Human disturbance and stage‐specific habitat requirements influence snowy plover site occupancy during the breeding season

Habitat use has important consequences for avian reproductive success and survival. In coastal areas with recreational activity, human disturbance may limit use of otherwise suitable habitat. Snowy plovers Charadrius nivosus have a patchy breeding distribution along the coastal areas on the Florida Panhandle, USA. Our goal was to determine the relative effects of seasonal human disturbance and habitat requirements on snowy plover habitat use. We surveyed 303 sites for snowy plovers, human disturbance, and habitat features between January and July 2009 and 2010. We made multiple visits during three different sampling periods that corresponded to snowy plover breeding: pre‐breeding, incubation, and brood‐rearing and used multi‐season occupancy models to examine whether human disturbance, habitat features, or both influenced site occupancy, colonization (probability of transition from an unoccupied site to an occupied site), and extinction (probability of transition from an occupied site to an unoccupied site). Snowy plover site occupancy and colonization was negatively associated with human disturbance and site extinction was positively associated with human disturbance. Interdune vegetation had a negative effect on occupancy and colonization, indicating that plovers were less likely to use areas with uniform, dense vegetation among dunes. Also, dune shape, beach debris, and access to low‐energy foraging areas influenced site occupancy, colonization, and extinction. Plovers used habitat based on beach characteristics that provided stage‐specific resource needs; however, human disturbance was the strongest predictor of site occupancy. In addition, vegetation plantings used to enhance dune rehabilitation may negatively impact plover site occupancy. Management actions that decrease human disturbance, such as symbolic fencing and signage, may increase the amount of breeding habitat available to snowy plovers on the Florida Panhandle and in other areas with high human activity. The specific areas that require this protection may vary across snowy plover life history stages.     

Multi‐season occupancy models identify biotic and abiotic factors influencing a recovering Arctic Peregrine Falcon Falco peregrinus tundrius population

Critical information for evaluating the effectiveness of management strategies for species of concern include distinguishing seldom occupied (or low‐quality) habitat from habitat that is frequently occupied and thus contributes substantially to population trends. Using multi‐season models that account for imperfect detection and a long‐term (1981–2002) dataset on migratory Arctic Peregrine Falcons Falco peregrinus tundrius nesting along the Colville River, Alaska, we quantified the effects of previous year's productivity (i.e. site quality), amount of prey habitat, topography, climate, competition and year on occupancy dynamics across two spatial scales (nest‐sites, cliffs) during recovery of the population. Initial occupancy probability was positively correlated with area of surrounding prey habitat and height of nest‐sites above the Colville River. Colonization probability was positively correlated with nest height and negatively correlated with date of snowmelt. Local extinction probability was negatively correlated with productivity, area of prey habitat and nest height. Colonization and local extinction probabilities were also positively and negatively correlated, respectively, with year. Our results suggest that nest‐sites (or cliffs) along the Colville River do not need equal protection measures. Nest‐sites and cliffs with historically higher productivity were occupied most frequently and had lower probability of local extinction. These sites were on cliffs high above the river drainage, surrounded by adequate prey habitat and with southerly aspects associated with early snowmelt and warmer microclimates in spring. Protecting these sites is likely to encourage continued occupancy by Arctic Peregrine Falcons along the Colville River and other similar areas. Our findings also illustrate the importance of evaluating fitness parameters along with climate and habitat features when analysing occupancy dynamics, particularly with a long‐term dataset spanning a range of annual climate variation.     

Determining productivity of Maui Parrotbills,an endangered Hawaiian honeycreeper

ABSTRACT Maui Parrotbills (Pseudonestor xanthophrys), critically endangered Hawaiian honeycreepers endemic to the island of Maui, are restricted to a single population of ～500 individuals located in remote, mountainous terrain. From January to June 2006–2011, we located nests and fledglings in the Hanawi Natural Area Reserve (NAR) in east Maui, Hawaii, to document nest success and annual reproductive success. Nest success is a commonly used measure of productivity and is a central component of many demographic studies. Annual reproductive success is less frequently documented because greater effort is required to monitor the reproductive success of breeding pairs through time. However, for species whose nests are difficult to locate or access, such as Maui Parrotbills, the presence or absence of fledged young may provide a more accurate measure of breeding success than monitoring nests. During our study, we located and determined the outcome of 30 nests to document nest success, and monitored 106 territories for the presence or absence of fledglings to calculate annual reproductive success. Nest success probability was 19% (N= 30) and seasonal nest success was 46%. During our monitoring efforts, 49 of 106 breeding pairs produced a single fledged young. Because parrotbills typically have single egg clutches and only re‐nest after nests fail, the presence or absence of a fledgling is an indication of a pair's overall reproductive success for a breeding season. Based on the number of fledglings per pair, our estimate of annual reproductive success was 46%, confirming our initial productivity estimate from nests. Thus, our results indicate that the two methods, determining annual reproductive success by monitoring fledglings and calculating nest success, provide similar estimates of annual productivity for Maui Parrotbills. Based on our estimates, the parrotbill population appears to be demographically stable. However, our productivity estimate was based only on the population at Hanawi, an area representing just 3% of the total range of parrotbills. Thus, our results may not accurately reflect the status of parrotbills over their entire range.     

An empirical demonstration of the ideal free distribution: Little Grebes Tachybaptus ruficollis breeding in intensive agricultural landscapes

The ideal free distribution (IFD) model predicts that a density‐dependent mechanism operates to regulate habitat selection and reproductive performance. We studied a Little Grebe Tachybaptus ruficollis population, which breeds on irrigation ponds in the Vega Baja Valley (southeastern Spain) to test the premises of the IFD model. These ponds are highly dynamic because they are managed according to agricultural requirements, and are subject to different levels of disturbance, which can change the quality of individual ponds across the landscape. Surveys were carried out during the breeding season from 2002 to 2006, with reproduction performance estimated during two consecutive breeding seasons, 2003 and 2004. Occupation frequency differed from random, indicating preference for some ponds over others. Habitat features such as pond construction and design, the presence of submerged vegetation, vegetation along the shore and reed beds, and pond area correlated with occupation frequency and might be considered to be indicators of pond quality. Ponds were occupied sequentially from best to worst. Thus, when the population size increased, the number of low‐quality ponds occupied also increased. High‐quality ponds held more breeding pairs than low‐quality ones, resulting in the mean reproductive success per breeding pair being independent of pond quality. Little Grebes therefore occupy ponds in a manner consistent with the expectations of the IFD model.     

Nest use dynamics of an undisturbed population of bald eagles

Management or conservation targets based on demographic rates should be evaluated within the context of expected population dynamics of the species of interest. Wild populations can experience stable, cyclical, or complex dynamics, therefore undisturbed populations can provide background needed to evaluate programmatic success. Many raptor species have recovered from large declines caused by environmental contaminants, making them strong candidates for ongoing efforts to understand population dynamics and ecosystem processes in response to human‐caused stressors. Dynamic multistate occupancy models are a useful tool for analyzing species dynamics because they leverage the autocorrelation inherent in long‐term monitoring datasets to obtain useful information about the dynamic properties of population or reproductive states. We analyzed a 23‐year bald eagle monitoring dataset in a dynamic multistate occupancy modeling framework to assess long‐term nest occupancy and reproduction in Lake Clark National Park and Preserve, Alaska. We also used a hierarchical generalized linear model to understand changes in nest productivity in relation to environmental factors. Nests were most likely to remain in the same nesting state between years. Most notably, successful nests were likely to remain in use (either occupied or successful) and had a very low probability of transitioning to an unoccupied state in the following year. There was no apparent trend in the proportion of nests used by eagles through time, and the probability that nests transitioned into or out of the successful state was not influenced by temperature or salmon availability. Productivity was constant over the course of the study, although warm April minimum temperatures were associated with increased chick production. Overall our results demonstrate the expected nesting dynamics of a healthy bald eagle population that is largely free of human disturbance and can be used as a baseline for the expected dynamics for recovering bald eagle populations in the contiguous 48 states.     

The reproductive success of Blackbirds Turdus merula in relation to habitat structure and choice of nest site

The reproductive success of a population of Blackbirds Turdus merula occupying farmland and woodland was studied over 3 years to investigate the effects of habitat on breeding success. Territory distribution was patchy in both farmland and woodland; some areas were unoccupied, while other areas were occupied at variable densities. Habitat structure appeared to influence occupation: the index of habitat complexity ("cover score") was higher in occupied areas than in unoccupied areas and high-density territories had higher cover scores than low-density territories. However, habitat structure had no significant effect on reproductive success because the cover scores of territories where pairs were successful did not differ significantly from those of territories where there were no successful breeding attempts. There was no evidence of differential mortality rates in adults according to habitat. The height, bulk and exposure of c. 430 nests were measured to determine the effect of nest and nest-site characteristics on reproductive success. Nest exposure was the only feature that differed between successful and failed nests, successful nests being less exposed than failed nests. The major cause of breeding failure was nest predation, but the effect of nest exposure operated only during the laying and incubation period and not during the nestling period. The significance of habitat structure for variation in population densities between habitats is discussed.     

Competitive interactions among raptors in boreal forests

We examined inter-specific interactions among goshawks (Accipiter gentilis), common buzzards (Buteo buteo) and honey buzzards (Pernis apivorus) in western Finland in 1983–1996. Because goshawks are among the largest birds of prey species in boreal forests they may take over the nest of smaller and less-competitive forest-dwelling raptors when searching for suitable places for breeding. Accordingly, more than half of newly established goshawk territories were found on the territories previously occupied by the common buzzard and the honey buzzard. Otherwise, territory sharing between these species was rare. Fledgling production of honey buzzards was not associated with the presence of goshawks, probably owing to the almost 2 months later onset of breeding. This probably decreases competitive interactions between these two species. An intensive interference competition, instead, seemed to be evident between common buzzards and goshawks, because the fledgling production of common buzzards was decreased by 20% as a result of failures during incubation and nestling period in the vicinity (<1 km) of occupied goshawk nests. Similarly, territory occupancy of common buzzards till the next breeding season was significantly reduced in the presence of goshawks. Relatively high proportions of occupied buzzard territories (17%) in the study area were shared by breeding goshawks on the same territory. This suggests that although their diets are dissimilar they inhabit similar habitats and might compete for the available prime nesting habitats within forest landscapes. In addition, goshawks benefit from taking over the complete nests of other raptors, imposing upon the original owners of the nest, because building a large stick nest is probably energetically costly. As a large raptor, the goshawk apparently has a competitive advantage over smaller ones, and may have an ever-increasing impact on smaller birds of prey, if there is a lack of sheltered forests inducing competition for the available nest sites.     

The importance of ant-rich habitats for the persistence of the Wryneck Jynx torquilla on farmland

The frequency of territory occupancy is a good indicator of territory quality. We studied territory occupancy in a Swiss population of the Wryneck Jynx torquilla , a declining farmland woodpecker, with the aim of identifying key habitat features for conservation management. Both static and dynamic approaches were applied using data on nest-site occupancy of 100 territories from six successive years. The static approach models the probability of territory occupancy; the dynamic approach estimates territory colonization and extinction. Frequently occupied territories were settled earlier in the season, suggesting that they may be of better quality, and birds settling in these territories had higher breeding success. Probability of territory occupancy increased with the area of old pear orchards and decreased with the area of vegetable cultivation. Both the area of old pear orchards and the presence of conspecifics within a territory were positively related to territory colonization, whereas territory extinction was negatively related to habitat heterogeneity. Old pear orchards were characterized by having both the highest density of ant nests and the greatest amount of bare ground. The latter is likely to facilitate access to ant prey. To ensure persistence of Wryneck populations in farmland, heterogeneous habitat matrices with high ant nest density and bare ground should be promoted. Finally, provision of artificial nesting cavities is likely to enhance territory occupancy. Providing that these key resources are present, Wrynecks are likely to persist even in intensively farmed areas.     

The breeding status of Peregrine Falcons Falco peregrinus in the UK and Isle of Man in 2002

Capsule Numbers of breeding Peregrines are now higher than ever recorded and the recovery of the species within the UK has continued since 1991.

Aims To estimate the current Peregrine breeding population and its changes over time by recording breeding evidence and nesting range occupancy at known and potential Peregrine eyries.

Methods Attempts were made to check all potentially suitable Peregrine nesting locations for signs of Peregrine occupation. Causes of nest failure were documented where possible. Estimates of occupancy of nesting ranges that could not be visited were based on the proportion of ranges occupied from visited nesting ranges in the same region.

Results In 2002, 1530 Peregrine nesting ranges were estimated to be occupied, comprising 1456 pairs or single birds confirmed as in occupation, and 74 estimated extras (5% of total occupied nesting ranges) that were not visited. Including non‐breeding singletons holding nesting ranges, the UK and Isle of Man figure of ‘Ratcliffe pairs’ was 1437. This showed a 12% increase from 1991 and a 64% increase from the 1930s. However, there were geographical differences in change, with rapid expansion in the south of England tempered by declines in northern Scotland.

Conclusions The primary reasons for the population increase is primarily because of range expansion driven by a plentiful food supply and perhaps an increased tolerance of human disturbance. In areas where the species has declined, various factors (separately or in combination) including reduced food supply and persecution are likely to be involved.     

Territory Occupancy and Parental Quality as Proxies for Spatial Prioritization of Conservation Areas

In order to maximize their fitness, individuals aim at choosing territories offering the most appropriate combination of resources. As population size fluctuates in time, the frequency of breeding territory occupancy reflects territory quality. We investigated the relationships between the frequency of territory occupancy (2002–2009) vs. habitat characteristics, prey abundance, reproductive success and parental traits in hoopoes Upupa epops L., with the objective to define proxies for the delineation of conservation priority areas. We predicted that the distribution of phenotypes is despotic and sought for phenotypic characteristics expressing dominance. Our findings support the hypothesis of a despotic distribution. Territory selection was non-random: frequently occupied territories were settled earlier in the season and yielded higher annual reproductive success, but the frequency of territory occupancy could not be related to any habitat characteristics. Males found in frequently occupied territories showed traits expressing dominance (i.e. larger body size and mass, and older age). In contrast, morphological traits of females were not related to the frequency of territory occupancy, suggesting that territory selection and maintenance were essentially a male''s task. Settlement time in spring, reproductive success achieved in a given territory, as well as phenotypic traits and age of male territory holders reflected territory quality, providing good proxies for assessing priority areas for conservation management.     

Cooperative enhancement of reproductive success in white-winged choughs

Summary White-winged choughs are a cooperatively breeding species which provide parental care to their young over an entire year. I traced the reproductive success of groups of white-winged choughs from the start of one breeding season to the next over 3 years. I examined the effect of helper number on timing of breeding, the success of each effort, the number of efforts made in a season, and the final reproductive success at the end of each year. Timing of commencement of breeding varied between years but was not related to group size. Early broods were not more successful than late broods. Nest building (July–September) commenced earlier in years which had high rainfall in July; choughs rely on rainfall for supplies of mud for nest construction. Most nest failures occurred gradually and were attributed to starvation of nestlings, although some sudden failures were attributed to predation. Large groups have more young by the beginning of the following season; this is due to higher fledging success and a greater likelihood of having second broods. Disappearance of young after fledging and during the transition to independence was not dependent on group size. Only groups of seven and above produce more than one young on average over the entire year; choughs provide one of the most marked cases for helpers enhancing the reproductive success of breeders. Large groups are virtually guaranteed of reproductive success over the whole year and grow more quickly than small groups. These results highlight the need to consider the effect of helpers over the entire period of reproduction and care of young, rather than just at fledging.     

Causes of variable reproductive performance by Southern Ground‐hornbill Bucorvus leadbeateri and implications for management

Range occupancy of the cooperatively breeding Southern Ground‐Hornbill Bucorvus leadbeateri in South Africa has decreased by 65% in the last three generations and the effective management of the remaining populations is hampered by a lack of fundamental understanding of the factors determining reproductive performance. We examined the influence of social and environmental factors on the species' reproductive success in South Africa using data gathered from 23 groups over eight breeding seasons. Some groups had access to artificial nest‐sites, others did not. High rainfall (> 500 mm) over the breeding season led to a decrease in reproductive success, with groups being most successful in years when rain in the vicinity of the nest ranged from 300 to 500 mm. Groups breeding in natural nests were successful only when the proportion of open woodland surrounding the nest‐site was high. Those that bred in artificial nests, where overall breeding success was more than twice as high as those in natural nests, were less dependent on the availability of open woodland. Large groups (more than three birds) bred more successfully than groups comprising only two to three individuals. Group size, helper effects and rainfall cannot be managed to increase the productivity of Ground‐Hornbills but the fact that the availability of artificial nest‐sites and the amount of open woodland around the nest‐site both contribute positively to breeding performance identifies practical and simple management options for increasing the reproductive output of Southern Ground‐Hornbill populations.     

Factors affecting breeding success of Peregrine and Lanner Falcons in South Africa

Jenkins, A.R. 2000. Factors affecting breeding success of Peregrine and Lonner Falcons in South Africa. Ostrich 71 (384): 385-392. Breeding success was recorded for three Peregrine Falcon, Falco peregrinus, populations in South Africa over nine years, and for Peregrine and Lanner Falcon, Ebiarmicus, populations in an area of sympatry over three years. The objectives of the study were to measure geographic and interspecific variation in reproductive performance, and determine environmental correlates of productivity. Territory occupancy, the frequency of breeding per occupied territory and clutch size did not vary significantly between the three Peregrine populations. However, Peregrine breeding success was generally lower on the Cape Peninsula (1. 11 young fledged per territorial poir), higher in the Soutpansberg (1.36) and highest on the Orange River (1.70). Overall, fledging rates of Soutpansberg Peregrines and Lanners were not significantly different, although annual productivity of the Lonner population was consistently higher. Neither species' breeding success was significantly depressed by the presence of close neighbouring pairs of the other, suggesting that they were not active competitors. Breeding performance of Peregrines on the Cape Peninsula correlated strongly with spring weather conditions: egg and hatchling survival was lower in wet years, and fledging rates were higher in warm years. Annual productivity of Orange River Peregrines correlated positively with the height of the river at the onset of breeding, and productivity of Soutpansberg Peregrines was higher in seasons following years of high rainfall. Elements of the physical structure of the nesting habitat (exposure of the nest ledge, height of the nest cliff) correlated positively with Peregrine breeding performance. Breeding success of Soutpansberg Lanners was largely unaffected by any of the environmental variables considered. Overall, it is proposed that Peregrine productivity reflected variation in the physical environment and its affect on prey availability.     

Territorial occupancy and breeding performance in a migratory raptor do not follow ideal despotic distribution patterns

It has commonly been argued that many territorial species select their breeding sites following an ideal despotic distribution model, in which the most productive, high-quality territories are more frequently occupied. Theoretical and empirical studies have shown that this occupancy pattern may have population regulatory consequences, leading to density dependence in heterogeneous habitats. During a 9-year research project in a forested area of south-eastern Spain, we tested some of the predictions of the ideal despotic distribution model and the site-dependent population regulation theory in a migratory raptor species, the booted eagle Hieraaetus pennatus . Contrary to the predictions of the despotic model, our results showed that the temporal pattern of territorial occupation did not differ from randomness, and that the territory occupancy rate was not significantly related to the reproductive parameters considered. At population level, the breeding variables were density independent, suggesting the absence of site-dependent regulation. In addition, we were unable to find significant differences in the habitat characteristics between high-quality and low-quality territories, classified according to the criteria of both occupancy frequency and average productivity. Overall, our results suggest that booted eagles select their territories at random, probably due to the lack of strong environmental heterogeneity, and that occupancy rate is not a good measure of territory quality for the population studied.     

Sprague's pipit breeding biology and reproductive success in planted and native grasslands

Much of the native grasslands in agricultural regions have been converted to cropland or tilled and seeded with non‐native grasses for livestock production. Several grassland songbird species occupy planted grasslands, but occupancy or density may not be a reliable indicator of habitat quality. I studied the breeding biology of Sprague's pipit Anthus spragueii from 2004 to 2008 in Saskatchewan, Canada. My objective was to determine the extent to which the breeding biology, density and reproductive success of pipits varied in planted and native grasslands. Peak clutch initiation occurred in mid‐ to late‐May in planted and native grassland. Peak pipit density also occurred in May, but density drastically declined over the breeding season in planted grassland. Clutch size varied among years and declined over the breeding season, but was similar in planted (4.7  0.1 SE) and native grasslands (4.5  0.1 SE). Daily nest survival rates varied with age of the nest and date, but the relationships differed in the two habitats and was likely a result of lower nestling survival in planted grassland compared to native grassland. The number of young fledged per nest increased as the season progressed and tended to be greater in native (1.2  0.1 SE) than planted (0.9  0.2 SE) grasslands. Seasonal productivity was much greater in native grassland. Only three nests were initiated after May in planted grassland and all were unsuccessful, whereas pipit young fledged at higher rates from nests initiated in native grassland in June and July than planted grassland nests initiated in May. The number of fledged young from successful nests did not vary strongly with habitat, date or year. This research indicates that planted grasslands attract pipits at the beginning of the breeding season, but habitat suitability and reproductive success substantially declines as the breeding season progresses compared to that found in native grassland.     

Influence of helping and breeding experience on reproductive performance in the Seychelles warbler: a translocation experiment

Reproductive success of the cooperative breeding Seychelleswarbler (Acrocephalus sechellensis) increases with age. Thisage effect is not due to differential survival or increasedreproductive effort, but to accumulated helping and breedingexperience. In their first year of breeding, reproductive performanceof inexperienced warblers with neither helping nor breedingexperience was significandy lower than that of warblers of thesame age with either previous helping or breeding experience.Reproductive performance was the same for primiparae with helpingexperience and for birds with breeding experience. Female primiparaewith helping experience or breeding experience built betternests and spent more time incubating than inexperienced females,which led to increased hatching success. Male primiparae withhelping experience or males with breeding experience guardedthe clutch better than inexperienced males, which led to reducedegg predation. Even-aged warblers with different previous experienceswere transferred to unoccupied islands, where birds startedbreeding immediately in high-quality territories. The experimentshowed that birds with helping experience produced their firstfledgling as fast as experienced breeders, and significandyfaster than inexperienced birds. Breeding performance did notimprove further with experience after the first successful breedingattempt. Only birds with previous breeding experience who pairedwith inexperienced birds, were likely to change mate. The otherpair combinations remained stable. Thus, primiparous birds withhelping experience have greater lifetime reproductive successthan inexperienced primiparae of the same age. This experimentshows that helping behavior has not only been selected for inthe context of promoting an individual's indirect fitness, butalso in the context of gaining helping experience which translatesinto improved reproductive success when a helper becomes a breeder.[Behav Ecol 7: 326-333 (1996)]     

Factors influencing territorial occupancy and reproductive output in the Booted Eagle Hieraaetus pennatus

During a 7-year research project in a forested area of southeastern Spain, we studied territorial occupancy and reproductive success in a Booted Eagle Hieraaetus pennatus population. We monitored 65 territories, gathering information on 406 occupancy events and 229 breeding attempts, including those of two potential competitors, the Northern Goshawk Accipiter gentilis and the Common Buzzard Buteo buteo . Generalized linear mixed models were used to explain occupancy and productivity, by evaluating the relative contribution of three different types of variables (habitat, competition and past events) and considering territory as a random effect. We examined a set of a priori hypothesized models, together with a number of additional models, and selected the best models following an information-theoretic approach. Our best models related territorial occupancy and productivity to previous breeding success (the fledging of one or two young), which appeared to be the most important factor determining the probability of reoccupation and the reproductive output in the subsequent year. The best occupation model revealed that the probabilities of occupancy were also conditioned by a competition variable (intraspecific nearest-neighbour distance) and two habitat variables (the location of the nest on the valley slope and the distance to the nearest forest track). Unlike the best occupation model, however, the selected model for reproductive output did not incorporate any competition variable besides previous breeding success, but included another two habitat variables (the effects of trunk height and NNE orientation).     

Depth of artificial Burrowing Owl burrows affects thermal suitability and occupancy

Many organizations have installed artificial burrows to help bolster local Burrowing Owl (Athene cunicularia) populations. However, occupancy probability and reproductive success in artificial burrows varies within and among burrow installations. We evaluated the possibility that depth below ground might explain differences in occupancy probability and reproductive success by affecting the temperature of artificial burrows. We measured burrow temperatures from March to July 2010 in 27 artificial burrows in southern California that were buried 15–76 cm below the surface (measured between the surface and the top of the burrow chamber). Burrow depth was one of several characteristics that affected burrow temperature. Burrow temperature decreased by 0.03°C per cm of soil on top of the burrow. The percentage of time that artificial burrows provided a thermal refuge from above‐ground temperature decreased with burrow depth and ranged between 50% and 58% among burrows. The percentage of time that burrow temperature was optimal for incubating females also decreased with burrow depth and ranged between 27% and 100% among burrows. However, the percentage of time that burrow temperature was optimal for unattended eggs increased with burrow depth and ranged between 11% and 95% among burrows. We found no effect of burrow depth on reproductive success across 21 nesting attempts. However, occupancy probability had a non‐linear relationship with burrow depth. The shallowest burrows (15 cm) had a moderate probability of being occupied (0.46), burrows between 28 and 40 cm had the highest probability of being occupied (>0.80), and burrows >53 cm had the lowest probability of being occupied (<0.43). Burrowing Owls may prefer burrows at moderate depths because these burrows provide a thermal refuge from above‐ground temperatures, and are often cool enough to allow females to leave eggs unattended before the onset of full‐time incubation, but not too cool for incubating females that spend most of their time in the burrow during incubation. Our results suggest that depth is an important consideration when installing artificial burrows for Burrowing Owls. However, additional study is needed to determine the possible effects of burrow depth on reproductive success and on possible tradeoffs between the effects of burrow depth on optimal temperature and other factors, such as minimizing the risk of nest predation.     

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Life history theory predicts that individuals should maximize lifetime reproductive success (LRS) by breeding as soon as they reach sexual maturity, yet many species delay breeding, either because there are insufficient available mates or breeding sites, or because delayed breeding yields higher LRS. Accipitriform species, such as Cooper's Hawk Accipiter cooperii, exhibit both delayed breeding and delayed plumage maturation. However, in certain circumstances, first‐year females in non‐definitive plumage do breed and apparently compete with older females for high‐quality breeding territories. We predicted that these young females are at a competitive disadvantage compared with older females and that older females would have both higher reproductive success and be able to acquire higher quality nesting territories. We conducted brood counts and measured prey delivery rates by male Cooper's Hawks in an expanding urban population located in Albuquerque, New Mexico (USA), to assess our prediction. We found that older females had higher reproductive success, fledging 1.6 more offspring than younger females, and that they occupied territories where males provisioned at higher rates of 0.37 more prey items per 2‐h period. Our results showed that older females fared better than first‐year females but it is unclear if this is the result of passive or active competition. Older females initiated nesting 14.3 days sooner than first‐year females and thus may have filled vacant, high‐quality territories before first‐year females began seeking mates. Additionally, first‐year females were never observed persistently to confront older females for breeding territories, but they did actively compete against each other. First‐year females may defer to older females who, in a direct competitive interaction, would be most likely to prevail. Thus, delayed plumage maturation in Cooper's Hawks may serve to focus competition for nesting territories within age classes.     

Age-specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

1. Using data from 327 nests over a consecutive 8-year period we examined age-specific variation in reproduction in a population of stitchbirds (or hihi) Notiomystis cincta and related how differences in reproductive performance were linked to the timing of territory establishment and breeding. 2. Across the population all reproductive parameters showed a quadratic relationship with an increase mainly between the first and second breeding season and a decline after the fourth year. A longitudinal analysis showed evidence of senescence by the sixth year in the numbers of chicks fledged and recruited. 3. Reproductive increases between years 1 and 2 were the result of poor-quality females dying after their first breeding season (differential selection hypothesis) in combination with surviving females showing improvements in reproduction in their second year (individual improvement/constraint hypothesis). 4. There was no effect of mate experience or territory quality on improvements in breeding between years. 5. The key variable influencing reproductive output was the timing of breeding. Birds that started laying earlier were more likely to lay multiple clutches in any given season. This was the main difference between first-year and older birds; generally first-year birds initiated egg laying later and consequently laid fewer clutches. 6. Approximately half of all first-year birds did not establish their territory until after the breeding season had begun. This delay in territory establishment resulted in these birds delaying breeding, which resulted in them having a lower reproductive output relative to all other birds. First-year birds that managed to establish their territory before breeding commenced, had similar rates of reproduction as older birds. 7. There was a positive relationship between the timing of territory establishment during a female's first year and her hatching date in the previous breeding season. We hypothesize that this was because late-hatched females were less able to effectively compete for territories against earlier-hatched members of their cohort, and this delayed their establishment and breeding in their first year. Thus, this social constraint is likely to be a major factor driving age-specific reproductive variation in this population.