Effect of boundary vegetation and landscape features on diversity and abundance of breeding bird communities of abandoned crop fields in southwest Poland

Capsule The number of territories of birds nesting in abandoned crop fields was most strongly positively affected by field size and the presence of a railway embankment.

Aims To assess the influence of different habitat features on the number of birds nesting in abandoned crop fields.

Methods A breeding bird survey was conducted in spring 2002 using the mapping method on 67 abandoned fields located in southwest Poland. The associations between eight habitat features of the abandoned fields and the numbers of particular species and groups of birds, as well as the whole bird community, were tested with a glm.

Results The models for eight individual species revealed the following ranking, in terms of number of species affected by each predictor: area of fields (5), railway embankments and adjacent crop fields (4), roads and power lines (2), and number of trees (1). The number of the most numerous group of birds (species nesting on the ground, 79% of all breeding pairs) was affected by four predictors: field area, railway embankments, power lines and roads. The number of all birds was affected by six predictors: field area, railway embankments, power lines, roads, ditches and trees.

Conclusion Limited effects of trees, hedgerows and ditches on the number of territories suggest that abandoned fields without woody vegetation are attractive breeding habitats for many farmland birds. One of the effective ways of protecting farmland bird species in central Europe may be the preservation of abandoned fields in their present form, especially those <5 ha in area.     

城市公共绿地常见木本植物组成对鸟类群落的影响

快速城市化背景下, 城市公共绿地已经成为重要的鸟类栖息地, 其中的木本植物群落构成对鸟类群落结构有显著影响, 研究木本植物配置与鸟类多样性的关系对提升城市公共绿地作为鸟类栖息地的生态服务功能有重要的理论和应用价值。我们于2009–2010年间在上海市滨江森林公园就木本植物和鸟类群落的相互关系展开研究。样线法结合样点调查共记录到鸟类10目25科64种5,368只(次), 鸟类多度全年变化显著, 峰值分别出现在4月和11月。丰富度全年也呈现双峰型变化, 峰值出现在4月和12月。全年鸟类多样性(Simpson指数)差异显著, 10月最高, 8月最低。样方调查共记录到77种木本植物, 其中有14种(乔木9种、灌木5种)出现率超过5个样方, 定义为常见种, 其果期主要集中在9月到翌年2月, 其上常见林业致病害虫的发生盛期集中在5–11月。主成分分析显示, 常见木本植物上观察到的鸟类可划分为8个鸟类集团, Spearman秩相关检验显示秋冬季常见木本植物果期与植食性、肉食性、食虫性、杂食性等多个鸟类集团的多度均呈显著正相关。说明在秋冬季鸟类迁徙高峰期不同鸟类集团均能获得丰富的食物资源。就常见木本植物对鸟类群落的重要值进行排序, 结果显示, 大叶杨(Populus lasiocarpa)、枫杨(Pterocarya stenoptera)、香樟(Cinnamomum camphora)等乔木对鸟类重要值较高, 而灌木层对鸟类的重要性整体偏低, 说明滨江森林公园的灌木层作为鸟类栖息地的功能建设尚需加强。根据以上研究结果, 我们提出了提高上海城市公园鸟类多样性的植被配置建议。     

Impacts of an invasive willow (Salix × rubens) on riparian bird assemblages in south‐eastern Australia

We explored how a woody plant invader affected riparian bird assemblages. We surveyed 15 200‐m‐long transects in riparian zones in a much‐changed landscape of eastern Victoria, Australia. Abundance, species‐richness, foraging‐guild richness and composition of birds were compared in transects in three habitat types: (i) riparian zones dominated by the invasive willow Salix × rubens; (ii) riparian zones lined with native woody species; and (iii) riparian zones cleared of almost all woody vegetation. We also measured abundance and richness of arthropods and habitat structure to explore further the effects of food resources and habitat on the avifauna. We observed 67 bird species from 14 foraging guilds. Native riparian transects had more birds, bird species and foraging guilds than willow‐invaded or cleared transects. Habitat complexity increased from cleared to willow‐invaded to native riparian transects, as did abundance of native and woodland‐dependent birds. Native shrub and trees species had more foliage and branch‐associated arthropods than did willows, consistent with a greater abundance and variety of foraging guilds of birds dependent on this resource. Willow spread into cleared areas is unlikely to facilitate greatly native bird abundance and diversity even though habitat complexity is increased. Willow invasion into the native riparian zone, by decreasing food resources and altering habitat, is likely to reduce native bird biodiversity and further disrupt connectivity of the riparian zone.     

High ambient temperatures induce aggregations of chimney swifts Chaetura pelagica inside a roost

One proposed advantage of communal roosting in birds is a reduction in the costs of thermoregulation. As thermoregulatory benefits are directly linked to the distance between roosting birds, we examined whether temperature is related to inter‐bird spacing in roosting chimney swifts Chaetura pelagica. To test the hypothesis that huddling is used to reduce the costs of thermoregulation, we predicted that swifts would cluster more at colder temperatures. We mounted an all‐weather camera atop a 61 m tall industrial masonry chimney, one of the largest swift roosts in the study region. We deployed temperature loggers inside the chimney and obtained ambient air temperature from a nearby weather station. From 16 May–24 July 2013, we captured hourly images of the positions of roosting swifts at night. We used image analysis software to mark the angular positions of all roosting swifts, and calculated mean angles of orientation (preferred direction) inside the roost and the circular variance (i.e. the concentration of swifts around the mean angle). We used a Gamma regression to relate temperature inside and outside the roost to the clustering of swifts around the mean angle for 3 time periods (pre‐nesting, nesting, and post‐nesting). Converse to our prediction, swifts were closer together when ambient air temperatures were warmer in all periods (pre‐nesting (p < 0.001, n = 168), nesting (p < 0.001, n = 224), and post‐nesting (p < 0.001, n = 135)). Our findings suggest that swifts do not increase clustering intensity in response to colder temperatures, but instead they increase clustering intensity in response to the warmest ambient temperatures. This likely a metabolic response to reduced prey availability at higher temperatures and/or an attempt to reduce evaporative water loss. We suggest clustering may be used by chimney swifts as an energy saving mechanism during periods of lowered food availability.     

Using infrared thermography to detect night‐roosting birds

Most birds sleep while roosting at night. Although a widespread behavior, few investigators have studied the nocturnal roosting behavior of birds. Studies conducted to date have either focused on species that roost communally or used radio‐telemetry to locate sleeping individuals of a few focal species. Portable thermal cameras capable of detecting infrared (IR) heat signals may provide a more efficient and less invasive means of detecting nocturnal‐roosting endotherms such as birds. Our objective was to assess the efficacy of using thermal cameras to detect roosting birds in a woodland bird community in southeastern Australia. To better understand the limitations of using thermography to detect roosting birds, paired bird surveys were conducted along 44 transects from May to September 2016 using both traditional survey techniques during the day and surveys with a thermal camera at night. We detected 195 birds representing 21 species at nocturnal roosts using IR thermography, with the detection rate of birds during nocturnal surveys approximately one‐third (29.1%) that during diurnal surveys. Detection rates during nocturnal surveys declined more steeply with distance from observers than for diurnal surveys. Detection rates were significantly higher during diurnal surveys for 14 species of woodland birds, but did not differ between diurnal and nocturnal surveys for eight other species. Roost height, roost visibility, bird mass, and cluster size (i.e., two or more birds in physical contact) did not differ between species categorized as having high or low detectability during nocturnal surveys. Variability among species in nocturnal‐detectability could not be attributed to roost‐site visibility, roost height, or bird size. Positive detection biases associated with diurnal behavior, such as movement and vocalizations, and limitations of current IR technology, e.g., low resolution, likely contributed to overall lower detection rates during nocturnal surveys. However, our results suggest that infrared thermography can be an effective and useful technique for detecting roosting birds and studying roosting behavior, as well as for population monitoring under certain conditions.     

The role of remnant forest trees in tropical secondary succession

This paper emphasizes the contribution of remnant trees to the establishment of woody species during succession on abandoned fields and pastures in the Mexican rain forest area, Los Tuxtlas, Veracruz. Remnant trees, original large forest trees left in the clearings by traditional farmers will become natural perching sites for both passing and resident birds. Frugivorous birds drop or regurgitate seeds and fruits which fall under the canopies of remnant trees during their stay, thus contributing to an accumulation of species, which make these remnant trees into ‘regeneration nuclei’. The species transported into these sites belong chiefly to older stages of successional development and reach these otherwise isolated areas, counteracting the depauperization of tropical land, brought about by both intensive and extensive clearing. In a study of seven remnant trees, 29 woody species and two climbers were found, 86% of which are bird dispersed. The total number of species per tree varied from 6 to 15 and was higher under remnant trees with fruits attractive to birds. Floristic variations of the understorey as detected by detrended correspondence analysis was correlated with the relative amount of shade-tolerant primary and late secondary trees versus light dependent pioneers and early successional trees.     

The role of farm structure on bird assemblages around a Kenyan tropical rainforest

Although it is clear that the farmlands neighbouring fragmented forests are utilized by some forest birds, it is not clear how birds in general respond to farmland habitat mosaic. An effort was made to determine how bird density and foraging assemblages were influenced by farm structural characteristics and distance from forest edge. Thirty farms up to a distance of 12 km around Kakamega forest in western Kenya were studied. Farm structure entailed size, hedge volume, habitat heterogeneity, woody plant density, plant diversity and crop cover. Birds were surveyed using line transects and DISTANCE analyses and classified into six feeding guilds and three habitat associations. Size of farms increased away from the forest, as woody plant density, plant diversity, indigenous trees and subsistence crop cover declined. The most important farm structure variable was hedge volume, which enhanced bird species richness, richness of shrub‐land bird species and insectivorous bird density (R = 0.58, P < 0.01). Bird density increased with tree density while indigenous trees were suitable for insectivores and nectarivores. There were very few forest bird encounters. Agricultural practices incorporating maintenance of hedges and sound selection of agroforestry trees can enhance conservation of birds on farmland, though, not significantly for forest species.     

Effects of forest regeneration on the structure of bird communities in northern Finland

Breeding bird communities in five stages of secondary forest succession were studied in northeastern Finland in 1980–82. Three groups of communities were distinguished: open land, brush phase and forest communities, dominated by Motacilla alba and Oenanthe oenanthe, Phylloscopus trochilus and Anthus trivialis, Phylloscopus trochilus and Fringilla montifringilla , respectively.
Pair density, number of species, biomass of adult birds and species diversity increased in the course of succession, none of these, however, monotonously. Average bird weight showed a decreasing trend although the variation was considerable. The degree of specialization in communities (measured by ratios derived from numbers of species, genera and families) increased in the course of succession with the exception that the initial stage had relatively high values. Species nesting and feeding in trees and shrubs increased in numbers during forest regeneration whereas species nesting and feeding on the ground showed the opposite trend. The proportions of hole-nesting and sedentary species increased with increasing forest age.
The initial stages of forest succession in the north are occupied by specialized open habitat species breeding originally on open bogs and shores. These communities thus clearly differ from those predicted from the general theory of succession, which postulates that the pioneer stages of succession are dominated by habitat generalists and that these communities should have relatively low values of community diversity.     

Nest boxes for Cape Parrots Poicephalus robustus in the Hogsback area,Eastern Cape,South Africa

Breeding propensity of tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. Artificial nests can be used to provide alternative nest sites. Cape Parrots Poicephalus robustus are nationally endangered and nest in existing tree-cavities in high-altitude fragmented Afromontane forests in South Africa, assumed to be in short supply due to historic and current logging practices. To increase nest site availability, 179 wooden bird boxes and 28 bee boxes (to ‘pull’ bees) were erected during 2011–2012 in Hogsback, Eastern Cape. In 2016, no bird boxes were occupied by Cape Parrots. A total of 43% were used by other species, 51% were unused and 6% could not be inspected due to tree instability and inaccessibility. Two bird boxes were inspected by two pairs of Cape Parrots, but were never occupied. Occupancy of boxes by birds was not associated with nest, tree or habitat characteristics. However, occupancy of boxes by bees was associated with habitat type and tree species. Future conservation efforts will include locating natural Cape Parrot nesting sites and reforestation efforts to ensure the long-term availability of natural nesting sites.     

Predation risk alters interactions among species: competition and facilitation between ants and nesting birds in a boreal forest

Although interactions between species are often assumed to be fixed, theory and empirical evidence suggest that they may be quite variable, changing in the presence of other species or environmental conditions. The interaction between ants and nesting birds exhibits such variability, ants sometimes being predators of bird nests and other times protectors of them. Hypothesizing that predation risk might be a critical factor in altering the interaction of ants with birds, I investigated the interaction of wood ants Formica aquilonia with nesting birds under different levels of predation risk. In a controlled field experiment, I allowed tits ( Parus major, P. caeruleus, P. ater ) and pied flycatchers ( Ficedula hypoleuca ) to select nest boxes in trees with ants (ant trees) or trees without ants. I found that birds usually nested in trees without ants, apparently to avoid the danger of injury from encounters with ants. Nesting in ant trees occurred mainly in the habitat where risk of predation was highest (along the forest edge), and with the bird taxa that lost nests most frequently in trees without ants (tits). Tits nesting on the forest edge achieved significantly greater nesting success, and fledged significantly more young, in ant trees compared with trees without ants. As the season progressed, ant traffic increased in trees without nesting birds, but decreased in trees with nesting birds, indicating that the outcome of interference competition between ants and nesting birds was reversed under increased predation risk. These results support the idea that predation risk can shift species interactions from predominately competitive processes to predominately facilitative processes.     

Relationships between bird community and habitat structure in shelterbelts of Hokkaido,Japan

Summary The relationship between the bird community and habitat structure in wind shelterbelts of Ishikari district was examined.Breeding birds were classified into nesting guilds (hole, canopy, and bush) and also into foraging guilds (outside, canopy, and bush) Both density and species richness in the outside-foraging guild were positively related to forest age variables. On the other hand, bird density in all three nesting guilds and the other two foraging guilds (canopy and bush) was correlated with the vegetation cover of their nesting or foraging sites, and species richness was positively correlated with tree species complexity variables.Bird species diversity (BSD) was closely related to tree species complexity, but not to foliage height diversity (FHD) within woods. However, if woods were re-classified into two groups such as natural and artificial and these were separately analysed, the correlation between BSD and FHD was significant.From these results, it is concluded that both FHD and tree species complexity should be considered together in order to predict BSD within forests. A new index is proposed for this purpose, and its usefulness discussed.     

人类休闲活动对森林鸟类群落无有害影响

我们对西班牙马德里森林深处(未受到人类干扰)、森林小路沿线(间或有徒步旅行者经过)以及森林野餐区(有较持久干扰)的鸟类进行了调查,以查明人类休闲活动对该地区鸟类群落的分布和多度的影响.结合样方法对以上3类区域鸟类群落的总体特征(如:鸟类的多度、物种的丰富度和多样性)、不同鸟类群体的特征(如:鸦科鸟类的多度,营巢或者取食集团的特征)、各鸟种的多度等参数进行了比较.结果表明:小路沿线和野餐区样方内鸟类的多度和物种丰富度比森林深处更高,已查明14种鸟类的多度在人为干扰区域比森林深处高,只有5种鸟类的多度在森林深处更高一些;在树冠层筑巢的鸟类、在树干和地面觅食的鸟类及鸦科鸟类在休闲活动区有更高的多度;地巢性鸟类在休闲区的多度较低,这种差别尤以阔叶落叶林中加明显.而森林小路的鸟类群落结构与森林内部非常相似,说明人类休闲活动对这些林区鸟类群落的影响更多缘自野餐.原因是野餐区常常具有以下特点:具有高大的乔木、中层植被稀疏、有较多的洞和缝隙以及野餐后会遗留下一些垃圾.以上结论与研究的预期目标正好相反,人类的这些休闲活动可能会降低地巢性鸟类的适宜度,但是对大多数鸟的类栖息地没有不利影响.     

Breeding birds in the tropical rain forests of Kibale National Park, Uganda

A combination of trapping and foot surveys was used to assess the breeding status of birds in unlogged and logged sites in the tropical rain forest of Kibale National Park, Uganda. Breeding of forest edge and gap species was greatly enhanced by logging, whereas crevice and hole nesting specialist breeders were adversely affected. Egg‐laying periods corresponded to higher rainfall regimes at the nearby field station. The relevance of these findings to bird conservation is discussed.     

Grey Parrots Psittacus erithacus in Kampala,Uganda – are they becoming suburbanised?

The globally Vulnerable Grey Parrot (Psittacus erithacus) has been seen in Kampala, Uganda’s capital city, in increasing numbers in recent years. This apparently new behaviour of a typically forest species is helped by the presence of many large trees, which provide roosting and nesting sites, and fruiting trees where they feed. Grey Parrots in Kampala potentially come from three sources: escapees, releases of captive birds or wild birds moving into a suburban environment. Birds mostly exhibit behaviours typical of wild birds, but as most, if not all, of the Grey Parrots in captivity are wild-caught and would revert to wild-caught behaviours when released, it is difficult to distinguish them from the wild population. However, we believe that at least some of the birds seen in Kampala are wild.     

Comparison of the ecology and evolution of plants with a generalist bird pollination system between continents and islands worldwide

Thousands of plant species worldwide are dependent on birds for pollination. While the ecology and evolution of interactions between specialist nectarivorous birds and the plants they pollinate is relatively well understood, very little is known on pollination by generalist birds. The flower characters of this pollination syndrome are clearly defined but the geographical distribution patterns, habitat preferences and ecological factors driving the evolution of generalist‐bird‐pollinated plant species have never been analysed. Herein I provide an overview, compare the distribution of character states for plants growing on continents with those occurring on oceanic islands and discuss the environmental factors driving the evolution of both groups. The ecological niches of generalist‐bird‐pollinated plant species differ: on continents these plants mainly occur in habitats with pronounced climatic seasonality whereas on islands generalist‐bird‐pollinated plant species mainly occur in evergreen forests. Further, on continents generalist‐bird‐pollinated plant species are mostly shrubs and other large woody species producing numerous flowers with a self‐incompatible reproductive system, while on islands they are mostly small shrubs producing fewer flowers and are self‐compatible. This difference in character states indicates that diverging ecological factors are likely to have driven the evolution of these groups: on continents, plants that evolved generalist bird pollination escape from pollinator groups that tend to maintain self‐pollination by installing feeding territories in single flowering trees or shrubs, such as social bees or specialist nectarivorous birds. This pattern is more pronounced in the New compared to the Old World. By contrast, on islands, plants evolved generalist bird pollination as an adaptation to birds as a reliable pollinator group, a pattern previously known from plants pollinated by specialist nectarivorous birds in tropical mountain ranges. Additionally, I discuss the evolutionary origins of bird pollination systems in comparison to systems involving specialist nectarivorous birds and reconstruct the bird pollination system of Hawaii, which may represent an intermediate between a specialist and generalist bird pollination system. I also discuss the interesting case of Australia, where it is difficult to distinguish between specialist and generalist bird pollination systems.     

Impacts of Tree Rows on Grassland Birds and Potential Nest Predators: A Removal Experiment

Globally, grasslands and the wildlife that inhabit them are widely imperiled. Encroachment by shrubs and trees has widely impacted grasslands in the past 150 years. In North America, most grassland birds avoid nesting near woody vegetation. Because woody vegetation fragments grasslands and potential nest predator diversity and abundance is often greater along wooded edge and grassland transitions, we measured the impacts of removing rows of trees and shrubs that intersected grasslands on potential nest predators and the three most abundant grassland bird species (Henslow’s sparrow [Ammodramus henslowii], Eastern meadowlark [Sturnella magna], and bobolink [Dolichonyx oryzivorus]) at sites in Wisconsin, U.S.A. We monitored 3 control and 3 treatment sites, for 1 yr prior to and 3 yr after tree row removal at the treatment sites. Grassland bird densities increased (2–4 times for bobolink and Henslow’s sparrow) and nesting densities increased (all 3 species) in the removal areas compared to control areas. After removals, Henslow’s sparrows nested within ≤50 m of the treatment area, where they did not occur when tree rows were present. Most dramatically, activity by woodland-associated predators nearly ceased (nine-fold decrease for raccoon [Procyon lotor]) at the removals and grassland predators increased (up to 27 times activity for thirteen-lined ground squirrel [Ictidomys tridecemlineatus]). Nest success did not increase, likely reflecting the increase in grassland predators. However, more nests were attempted by all 3 species (175 versus 116) and the number of successful nests for bobolinks and Henslow’s sparrows increased. Because of gains in habitat, increased use by birds, greater production of young, and the effective removal of woodland-associated predators, tree row removal, where appropriate based on the predator community, can be a beneficial management action for conserving grassland birds and improving fragmented and degraded grassland ecosystems.     

Multi-scale habitat models for reintroduced bird populations: a case study of South Island saddlebacks on Motuara Island

Understanding resource selection by animals is important when considering habitat suitability at proposed release sites within threatened species recovery programmes. Multi-scale investigatory approaches are increasingly encouraged, as the patchy distribution of suitable habitats in fragmented landscapes often determines species presence and survival. Habitat models applied to a threatened New Zealand forest passerine, the South Island saddleback (Philesturnus carunculatus carunculatus), reintroduced to Ulva Island (Stewart Island) found that at landscape scale breeding pairs? preferences for sites near the coast were driven by micro-scale vegetation structure. We tested these results by examining models of breeding site selection by a reintroduced saddleback population on Motuara Island (Marlborough Sounds) at two scales: (1) micro-scale, for habitat characteristics that may drive breeding site selection, and (2) landscape scale, for variations in micro-scale habitat characteristics that may influence site colonisation in breeding pairs. Results indicated that birds on Motuara Island responded similarly to those on Ulva Island, i.e. birds primarily settled at the margins of coastal scrub and forest and later cohorts moved into larger stands of coastal forest where they established breeding territories. Plant species composition was also important in providing breeding saddleback pairs with adequate food supply and nesting support. However, Motuara Island birds differed in their partitioning of habitat use: preferred habitats were used for nesting while birds were foraging outside territorial boundaries or in shared sites. These differences may be explained because Motuara has a more homogeneous distribution of microscale habitats throughout the landscape and a highly bird-populated environment. These results show that resource distribution and abundance across the landscape needs to be accounted for in the modelling of density?bird?habitat relationships. In the search for future release sites, food (invertebrates and fruiting tree species) should be abundant close to available nesting sites, or evenly spread and available throughout the landscape.     

南京中山植物园鸟类对香樟 果实（种子）的取食

香樟(Cinnamomum camphora)是亚热带地区广泛分布的常绿阔叶树种,其果实数量多、果期长,可为鸟类提供大量食物资源。2018年11月至2019年2月,借助Safari 10×26变焦双筒望远镜,采用焦点扫描法对南京中山植物园内访问香樟果实(种子)的鸟类行为进行观察,详细记录鸟类的种类、取食基质、取食次数、取食时间、取食数量和取食方式等信息。研究期间有效记录达48d,累计记录到27种鸟类1021次取食香樟果实(种子)行为,存在2种取食基质(地面和树上)和3种取食方式(整吞果实、啄食果肉和取食种子)。T检验显示,不同鸟类对香樟果实(种子)的取食次数存在显著差异(t=3.096,df=26,P 0.01);不同月份间鸟类对香樟香樟果实(种子)的平均访问只数、平均取食次数、平均取食时间和取食数量均存在极显著差异(P0.001)。白头鹎(Pycnonotussinensis)、乌鸫(Turdusmendarinus)和灰喜鹊(Cyanopicacyanus)是访问次数及取食量最多的3种鸟类。单因素方差分析(One-way ANOVA)表明,上述这3种鸟类的取食数量存在极显著差异(F3, 598=25.219,P 0.001)。按照时间统计,11月份访问的鸟类种类和数量最多,1月份鸟类的取食次数、时间和数量最多。鸟类的形态特征(体重、体长和嘴峰长)与取食数量呈显著正相关,其中,体重和体长对取食数量的影响比嘴峰长的影响更显著,但嘴峰长影响鸟类对果实的取食方式。在鸟类常活动和停歇的树木下方地面往往散落着较多表面洁净、无果肉包裹的香樟种子,且园内人工林和自然更新林地可见许多香樟幼苗,表明鸟类对香樟具有潜在传播作用。     

Habitat selection in reintroduced bird populations: a case study of Stewart Island robins and South Island saddlebacks on Ulva Island

An understanding of the mechanisms influencing habitat selection in reintroduced bird populations is fundamental for successful translocation programmes. Plant species composition, abundance, structure and food availability are likely to influence animal movement and habitat choice, but few studies have evaluated their combined effect on habitat selection of translocated birds. Stewart Island robins (Petroica australis rakiura) and South Island saddlebacks (Philesturnus carunculatus carunculatus) are two threatened New?Zealand bird species that have been reintroduced to Ulva Island (Stewart Island). We hypothesised that their initial settlement patterns were driven by habitat quality. We tested this hypothesis by comparing habitat components between occupied and unoccupied habitats as the population grew after initial tanslocation. We also modelled probabilities of site selection as a function of the composition and structure of vegetation, availability of food (invertebrate composition) and nesting resources (cavity type). Founding pairs of both species first established territories in coastal habitat in the western part of the island, which is characterised by structurally complex broadleaved vegetation. Birds also selected sites with a greater abundance and diversity of food resources. Thus in the early stages of population establishment robins and saddlebacks appear to select high quality habitat that offers enhanced cover and foraging opportunities.     

Presence of Breeding Birds Improves Body Condition for a Crocodilian Nest Protector

Ecological associations where one species enhances habitat for another nearby species (facilitations) shape fundamental community dynamics and can promote niche expansion, thereby influencing how and where species persist and coexist. For the many breeding birds facing high nest-predation pressure, enemy-free space can be gained by nesting near more formidable animals for physical protection. While the benefits to protected species seem well documented, very few studies have explored whether and how protector species are affected by nest protection associations. Long-legged wading birds (Pelecaniformes and Ciconiiformes) actively choose nesting sites above resident American alligators (Alligator mississippiensis), apparently to take advantage of the protection from mammalian nest predators that alligator presence offers. Previous research has shown that wading bird nesting colonies could provide substantial food for alligators in the form of dropped chicks. We compared alligator body condition in similar habitat with and without wading bird nesting colonies present. Alligator morphometric body condition indices were significantly higher in colony than in non-colony locations, an effect that was statistically independent of a range of environmental variables. Since colonially nesting birds and crocodilians co-occur in many tropical and subtropical wetlands, our results highlight a potentially widespread keystone process between two ecologically important species-groups. These findings suggest the interaction is highly beneficial for both groups of actors, and illustrate how selective pressures may have acted to form and reinforce a strongly positive ecological interaction.