benefit from fine-scale management for nesting habitat, especially where fragmentation impedes conservation at the landscape scale. We examined how habitat characteristics at the nest tree and territory core scales influenced nest site selection by Loggerhead Shrikes in the coastal plain of South Carolina. We found 41 Loggerhead Shrike nests and measured habitat characteristics at the nest site and at available sites to model selection factors at the tree and territory core scales. Loggerhead Shrikes selected for low heterogeneity of vegetation density, high heterogeneity of vegetation height, and lower shrub and tree densities at the territory core scale. Loggerhead Shrikes also preferred nest trees with larger diameters at breast height. Overall, Loggerhead Shrikes appeared to select for nest site characteristics that enhanced foraging ease and success, and limited predation risk. We suggest that landowners in the southeastern coastal plain increase grassy habitat on their property and retain large trees in suitable nesting locations to increase optimal nesting habitat for Loggerhead Shrikes.

Applying economic and ecological criteria to design cost-effective monitoring for elusive species

Monitoring programs of long-lived and elusive species often incur high costs in terms of field effort and economical budget, but both components are often considered separately. Also, there is scant information on the use of reliable detectability estimates under imperfect detection conditions based on environmental factors, which is key to accurately estimate financial costs and define optimum monitoring strategies. In this study, we use an intensive survey program (2017–2018) of the Egyptian vulture Neophron percnopterus population in Bizkaia (northern Spain) to model detectability at nests taking into account imperfect detection. Our main goal is to estimate both the number and timing of surveys, and the allocation of survey effort/costs, in order to design cost-effective monitoring programs. Firstly, throughout the breeding seasons, we used focal sampling methods on 19 nesting territories historically occupied by the study species. Then, we employed single-season occupancy models to assess detectability considering different levels of effort (from 1 to 5 h) at each nest, including both species breeding phenology and environmental covariates that could modify detection probabilities. Our results showed that the species was more likely to be detected in dry years and when the nest was visible during the nestling period, investing five hours of the survey. The optimal number of monitoring days required to account for 95% of false negatives for a single nest was eight days, investing one hour per breeding stage. The optimal monitoring cost was reached in dry years when the nest was visible, investing one hour per breeding stage (ca. 242 €/nest). The cost of monitoring was highest in rainy years when the nest was not visible (ca. 1954 €/nest). The cost of monitoring entire occupied nesting territories without accounting for covariates was of 23,294 € (n = 19). In order to offer reliable species assessments, design rigorous surveys and accurately estimate monitoring costs, studies should account for imperfect detection, particularly for long-lived vertebrates. Here, we show that monitoring programs ought to (a) consider the effort necessary to detect the species while accounting for species-specific breeding ecology and, (b) adjust field effort based on lower costs and environmental conditions. Our results provide simple and practical guidelines for the efficient allocation of human and economic resources, which could be of interest to those practitioners involved in the regular monitoring of elusive species.

A Genetic Assessment of Parentage in the Blackspot Sergeant Damselfish, Abudefduf sordidus (Pisces: Pomacentridae)

Microsatellite markers were used to investigate the reproductive behavior of the damselfish Abudefduf sordidus at Johnston Atoll, Central Pacific Ocean. Genetic results indicated that ten males maintained guardianship over their nest territories for up to nine nest cycles during a 3.5 month period. Genotypes of 1025 offspring sampled from 68 nests (composed of 129 clutches) were consistent with 95% of the offspring being sired by the guardian male. Offspring lacking paternal alleles at two or more loci were found in 19 clutches, indicating that reproductive parasitism and subsequent alloparental care occurred. Reconstructed maternal genotypes allowed the identification of a minimum of 74 different females that spawned with these ten territorial males. Males were polygynous, mating with multiple females within and between cycles. Genetic data from nests, which consisted of up to four clutches during a reproductive cycle, indicated that each clutch usually had only one maternal contributor and that different clutches each had different dams. Females displayed sequential polyandry spawning with one male within a cycle but switched males in subsequent spawning cycles. These results highlight new findings regarding male parasitic spawning, polygyny, and sequential polyandry in a marine fish with exclusive male paternal care.

Early Ontogeny of the Behavior of Young in Large-Billed Crows (Corvus macrorhynchos) in Their Natural Habitat

The early ontogeny of behavior of corvid juveniles in their natural habitat was studied, and the large-billed crow (Corvus macrorhynchos) taken as an example. Research was carried out from May to October, 2012, in a wildlife area (Malye Kurily Reserve, part of the Kuril’skii State Nature Biosphere Reserve, Shikotan Island) on a free-living population of these birds. Twenty-five individually marked chicks from ten broods were observed from the moment of their hatching (early June) to the beginning of September (the time when fledglings became independent). The results obtained allowed us to follow not only the development of individual forms of behavior in chicks, but also the process of their incorporation into the population’s social structure. The development of the behavioral repertoire in large-billed crows in their natural habitat was shown to be identical to that of hooded crows. But in contrast to hooded crows, large-billed crows continue looking after their young even after the latter leave their nest territory. This may expand the capacities of social learning and skill transfer. Unlike the large-billed crow adults of the Shikotan population, in which aggression to their kin is very high, the young show no aggression to other juveniles. Moreover, we observed the formation of positive contacts between fledglings from different families during their play. This feature of fledgling behavior probably plays an important role in the incorporation of the young into the social structure of the population.

A multi‐state, time‐removal model for population dynamics of cliff‐nesting raptors

ABSTRACTCliff‐nesting raptors present considerable challenges for population estimation due to their sparse distribution across remote landscapes and the multiple occupancy states (e.g., unoccupied, occupancy without breeding, breeding occupancy) through which we observe their nesting territory dynamics. To increase the efficiency and spatial inference of surveys, we developed 2 versions of a multi‐state, time‐removal model: 1 for long‐term monitoring studies and the other for population inventories or single‐season surveys in which there is no prior knowledge of nest locations. We focused our development of these methods in the context of a combined aerial and ground‐based survey approach, which permits efficient surveying at landscape scales. The approach, however, is also applicable to designs restricted to ground surveys. For long‐term monitoring of species with alternative nests, we formulated a version of the model that accounts for state uncertainty at the territory level caused by a failure to observe all nests within a territory. Simulations based on the long‐term monitoring model indicated adequate (near nominal) coverage and low relative bias (<0.05) for nearly all parameters. In the simulation study for the inventory model, population size estimates showed negligible bias for a survey duration of 90 minutes. We applied our approach to a long‐term study of golden eagles (Aquila chrysaetos) in Alaska and demonstrated that the maximum effort spent on any nesting territory could be reduced by up to almost 90% of that recommended by standard protocols. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Effects of Supplemental Food on the Behaviour and Paternity Status of Male Indigo Buntings (Passerina CyaNea)

Breeding is energetically costly and, if energy-limited, birds may alter their time budgets, spending less time engaged in some activities and more time in others. Investigators who have provided breeding birds with supplemental food have noted changes in time budgets, but the extent and types of changes have been found to vary among species. Our objective was to determine how food supplementation might influence the time budgets and paternity status of male Indigo Buntings (Passerina cyanea). We studied Indigo Buntings from 8 May to 15 August 2009 in Madison County, Kentucky. Territories of male Indigo Buntings (n=30) were randomly assigned as either food supplemented (n=8) or controls (n=22). During time-budget observations, all behaviours were noted. To determine paternity status, blood samples were collected from adults and nestlings at 16 nests. Males with feeders in their territories spent significantly less time foraging and more time vocalising (chip notes) than males without feeders. Time spent singing and mate guarding by treatment and control males did not differ. Differences in the proportion of extra-pair young did not differ between nests in territories with and without supplemental food. Our results suggest that, when provided with supplemental food, male Indigo Buntings spend less time foraging and more time engaged in other activities. However, neither the presence of supplemental food nor differences in the behaviour of males in food-supplemented versus non-supplemented territories affected rates of extra-pair paternity.

Parental females of a nest-brooding cichlid improve and benefit from the protective value of young masquerading as snails

Masquerade is a strategy whereby prey animals resemble environmental objects (e.g. twigs, bird droppings and stones) or inedible animals to avoid predatory attack. However, most studies of this strategy have been restricted to only a few animal groups. Therefore, novel examples are required to elucidate the diversity of masquerade strategies. Neolamprologus furcifer is a maternal nest-brooding cichlid inhabiting shaded areas of large rocks in Lake Tanganyika. In contrast to the cryptic, dark brown adults, the small young have well-defined white stripes on their brown trunk in nest territories where many white-striped snails Reymondia horei are present. We hypothesized that young N. furcifer masquerade as the model snail R. horei. We found four results consistent with our hypothesis. (1) The size, coloration, shape and posture of the young fish resembled those of the snail. (2) Experimental removal of the model snail from territories caused females to attack predators more frequently than before the removal, indirectly suggesting the protective value of the young fish's coloration. (3) Parental females selectively removed nonmodel snails from their territory, probably causing the higher density of R. horei observed at nest sites. (4) Guarded young had black/white coloration only in populations where the model snails were present. Therefore, we suggest that young N. furcifer masquerade as the model snail R. horei. This study describes a novel masquerade pattern in which the protective value is improved by, and beneficial to, a third party.

Breeding season microhabitat use by Cerulean Warbler (Setophaga cerulea) in an experimentally-managed forest

Cerulean Warbler (Setophaga cerulea) populations have undergone significant declines over the past four decades, and the species is considered state endangered in Indiana. These migratory songbirds nest in the canopies of mature deciduous forests throughout eastern North America, but local microhabitat preferences vary by geography and scale, and may influence differential nest success rates across the breeding range. Between 2010 and 2015, we searched for nests, mapped out male territories, and monitored nest success in the Hardwood Ecosystem Experiment in central Indiana. We collected data on a variety of microhabitat features at the territory, nest patch, and nest site levels, as well as at non-use points, and evaluated the influence of several characteristics on nest success. We evaluated nest patch and territory attributes using binomial generalized linear models and nest success with a generalized linear mixed-effects model. Cerulean Warblers selected nest patches characterized by taller trees and located on ridges and valleys rather than on mid-slopes, while males selected territories that were located on steeper northeast-facing slopes closer to roadways than random points. Successful nests were placed lower in the nest tree and were found in areas with shorter trees; several features selected by Cerulean Warblers at the nest patch and territory levels were associated with lower nest success rates. As elsewhere in the range, white oak was an important nest tree species. In developing forest management strategies, land managers must strive to balance small-scale microhabitat preferences with the need for regenerating oak-hickory forests to sustain Cerulean Warbler breeding populations.

Breeding in a den of thieves: pros and cons of nesting close to egg predators

AbstractBreeding success of many Arctic‐breeding bird populations varies with lemming cycles due to prey switching behavior of generalist predators. Several bird species breed on islands to escape from generalist predators like Arctic fox Vulpes lagopus, but little is known about how these species interact. We studied brent geese Branta bernicla bernicla that share islands with gulls (Larus spec.) in Taimyr, Siberia (Russia). On one hand, gulls are egg predators, which occasionally steal an egg when incubating geese leave the nest for foraging bouts. On the other hand, gulls import marine resources to the islands, enriching the soil with their guano. We considered three hypotheses regarding clutch size of brent geese after partial nest predation. According to the “predator proximity hypothesis”, clutch size is expected to be smallest close to gulls, because of enhanced predator exposure. Conversely, clutch size is expected to be largest close to gulls, because of the supposedly better feeding conditions close to gulls, which might reduce nest recess times of geese and hence egg predation risk (“guano hypothesis”). Furthermore, gulls may defend their nesting territory, and thus nearby goose nests might benefit from this protection against other gulls (“nest association hypothesis”). We mapped goose and gull nests toward the end of the goose incubation period. In accordance with the latter two hypotheses, goose clutch size decreased with distance to the nearest gull nest in all but the lemming peak year. In the lemming peak year, clutch size was consistently high, indicating that partial nest predation was nearly absent. By mapping food quantity and quality, we found that nitrogen availability was indeed higher closer to gull nests, reflecting guanofication. Unlike predicted by the nest association hypothesis, a predation pressure experiment revealed that egg predation rate decreased with distance to the focal gull nests. We therefore propose that higher food availability close to gulls enables female geese to reduce nest recess time, limiting egg predation by gulls.

Using Field Data and GIS-Derived Variables to Model Occurrence of Williamson's Sapsucker Nesting Habitat at Multiple Spatial Scales.

Williamson's sapsucker (Sphyrapicus thyroideus) is a migratory woodpecker that breeds in mixed coniferous forests in western North America. In Canada, the range of this woodpecker is restricted to three small populations in southern British Columbia, precipitating a national listing as ‘Endangered’ in 2005, and the need to characterize critical habitat for its survival and recovery. We compared habitat attributes between Williamson’s sapsucker nest territories and random points without nests or detections of this sapsucker as part of a resource selection analysis to identify the habitat features that best explain the probability of nest occurrence in two separate geographic regions in British Columbia. We compared the relative explanatory power of generalized linear models based on field-derived and Geographic Information System (GIS) data within both a 225 m and 800 m radius of a nest or random point. The model based on field-derived variables explained the most variation in nest occurrence in the Okanagan-East Kootenay Region, whereas nest occurrence was best explained by GIS information at the 800 m scale in the Western Region. Probability of nest occurrence was strongly tied to densities of potential nest trees, which included open forests with very large (diameter at breast height, DBH, ≥57.5 cm) western larch (Larix occidentalis) trees in the Okanagan-East Kootenay Region, and very large ponderosa pine (Pinus ponderosa) and large (DBH 17.5–57.5 cm) trembling aspen (Populus tremuloides) trees in the Western Region. Our results have the potential to guide identification and protection of critical habitat as required by the Species at Risk Act in Canada, and to better manage Williamson’s sapsucker habitat overall in North America. In particular, management should focus on the maintenance and recruitment of very large western larch and ponderosa pine trees.

The role of territory settlement, individual quality, and nesting initiation on productivity of Bell's vireos Vireo bellii bellii

Variation in habitat quality among territories within a heterogeneous patch should influence reproductive success of territory owners. Further, territory settlement order following an ideal despotic distribution (IDD) should predict the fitness of occupants if territory selection is adaptive. We recorded settlement order and monitored nests in territories occupied by individually marked Bell's vireos Vireo bellii bellii across a range of shrubland habitats in central Missouri, USA. We used an information theoretic approach to evaluate multiple hypotheses regarding the relationship between territory settlement order and seasonal territory productivity (productivity), which we define as the number of young fledged from all nest attempts in a territory. Territory settlement order and arrival date were not analogous and later arriving males displaced early settlers in 13 of 49 territories. Settlement order and lay date together were the best predictors of a territory's productivity; productivity decreased 2.08 young from earliest to latest settlement rank and lay date. Males that defended the same territory in successive years occupied territories with earlier settlement dates, but we found little evidence that age or prior ownership influenced productivity. Territory selection by male Bell's vireos was adaptive because males preferred to settle in territories that had high seasonal offspring production, but even though settlement rank was linked to territory quality, high productivity was only realized on high quality territory when also linked to early nest initiation date. While settlement rank was related to territory quality, obtaining a high quality territory had to be combined with early nest initiation to maximize productivity. We found support for the IDD hypothesis because the highest quality territories, (i.e. most productive), were settled earlier. Research that identifies high quality habitat by linking individual fitness with habitat characteristics may elucidate the importance of habitat quality, individual experience and temporal factors to productivity of Bell's vireos.

Influence of Habitat and Nest-Site Quality on the Breeding Performance of Lanner FalconsFalco biarmicus

Abstract. Site quality may influence breeding performance especially in raptors showing strong territory fidelity as predicted by the site-dependent population regulation hypothesis. Thus, the occupancy of nest-sites is non-random, indicating a preference of certain territories, apparently of higher quality. During four breeding seasons (2003–2006), we recorded the occupancy rate and the number of young fledged from Lanner Falcon Falco biarmicus feldeggii nest-sites in eastern Sicily, Italy. Breeding sites with different occupancy rates showed significant differences in environmental attributes, mainly altitude. A generalised linear model revealed a significant effect of the slope of the nest-site on mean fledgling number per successful pair. In addition, the mean slope of the nest territory and the slope of the nest-site are the main predictors for differentiating the cliff selection by Lanners and by much more competitive Peregrine Falcons Falco peregrinus. Finally, our results suggest a crucial role of...

Reaching independence: food supply, parent quality, and offspring phenotypic characters in kestrels

The duration of the postfledging dependence period (PFDP) is supposed to be modulated by the parent‐offspring conflict: Offspring should extract the highest levels of parental investment, although parents may respond by setting fixed limits to the level of investment or by raising the costs of attempts to extract additional investment. In this context, longer PFDPs are expected in nests tended by higher quality parents and in dominant siblings. We explored these hypotheses with a combination of experimental and correlative results. First, we food supplemented offspring during the PFDP to study whether food supply during fledging, an indicator of parental quality, has an effect on the PFDP duration in the Eurasian kestrel. We found that the PFDP was longer in food-supplemented nests. Second, we measured the duration of the PFDP over 3 years under different environmental conditions to explore whether the quality of parents and nestling phenotype were correlated with the duration of PFDP. Correlative results suggest that fledglings raised by higher quality parents and in the year with poorer food conditions showed longer PFDP. Furthermore, male fledglings showing grayer coloration in the rump (an index of competitive capacity) have longer PFDPs than browner males. Overall, our results suggest that parent, rather than offspring characteristics, can modulate the PFDP duration mediated by food conditions, although more colored nestlings stay in the nest territory for longer periods. Key words: environment conditions, Eurasian kestrel, Falco tinnunculus, melanic coloration, parent‐offspring conflict, sibling competition. [Behav Ecol]

DIetary Shifts Based Upon Prey Availability in Peregrine Falcons and Australian Hobbies Breeding Near Canberra, Australia

We collected prey remains and pellets at 16 Peregrine Falcon (Falco peregrinus) nest territories (975 prey items from 152 collections) and one Australian Hobby (F. longipennis) territory (181 prey items from 39 collections) during four breeding seasons in two time periods: 1991–1992 and 2002–2003, a total of 60 peregrine nest-years and three hobby nest-years. By number, European Starlings (Sturnus vulgaris) were the main prey taken by both falcons in 1991–1992 and 2002–2003, but starlings made up a smaller percentage of the diet by number in the latter period, apparently because their numbers had declined in the wild. Although the geometric mean of prey weights and geometric mean species weights were similar in the two time periods, both falcons compensated for the decline in European Starlings in the latter period by taking a greater variety of bird species, particularly small numbers of mostly native birds, rather than taking more of one or two other major prey species. Peregrines took 37 bird species in the latter period not found among their prey remains in the earlier period, and more individuals of some large species such as Gang-gang Cockatoos (Callocephalon fimbriatum), Galahs (Cacatua roseicapilla), and Rock Pigeons (Columba livia). Prolonged drought and competition from increasing numbers of Common Mynas (Acridotheres tristis) may have caused European Starlings to decline, but neither falcon species compensated by catching Common Mynas, even though they are of optimal prey size. Though both falcons, especially peregrines, took the more common bird species found in surveys in the Australian Capital Territory, both tended to avoid large or dangerous species, or agile species that foraged close to cover, such as Common Mynas.

Parental Behaviour of Common Terns (Sterna Hirundo): Sexual Differences and Changes in the Course of the Reproduction Season

Differences and changes in the behaviour of females and males of Common Terns (Sterna hirundo) in the course of the reproduction season were studied in 2001–2003 in South Lithuania. During the incubation, hatching and chick raising periods, females spent more time incubating eggs and warming chicks than males, whereas the duration of other female activity (sleeping, feather cleaning, standing) in the nest territory was reliably greater than that of males in the chick raising period only; besides in the course of the reproduction season the duration of such other activity was increasing. During the hatching and chick raising periods, the occurrence of agonistic contacts of females with other adult birds was more frequent than that of males, whereas the frequency of female agonistic contacts with alien chicks was higher in the chick raising period only. Males, as a rule, brought food to chicks more frequently than females. The comparison of frequency of bringing food to the same chick in case of two-chick a...