Comparative nest habitat characteristics of sympatric White‐tailed Haliaeetus albicilla and Golden Eagles Aquila chrysaetos in western Scotland

Capsule Golden and White‐tailed Eagles selected different habitats for nesting.

Aim To investigate differences in nesting habitat used by sympatrically breeding eagles in western Scotland, following reintroduction of White‐tailed Eagles from 1975 onwards.

Methods Nest‐site locations from national surveys in 2003–05 were entered into a geographical information system (GIS) in order to measure a set of geographic parameters for each nest site. Binary logistic regression with backwards deletion of non‐significant terms was used to derive minimum adequate models at two spatial scales of the likelihood of an eagle nest belonging to one species or the other. We compared changes in occupancy between 1992 and 2003 of Golden Eagle territories inside and outside a GIS model of potential White‐tailed Eagle habitat and according to proximity to White‐tailed Eagle nests.

Results White‐tailed Eagles nested at lower altitudes than Golden Eagles, in more wooded habitats with more open water close by, tending to nest in trees where these were present. There were 3359 km² of potential White‐tailed Eagle nesting habitat within 25 km of existing White‐tailed Eagle nests, containing 54 Golden Eagle territory centres, but we found no difference in change of occupancy for Golden Eagle territories close to White‐tailed Eagles compared with those further away.

Conclusion White‐tailed and Golden Eagles appear to partition nesting habitat in the west of Scotland by altitude. This corresponds with behaviour in western Norway and with the situation described in historical accounts of nest‐sites in western Scotland prior to extinction of White‐tailed Eagles. It is also consistent with recent studies showing little overlap in breeding season diet of Golden and White‐tailed Eagles in western Scotland, and likely partitioning of foraging habitat by altitude. We conclude that the likelihood of competitive exclusion is less than previously suggested.     

Hints on Research for Bird-watchers

Capsule Fledgling Golden Eagles in northern Sweden preferred clearcuts and other open forest habitats, as well as steep slopes.

Aims To study the post-fledging habitat use and ranging behaviour of juvenile Golden Eagles on their natal territories.

Methods Fourteen juvenile Golden Eagles in northern Sweden were marked with GPS transmitters and tracked until they left their natal territory.

Results Eagles fledged at the end of July–beginning of August and remained on their natal territories until October–early November. Fledged eagles' home range size before flying south was on average 41?km². Juvenile eagles showed a preference for clearcuts, coniferous forest on lichen-covered bedrock and edges between clearcuts and forest, whilst all other habitat types were used less than expected. The eagles showed a preference for steep slopes, in particular south-facing ones, whilst north-facing slopes were used less than expected.

Conclusion Golden Eagles' preference for clearcuts and steep slopes can be used in the planning and management of ‘eagle friendly’ wind farms.     

Winter territoriality and its implications for the breeding ecology of White-throated Dippers Cinclus cinclus

Capsule: Pairs of White-throated Dippers Cinclus cinclus which defended winter territories bred earlier than non-territorial individuals, but there was no difference in reproductive success.

Aims: The effect of winter territoriality on breeding ecology has rarely been studied in resident birds. We carried out a preliminary investigation of whether winter territorial behaviour and territory size affect the timing of reproduction, breeding territory size and reproductive success in a riverine bird, the White-throated Dipper.

Methods: We monitored an individually marked population of White-throated Dippers in the UK. Wintering individuals were classified as either territorial or ‘floaters’ according to their patterns of occurrence and behaviour, and their nesting attempts were closely monitored in the subsequent months. Winter and breeding territory sizes were measured by gently ‘pushing’ birds along the river and recording the point at which they turned back.

Results: All birds defending winter territories did so in pairs, but some individuals changed partners before breeding. Territorial pairs that were together throughout the study laid eggs significantly earlier than pairs containing floaters and those comprising territorial birds that changed partners. However, there were no significant differences in clutch size, nestling mass or the number of chicks fledged. There was no relationship between winter territory length and lay date or any measure of reproductive success, although sample sizes were small. Winter territories were found to be significantly shorter than breeding territories.

Conclusion: Winter territoriality may be advantageous because breeding earlier increases the likelihood that pairs will raise a second brood, but further study is needed. Territories are shorter in winter as altitudinal migrants from upland streams increase population density on rivers, but this may also reflect seasonal changes in nutritional and energetic demands.     

Breeding behaviour and time-activity budgets of Bonelli’s Eagles Aquila fasciata: marked sexual differences in parental activities

ABSTRACT

Capsule: Differences in parental investment between sexes and stage of the breeding period were found in Bonelli’s Eagles Aquila fasciata.

Aims: To describe the sexual differences in parental behaviour of Bonelli’s Eagles and to assess the sex-specific pattern of variation in parental investment in relation to the breeding period.

Methods: Between 2006 and 2016, we monitored the parental behaviour of 11 pairs of Bonelli’s Eagles during the incubation and chick-rearing periods in southeastern Spain. Observations were made using 20–60× telescopes from points overlooking the territory at a distance of about 500–800?m from the nest.

Results: Our results reveal a marked division in parental duties in Bonelli’s Eagles. Females invested more effort in incubation, nest attendance, chick feeding and nest-building, while males contributed more to food provisioning. Nest attendance and feeding by females decreased with time, and both parents adjusted their provisioning effort in relation to nestling age. Most changeovers took place during the middle of the day, when male provisioning rates and temperatures reach their maximum.

Conclusion: Intersexual differences are discussed in the context of the prey capture difficulty hypothesis, which proposes that intra-pair prey differences, due to large sexual size dimorphism, should be particularly advantageous among raptors that pursue agile prey.     

Status of Golden Eagle Aquila chrysaetos in Britain in 2015

Capsule: A complete survey of Golden Eagles Aquila chrysaetos in Britain in 2015 found that the population had increased by 15% since 2003 to 508 territorial pairs.

Aims: The survey aimed to investigate the population size, distribution and breeding success of Golden Eagles in Britain, and to compare results with similar surveys since the early 1980s.

Methods: Every home range was visited on a minimum of three occasions between January and August 2015. First, to look for eagles or signs of their presence (January–March), then to look for evidence of breeding or further checks for occupation (April–June) and finally to record productivity of nesting pairs (July–August).

Results: The figure of 508 territorial pairs represents a 15% increase in the population from 442 pairs in 2003. The proportion of home ranges occupied was 70%. The largest increases in the proportion of occupied home ranges were in south-central Highlands (71%), northern moors and flows (38%) and northwest Highlands (29%), with modest increases of up to 10% in the other regions. Productivity was lower in 2015 than in 2003, and there was significant variation in breeding success between regions.

Conclusion: The British Golden Eagle population has increased since 2003, although the species is absent from England and Wales. The population now meets the abundance target identified to define favourable conservation status in Scotland, and while home range occupancy has increased there is regional variation, with some regions falling below the target levels. A combination of increased annual monitoring and tagging of eagles, as well as the introduction of new legislation, may serve as effective deterrents against persecution of eagles thus facilitating this population increase. However, concerns remain over low levels of home range occupancy particularly in the east Highlands, but also the proportion of sub-adult pairs holding territory in that region and in the south-central Highlands. Persecution associated with grouse moor management has been highlighted as a particular population constraint in both of these areas.     

Seasonal Changes of Vocal Rates and Their Relation to Territorial Status in Male Galápagos Sea Lions (Zalophus wollebaeki)

Male vocal displays play an important role in sexual selection through both male–male competition and female choice. While this is supported by numerous studies in birds, much less attention has been paid to the role of such displays in mammals. We investigated the function of vocal displays in a polygynous mammal, the Galápagos sea lion (Zalophus wollebaeki). In our study population a large proportion of mature males are unable to establish a territory, providing the opportunity to compare the vocal behaviour between territorial and non‐territorial males. We examined how seasonal patterns of vocalizations differed between territorial and non‐territorial males and how the number of females present in a territory influenced behaviour of territorial males. We found that territorial males vocalized at higher rates than non‐territorial males, and territorial males vocalized more at the onset than towards the end of territory tenure. During the onset of territory‐tenure vocalizations of territorial males were directed more often towards other males than females. Furthermore, we found that vocalizations of territorial males were not only given in male–male interactions, but were also actively directed towards females. Territorial males vocalized at higher rates when more females were present in their territory. Our results suggest that vocalizations are important in male–male interactions, are relevant in territorial disputes and are used as a proxy for females to assess a male’s quality.     

Cooperative nest‐defence behaviour and territory quality in a resident and socially monogamous passerine

Nest defence is a fundamental aspect of parental care in secondary cavity‐nesting birds, and predation or competition for nesting sites can involve different defensive behaviours. Because habitat quality determines breeding success, we were interested in whether breeding pairs of the Eurasian nuthatch, Sitta europaea, established in more favourable environment also manifest higher probability of cooperative behaviour during their nest‐site defence. To explore this relationship, we quantified behavioural displays of both parents and analysed activity budget ethogram data from simulated territorial intrusions performed in the chick‐feeding phase with one conspecific and two different heterospecific stimuli (dummies of nuthatch, starling and woodpecker). We found that paired individuals shared their roles during nest‐site defence to a considerable extent. Males had a significantly higher number of attacks on intruders than females, and females performed more threat displays and controls of the brood than males. Multinomial analysis of the cooperative behaviour suggested that pairs in a high‐quality territory had higher probability of reciprocal substitution of different roles towards a balance between attacks, threat displays and nest controls. Contrary to this, pairs in a low‐quality territory had less likely pairwise combinations of simultaneous behavioural states that are associated with effective nest‐site defence. The difference in response probability according to territory quality was, however, highly variable in view of the stimulus that was used in simulated territorial intrusion. Because individual roles and the complex behavioural repertoire of pairs altered in response to territory quality and potential nest‐site competitor or brood predator, our results suggest that the cooperative nest‐defence behaviour could be linked to the breeding success of this year‐round territorial species living in a heterogeneous forest habitat.     

Complex effects of habitat loss on Golden Eagles Aquila chrysaetos

The development of commercial forests presents potential threats to large raptors that rely on prey caught in open country. We examined the effect of afforestation of breeding habitat used by a population of Golden Eagles Aquila chrysaetos in Scotland where, over the last 50 years, extensive stands of exotic conifers have been planted. Using data for 31 years on territory occupancy and breeding success, together with spatiotemporally dynamic mapping of forest cover and predicted areas of territory‐use in a Geographical Information System, we examined relationships between forest cover and Eagle ecology at landscape and individual territory scales. Several territories were abandoned during the earliest phases of forest planting, but relatively few were apparently lost to later plantings. Territories with poorer breeding productivity appeared to be more vulnerable to abandonment than territories with better breeding productivity. At the landscape scale, temporal differences in breeding productivity were negatively related to the extent of forest cover, although productivity of individual territories showed no clear relationship with forest cover. Several territories with less than a 5% increase in forest cover experienced reduced productivity; however, territories least constrained by neighbouring pairs of Eagles showed an increase in productivity. Territories experiencing the greatest increases in forest cover showed a greater use of spatially separated nest‐sites by occupying pairs. Hence, pairs that were less constrained by neighbours appeared to compensate for loss of open habitat by shifting their territory‐use, whereas pairs that were more constrained could not compensate for open habitat loss and suffered reduced productivity (and, probably in some cases, abandoned the territory). We suggest that simple guidelines based on the extent and locations of habitat loss are inadequate when predicting effects on large territorial raptors such as Golden Eagles. Consideration should also be given to the ‘quality’ of a territory or occupying pair, as well as the extent to which territory‐use is constrained by neighbouring pairs or other ‘unsuitable habitat’ which may have been affected by previous episodes of open habitat loss.     

Structure of tree vegetation may reduce costs of territory defence in Eurasian Nuthatch Sitta europaea

Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.

Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.

Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50?×?50?m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.

Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93?ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83?99). For cavity density, the probability of territory occurrence was about 74% (52?89) at the level of 60 cavities per ha.

Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole.     

Ranging distance of resident Golden Eagles Aquila chrysaetos in western Scotland according to season and breeding status

Capsule Home-range of resident pairs of Golden Eagle was usually smaller during a successful breeding season than during winter and during an unsuccessful breeding season.

Aims To examine how Golden Eagles use space around their nests with respect to season and breeding status, and to compare home-range-use between a high and a low density region.

Methods Nine adults in six mainland Argyll ranges were radiotracked between 1991 and 1996. On the island of Mull visual observations of range-use were obtained for five ranges between 1994 and 1998.

Results Overall, Mull ranges were smaller than the Argyll ranges, reflecting the much higher range density on Mull. In both regions there were significant differences between ranging distances with season and breeding status. In general, ranging distances were smallest during breeding seasons when young were fledged.

Conclusions Studies of range-use in Golden Eagles must be conducted across a 12-month period, as a minimum.     

Nest use by territorial males in a shell-brooding cichlid: the effect of reproductive parasitism

Male Telmatochromis vittatus, a substrate-brooding Tanganyikan cichlid, exhibit two parasitic reproductive tactics: takeover of spawning by larger males (pirates) and sneaking by smaller males (sneakers). Medium-sized males are territorial and pair-spawn within nests of clumped shells that harbor several resident females that are potential mates of the territory owner. To study nest use by territorial males, we analyzed the relationship between the body size of territorial males and nest quality, the number of females per nest, the distance between nests, and the frequency and intensity of reproductive parasitism. The size of males was not correlated with nest quality, the number of females, or the number of sneakers, but was negatively correlated with the frequency of intrusion by pirates and was positively correlated with the distance between nests. Territorial males effectively defended nests against sneakers but failed to defend against pirates. These results suggest that larger territorial males selected nests that have a lower risk of usurpation of spawning. We hypothesize that the risk of intrusion by pirate males affects the selection of nests by territorial males in this species.     

The courtship and spawning behaviors ofCanthigaster valentini (Tetraodontidae)

Synopsis The sharpnose puffer,Canthigaster valentini, occurs in male-dominated harems of territorial females at Lizard Island (Australia). Spawning occurs daily and year-round. Males only spawn with the females of their social group, inside the female's territory. Females signal their readiness to begin courtship with a display that exposes their egg swollen abdomen. Courtship is long and males do not develop specific courtship colors or perform unique displays. Eggs are fertilized in a demersal nest and there is no parental care.     

COMPARISONS AND FUNCTIONS OF SKY-DANCING DISPLAYS OF CIRCUS HARRIERS: UNTANGLING THE MARSH HARRIER COMPLEX

Simmons, R. 1991. Comarisons and functions of sky-dancing displays of Circus harriers: untangling the marsh harrier complex. Ostrich 62:45-51.

African Marsh Hamers Circus ranivorus perform aerial displays known as “sk-dancing” most frequently just before breeding and at other times during territorial takeovers. Both mares and females display and food supplements to seven pairs over two years verified sexual selection arguments that birds in better condition display more freuently than unfed controls. Typical sky-dancing birds soared to 400 m or more, and performed up to 20 U-shaped undulations in a horizontal plane, while sky-spiruffing birds performed vertical displas, dropping in a series of descending U-shaped undulations, whilst twisting about their axis. Displaying girds stimulated others to perform and up to eight birds displayed in the same aerial arena. I interpret both displas as mainly territorial in function but rovide evidence that they also have a mate attraction component. in form, the display resembles that or the Australasian Hamer C. uproxi mans, but not that of the European Marsh (C. aeruginosus) nor the Reunion Malagasy (C. a. maifardii Hamer, providing evidence contrary to the traditional belief that African birds are subspecies of aeruginosus     

CHARACTERISTICS OF TERRITORIAL AND MATING CALLS IN WILLOW PTARMIGAN LAGOPUS L. LAGOPUS

ABSTRACT

During territorial behaviour and pair formation willow ptarmigan cocks and hens use several different calls. Cocks use mainly a “flight call”, a “ground call” and three different “threat calls”. Hens give similar calls to cocks. It is suggested that the structure of the calls is well adapted to (1) transmit their possible information content over long distances, and (2) make localization easier for birds during the territorial display periods, which take place mainly in poor light at dusk and dawn. We also suggest that the cock and hen calls express different degrees of aggressiveness, and that hen calls, in addition to attracting cocks, function as territorial “keep out” signals to other hens.     

Ecological and environmental correlates of territory occupancy and breeding performance of migratory Golden Eagles Aquila chrysaetos in interior Alaska

Understanding relationships between environmental conditions and reproductive parameters is important when interpreting variation in animal population size. The northwestern North American population of Golden Eagles Aquila chrysaetos canadensis initiates courtship and nesting in early spring when prey diversity is low and weather conditions are severe. Snowshoe Hare Lepus americanus and Willow Ptarmigan Lagopus lagopus, the primary prey of Golden Eagles early in their nesting season in interior Alaska, both exhibit cyclical fluctuations in abundance, providing the opportunity to investigate such relationships. We used Bayesian hierarchical models to explore variation in territory occupancy, nesting rates, nesting success and productivity of Golden Eagles from 1988 to 2010 in Denali National Park and Preserve, Alaska, in relation to annual and site‐specific parameters including prey abundance, weather conditions, elevation and human activity. We also investigated the long‐term fluctuations of breeding performance over the course of the study. The abundance of Hares influenced both the number of Eagles that laid eggs and the number of Eagles that produced fledglings. The conditions on the breeding ground did not explain observed declines in nesting rates and fledgling production, suggesting that other factors such as change in the age structure of the population, increased intraspecific competition or deterioration of migration and wintering habitat are driving the long‐term trends of these parameters.     

Social class,socially-induced loss,recruitment and breeding of red grouse

Summary Individually marked red grouse (Lagopus lagopus scoticus) could be distinguished as territorial or non-territorial from November till the next spring. Territorial birds survived well and many reared young, but numerous nonterritorial birds died or disappeared, and none paired up or reared young. Differences in spring sex ratio between years had already been set in the previous autumn's territorial stock. Many old birds which had been territorial in earlier seasons lost territories after an annual re-distribution of territory each October–November. Thereafter very few of them were seen alive on the area over the winter, and many were found dead, whereas nearly all old birds that kept their territories were still there in spring. The number of birds in spring and the fate of individuals over winter were predicted reasonably accurately from observations of behaviour in the previous November–December. Thus, differences of social class in autumn were critical to a bird's survival to breed in the next summer and to its chances of contesting for territory and breeding in subsequent years.     

Woodlarks Lullula arborea and landscape heterogeneity created by land abandonment

Capsule Fine‐grained landscape heterogeneity may be a major factor in the recent expansion of Woodlark populations.

Aim To determine the factors which may have led to the increase in Woodlark populations in the Mediterranean region.

Methods Woodlark habitat selection was determined using territory mapping in an area that had undergone widespread land abandonment during the past 50 years. Remote sensing data were used to study landscape changes within the study area between 1978 and 2003.

Results Most Woodlark territories included a combination of farmland and shrubland patches. These fulfilled the birds’ requirements for territorial display and for foraging. Land abandonment has increased the availability of open shrubland, the dominant land‐cover type selected by Woodlarks.

Conclusions Increased fine‐grained landscape heterogeneity following farm abandonment has created opportunities for habitat use by Woodlarks and may be a major factor in the Woodlark population expansion observed between 1978 and 2003.     

Seasonal and Diurnal Changes in Aggression and Territory Size in the Black-headed Gull (Larus ridibundus L.) on Islands in the Middle Reaches of the Vistula River

Seasonal and diurnal changes in territory size and frequency of aggressive interactions of various intensity were examined in colonies of the black-headed gull (Larus ridibundus) on river islands and ponds of central Poland. The highest frequency of the total aggression and the largest territories were recorded before the egg-laying stage, this being related to the establishing of territories, defence of the mate, and defence of nest material. Later in the season both aggression and territory size declined. Unlike the large species of gulls, black-headed gulls did not increase their aggression and territory size during hatching of the young. High-intensity aggressive behaviours (choking, attacking and fighting) were not so frequently displayed as low-intensity aggressive postures (upright, long call, forward) in each phase of the breeding cycle. Presumably this was because the former were more costly in terms of energy. Peak territorial activity occurred in the late afternoon. An increase in the frequency of intense aggressive behaviours (attack, fight) at that time was combined with an increased mobility of birds (departures to and arrivals from foraging sites). A reduced frequency of high-intensity aggressive displays in the period when the largest number of birds was present in the colony was likely to be adaptive.     

Acoustic Monitoring Reveals Congruent Patterns of Territorial Singing Behaviour in Male and Female Tropical Wrens

Many animals defend territories against conspecific individuals using acoustic signals. In birds, male vocalizations are known to play a critical role in territory defence. Territorial acoustic signals in females have been poorly studied, perhaps because female song is uncommon in north‐temperate ecosystems. In this study, we compare male vs. female territorial singing behaviour in Neotropical rufous‐and‐white wrens Thryothorus rufalbus, a species where both sexes produce solo songs and often coordinate their songs in vocal duets. We recorded free‐living birds in Costa Rica using an eight‐microphone Acoustic Location System capable of passively triangulating the position of animals based on their vocalizations. We recorded 17 pairs of birds for 2–4 consecutive mornings and calculated the territory of each individual as a 95% fixed kernel estimate around their song posts. We compared territories calculated around male vs. female song posts, including separate analyses of solo vs. duet song posts. These spatial analyses of singing behaviour reveal that males and females use similarly sized territories with more than 60% overlap between breeding partners. Territories calculated based on solo vs. duet song posts were of similar size and similar degrees of overlap. Solos and duets were performed at similar distances from the nest for both sexes. Overall, male and female rufous‐and‐white wrens exhibit very similar spatial territorial singing behaviour, demonstrating congruent patterns of male and female territoriality.     

Golden Plover Pluvialis apricaria breeding success on a moor managed for shooting Red Grouse Lagopus lagopus

Capsule The best estimate of breeding success was a mean of 0.57 fledglings per pair, which when combined with adult survival rates, successfully explained the observed population trend.

Aims To quantify Golden Plover breeding success on a moor managed for shooting Red Grouse Lagopus lagopus.

Methods An intensive study recorded the fate of individual Golden Plover nests and, using radiotelemetry, chicks. The factors associated with mortality were examined, allowing the construction of a model of breeding success. Adult survival was estimated from return rates of colour-ringed birds.

Results Estimated rates of daily nest survival during laying (0.8636) were significantly lower than during incubation (0.9913). The daily survival rate of chicks less than nine days (0.8868) was significantly lower than for older chicks (0.9792). A population model based on these parameters overestimated the rate of nest losses, but accurately described brood survival and fledging success. Although predation rates were low, poor survival of young chicks through starvation or exposure suggest other factors were limiting breeding success at the study site.

Conclusions Predation rates of Golden Plover nests and chicks can be low on moorlands managed for shooting Red Grouse. However, in the absence of predation, other factors may still reduce chick survival and limit breeding success.