Secondary Cavity Nesters Research Articles

How Important are Nest Cavities Made by the Three-Toed Woodpecker Picoides tridactylus for Cavity-Nesting Forest Bird Species?

Woodpeckers are important primary excavators that produce nest-sites that are also used by several other cavity-nesting animals. However, the value of nest sites produced by different woodpecker species for other cavity-nesters is not generally known. We studied old Three-toed Woodpecker Picoides tridactylus cavities to examine their importance for other cavity-nesting forest bird species. Over a 31-year period (1987–2017), we annually monitored the occupancy of 655 cavities excavated by the Three-toed Woodpecker in 86 territories of the species in a 170-km2 area in southern Finland. Eight bird species used old Three-toed Woodpecker cavities for breeding, and the occupancy of these cavities by all secondary users was 21.3%. The expected mean number of lifetime occupancies by secondary cavity-nesters for a single cavity was 2.03. This is equivalent to a mean of two cavities occupied per territory per year, if we assume that Three-toed Woodpeckers produce a new cavity every year. The actual numbers of annually occupied cavities by secondary cavity-nesters can be substantially lower especially in territories that are not constantly occupied by the Threetoed Woodpecker. Based on the use of old cavities and densities of secondary cavity-nesting bird species, we conclude that cavities made by Three-toed Woodpeckers are most significant for the species itself, which accounted for 23.3% of nests in old Three-toed Woodpecker cavities. When Three-toed Woodpeckers reused an old cavity rather than occupy a freshly excavated cavity, 93% of cavities selected were originally excavated by Three-toed Woodpeckers. In addition, old cavities are important for the Pygmy Owl Glaucidium passerinum — up to 26–31% of breeding attempts were in old Three-toed Woodpecker cavities. The importance of old cavities for other hole-nesting bird species like the Pied Flycatcher Ficedula hypoleuca or the Great Tit Parus major was rather minor considering their densities within woodpecker territories.

Sequential Use of Tree Cavities by Birds and Nest Web in a Riparian Forest in Southwest India

We studied the sequential use of tree cavities by the cavity-nesting bird community in a riparian forest ecosystem of south-western India during 2013–2015. During the study period, a total of 376 nests of 20 cavity-nesting bird species comprising six primary and 14 secondary cavity nesters were located in the riparian forest. The cavity use pattern showed that one-third of the cavities were reused by birds and that the majority of the reused cavities were located in live trees. A lesser proportion (5%) of cavities used by birds was reused by other animal taxa. Competition for nest cavity use was observed among bird species in which Common Myna Acridotheres tristis was found to be the major competitor. A strong correlation was found between the bird body mass and nest cavity dimensions. Cluster analysis based on tree and cavity characteristics divided the avian community into five groups. We constructed a nest web for community structure that showed cavity resource use by various primary and secondary cavity-nesters. Woodpeckers (Greater Golden-backed Woodpecker Chrysocolaptes guttacristatus, White-naped Woodpecker C. festivus, and Browncapped Pygmy Woodpecker Dendrocopos nanus) as well as barbets (Brown-headed Barbet Psilopogon zeylanica, Coppersmith Barbet P. haemacephala and White-cheeked Barbet P. viridis) formed the key excavators in the riparian forest. While many of the smaller secondary cavity-nesting birds depend on the excavated cavities for nesting and reproduction, large-sized birds used decay formed cavities.

Physiological condition of nestling great tits Parus major in response to experimental reduction in nest micro- and macro-parasites.

Most passerines use nests as the exclusive place to lay and incubate eggs and bring nestlings up to fledging. Nests of secondary cavity nesters, like tits, provide a moist, warm and protected habitat for reproduction of blood parasites. Offspring fitness depends on interactions between parental care and environmental constraints. Life-history theory suggests that macro- and micro-parasites may generate selection pressures by affecting host health. In the present study, we replaced natural great tit Parus major nests in two, structurally and floristically contrasting sites (an urban parkland and a rich deciduous forest, located 10 km apart in Łódź, central Poland), with fresh, sterilized, artificial moss-cotton wool nests, twice, on the fifth and tenth day of nestlings life. We then examined haematological condition indicators (haemoglobin and glucose concentrations) of about 14-day-old nestlings. Nestlings that were developing in treated nests improved their health status in comparison with control nestlings. The mean haemoglobin and glucose concentrations (treated and control) also varied between both study areas. Our study confirms that the level of haemoglobin and especially the level of glucose may be treated as reliable indicator of environmental characteristics in great tits.

Correction to: The conservation value of tree decay processes as a key driver structuring tree cavity nest webs in South American temperate rainforests

South American temperate rainforests, a global biodiversity hotspot, have been reduced to nearly 30% of their original extent and most remaining stands are being degraded. Cavity-nesting vertebrate communities are dependent on cavity-bearing trees and hierarchically structured within nest webs. Evaluating the actual degree of cavity dependence (obligate, non-obligate) and the preferred attributes of trees by cavity nesters is critical to design conservation strategies in areas undergoing habitat loss. During three breeding seasons (2010–2013), we studied the cavity-nesting bird community in temperate rainforests of Chile. We found the highest reported proportion of tree cavity nesters (n = 29 species; 57%) compared to non-cavity-using birds for any forest system. Four species were excavators and 25 were secondary cavity nesters (SCNs). Among SCNs, ten species were obligate and 15 were non-obligate cavity nesters. Seventy-five percent of nests of SCNs were located in cavities produced by tree decay processes and the remaining 25% were in cavities excavated mainly by Pygarrhichas albogularis and Campephilus magellanicus. Nest web structure had a low dominance and evenness, with most network interactions occurring between SCNs and large decaying trees. Tree diameter at breast height (DBH) was larger in nest-trees (57.3 cm) than in available trees (26.1 cm). Cavity nesters showed a strong preference for dead trees, both standing and fallen (58% of nests). Our results stress that retaining large decaying and standing dead trees (DBH > 57 cm), and large fallen trees, should be a priority for retention in forest management plans in this globally threatened ecosystem.

Nest temperature fluctuations in a cavity nester, the southern ground-hornbill

Southern ground-hornbills Bucorvus leadbeateri inhabit savanna and bushveld regions of South Africa. They nest in the austral summer, which coincides with the wet season and hottest daytime temperatures in the region. They are secondary cavity nesters and typically nest in large cavities in trees, cliffs and earth banks, but readily use artificial nest boxes. Southern ground-hornbills are listed as Endangered in South Africa, with reintroductions into suitable areas highlighted as a viable conservation intervention for the species. Nest microclimate, and the possible implications this may have for the breeding biology of southern ground-hornbills, have never been investigated. We used temperature dataloggers to record nest cavity temperature and ambient temperature for one artificial and 11 natural southern ground-hornbill tree cavity nests combined, spanning two breeding seasons. Mean hourly nest temperature, as well as mean minimum and mean maximum nest temperature, differed significantly between southern ground-hornbill nests in both breeding seasons. Mean nest temperature also differed significantly from mean ambient temperature for both seasons. Natural nest cavities provided a buffer against the ambient temperature fluctuations. The artificial nest provided little insulation against temperature extremes, being warmer and cooler than the maximum and minimum local ambient temperatures, respectively. Nest cavity temperature was not found to have an influence on the breeding success of the southern ground-hornbill groups investigated in this study. These results have potentially important implications for southern ground-hornbill conservation and artificial nest design, as they suggest that the birds can tolerate greater nest cavity temperature extremes than previously thought.

Sexual differences in the effect of previous breeding performance on nest-box reuse and mate retention in White-rumped Swallows (Tachycineta leucorrhoa)

ABSTRACTIn birds, the selection of nesting sites and mates has a profound influence on the daily interactions of individuals. Both behaviours are energetically costly and time-consuming and can strongly affect the Darwinian fitness of individuals. Using a 12-year dataset on banded returning breeders, we explored variables associated with nest-box choice and mate choice in the White-rumped Swallow, a socially monogamous migratory passerine. Females reusing nest-boxes, but not males, produced significantly more fledglings than did those that changed nest-boxes. Females and males that retained mates produced significantly more fledglings than did those that divorced. General linear mixed models revealed that the number of fledglings produced in previous seasons significantly explained the reuse of particular nest-boxes by females, but not by males. Mate choice by females was not strongly affected by either past breeding performance or nest-box reuse, but nest-box reuse alone predicted mate choice by males. Nest-box reuse by males was apparently more related to retention of female partners. This study revealed that sexual differences in the nesting and mating decisions were guided by the use of information on past breeding performance in a subtropical, secondary cavity nester.

Lophozonia tree cavities used for nesting by Slender-billed Parakeets (Enicognathus leptorhynchus) in the central valley of southern Chile: a potentially vanishing keystone resource

BackgroundThe Slender-billed Parakeet (Enicognathus leptorhynchus) is a psittacine endemic to southern Chile and an obligate secondary cavity-nester. In the central valley of southern Chile, most (94%) of the known Slender-billed Parakeet nests have occurred in large, mature southern beech (Lophozonia obliqua) trees (locally known as “pellines”). As relicts of the original old-growth forests of southern Chile, most pellines have been lost due to extensive land-clearing throughout the region, potentially threatening long-term persistence of the Slender-billed Parakeet.MethodsWe conducted our study in the central valley of southern Chile, near the city of Osorno during three consecutive nesting seasons (November–January, 2008–2011). Nest trees used by Slender-billed Parakeets were located by direct observation of parakeet activities and through interviews with local residents, some of whom were former parrot nest poachers. Nest cavities were accessed, inspected and measured using single-rope climbing techniques. We report means, standard errors, 95% confidence intervals and ranges for 11 cavity-related variables. We also report clutch sizes encountered in active nests, and age estimates of nest trees based on known growth rates of Lophozonia trees in southern Chile. Linear regressions were used to evaluate potential relationships between cavity-related variables and clutch size.ResultsWe located and measured 38 Lophozonia tree cavities used for nesting by Slender-billed Parakeets. Compared to those used by other psittacines, nest trees were relatively large, averaging 30.4 ± 1.1 m in height with a mean diameter at breast height of 134.5 ± 4.7 cm. Based on estimated annual diameter increment, ages of nest trees ranged from approximately 209–485 years. Nest cavities entrances averaged 12.5 ± 0.9 m in height above ground level. Cavity entrance widths averaged 51.0 ± 13.3 cm (vertical) by 11.5 ± 0.7 cm (horizontal). Cavity entrance orientations were apparently random, with no directional preferences detected. Nest cavities were also relatively large, with a mean internal diameter of 39.6 ± 2.4 cm and mean depth of 90.3 ± 24.2 cm. Clutch sizes (2–9) were unusually large for psittacines of this size (ca. 280–300 g) and broods of up to seven well-developed nestlings were observed.ConclusionsWe found that the deep and spacious cavities provided by pellines facilitate successful rearing of large broods, thereby maximizing productivity and fitness. The existence of pellines has apparently allowed Slender-billed Parakeets to adapt successfully to a wholesale loss of ancestral habitat to anthropogenic modifications. Immediate and strategic conservation measures, such as protection of existing pellines and the regeneration and recruitment of additional ones, are recommended for ensuring the survival of Slender-billed Parakeet populations throughout the central valley of southern Chile.

Effects of landscape composition and native oak forest configuration on cavity-nesting birds of North Africa

In the Kroumirie ecoregion of northwestern Tunisia, habitat fragmentation and degradation are the main drivers of contemporary landscape change. Continuous native oak forests have been converted into heterogeneous landscapes characterized by small forest fragments surrounded by a scrubby matrix. We examined the response of five species of cavity-nesting birds to these phenomena because they play a keystone role in these forest ecosystems. We quantified the relative effects of landscape composition and the configuration of mature oak forest on the occurrence of the focal species. We hypothesized that the occurrence of all focal species would increase with forest cover, whereas the effects of matrix type and mature forest configuration would be species-specific. For each focal species, we tested a set of 12 candidate models predicting their occurrence. Each model included landscape metrics describing oak forest configuration and landscape composition. We applied multimodel inference and model averaging on generalized linear models. Forest cover at the landscape level was the main driver of species occurrence. Secondary cavity-nesters responded positively to the proportion of oak forest at landscape and local scales, whereas the five focal species responded negatively to the proportion of low scrub. Great spotted woodpecker (Dendrocopos major) and Levaillant’s woodpecker (Picus vaillantii) responded positively to both forest amount and high scrub, suggesting a landscape complementation process. Lesser spotted woodpecker (D. minor) was the only species responding to forest configuration, possibly as a result of landscape supplementation. High scrub appeared to moderate the contrast between low scrub and forest fragments for primary cavity-nesters. However, it did not influence the occurrence of secondary cavity-nesters (e.g., Atlas flycatcher Ficedula speculgera and short-toed treecreeper Certhia brachydactyla). If an increase in the amount of mature oak forest cannot be achieved over the short term, the maintenance of high scrub around forest fragments and an improvement in the quality of low scrub through the addition of vertical structure should increase the frequency of occurrence of many of our focal species in oak forest of the Mediterranean Basin.

Northern flickers only work when they have to: how individual traits, population size and landscape disturbances affect excavation rates of an ecosystem engineer

Woodpeckers are considered ecosystem engineers because they excavate tree cavities which are used subsequently by many species of secondary cavity nesters for breeding. Woodpeckers have the choice of excavating a new hole or reusing an existing one, and this propensity to excavate (e) may affect community dynamics but has rarely been investigated. Using 18 years of data on a population of northern flickers Colaptes auratus, I tested six hypotheses to explain the propensity to excavate (e) in a landscape which experienced two types of disturbance: pine beetles and wildfires. Woodpecker age, breeding experience and mate retention had little influence on e which varied between 13–39% annually and averaged 23% for 1843 first nests over the 18 yr. Body size and body condition of males and females were not associated with e but rates of excavation declined seasonally, suggesting time rather than energy costs limited excavation effort. Reduced cavity availability mediated through high conspecific density coupled with wildfires triggered relatively high excavation rates, up to 39% but e decreased to baseline levels three years after the landscape disturbances. Nearly 2/3 of males did not excavate in their lifetime but apparently, e is great enough to balance the average rate of cavity tree loss in this forest which is 11% annually. Excavation propensity in flickers is flexible, but the birds reduce their work levels if there is a surplus of holes available.

Nesting success of the oriental magpie robin Copsychus saularis in nest boxes and tree cavities

Information on the nesting success of birds in the Indian subcontinent is almost negligible. In the present study factors affecting nesting success were studied over four years (i.e. 2011–2014) in a color ringed population of the oriental magpie robin (OMR) in an urban habitat of Haridwar district (29°55′N, 78°08′E), Uttarakhand, India. Objectives of our study were 1) to assess whether nest box affects nesting success in the OMR or not 2) to compare breeding data obtained from nest boxes with tree cavities.Out of total 114 nests built in both nest boxes and tree cavities, 80 nests were successful in producing at least one fledgling resulting 69.25% nesting success. Nesting success did not differ significantly between nest boxes and tree cavities or during different years. No correlation was found between territory size and nesting success (correlation coefficient = 0.41). Observations indicated that predation accounted for the maximum egg loss and nestling mortality. Predation rate was higher in tree cavities but did not differ significantly during different years and between nest boxes and tree cavities. In all years but 2011 clutch size was significantly higher in nest boxes than in tree cavities. However, incubation period, provisioning period, number of eggs hatched and number of young fledged did not differ significantly between nest boxes and tree cavities. When provided, nest boxes were occupied more frequently at all study sites indicating that nest box may act as an alternative nesting site for the OMR and perhaps for other secondary cavity nesters facing scarcity of nesting sites due to rapid urbanization.

Distribution and abundance of hole-nesting birds in Mediterranean forests: impact of past management patterns on habitat preference

This study explores the relative abundance of hole-nesting birds in fourMediterranean forest types, each of which has undergone different patterns of forest management. Nine species were sampled in 24 study plots, to compare cork oak forest, turkey oak forest, holm oak forest and pine plantation. The abundance of hole-nesters was greater in cork oak forest and turkey oak forest. Three species were most frequently detected: Great Tit (Parusmajor), Blue Tit (Cyanistes caeruleus) and Nuthatch (Sitta europaea). Bird abundancewas significantly lower in holmoak forest, particularly in the cases of Great Spotted Woodpecker (Dendrocopos major), Green Woodpecker (Picus viridis), Nuthatch and Short-toed Treecreeper (Certhia brachydactyla). TheGreat SpottedWoodpecker showed a positive correlation with the abundance of three secondary cavity nesters: Nuthatch, Short-toed Treecreeper and Starling; in contrast, Green Woodpecker showed a negative correlation with Starling. Habitat structure varied significantly among forest types, especially themean andmaximumtree height, these being lower in holmoak forest. The Great SpottedWoodpecker proved to be a good indicator of less disturbed woodlands. In fact, maximum tree height turned out to be a significant and positive explanatory variable for woodpecker abundance.We consider that intensive coppicing and timbermanagement in holm oak forest during the 20th century widely affected trees’ age-profile, with consequences for their suitability forwoodpeckers and other hole-nesting birds. Tomonitor the response of hole-nesting birds to forest management in terms of abundance, we propose the use of the great spotted woodpecker as an indicator species.

Breeding habitat characteristics and nest survival of yellow-rumped flycatcher (Ficedula zanthopygia) in natural tree-cavities

Studies of nest-site selection and reproduction are essential for bird species assessment and conservation. We compared breeding habitats and random sites within a secondary cavity-nesting bird, Yellowrumped Flycatcher (Ficedula zanthopygia), in a 5-year studying period in northeast China. We also modeled the effects of factors on daily nest survival rates. The flycatcher nest cavities were mostly located in tree trunks, with only 15% found in limbs. They often located their nests in east and south direction (45°–180°) with dense canopy cover surrounding the nest trees. Yellow-rumped Flycatcher nest-site selection appears to be nonrandom, such that they select nest sites with higher tree density and higher canopy closure. Yellowrumped Flycatcher daily nest survival rate was 0.9731 ± 0.007. Daily nest survival increased with increasing percent cover of canopy closure and decreased with the distance closing to the edges. The causes for nest failure were mainly nest usurpation by other secondary cavity-nesters. Predation rate and the competition for cavities with other secondary cavity-nesters may constrain the ability of Yellow-rumped Flycatchers to optimize nest nest-site selection.

Habitat indicators for cavity-nesters: The polypore Phellinus pini in pine forests

Foresters and arborists have long used fruit-bodies of heart-rot fungi as signs of advanced live-tree decay, but such usage has not been elaborated for forest conservation. I analysed relationships between a heart-rot fungus, tree-cavity supply, and cavity-nesting bird assemblage in wet hemiboreal Scots pine (Pinus sylvestris) forests in Estonia. The focal species, Phellinus pini, is the main heartwood decayer of live pines; it typically forms fruit-bodies at the stage of advanced decay on old trees. I found that the pine wetlands had few tree-cavities (mostly in snags) and cavity-nesting birds (woodpeckers being almost absent) despite abundant snag supply. Only one fruit-body of P. pini was found on cavity-tree but stand-scale abundance of the fruit-bodies correlated well with cavity-nester densities. Multifactor models indicated that cavity formation, not tree death, was the limiting process for secondary cavity-nesters, and P. pini could indeed be used (in combination with old-pine abundance) for assessing their habitat quality. This fungus could also serve as an educational flagship species to bridge conservation biology and forest pathology, and its fruit-bodies can signal trees to be retained at harvesting in pine forests. The conclusion is that there is hope for developing practical indicators to manage for the hidden decay processes that govern tree-cavity development.

Reproductive life-history variation in a secondary cavity-nester across an elevational gradient in Andean temperate ecosystems

ABSTRACT Avian reproductive strategies have been hypothesized to vary with elevation. Shorter breeding seasons due to harsh environmental conditions, and potentially higher predation risks, may reduce clutch sizes at higher elevations, which in some species leads to increased parental care and offspring survival. However, this phenotypically plastic and potentially adaptive response has been documented only in a handful of species in the Northern Hemisphere. For the first time in a southern temperate ecosystem, we studied whether the breeding strategy of a secondary cavity-nester varied along an elevational gradient in Andean temperate forests, Chile. We installed 240 nest-boxes at 260–1,115 m elevation and monitored the breeding activity of 162 nests of Thorn-tailed Rayaditos (Aphrastura spinicauda) over 2 seasons (2010–2012). We included 50 nests from a third season only for recording clutch size and nestlings per clutch. As predicted, the breeding season was shorter in highland forests than in lower el...

The Habitat-Trees experiment: using exotic tree species as new microhabitats for the native fauna

The cavities that develop in veteran trees represent a key microhabitat for forest biodiversity and especially for secondary cavity nesters that rely on this resource for shelter. Since the availability of deadwood, veteran and hollow trees is threatened by forest management, we explored the possibility of increasing the presence of these scarce resources. To increase the abundance of dead wood-microhabitats, 113 trees of the hybrid planes (Platanus x acerifolia) were converted into new living structures, the Habitat Trees (HT). To investigate the potential of this resource on the native avian fauna, six types of cavities were designed according to the size requirements of the target bird species. The temporal evolution of the cavities and their use by birds were then studied for eight years. The artificial cavities generally did not compromise growth and stability of the trees, and the majority remained alive. These hollows offered better thermal insulation compared to traditional nest-boxes and natural cavities. Their use increased during the first three years, reaching the 80%. In the following years, the use declined (probably because of the increase of rot and displacement of the lids).This highlights the need of management to maintain their suitability through time. Our results suggest a possible cost-effective alternative use of alien tree species, which should be included in management actions to compensate the shortage of hollow trees in managed forests.

Facultative interspecific brood parasitism in tits: a last resort to coping with nest-hole shortage

We studied the occurrence of facultative interspecific brood parasitism (eggs from two species incubated by a single female) in two bird species, the blue (Cyanistes caeruleus) and the great tit (Parus major). These species are secondary cavity nesters. We monitored 38 forest plots of variable size over 3 years. We found a total of 39 mixed-species clutches in 1285 nests, representing a prevalence of 3.0 %, but it reached 7.2 % in small woodlands. Seventeen mixed-species clutches involved blue tit facultative interspecific brood parasitism, with the same number of great tits usurping and directly laying in blue tit clutches. The higher the nest-box occupation rate, the greater the prevalence of mixed-species clutches of any origin. However, the two tit species behaved differently when faced with nest-hole shortage, with blue tits dumping one or two eggs into clutches incubated by great tits and these taking over the entire blue tit clutch. Nest takeovers were more frequent at the end of the season. These differences in behaviour are likely mediated by differing dominance status, with great tits being larger. The difference in size could also explain why great tit chicks presented larger hatching and fledging rates than their blue tit broodmates. These rates were lower in blue tit chicks from mixed-species broods compared with pure ones, and no advantages were found in usurper great tit chicks compared to pure broods. Mixed-species clutches appear to be a response to nest-hole shortage, a concept that we have termed the ‘last resort hypothesis’.

Habitat selection of cavity‐nesting birds in the Hyrcanian deciduous forests of northern Iran

AbstractThe Hyrcanian forests of northern Iran support a great diversity of bird species. Yet, the ecological relationships of cavity‐nesting birds (CNBs), the main components of forest bird communities in this area, remain unknown. We examined the importance of ecological factors in 90 study plots during the breeding season to predict the probability distribution and habitat suitability of primary cavity nesters (PCNs), secondary cavity nesters (SCNs) and weak primary cavity nesters (WPCNs). Ecological factors included forest structure, habitat complexity, geographical attributes and dead tree features. The significant habitat parameters determining the presence‐absence of each CNB species were also determined. PCN richness and abundance were most influenced by the density of larger trees, snags (standing dead trees) and logs (fallen dead trees). The densities of snags, logs and larger trees and the extent of the shrub layer influenced distributions of SCNs. The Eurasian nuthatch (Sitta europaea) was the only WPCN identified, and its distribution was strongly affected by altitude and by larger snags and trees in complex habitats. Our results showed that CNB species could be classified in three groups: (1) species dependent on mature forests, (2) species dependent on younger forests and (3) species adaptable to different forest stages. Overall, snags and logs played vital roles in the habitat preferences of CNB communities as well as in forest structure and complexity.

Resource requirements of parrots: nest site selectivity and dietary plasticity of Psittaciformes

Parrots (Order Psittaciformes) are secondary cavity-nesters that depend on existing cavities for nest sites, and consume plant resources of fruits, seeds, and flowers that are highly variable, but little is known of resource selectivity by parrots, or how they deal with variable environments. We reviewed published studies of nest-cavity use by parrots, and those evaluating parrot diet and their relationship with food resources. Most studies have been conducted within the last 20 years and these present data on resource use for only one-third of parrot species worldwide. However, basic information on resource requirements is lacking for the vast majority of Psittaciformes, particularly for species from the Asian region. Nesting studies have found that parrots use nest cavities in large trees, high above the ground, with large nest chambers, of 0.5–1 m deep, and entrance diameters related to body size of the parrot species. A few studies demonstrate that parrots select nest sites based on cavity characteristics, which may influence nest success, but a complete evaluation of adaptive nest site selection by Psittaciformes is lacking. Parrots have varied diets and may employ a combination of strategies of diet switching, habitat shifts, and movements to track food resources. This plasticity in diet and foraging strategy may influence the extent to which parrots can respond to anthropogenic pressures of global change. Parrots may also play an important functional role in forest ecosystems, yet little is currently known of plant–animal interactions of parrots, or the impact of parrot populations on forest dynamics. Based on our review of the literature, we suggest that to meet their resource requirements, parrots employ resource selection strategies of hierarchical nest site selection to increase the likelihood of nest success, and plasticity in diet and foraging strategy to track variable food resources. Future studies need to evaluate resource selection and the consequences of this for fitness in order to assess the potential impacts of global change on parrot populations, and to identify characteristics which make species vulnerable to human pressures.

Temporal dynamics of a commensal network of cavity-nesting vertebrates: increased diversity during an insect outbreak.

Network analysis offers insight into the structure and function of ecological communities, but little is known about how empirical networks change over time during perturbations. "Nest webs" are commensal networks that link secondary cavity-nesting vertebrates (e.g., bluebirds, ducks, and squirrels, which depend on tree cavities for nesting) with the excavators (e.g., woodpeckers) that produce cavities. In central British Columbia, Canada, Northern Flicker (Colaptes auratus) is considered a keystone excavator, providing most cavities for secondary cavity-nesters. However, roles of species in the network, and overall network architecture, are expected to vary with population fluctuations. Many excavator species increased in abundance in association with a pulse of food (adult and larval beetles) during an outbreak of mountain pine beetle (Dendroctonus ponderosae), which peaked in 2003-2004. We studied nest-web dynamics from 1998 to 2011 to determine how network architecture changed during this resource pulse. Cavity availability increased at the onset of the beetle outbreak and peaked in 2005. During and after the outbreak, secondary cavity-nesters increased their use of cavities made by five species of beetle-eating excavators, and decreased their use of flicker cavities. We found low link turnover, with 74% of links conserved from year to year. Nevertheless, the network increased in evenness and diversity of interactions, and declined slightly in nestedness and niche overlap. These patterns remained evident seven years after the beetle outbreak, suggesting a legacy effect. In contrast to previous snapshot studies of nest webs, our dynamic approach reveals how the role of each cavity producer, and thus quantitative network architecture, can vary over time. The increase in interaction diversity with the beetle outbreak adds to growing evidence that insect outbreaks can increase components of biodiversity in forest ecosystems at various temporal scales. The observed changes in (quantitative) network architecture contrast with the relatively stable (qualitative) architecture of empirical mutualistic networks that have been studied to date. However, they are consistent with recent theory on the importance of population fluctuations in driving network architecture. Our results support the view that models should allow for the possibility of rewiring (species switching partners) to avoid overestimation of secondary extinction risk.

Nestling Mortality as a Consequence of Interspecific Competition between Secondary Cavity Nesters in the Sub-Antarctic Forests of Chile

ABSTRACT Interspecific competition among secondary cavity nesters can involve physical conflicts between individuals, which may lead to serious injuries or death. Here we report a case of aggression by a pair of Chilean Swallows (Tachycineta meyeni) towards a nestling of the Thorn-tailed Rayadito (Aphrastura spinicauda) in the sub-Antarctic forests of Chile. This aggression caused the displacement of the breeding rayaditos from an occupied nest box and it appears, nestling mortality. Since levels of aggression among cavity nesters depend on the synchrony of their breeding phenologies, further research is needed to study the prevalence of nest usurpation by Chilean Swallows and its relation to the degree of breeding synchrony with other cavity nesters inhabiting the sub-Antarctic forests.