Nest habitat selection by the Austral parakeet in north‐western Patagonia

Identifying habitat or nesting microhabitat variables associated with high levels of nest success is important to understand nest site preferences and bird–habitat relationships. Little is known about cavity availability and nest site requirements of cavity nesters in southern hemisphere temperate forests, although nest site limitation is suggested. Here we ask which characteristics are selected by the Austral parakeet (Enicognathus ferrugineus) for nesting in Araucaria araucana–Nothofagus pumilio forest in Argentine Patagonia. We compared nest plot and tree characteristics with unused plots and trees among areas of different A. araucana–N. pumilio density. We also examine whether nest plot and tree use and selection, and the associated consequences for fitness of Austral parakeets are spatially related to forest composition. Austral parakeets showed selectivity for nests at different spatial scales, consistently choosing isolated live and large trees with particular nest features in a non‐random way from available cavities. Mixed A. araucana–N. pumilio forests are ideal habitat for the Austral parakeets of northern Patagonia, offering numerous potential cavities, mainly in N. pumilio. We argue that Austral parakeet reproduction and fitness is currently very unlikely to be limited by cavity availability, although this situation may be rapidly changing. Natural and human disturbances are modifying south temperate forests with even‐aged mid‐successional stands replacing old growth forests. Cavity nesting species use and need old growth forests, due to the abundance of cavities in large trees and the abundance of larvae in old wood. Neither of the latter resources is sufficiently abundant in mid‐successional forests, increasing the vulnerability and threatening the survival of the Austral.     

The evolution of parental and alloparental effort in cooperatively breeding groups: when should helpers pay to stay?

We used a reproductive skew framework to consider the evolutionof parental and alloparental effort in cooperatively breedinggroups. The model provides the first theoretical treatmentof rent payment (the "pay-to-stay" hypothesis) for the evolutionof helping behavior of subordinates. According to this hypothesis,not all helping behavior is kin selected, but group membershelp in order to be allowed to stay in the group and potentiallygain breeding positions later in life. We show that reproductiveconcessions may be replaced by complete skew and voluntary,costly alloparental effort by subordinates once future prospectsare included in fitness calculations. This suggests that incompleteskew observed in long-lived species is not due to dominantcontrol over reproduction. Rent payment is predicted to occurwhen relatedness between subordinate and dominant is low, survivalis high, ecological constraints are at least moderately tight,and retaining nonhelping subordinates harms the dominant'sfitness. Rent may also be required from related subordinatesif helping is very costly (leading to low voluntary helpingeffort) and ecological constraints are moderately tight. However, related subordinates do not need to have a positive net effecton the dominant's direct fitness to be accepted as group members.We also consider compensatory responses of dominant group membersas a potential threat to the stability of renting behavior.If dominants trade off parental effort against their own survival,they may selfishly reduce their own parental effort as a responseto increased help. As this improves their own survival, theprospects of territorial inheritance diminish for the subordinate,and subordinates should hence be less willing to accept therent agreement. However, we show that compensatory responsesby "lazy" parents prevent group formation only in borderlinecases.     

Nest Site Selection Influences Cinnamon Teal Nest Survival in Colorado

Nest survival of ducks is partially a function of the spatiotemporal characteristics of the site at which a bird chooses to nest. Nest survival is also a fundamental component of population growth in waterfowl but is relatively unstudied for cinnamon teal (Spatula cyanoptera). We investigated cinnamon teal nest survival in a managed wetland complex in southern Colorado, USA, and assessed nest site selection to determine whether nest site characteristics were adaptive. We monitored 85 nests in 2015–2017 on Monte Vista National Wildlife Refuge, Colorado and did not detect a difference in nest survival across years. Based on nest site selection data from 2017, cinnamon teal selected nest sites characterized by a lower proportion of forbs than available sites. The relationships between habitat characteristics and nest survival were variable. Microhabitat characteristics exhibited only weak effects on nest survival during the laying stage. Nest survival during incubation was negatively related to the proportion of forbs at the nest site and, to a lesser extent, the proportion of grasses. Nest site selection was predictive of future nest survival based on the percent of forbs and grasses around the nest site, suggesting teal select nest locations to benefit reproductive success. These results have the potential to guide local habitat management actions for breeding waterfowl. © 2020 The Wildlife Society.     

Helper effects on pup lifetime fitness in the cooperatively breeding red wolf (Canis rufus)

The evolutionary maintenance of cooperative breeding systems is thought to be a function of relative costs and benefits to breeders, helpers and juveniles. Beneficial effects of helpers on early-life survivorship and performance have been established in several species, but lifetime fitness benefits and/or costs of being helped remain unclear, particularly for long-lived species. We tested for effects of helpers on early- and late-life traits in a population of reintroduced red wolves (Canis rufus), while controlling for ecological variables such as home-range size and population density. We found that the presence of helpers in family groups was positively correlated with pup mass and survival at low population density, but negatively correlated with mass/size at high density, with no relation to survival. Interestingly, mass/size differences persisted into adulthood for both sexes. While the presence of helpers did not advance age at first reproduction for pups of either sex, females appeared to garner long-term fitness benefits from helpers through later age at last reproduction, longer reproductive lifespan and a greater number of lifetime reproductive events, which translated to higher lifetime reproductive success. In contrast, males with helpers exhibited diminished lifetime reproductive performance. Our findings suggest that while helper presence may have beneficial short-term effects in some ecological contexts, it may also incur long-term sex-dependent costs with critical ramifications for lifetime fitness.     

Nest site, laying period, and breeding success of the Woodchat Shrike (Lanius senator) in Mediterranean France

Summary Breeding habitats in Mediterranean France consist in open, dry grasslands with a low and discontinuous grass layer and scattered bushes and trees. The choice of nest supports was largely opportunistic, the most abundant suitable nest support type (bush or tree) and the most abundant species being present at each study site have been used. About 75% of the nests were placed at heights between 1 and 3 m. Laying period lasted from 9 May until 6 July (peak of first clutches: 21–30 May). Mean clutch size was 5.14±0.82 eggs (n=114). Breeding success was independent from the site, the height and the concealment of nests. Mean survival rate of nests from laying to fledgling was 0.365. The main cause of low breeding success was high nest predation exerted by a rich guild of predators. The species is mainly threatened through dramatic habitat shrinkage due to pastoralism reduction leading to closures of lightly bushed grasslands in Mediterranean France.

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Nistplatzwahl, Legeperiode und Bruterfolg des Rotkopfwürgers (Lanius senator) in Südfrankreich

Zusammenfassung Als Bruthabitat bevorzugt der Rotkopfwürgers im mediterranen Südfrankreich offene und trockene Graslandlandschaften mit niedrigem oder lückigem Grasbewuchs und einzelstehenden Büschen und/oder Bäumen. Häufigster Nestträger ist die jeweils im Brutterritorium häufigste Baum- oder Buschart. Ungefähr 75% der Nester standen zwischen 1 und 3 m über Boden. Die Legeperiode reichte vom 9. Mai bis 6. Juli (Gipfel der Erstgelege am 21.–30. Mai und der Ersatzgelege am 20.–24. Juni). Die Gelegegröße bestand aus 3 bis 7, meist 5 Eier (Erstgelege im Mittel 5,35±0,71 Eier, Ersatzgelege: 4,68±0,85). Der Bruterfolg war unabhängig von der Lage, der Höhe und der Verborgenheit des Nestes. Die mittlere Überlebensrate eines Nestes zwischen Bebrütung des Geleges und Ausfliegen der Jungen betrug 0,365. Dieser niedrige Bruterfolg wurde hauptsächlich durch Nesträuber verursacht. In Südfrankreich ist die Art aber vor allem durch die zunehmende Verschließung der Bruthabitate infolge des Rückgangs des extensiven Weidebetriebs gefährdet.

     

Helping effort in a dominance hierarchy

In many cooperatively breeding species, group members form adominance hierarchy or queue to inherit the position of breeder.Models aimed at understanding individual variation in helpingbehavior, however, rarely take into account the effect of dominancerank on expected future reproductive success and thus the potentialdirect fitness costs of helping. Here we develop a kin-selectionmodel of helping behavior in multimember groups in which onlythe highest ranking individual breeds. Each group member caninvest in the dominant's offspring at a cost to its own survivorship.The model predicts that lower ranked subordinates, who havea smaller probability of inheriting the group, should work harderthan higher ranked subordinates. This prediction holds regardlessof whether the intrinsic mortality rate of subordinates increasesor decreases with rank. The prediction does not necessarilyhold, however, where the costs of helping are higher for lowerranked individuals: a situation that may be common in vertebrates.The model makes two further testable predictions: that the helpingeffort of an individual of given rank should be lower in largergroups, and the reproductive success of dominants should begreater where group members are more closely related. Empiricalevidence for these predictions is discussed. We argue that theeffects of rank on stable helping effort may explain why attemptsto correlate individual helping effort with relatedness in cooperativelybreeding species have met with limited success.     

Nest reuse in arctic‐breeding shorebirds: an analysis of potential benefits and factors affecting the occurrence of this rare behavior

During a 13‐yr study near Utqia?vik (formerly Barrow), Alaska, we documented the prevalence of nest reuse in eight arctic‐breeding shorebirds. We evaluated whether nest reuse saved individuals time and energy, enhanced nest survival, or was related to nest density. We documented 208 (6.2%) cases of nest reuse among 3336 nesting attempts. Nest reuse occurred in all years but the first and in all species, with greatest reuse in semipalmated sandpiper (10.9%) and American golden‐plover (10.0%). While most cases of nest reuse occurred with conspecifics, many cases of heterospecific nest reuse were also observed, indicating high niche overlap in nest site preferences among species. We found that individuals reusing old nests may have benefited by nesting earlier, but nest reuse did not generally enhance nest survival. A significant positive relationship was also found between nest reuse and nest density at the community level and for four of the eight species, suggesting high inter‐ or intraspecific competition combined with limited suitable nest sites may force individuals to reuse old nests. Our observations also suggest that upland nesting species may be the most dependent on old nest sites. Preferential development of these sites may therefore have a previously unknown detrimental effect on these species, although further study is needed to better determine the impact of such habitat loss.     

Nest sites as limiting resources for cavity‐nesting birds in mature forest ecosystems: a review of the evidence

ABSTRACT Assumptions that populations of cavity‐nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest‐box‐addition experiments or tree‐cavity‐blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human‐altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest‐cavity‐removal or addition experiments conducted with 20 species of cavity‐nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest‐site limitation at the population‐ and landscape‐level in mature, unmanaged forests. I review the challenges in designing and interpreting box‐addition experiments and highlight the main gaps in knowledge that should be targeted in the future.     

Nest monitoring does not affect nesting success of Whinchats Saxicola rubetra

It is important to assess the effect that research activities may have on animals in the wild, especially when key parameters, such as breeding success, could potentially be influenced by observer activity. For birds, some studies have suggested that nest monitoring can increase the chances of nest failure due to predation, whereas others suggest that human nest visits may actually deter mammalian predators. Nest monitoring visits can also influence breeding success more indirectly by altering parental provisioning behaviour. Here, the influence of monitoring activities on nest success was examined in a ground‐nesting grassland bird, the Whinchat Saxicola rubetra. During the egg phase, a sample of nests were not visited between the initial finding event and the estimated hatching date; instead, the nest status was assessed at a distance. Daily survival rates (DSR) for these nests were compared with that of nests visited every 2 days. During the nestling phase, the effects of observer nest visits on parental provisioning behaviour were determined. Nest visits were found not to affect egg DSR significantly, and parental provisioning was disrupted for a maximum of 20 min (0.52% of the nestling period) following an observer visit. Given the variation in response to nest visits across species, we suggest that consideration should be given to observer impact in all studies where predation risk is high. Here, we illustrate a method for researchers to assess the impact of their nest visits to ensure they are not biasing estimates of breeding success.     

Nest predators of woodland open-nesting songbirds in central Europe

I used time-lapse videotaping to identify predators of open songbird nests in fragmented deciduous woodland (nine plots, 2–10 ha each) in the Czech Republic from 2002 to 2006. I documented 22 species of predators at 171 nests of 13 species (mainly Blackcap Sylvia atricapilla , Song Thrush Turdus philomelos , Common Blackbird Turdus merula , Yellowhammer Emberiza citrinella and Chaffinch Fringilla coelebs ). The main predators were Pine Marten Martes martes (37% of 178 predation events), Jay Garrulus glandarius (29%), Buzzard Buteo buteo (7%) and Great Spotted Woodpecker Dendrocopos major (7%); mammals accounted for 48% of total predation. At least 3% of nests were depredated by multiple predators. In spite of their local abundance, Hooded Crows Corvus cornix did not present a serious threat for shrub nesting songbirds (< 1% of total predation). No predation by mice was recorded, suggesting that their importance has been overestimated in artificial nest studies. The proportional species composition of predators depended on which species occupied the monitored nest and location (study plot), but not on the year or the time of season. Corvids and raptors accounted for a relatively larger percentage of total predation of small ('warblers') and large ('thrushes') prey species, respectively, whereas carnivores were important predators of all prey species. Active nests of thrushes were only rarely robbed by Jays (< 4% of 52 events), presumably due to parental nest defence. Predation by woodpeckers was spatially clumped, probably due to individual foraging specialization. Predation by the other major predators was documented on most/all study plots.     

浙江五峙山列岛黄嘴白鹭的巢位选择研究

黄嘴白鹭(Egretta eulophotes)是全球性受威胁鸟类。2005年7月, 我们在浙江五峙山列岛对黄嘴白鹭的巢位选择进行了研究, 共测量了74个巢。研究发现, 在0.99 hm2的馒头山小岛上, 黄嘴白鹭的巢呈聚集性分布, 平均巢间距为119.6 cm, 最小巢间距为15 cm。黄嘴白鹭对巢位具有明显的选择性, 优先选择在灌丛, 尤其是那些相对较高的灌丛(高于50 cm)下营巢, 其次是较低的灌木(低于64 cm)内部和草丛上。多数巢存在遮蔽物。避风和遮荫是黄嘴白鹭巢位选择的主要要求。台风是决定五峙山列岛黄嘴白鹭巢位选择的最主要因素, 而高灌木的数量直接影响五峙山列岛黄嘴白鹭的繁殖成功和今后的资源状况。     

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

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

Using Nest Temperature to Estimate Nest Attendance of Piping Plovers

Abstract: Recent technological innovations allow remote monitoring of avian nest temperature that minimizes disturbance and expense without altering clutch sizes. However, the efficacy of such techniques has not been determined for ground-nesting birds. We compared the efficacy of 2 techniques, iButton® data loggers (Maxim/Dallas Semiconductor Corp., Sunnyvale, CA) and custom-built thermocouples, to measure nest temperature of piping plovers (Charadrius melodus) relative to nest attendance at Cape Cod National Seashore, Massachusetts, USA. Neither technique affected hatching success (U = 389.5, P = 0.874) or rates of predation of nests containing devices (P = 0.894). We estimated nest attendance successfully with thermocouples in nests as long as air and surface temperatures were <29° Cand 43° C, respectively. Although iButtons could not be used to determine duration of on-bouts and off-bouts of incubating piping plovers, they were effective at determining when nests were abandoned or predated. We recommend the use of thermocouples for studying nest attendance of ground-nesting birds, in general, and of threatened and endangered species, in particular, where disturbance should be minimized and altering clutch sizes is not feasible.     

ECOLOGICAL CONSTRAINTS INFLUENCE THE EMERGENCE OF COOPERATIVE BREEDING WHEN POPULATION DYNAMICS DETERMINE THE FITNESS OF HELPERS

Cooperative breeding is a system in which certain individuals facilitate the production of offspring by others. The ecological constraints hypothesis states that ecological conditions deter individuals from breeding independently, and so individuals breed cooperatively to make the best of a bad situation. Current theoretical support for the ecological constraints hypothesis is lacking. We formulate a mathematical model that emphasizes the underlying ecology of cooperative breeders. Our goal is to derive theoretical support for the ecological constraints hypothesis using an ecological model of population dynamics. We consider a population composed of two kinds of individuals, nonbreeders (auxiliaries) and breeders. We suppose that help provided by an auxiliary increases breeder fecundity, but reduces the probability with which the auxiliary becomes a breeder. Our main result is a condition that guarantees success of auxiliary help. We predict that increasing the cost of dispersal promotes helping, in agreement with verbal theory. We also predict that increasing breeder mortality can either hinder helping (at high population densities), or promote it (at low population densities). We conclude that ecological constraints can exert influence over the evolution of auxiliary help when population dynamics are considered; moreover, that influence need not coincide with direct fitness benefits as previously found.     

Helpers at the nest compensate for reduced maternal investment in egg size in carrion crows

Life history theory predicts that mothers should trade off current and future reproductive attempts to maximize lifetime fitness. When breeding conditions are favourable, mothers may either increase investment in the eggs to improve the quality of the offspring or save resources for future reproduction as the good raising environment is likely to compensate for a 'bad start'. In cooperatively breeding birds, the presence of helpers improves breeding conditions so that mothers may vary the number, size and quality of the eggs in response to the composition of the group. Here, we show that in cooperatively breeding carrion crows Corvus corone corone, where nonbreeding males are more philopatric and more helpful at the nest than females, breeding females decreased egg size as the number of subordinate males in the group increased. However, despite the smaller investment in egg size, fledglings' weight increased in groups with more male subordinates, improving post-fledging survival and indicating that helpers fully compensated for the initial 'bad start'. These results highlight a 'hidden effect' of helpers that bears profound implications for understanding the ultimate function of helping.     

Reproductive success depends on the quality of helpers in the endangered,cooperative El Oro parakeet (Pyrrhura orcesi)

In cooperative species, helping behaviour and reproductive success can be correlated, but understanding this correlation is often impaired by the difficulty to correctly infer causation. While helpers can incur costs by participating in brood care, it is yet unclear if their help depends on their individual quality. We address these questions in the previously unknown cooperative breeding system of the endangered El Oro parakeet (Pyrrhura orcesi). Specifically, we ask (i) whether breeders benefit directly from helpers by an enhanced reproductive success and if so, (ii) whether the amount of this potential benefit is regulated by the quality of contributing group members. Groups consist of a dominant breeding pair accompanied by helpers, but cooperation is not obligate. Microsatellite heterozygosity was used to assess individual quality; its suitability as indicator of quality was reflected in the positive relationship between offspring heterozygosity and recruitment into the population. The reproductive success of breeding pairs depended on helper (genetic) quality and the number of helpers. This relationship occurred on two different levels: clutch size and fledging success, indicating (i) that females profit from high‐quality helpers and probably adjust clutch size accordingly and (ii) that the helpers increase fledging success. Congruently, we found that offspring body condition is positively affected by helper quality, which is most probably explained by the increased feeding rates when helpers are present. We suggest a causal link between cooperation and reproductive success in this frugivorous, endangered parakeet. Further, helper (genetic) quality can be a relevant factor for determining reproductive fitness in cooperative species, particularly in small and bottlenecked populations.     

Sex ratios when helpers stay at the nest

This study investigates the evolution of the sex ratio (parental investment in sons) when breeding adults are supported by help provided by nonbreeding individuals of one sex. The study also assumes that the helping sex remains on its natal site to compete for the opportunity to breed, whereas the nonhelping sex disperses. Two kin-selection models are presented, both of which incorporate the age structure found in many natural populations where such helping occurs. The first model assumes that helpers increase the survival of their parents. The second model assumes that helpers are indiscriminant: a helper chooses to increase the survival of a random pair of adults breeding on its natal patch. In both models, sex ratios are not always biased toward the sex that provides the most help. When helpers do not discriminate (second model), the direction of sex-ratio bias is determined solely by the size of the benefit of helping behavior. When this benefit is small, sex-ratio evolution is primarily influenced by local resource competition and sex ratios are biased toward the nonhelping (dispersive) sex. If the benefit of help is large enough, the effect of local resource competition is reduced and sex-ratio bias favors the helpful sex. When helpers help only their parents, the same qualitative relationship exists between the direction of sex-ratio bias and the benefit of helping. In this case, however, the direction of sex-ratio bias is also influenced by the size of the social group, mortality, and which individual (mother or father) controls the sex ratio. This study also investigates a sex-ratio conflict that exists between mates. Helping behavior of nonbreeders can act to alleviate the disparities between the optimal sex ratio from the perspective of a mother and that from the perspective of a father. This consequence of helping has not been previously recognized.     

四川南充市城市白头鹎的巢址选择和巢材研究

2005年3~9月,在四川南充市对白头鹎巢址进行了研究。主成分分析表明:影响白头鹎巢址选择的主要因素有7种,依次为巢位高度需求因素、栖位因素、巢上隐蔽因素、食物因素、种竞争因素、种内竞争因素、水源因素;其巢材较为广泛。