Primary Excavators Research Articles

Nest site selection of cavity-nesting birds at Jahangirnagar University campus, Bangladesh

Understanding nest site selection by cavity-nesting birds is important for their conservation implications. We examined the preferences and characteristics of nesting trees and cavities used by cavity-nesting birds at Jahangirnagar University (JU) campus from January 2020 to October 2021. A total of 30 tree- cavity nests of 11 species of birds belonging to 4 orders and 7 families were recorded where 36% were primary excavators and 64% were secondary cavity-nesters. Out of 14 species of trees used in cavity-nesting, the most of the nests were built in Mahogany Swietenia mahagoni (n=8) followed by White siris Albizia procera (n=6) and Rain tree Samania saman (n=3). Diameter at breast height (DBH) of the nesting trees varied from 27 cm to 112 cm (52±23.2 cm). The highest mean DBH was recorded in Samania saman (85 cm) followed by Swietenia mahagoni (67 cm). Common Myna showed the widest selection of nesting tree species (n=9) followed by Black-rumped Flameback (n=4) and Lineated Barbet (n=4). Majority of the nesting trees (87%) were found in roadside (within 1-5 m) vegetation while 60% nesting trees located within 30 m from the nearby water bodies. The cavity-nesting species preferred to nest between 2 m to 12 m (5.2±2.6 m) height from the ground level. The entrance width and the depth of tree holes (n=30) used by cavity-nesters varied from 5 cm to 22 cm (7.5±3.5 cm) and 13 cm to 45 cm (23.2±6.5 cm), respectively. Suitable cavities are critical for reproductive success of cavity-nesting birds and our results highlight the conservation value of cavity-bearing large trees to maintain a healthy population of cavity-nesting birds at JU campus. Jahangirnagar University J. Biol. Sci. 12(1 & 2): 1-10, 2023 (June & December)

Unravelling the cavity‐nesting network at large spatial scales: The biogeographic role of woodpeckers as ecosystem engineers

AbstractAimPrimary cavity nesters (e.g. woodpeckers) act as ecosystem engineers by providing tree cavities to several vertebrates that use them as nests or refuges. Although diverse assemblages of primary excavators are assumed to increase the number of tree cavities, environmental factors can limit populations of primary excavators, thus weakening their ecological function. We aim to test the biogeographical‐scale relationships between primary excavators and cavity users by distinguishing the contribution of environmental variables.LocationSouthern South America.Materials and MethodsWe used species distribution models, which combine bioclimatic and remote sensing derived variables, to map the richness of vertebrates composing the cavity‐network of temperate and Mediterranean forests of South America. Based on a resampling procedure for ensuring spatial independence, we fitted structural equation models to estimate relationships between forest characteristics and cavity user vertebrates.ResultsRichness of secondary cavity users (mammals, obligated, habitat generalists and forest specialists) were positively and strongly influenced by the richness of primary excavators. Environmental variables affected differently the richness of primary and secondary cavity users. The richness of primary cavity users responded to tree richness and height while that of habitat specialist secondary users was positively affected by primary productivity and negatively by sclerophyll forests.Main ConclusionsOur results confirm the role of primary excavators as ecosystem engineers but highlight the importance of considering large spatial scales when analysing cavity‐nesting networks. Biogeographical patterns of tree diversity and forest structure can be important drivers of cavity nesting networks that remain hidden when studies are conducted over fine spatial scales.

Cavity-nesting birds in the forest patch around urban areas: A case study in Bogor, Indonesia

Cavity-nesting birds lay eggs and raise chicks within their nest inside the cavities. The existence of cavity-nesting birds in nature has important ecological roles. This study aimed to identify and analyze cavity-nesting bird species in the tropical lowland forest patches, particularly in Bogor, West Java Province, Indonesia. The study was conducted in the forested area within the Dramaga Experimental Forest and the Dramaga Campus of IPB University. The cavity-nesting bird species were observed during September – December 2020 and September – December 2021. Each cavity-nesters observed was classified based on how to make and utilize the nesting site (i.e., primary excavator, facultative excavator, non-excavator) and their nest locations (i.e., nesting in the trees or other locations). We observed 12 cavity-nesters in the study area, consisting of 4 primary excavators, 2 facultative excavators, 3 non-excavators in the trees, and 3 non-excavators in the riverbanks. Cavity-nesting bird richness in the Dramaga Campus (12 species) was higher than in the Dramaga Experimental Forest (9 species). This study revealed that the two study areas still provide suitable habitats for cavity-nesting birds. Therefore, it is essential to maintain the presence of cavity-nesting birds and their habitat by initiating conservation efforts, such as habitat management, strengthening conservation actions and policies, and increasing public awareness.

Using acoustic recording units to investigate the effects of logging of indigenous trees in the Amathole forests, South Africa on Cape Parrot Poicephalus robustus breeding and the presence of three primary cavity-excavating bird species

Summary The Amathole forest complex is the breeding stronghold of the endemic and vulnerable Cape Parrot Poicephalus robustus, and is also one of only two forest complexes in South Africa formally harvested for timber. The aim of this study was to determine if formal harvesting of indigenous trees, primarily the two yellowwood species Afrocarpus falcatus and Podocarpus latifolius, in 9 of 16 Amathole forests has had any effect on the presence of Cape Parrots and three primary nest-excavating species, as well as on parrot breeding. The study used logging data from the past 25 years (1997–2021) as well as data collected by acoustic recording units over two breeding seasons from 2019 to 2021. Cape Parrots were present in 15 of 16 forests, but breeding calls were identified in only seven forests: five in logged and two in unlogged forests. Fourteen of the forests harboured all three primary excavators: Knysna Woodpecker Campethera notata, Olive Woodpecker Dendropicos griseocephalus, and Red-fronted Tinkerbird Pogoniulus pusillus. The last two species were absent from the adjacent Mount Thomas and Kologha forests, respectively, in which parrots were present, but no breeding calls were recorded. Logging of yellowwoods was not found to affect parrot breeding. However, due to the overlap between preferred parrot breeding sites and preferred trees for harvesting, we recommend that harvesting in the five harvested forest blocks where parrot breeding occurs be limited to tree falls, with no standing dead, dying, or damaged trees harvested, to ensure that potential nesting trees are not harvested.

Artificial cavities and substrates for cavity-nesting birds in Neotropical urban environments: A novel resource or the last opportunity to breed?

Urban development reduces the abundance of most natural resources for some birds but also provides new opportunities for others. One group that is more likely affected by urban development is the cavity-nesting species (primary excavators and cavity-adopters), because the main substrates used for nesting, such as dead trees or dirt banks, are frequently removed for security or aesthetic reasons. However, urban development also provides artificial resources that may be used for some cavity-nesting birds such as wooden posts, poles, pipes, holes in house roofs, or building crevices. How cavity-nesting species use these new artificial resources for nesting is poorly understood. Our goal is to provide information on the use of artificial cavities and artificial substrates in urban and human-altered areas for cavity-nesting birds. We opportunistically collected observations of the use of those cavities and substrates from 2003 to 2019 in Costa Rica and found that 20.2% of the 94 Costa Rican bird species that are known to nest in wooden cavities and 9.5% of the 21 Costa Rican bird species that are known to nest in burrows use artificial cavities or artificial substrates for nesting. Although our observations showed that some species are capable of responding to the reduction of natural substrates or cavities in urban habitats through the use of artificial structures, the reproductive success of these birds is still unknown.

Conserving nest trees used by cavity-nesting birds from endangered primary Atlantic forest to open farmland: Increased relevance of excavated cavities in large dead trees on farms

Understanding nest-site selection is critical to conserving tree-cavity-nesting wildlife, but nest-sites may vary across landscapes. We examine variation in the characteristics of trees and cavities used by cavity-nesting birds from globally-threatened primary Atlantic Forest to open farmland with isolated trees. We predicted that nests would occur in the largest trees available, but that secondary cavity nesters (non-excavators) would increase their use of bird-excavated cavities and dead and exotic trees in open farmlands. We used a stratified case-control design and 20 random plots to assess variation in characteristics of trees and cavities (used and available) across gradients of canopy cover and distance to forest edge in subtropical Argentina. For secondary cavity nesters, nest cavities were more likely to occur in larger-diameter trees across all stand conditions, but more likely to occur in dead trees as canopy cover declined (i.e., in open farmland; n = 123 nest trees). For primary excavators, nest cavities were more likely to occur in dead (vs. live) trees, with larger diameter, regardless of stand conditions (n = 54 nest trees). Available cavities declined from 4/ha in primary forest to 0.4/ha in open farmland. Cavities were increasingly of excavated origin in open farmland, including both available cavities and those used by secondary cavity nesters, which indicates that avian excavation may partly compensate for the loss of decay-formed cavities when large trees are cleared. As forest landscapes shift toward a predominance of agroecosystems, dead trees and primary cavity nesters may take on important roles in conserving cavity-nesting communities and their ecosystem functions. However, nest cavities declined in height and depth, and increased in entrance size toward open farmland, raising the possibility that birds increasingly use suboptimal cavities as forest cover declines.

Predictors of habitat use and nesting success for two sympatric species of boreal woodpeckers in an unburned, managed forest landscape

Forest harvesting reduces mean stand age and dead wood amount. Among species dependent upon older forests and dead wood, primary excavators such as woodpeckers play an important ecological role by providing cavities for many other species. Conservation of these species thus requires striking a balance between timber harvesting and dead wood supply, especially under moderate natural disturbance regimes. In this study, we quantified habitat use in two closely-related, sympatric species: Black-backed (Picoides arcticus) and American Three-toed (P. dorsalis) Woodpecker, in the highlands of northern New Brunswick, Canada. Natural fires are rare in this ecoregion and forest harvesting is the main agent of landscape change, along with infrequent outbreaks of spruce budworm (Choristoneura fumiferana). Based on its habitat use patterns in other ecoregions, we hypothesized that Black-backed Woodpecker would select nest sites in mature coniferous forest stands and we expected that it would achieve a higher nest survival rate in forest stands than within, or at the edge of, cutblocks. Owing to sample size limitations for American Three-toed Woodpecker, statistical analyses were restricted to its occurrence patterns. Both species co-occurred, and there was no difference in detectability following conspecific and heterospecific playbacks. Contrary to our prediction, Black-backed Woodpecker selected nest sites with higher proportions of recently cut areas within 50 m than at randomly selected sites. Black-backed Woodpecker selected cutblocks for nesting when suitable snags were available and mature forest stands were present nearby as foraging habitat. For the species to persist in this landscape, the supply of snags must be continuous and forest stands must be sufficiently mature to host saproxylic insects.

Does cavity reuse affect timing of reproduction and fledgling success in the Black Woodpecker?

Nesting in old cavities may be adaptive for birds as it may offer an advantage of earlier laying and higher fitness through more recruiting offspring. Black Woodpeckers frequently use old cavities, which gives the opportunity to test how this behavior affects the timing and the success of reproduction. In this paper, we have tested a prediction that excavating a new cavity causes a delay in breeding, and that it is linked to lower productivity. We found that in the Wielkopolski National Park (western Poland) Black Woodpeckers nested exclusively in European beeches, mainly in living trees, and most frequently in their old cavities. The median relative egg-laying date in old cavities was 5.5 days earlier than in new cavities. We did not find a difference in clutch size between old and new cavities due to its low variation in the population. The proportion of offspring surviving to the end of the nestling period was 0.812 in old cavities and 0.632 in new cavities, although this did not differ significantly. However, survivorship dropped rapidly in the hatching period, especially in new cavities. In Black Woodpecker, the number of fledglings that succeeded was best explained by a model including the age of the cavity and the relative laying date. The estimated parameters of the best ranked model revealed that the number of fledglings is affected by the age of the cavity as it was higher for old cavities than for new cavities. This study shows that nest reuse is adaptive for primary excavators as it offers time and energy savings needed for cavity excavation, and increases productivity, compared to those pairs of birds that are forced to excavate a new cavity. These data are consistent with the hypothesis that cavity excavation is energetically expensive and support the prediction of tradeoffs between nest building and different components of reproduction. Responsible forest management should consider the need to protect living beeches with old cavities, which are frequently used by Black Woodpeckers.

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.

The diversity, distribution and conservation status of the tree‐cavity‐nesting birds of the world

AbstractAimGlobally, many bird species nest in tree cavities that are either excavated or formed through decay or damage processes. We assembled an overview of all tree‐cavity nesters (excavators and non‐excavators) in the world, analysed their geographic distribution and listed the conservation status of all species.LocationThis is a global analysis of species from every continent except for Antarctica where the lack of trees precludes the occurrence of this group.MethodsWe reviewed the online version of the Handbook of the Birds of the World Alive,http://www.hbw.com/, and primary literature for species known to nest in tree cavities, with tree cavities defined as holes that a bird can enter such that it is not visible from the outside. We classified species by nester type (excavator or non‐excavator, and obligate or facultative where possible), conservation threat status and zoogeographic region, and tested for statistical differences in species distributions across realms using chi‐square tests.ResultsAt least 1878 species (18.1% of all bird species in the world) nest in tree cavities, of which we considered 355 to be primary excavators, 126 facultative excavators and 1357 non‐excavators (we were unable to classify nesting type for 40 species). At least 338 species use cavities created by woodpeckers (Picidae), excluding reuse by woodpeckers themselves. About 13% (249 species) of tree‐cavity nesters experience major threats (i.e., status of vulnerable, endangered or critically endangered). The highest richness of tree‐cavity nesters is found in the Neotropical (678 species) and Oriental (453) regions, and the highest proportion of threatened species in Australasia (17%).Main conclusionMaintenance of a continual supply of cavities, a process in which woodpeckers and the processes of decay play critical roles, is a global conservation priority as tree cavities provide important nesting sites for many bird species.

Pre- and post-experimental manipulation assessments confirm the increase in number of birds due to the addition of nest boxes.

Secondary cavity nesting (SCN) birds breed in holes that they do not excavate themselves. This is possible where there are large trees whose size and age permit the digging of holes by primary excavators and only rarely happens in forest plantations, where we expected a deficit of both breeding holes and SCN species. We assessed whether the availability of tree cavities influenced the number of SCNs in two temperate forest types, and evaluated the change in number of SCNs after adding nest boxes. First, we counted all cavities within each of our 25-m radius sampling points in mature and young forest plots during 2009. We then added nest boxes at standardised locations during 2010 and 2011 and conducted fortnightly bird counts (January–October 2009–2011). In 2011 we added two extra plots of each forest type, where we also conducted bird counts. Prior to adding nest boxes, counts revealed more SCNs in mature than in young forest. Following the addition of nest boxes, the number of SCNs increased significantly in the points with nest boxes in both types of forest. Counts in 2011 confirmed the increase in number of birds due to the addition of nest boxes. Given the likely benefits associated with a richer bird community we propose that, as is routinely done in some countries, forest management programs preserve old tree stumps and add nest boxes to forest plantations in order to increase bird numbers and bird community diversity.

Tree cavities and associated vertebrate fauna in a coniferous forest of Dhirkot, Azad Jammu and Kashmir part of Pakistan

Tree cavities are a globally important structural element of forest ecosystems that host numerous cavity-dwelling vertebrates, but they have received little research in Pakistan. We investigated cavity-bearing trees, the attributes of their cavities, and their associated vertebrate fauna in a coniferous forest of Pakistan. We recorded 1140 trees in a 2-km^2 sampled area. We found 211 cavities (64% decay-formed and 36% excavated cavities) in 83 trees (41% live and 59% snags). Of the cavities found, 74% were recorded in trunks and 26% were in branches. Only 28% of the cavities showed signs of recent use by any vertebrate species. We observed 19 vertebrate species using cavities: 2 mammals, 13 birds (including 5 woodpecker species as primary excavators), and 4 reptiles. Height from the ground, entrance diameter, and depth of the cavities used by mammals were greater than those measurements of the cavities occupied by birds and reptiles. Our study shows that tree cavities have a critical role in providing nesting sites to many vertebrate species of Pakistan that require tree cavities in order to breed. We recommend such research be done in other forests of the country to investigate cavity availability and requirements of cavity users. We suggest that certain minimum populations of cavity-bearing trees should be maintained during silviculture practices to support populations of tree-dwelling vertebrates in the coniferous forests of Pakistan.

Woodpecker excavations suitability for and occupancy by cavity users in the boreal mixedwood forest of eastern Canada

In the boreal forest, where tree cavities are mainly excavated by woodpeckers, many holes are incomplete excavations that are not suitable cavities for most other cavity users that form nest webs. We assessed cavity suitability for and use by a community of primary excavators and secondary users in managed and unmanaged landscapes in the boreal mixedwood forest of eastern Canada. We compared ground surveys of tree holes with direct inspections of the inside of potential cavities in remnant habitats surrounded by cutover areas and in large tracts of unharvested forest. We found that ground surveys overestimated suitable cavity abundance: only 38% of the potential cavities detected by ground surveys were suitable for nesting in both managed and unmanaged landscapes. Ground surveys of active nests correctly detected a greater proportion of primary (93%) than secondary cavity nesters (48%). In nest webs such as those of the boreal forest, where cavities are mainly created by woodpeckers, our results indicate that a large proportion of holes detected from the ground are not suitable for cavity nesters, thus overestimating the actual availability of nest sites. Furthermore, when nest cavities are active, ground surveys are satisfactory for detecting primary cavity nesters, but they are inadequate for detecting secondary cavity nesters.

Factors associated with nest- and roost-burrow selection by burrowing owls (Athene cunicularia) on the Canadian prairies

We examined nest- and roost-burrow characteristics from a declining population of burrowing owls (Athene cunicularia (Molina, 1782)) in Saskatchewan. Between 1992 and 2003, 84% of the 584 nests we found were in grassland pastures, even though these pastures constituted only 7% of the potentially available nesting area within our study area. In contrast, less than 3% of nests were in crop fields, despite these fields comprising 90% of the potentially available area. Within grassland pastures, owls selected nest burrows in areas with a higher density of burrows within 75 m (11.1 burrows/ha) compared with non-nest burrows of similar dimensions (5.6 burrows/ha). Richardson's ground squirrels (Spermophilus richardsonii (Sabine, 1822)) and badgers (Taxidea taxus (Schreber, 1777)) are the primary excavators of suitable nesting burrows in prairie Canada. In our study area, burrowing owls chose to nest and roost in badger-sized burrows, selecting those with taller tunnel entrances and soil mounds relative to unused burrows. We suggest that management for burrowing owl nesting habitat in Canada should consider the owls' avoidance of crop fields and their preference for grassland pastures. Managers should also consider the owls' apparent preference for nesting in areas of high burrow densities and their selection of badger-sized burrows for nesting and roosting.

Sapsuckers Usurp a Nuthatch Nest

We document for the first time a Red-naped Sapsucker (Sphyrapicus nuchalis) usurping the nest of a Red-breasted Nuthatch (Sitta canadensis). A nuthatch nest in the incubation phase was usurped by a male Red-naped Sapsucker on 23 May 2003, and a sapsucker nest was initiated in the cavity on 1 June. Red-naped Sapsuckers are primary cavity excavators that normally nest in live and dead quaking aspens (Populus tremuloides) infected with heart rot fungus (Fomes spp.). Red-breasted Nuthatches are weak excavators that most commonly nest in broken-topped conifer snags. Nest usurpation was likely due to a shortage of suitable nest sites in our study plot.

Influence of Gambel Oak on Breeding Birds in Ponderosa Pine Forests of Northern Arizona

Gambel oak (Quercus gambelii) is widely distributed in the Southwestern United States, where it frequently occurs in association with ponderosa pine (Pinus ponderosa). Fire suppression and fuelwood harvest likely have reduced oak abundance within the pine-oak type. Gambel oak occurs in multiple age-related growth forms, from small shrubs to large, old trees, and may provide important foraging and nesting habitat for breeding birds. I compared attributes of breeding bird communities in 16 northern Arizona ponderosa pine stands from 1993-1995, that were structurally similar except for the presence or absence of Gambel oak. Overlap in bird species composition was high; pine and pineoak stands had a mean Jaccard similarity value of 0.67. Five species were unique to pine stands, whereas 10 species were largely restricted to or only found in pine-oak stands. Overall bird diversity was significantly higher in pine-oak stands, which also had more species of Neotropical migrants, ground nesters, primary cavity excavators, and secondary cavity users than did pine stands. Pine and pine-oak stands had similar species evenness and similar rates of annual species turnover. Total bird abundance did not differ between cover types; however, primary cavity excavators were more abundant in pine-oak stands. Because of the apparent positive influence of oak on breeding birds, forest managers are encouraged to use treatments that retain and enhance the various growth forms of Gambel oak found in pine-oak stands.

Forest Issues 2: Conserving Hollow-dependent Fauna in Timber-production Forests (Environmental Heritage Monograph Series No 3)

In the absence of primary excavators, such as woodpeckers, the formation of tree-hollows suitable for occupation by hollow-dependent fauna in Australia may take several hundred years. However, intervals between logging operations in timberproduction forests are typically between 40 and 120 years with the result that hollow-dependent fauna are threatened over large areas of Australia's eucalypt forests. Many species of mammals, birds and invertebrates depend upon tree hollows for dens, roosting or nesting, and habitat. Therefore, there is a strong need to retain and conserve suitable hollowbearing trees within Australian forests in the face of increasingly more intensive and destructive timber harvesting practices.

Predictable effects of agricultural development on the long-term availability of hollows for animals: observations from the Western Australian wheatbelt

Australia lacks primary excavators of eucalypts (excluding wood-boring insects), and animals using hollows in trees for shelter or nesting are dependent on hollows created by termites (for processes of termite invasion of eucalypts, and hollow formation, see Mackowski 1984; Perry et al. 1985). The abundance of hollows of various sizes has been used to explain why Australia has the largest number of obligate hole-nesting birds, especially the parrots (Saunders et al. 1982). The importance of tree hollows to many small mammals is also well documented (e.g., Mackowski 1984; Dickman 1991). Once the hollowed tree has fallen, it represents an important shelter and bolt hole site for small mammals (e.g., Friend 1990; Abensperg-Traun 1991; Dickman 1991). Logs also provide many invertebrates (e.g., cockroaches, beetles, spiders, isopods) and lizards with shelter, breeding and feeding sites. However, the importance of this habitat for these species has not been documented.