Cavity-nesting birds are limited by nesting habitat in Neotropical agricultural landscapes

Most studies comparing biodiversity between natural and human-modified landscapes focus on patterns in species occurrence or abundance, but do not consider how different habitat types meet species' breeding requirements. Organisms that use or nest in tree cavities may be especially threatened by habitat conversion due to the loss of their nesting sites. Although cavity-nesting bird diversity is highest in the tropics, little is known about how tropical birds use cavities, how agriculture affects their reproductive biology, and how effective nest boxes could be as a conservation strategy in tropical agriculture. Here, we explored how habitat conversion from tropical forests to pasture affects the abundance, nesting habitat availability, and nest success of cavity-nesting birds in Northwest Ecuador. We conducted bird surveys and measured natural cavity availability and use in forest and agriculture. We also added artificial nest boxes to forest and agriculture to see whether cavity limitation in agriculture would elicit higher use of artificial nest boxes. We found evidence of cavity limitation in agriculture—there were many more natural cavities in forest than in agriculture, as well as more avian use of nest boxes placed in agriculture as compared to forest. Our results suggest that it is important to retain remnant trees in tropical agriculture to provide critical nesting habitat for birds. In addition, adding nest boxes to tropical agricultural systems could be a good conservation strategy for certain species, including insectivores that could provide pest-control services to farmers. Abstract in Spanish is available with online material.     

PVC nest boxes are less at risk of occupancy by feral honey bees than timber nest boxes and natural hollows

Feral European Honey Bee (Apis mellifera) has been identified as a potential nest competitor for Australian hollow nesting species, but few studies have investigated the impact of feral honey bee competition on Threatened species. Our study used data from Glossy Black‐cockatoo (Calyptorhynchus lathami halmaturinus) nests on Kangaroo Island, monitored and managed over an 11‐year period, and found 12% of nests became occupied by feral honey bees during that period. Our results indicate that feral honey bees were less likely to occupy nest boxes made of PVC (5%) compared with wooden nest boxes (24%) or natural hollows in Eucalyptus trees (14%). The removal of feral honey bee hives from nests is a priority for long‐term conservation of glossy black‐cockatoos on Kangaroo Island. We recommend that PVC nest boxes are chosen for future nesting habitat restoration, due to the more frequent use of wooden nest boxes by feral honey bees.     

Natural cavity restoration as an alternative to nest box supplementation

Nest box supplementation is widely used to increase nest‐site availability for cavity nesting animals but the analysis of its effects on individuals breeding in natural cavities is often neglected. This study offers a novel restoration technique to revert abandonment of natural breeding sites by a secondary cavity avian bird, the European roller (Coracias garrulus), and other ecologically similar species. We found that, after a program of nest box supplementation with ensuing monitoring, rollers gradually abandon nesting in natural and seminatural cavities in favor of nest boxes because the latter are of higher quality. We examine whether reducing the entrance size of natural and seminatural cavities improves their suitability for rollers. A 6‐year program reduced the diameter of the entrance of sandstone cavities and cavities in bridges. This led to a high occupancy (59%) of manipulated nest‐sites. Manipulated sites were most frequently occupied by rollers and little owls (Athene noctua) (31 and 18% of sites, respectively). Manipulation did not affect clutch size or fledgling success. We suggest that nest‐site diversity and nesting in natural cavities should be preserved to reduce nest box dependence. Our study illustrates the value of nest boxes when used alongside restoration of natural breeding sites and provides insights for the management of natural cavities.     

Enriching small trees with artificial nest boxes cannot mimic the value of large trees for hollow‐nesting birds

Large trees support unique habitat structures (e.g. hollows) that form over centuries and cannot be provided by small trees. Large trees are also declining in human‐modified landscapes worldwide. One restoration strategy gaining popularity involves adding nest boxes to smaller trees to replicate natural hollows. However, limited empirical research has tested how hollow‐nesting fauna responds to the presence of nest boxes. We asked: can the addition of nest boxes increase tree visitation by hollow‐nesting birds? We conducted a before‐after control‐impact (BACI) experiment using 144 nest boxes and 96 sample trees comprised of three sizes (small [20–50 cm dbh], medium [51–80 cm], and large [>80 cm]) and located in four landscape contexts (reserves, pasture, urban parklands, and urban built‐up areas). We recorded a significant increase in hollow‐nesting bird abundance and richness at large trees after nest box additions. However, the same response was not observed at medium, small, or control trees. We also recorded nonsignificant increases in hollow‐nesting bird abundance and richness at trees in modified landscapes after nest box additions compared to trees in reserves and control trees. Our results suggest that adding nest boxes to smaller‐sized trees may not attract hollow‐nesting birds. Therefore, nest box management strategies may require re‐evaluation as it is often assumed that hollow supplementation will attract hollow‐using fauna and sufficiently ameliorate the loss of large, hollow‐bearing trees. We advocate that large tree retention remains crucial and should be prioritized. Large trees could be effective target structures for habitat restoration, especially in modified landscapes.     

Adaptive habitat preferences in the Tawny Owl Strix aluco

Capsule: Tawny Owls Strix aluco occupying nest boxes preferred habitats which were positively associated with the probability of nesting success.

Aims: We aimed to determine whether or not: (1) Tawny Owls showed habitat preferences when occupying nest boxes; (2) nesting performance was related to the habitats around occupied nest boxes and (3) habitat availability had changed around available and occupied nest boxes between 1995–2004 and 2005–14.

Methods: Tawny Owls were studied using nest boxes erected in a commercial forest. During nest boxes checks (724 cases), data on occupancy and nesting performance (88 cases) were recorded, and habitat within a 0.4?km radius around nest boxes was analysed.

Results: Tawny Owls had preferences for clearings within forests, mature forests and grasslands but avoided young forests. We found a positive relationship between nesting success and abundance of clearings within the forest, and a negative relationship between nesting success and abundance of young forests. A change in habitat preferences over the two decades was evident, but habitat availabilities remained similar.

Conclusions: Findings indicate adaptive habitat selection in Tawny Owls because preferred habitats were associated with higher fitness and this type of habitat became more frequently selected over time.     

Cliff characteristics,neighbour requirements and breeding success of the colonial Cape Vulture Gyps coprotheres

The breeding success of endangered colonial nesting species is important for their conservation. Many species of Gyps vultures form large breeding colonies that are the foci of conservation efforts. The Cape Vulture is a globally threatened species that is endemic to southern Africa and has seen a major reduction in its population size (≥ 50% over 48 years). There is evidence that breeding colonies are prone to desertion as a result of human disturbance. Factors that influence the occupancy and breeding success of individual nest‐sites is not fully understood for any African vulture species. We investigated cliff characteristics and neighbour requirements of the Msikaba Cape Vulture colony, a major breeding colony in the southern node of the population in the Eastern Cape, South Africa, together with their nest‐site occupation and breeding success over 13 years. In total, 1767 breeding attempts were recorded. Nest‐sites that had a higher elevation, smaller ledge depth, greater total productivity and were surrounded by conspecifics were more likely to be occupied, although the amount of overhang above the nest was not an important predictor of occupancy. In accordance with occupation, nest‐sites with a smaller ledge depth had higher breeding success; however, nests with a greater overhang were also more successful and height of the nest‐site was not an important predictor of breeding success. The breeding success of a nest‐site in a given year was positively influenced by the number of direct nest neighbours, and nests in the middle of high‐density areas had greater breeding success. This suggests that maintaining a high nest density may be an important consideration if declines of reproducing adults continue. Breeding success declined over the study period, highlighting the effects of a temporal variation or observer bias. Our results identified optimal nest‐site locations (ledge depths of 1 m, at a height of 180 m) and their effects on breeding success. This information can be used for planning reintroduction efforts of the endangered Cape Vulture and for their ongoing conservation.     

An assessment of tree availability as a possible cause of population declines in scavenging raptors

Lack of suitable nesting trees is an increasingly common issue for avian conservation given rampant habitat and tree destruction around the world. In the African savannah, habitat loss and particularly tree damage caused by elephants have been suggested as possible factors in the decline of large bird species. Given the recent declines of vultures and other scavenging raptors, it is critical to understand if nest availability is a limiting factor for these threatened populations. Loss of woodland, partially due to elephant populations, has been reported for the Mara‐Serengeti ecosystem. Data on characteristics of trees used for nesting were collected for white‐backed, lappet‐faced, white‐headed vulture, and tawny eagle nests in Masai Mara National Reserve, Kenya. Nest tree characteristics were compared with the distribution of a random subsample of trees to assess nest preferences and determine suitability of available trees. Nearest neighbor distances were estimated as well as availability of preferred nesting trees to determine if tree availability is a limiting factor for tree‐nesting vultures. Tree availability was found to greatly exceed nesting needs for African vultures and tawny eagles. We thus conclude that on a landscape scale, tree availability is not a limiting factor for any of the species considered here (white‐backed, lappet‐faced, white‐headed vultures and tawny eagles).     

Breeding biology of the Cape Parrot,Poicephalus robustus

Breeding biology and nesting requirements of Cape Parrots in their natural habitat and in captivity were investigated. Few nests were found, suggesting that nest-sites are limiting, and that the parrots have specific nesting requirements. Nests were secondary cavities in dead Podocarpus spp. (branches), high up in forest canopy trees. Breeding usually occurred from August to February, but was observed in other months, particularly in captive birds. Clutch size varied from 2–5, incubation was by the female and lasted 28–30 days, with fledging a further 55–79 days. In captive birds the ovaries are mature at 2.5 years, but age at first breeding is usually at 4–6 years.     

Nesting Habitat of the Lilac-crowned Parrot in a Modified Landscape in Mexico

Parrot populations are being increasingly pressured to occupy modified or fragmented landscapes, yet little is known of the habitat requirements of most species, particularly with regard to the effects on breeding habitat. We evaluated nesting habitat of the lilac-crowned parrot Amazona finschi in the modified landscape of coastal Michoacan in Mexico. We located 90 parrot nests in 12 tree species in Michoacan, with lilac-crowned parrots presenting a narrow niche-breadth of tree species used for nesting. Considering an additional 82 nest trees recorded for lilac-crowned parrots in Jalisco, we determined a 51 percent similarity in cavity resource use by parrots in the two dry forest regions. Overall, the predominant nest tree species with 76 percent of nests were Astronium graveolens , Piranhea mexicana , Brosimum alicastrum , and Tabebuia spp., all characteristic of semi-deciduous forest. Only 8 percent of nests occurred in trees characteristic of deciduous forest. Parrots utilized large trees with canopy level cavities as nest sites, and preferred conserved semi-deciduous forest for nesting, with fewer nests than expected in deciduous forest and transformed agricultural land. Nest areas in semi-deciduous forest occurred on significantly steeper terrain, as remnant semi-deciduous forest is restricted to steep ridges and canyons. Those parrot nests in modified habitats and forest patches were located near to continuous forest, with nest trees in open agricultural land being significantly closer to continuous forest than nests in disturbed forest patches. These results demonstrate the importance of conserved semi-deciduous forest as breeding habitat for the threatened, endemic lilac-crowned parrot, making wild populations of the species vulnerable to the high rate of transformation and fragmentation of tropical dry forest.     

Ousting of the Common Redstart (Aves: Turdidae: Phoenicurus phoenicurus) from its nests by the bumblebee Bombus niveatus vorticosus (Hymenoptera: Apidae)

During a study of bird nesting in SW. Anatolia, 125 man-made nest boxes have been installed, 3 m high, in the trees. These nest boxes have been occupied by several bird species (Phoenicurus phoenicurus, Parus major, Parus ater, Sitta krueperi, Certhia brachydactyla). Of the 48 Redstart nests, 19 (40 %) had been successfully invaded by the bumblebee Bombus niveatus vorticosus. This invasion occurred at different times in the nest building cycle: - during the building of the nest, - during the incubation or - after the hatching of the young. Once installed in the nest of the Redstart, the bumblebee does not directly attack the bird, but disturbs it by continuously rearranging the nesting material and by covering the bird’s brood. Eventually, the bird deserts its nest and brood. The Redstart does not display any agonistic behaviour towards the bumblebee. Nests of other bird species are never invaded.     

Effects of habitat simplification on assemblages of cavity nesting bees and wasps in a semiarid neotropical conservation area

Habitat complexity is directly correlated to insect diversity in most natural environments. Structural complexity reflects an increase in vertical stratification and plant diversity and often leads to a greater availability of floral resources and nesting sites. Efficient conservation strategies require understanding of how changes in habitat structure affect insects that provide essential ecosystem services. We analyzed how the diversity and species composition of bees and wasps that nest in pre-existing cavities is affected by habitat complexity. Our study was developed in the semiarid region of northeastern Brazil, in the Ubajara National Park and surrounding area. Four types of habitats within two physiognomies were sampled for two consecutive years. We used 120 trap-nest (9000 cavities) distributed in 40 sample points. Overall, 657 cavities were occupied by 11 species of bees, nine of wasps, and six of cleptoparasitic/parasitoids. Bees and wasp diversity increases with habitat complexity. While species richness was higher in more complex physiognomies, abundance was higher in disturbed areas. Species composition also varied with habitat structure. Habitat simplification has adverse effects on the diversity and composition of assemblages. These effects are stronger in more complex habitats indicating that conservation of humid habitats within semiarid areas is essential to maintain bee and wasp regional diversity.     

A push‐pull integrated pest management scheme for preventing use of parrot nest boxes by invasive Africanized honey bees

Africanized honey bees (Apis mellifera scutellata) compete with endangered parrots for nest boxes and can hamper conservation efforts. We tested an integrated pest management push‐pull protocol in the Atlantic Forest in São Paulo, Brazil, in an effort to prevent bee swarms from colonizing nest boxes (N = 30 in the forest plus five in aviaries) meant for use by Vinaceous‐breasted Amazons (Amazona vinacea). Fifteen parrot nest boxes were treated with a permethrin insecticide to “push” scout bees away and each parrot box was paired with a bee trap box containing a pheromone lure to “pull” bees. Over a 1‐yr period (March 2013 to March 2014), 29 insect colonies moved into 18 of the 35 trap boxes. Nine Africanized honey bee, three native Jatai bee (Tetragonisca sp.), and 17 wasp colonies occupied trap boxes. Only one experimental push‐pull pair untreated parrot box was invaded by bees and no parrot boxes in aviaries were colonized. Four of the parrot nest boxes were occupied by birds during our study. Although none were used by Vinaceous‐breasted Amazons, Southern House Wrens (Troglodytes musculus), Green‐winged Saltators (Saltator similis), and Plain Parakeets (Brotogeris tirica) nested in the boxes and all nests were successful. Although long‐term studies are needed before drawing conclusions about the effectiveness of trap boxes, our results suggest that a push‐pull protocol may prove useful for reducing the use of nest boxes meant for parrots and other cavity‐nesting birds by Africanized honey bees and other insects.     

The value of 'bat boxes' for attracting hollow-dependent fauna to farm forestry plantations in southeast Queensland

Summary Small artificial nest/roost boxes, originally designed for microbats, were deployed in three farm forest plantations and at one native forest site in southeast Queensland in order to assess their use by vertebrates and their contribution toward enhancing biodiversity in plantation forests through the provision of habitat. Two sites were located in a relatively 'intact' forest landscape (SF 351 and Strano) and two sites in a more 'fragmented' or 'variegated' landscape (Askham and Thomas). Twenty-four boxes were placed at each site over an area covering approximately 1.2–1.8 ha. Each site was checked from five (SF 351) to nine (Askham) times between April 1996 and November 2000. The artificial nest/roost boxes were attractive to a range of small fauna that included Feathertail Gliders ( Acrobates pygmaeus ), Sugar Gliders ( Petaurus breviceps ), Squirrel Gliders ( Petaurus norfolcensis ) and the Yellow-footed Marsupial Mouse ( Antechinus flavipes ), all of which constructed nests inside boxes. Gould's Long-eared Bats ( Nyctophilus gouldi ) used boxes primarily as roosts and maternity sites. In general, fewer animals were recorded in boxes at the two sites located within a relatively 'intact' landscape, while the highest numbers of animals were recorded in boxes in two farm forest plantations within 'variegated' landscapes. The availability of alternative natural hollows and landscape factors appear to be important determinants of the extent to which boxes are occupied. The present study indicates that the biodiversity of farm forests can be enhanced through simple habitat manipulation utilizing artificial roosting or nesting boxes.
Key words Antechinus, biodiversity, farm forestry, glider, marsupial, microbat, nest box, roost.     

Are house sparrow populations limited by the lack of cavities in urbanized landscapes? An experimental test

Current urban policies are associated with deep changes in urban structures, which may impoverish urban biodiversity. A major concern is the disappearance of nesting sites for wild vertebrate species living in urban areas. New urban structures without any cracks or cavities may especially preclude cavity nesters from breeding in cities and they may cause population declines. In that context, we experimentally investigated this question in an urban exploiter bird species (the house sparrow Passer domesticus), which is dramatically declining in most European cities. To test if the lack of cavities is limiting house sparrow populations in urban areas, we equipped 11 sites along an urbanization gradient with nest boxes and we then evaluated the rate of occupancy of these nest‐boxes. This urbanization gradient was characterized by very rural places (isolated farms) and moderately urbanized areas (town of medium size, i.e. 60 000 inhabitants). Surprisingly, rural nest boxes were more occupied than urban ones, suggesting that cavity availability is probably more constraining in rural areas relative to urban ones. Therefore, our study suggests that urban house sparrow populations are probably not constrained by a lack of nesting sites in medium size cities with urban designs similar to our city of interest (Niort, western France). This hypothesis definitely needs now to be tested in further urban landscapes (e.g. large cities and urban landscapes with other architecture and management policies).     

Specific nest box designs can improve habitat restoration for cavity‐dependent arboreal mammals

Tree‐cavity‐dependent wildlife faces future shortages of cavities due to a decline in the abundance of large, old trees in many parts of the world. Nest boxes are proposed as a tool to restore habitat value but evidence of their effectiveness for arboreal mammals remains equivocal. This may arise from a poor understanding of design preferences. We conducted investigations in two landscapes in eastern Australia to determine whether species show a preference for specific designs. We observed a preference by some mammal species for particular designs (33–78% occupied/used), suggesting that design refinement can improve the frequency with which nest boxes are used. Although feral species may out‐compete target species for nest boxes, we did not observe this. We recorded feral honeybees (Apis mellifera) in 6–9% of nest boxes but they did not remain, and many occupied boxes were later used by mammals. The introduced common myna bird (Acridotheres tristis) was prevalent in one landscape, but competition for nest boxes was localized. For nest boxes to be an effective habitat restoration tool, they must be able to be occupied over long periods of time. We investigated this for the squirrel glider (Petaurus norfolcensis), an arboreal marsupial threatened through part of its geographic range. Squirrel gliders occupied and bred within nest boxes (100% used) at two locations continuously over a 10‐year period with minimal nest box maintenance. Individuals occupied boxes for up to 7 years. This confirms that targeted nest box programs can be an effective restoration tool for cavity‐dependent arboreal mammals.     

Competition, predation and nest niche shifts among tropical cavity nesters: ecological evidence

I studied cavity-nesting birds in an undisturbed site in lowland Peru to determine the relative roles of competition and predation in favoring termitarium nesting over tree cavity nesting. Occupancy rates of both nest boxes and natural tree cavities near 2% suggest that competition for tree cavities is not favoring the use of termitaria. Artificial nests and bird nests in termitaria suffer significantly lower predation rates than similar nests in old tree cavities showing that predation is favoring the use of termitaria over old tree cavities. Bird nests in newly excavated tree cavities also show lower predation rates than older cavities suggesting that cavity age is more important than substrate (tree or termitaria) per se . This study suggests that nest predation has a greater influence than nest competition on life history evolution for many cavity-nesting birds.     

‘Bee Hotels’ as Tools for Native Pollinator Conservation: A Premature Verdict?

Society is increasingly concerned with declining wild bee populations. Although most bees nest in the ground, considerable effort has centered on installing ‘bee hotels’—also known as nest boxes or trap nests—which artificially aggregate nest sites of above ground nesting bees. Campaigns to ‘save the bees’ often promote these devices despite the absence of data indicating they have a positive effect. From a survey of almost 600 bee hotels set up over a period of three years in Toronto, Canada, introduced bees nested at 32.9% of sites and represented 24.6% of more than 27,000 total bees and wasps recorded (47.1% of all bees recorded). Native bees were parasitized more than introduced bees and females of introduced bee species provisioned nests with significantly more female larva each year. Native wasps were significantly more abundant than both native and introduced bees and occupied almost 3/4 of all bee hotels each year; further, introduced wasps were the only group to significantly increase in relative abundance year over year. More research is needed to elucidate the potential pitfalls and benefits of using bee hotels in the conservation and population dynamics of wild native bees.     

Factors influencing the abundance of parrots and hornbills in pristine and disturbed forests on New Britain, PNG

We estimated densities of parrot and hornbill species in primary and selectively logged forest and forest gardens at two lowland sites on New Britain, PNG. We related differences in abundance to food and nest-site availability in the different habitats and determined whether nest-site availability might limit local breeding populations. Blue-eyed Cockatoo Cacatua ophthalmica and Blyth's Hornbill Rhyticeros plicatus were usually rarer in forest gardens than in primary forest, but both fared well in logged forest. Eclectus Parrot Eclectus roratus was more common in all human-altered forests than in primary forest, and Eastern Black-capped Lory Lorius hypoinochrous was reasonably common throughout but extremely abundant in forest gardens at one site. Parrots and hornbills were recorded eating fruits of 15 tree species and flowers of nine species. Densities of these fruiting and flowering trees were highest in logged forest and forest gardens, respectively, indicating the importance of these anthropogenic habitats as feeding grounds for the assemblage. Active nest cavities were found in large individuals of 12 tree species. Densities of potential nest cavities were highest in primary forest and lowest in forest gardens. At both sites, estimates of potential nest-site density were significantly lower than estimates of the density of pairs of all species of parrots and hornbills: there may be 10–20 parrot/hornbill individuals per nest-hole. Continuing forest alteration, whilst further reducing nest-site availability, may allow large populations of parrots and hornbills to persist due to increased availability of food in some anthropogenic habitats. However, current abundance of such bird species may be a poor correlate of future extinction risk as long-lived taxa may remain common for some period even when annual recruitment has declined to critically low levels.     

Nest niche dynamics of Meyer's Parrot Poicephalus meyeri in the Okavango Delta,Botswana

Meyer's Parrot Poicephalus meyeri is the only cavity-nesting bird species that breeds during winter in the Okavango Delta. This is facilitated by exclusive access to arthropod larvae incubating inside and feeding on fruits and pods in their diet. To minimise predation risk and overcome low overnight temperatures they have specialised, non-random nest cavity preferences that restrict them to 4.5% of the available nest cavities in the study area. Here we evaluated the nest niche of Meyer's Parrot by studying the nest tree preferences and ecological context of all nest cavities to determine factors that may restrict breeding success in disturbed or altered habitat. Although specific nest tree preferences were significantly different between host tree species, Meyer's Parrot preferred trees greater than 14 m in height that were in relatively poor condition (e.g. portion of the canopy dead). A comparison of nest tree characteristics (n = 75) and the availability of these tree specifications in a representative sample of the different habitat types (n = 1 129) within the sample area indicated that Meyer's Parrot are dependent on riverine forest, Acacia-Combretum marginal woodland and dry mopane woodland for nesting opportunities. Disturbance to hardwood trees by African elephants Loxodonta africana and fungal attack (e.g. Coriolus versicolor) are likely important dynamics in supporting healthy Meyer's Parrot populations and cavity-nesting bird communities.     

Nesting success of wood‐cavity‐nesting bees declines with increasing time since wildfire

Bees require distinct foraging and nesting resources to occur in close proximity. However, spatial and temporal patterns in the availability and quantity of these resources can be affected by disturbances like wildfire. The potential for spatial or temporal separation of foraging and nesting resources is of particular concern for solitary wood‐cavity‐nesting bees as they are central‐place, short‐distance foragers once they have established their nest. Often the importance of nesting resources for bees have been tested by sampling foraging bees as a proxy, and nesting bees have rarely been studied in a community context, particularly postdisturbance. We tested how wood‐cavity‐nesting bee species richness, nesting success, and nesting and floral resources varied across gradients of wildfire severity and time‐since‐burn. We sampled nesting bees via nesting boxes within four wildfires in southwest Montana, USA, using a space‐for‐time substitution chronosequence approach spanning 3–25 years postburn and including an unburned control. We found that bee nesting success and species richness declined with increasing time postburn, with a complete lack of successful bee nesting in unburned areas. Nesting and floral resources were highly variable across both burn severity and time‐since‐burn, yet generally did not have strong effects on nesting success. Our results together suggest that burned areas may provide important habitat for wood‐cavity‐nesting bees in this system. Given ongoing fire regime shifts as well as other threats facing wild bee communities, this work helps provide essential information necessary for the management and conservation of wood‐cavity‐nesting bees.