Nest Cavities Research Articles

Bee discovery suggests the importance of urban gardens in a changing world

AbstractThe diversity and distribution of wild bees are dramatically changing due to habitat fragmentation, agricultural intensification and climate change. In cities, urban gardens are proposed ‘island’ habitats for bees offering floral and nesting resources. Yet, it is largely unclear how gardens play a role in changes in species diversity and distribution. This paper reports on the discovery of a bee species to our knowledge previously undocumented in the region of Berlin, Germany. We discovered Lasioglossum limbellum in a community garden created on concrete slabs of annual and perennial vegetation. As a cavity nester in soft rock cliffs—a natural habitat functionally not existent in urban areas—the life history of this species makes this discovery particularly interesting, and an opportunity to explore the role of urban gardens in biodiversity change. This report aims to spur future research, reporting and discussion on the changes in diversity and distribution of wild bees specifically in urban areas.

Breeding mason bees for the pollination of fruit orchards in Central Europe

Solitary bees pollinate wild plants and crops. In the temperate zone, they mainly pollinate fruit trees. Most species nest in the soil, but mason bees nest in wooden cavities above ground. Their presence in orchards can be augmented by provision of artificial nesting sites. Two species of mason bees frequently use these artificial nesting opportunities in Central Europe. The red mason bee (Osmia bicornis) is the most common species in this region, which preferentially collects pollen from oak trees. The European orchard bee (Osmia cornuta) prefers pollen from fruit trees, but it is more thermophilic. Its spread to higher altitudes can be expected in response to climate change. A breeding technology based on detachable wooden nests is summarized in this paper based on a literature review and experimental experience in fruit orchards in Czechia.

Cavities excavated by woodpeckers limit populations of other cavity-nesting birds.

Research Highlight: Trzcinski, M., Cockle, K., Norris, A., Edworthy, A., Wiebe, K., & Martin, K. (2022). Woodpeckers maintain the diversity of cavity-nesting vertebrates in a temperate forest. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13626. Whether populations of hole-nesting birds are limited by the availability of cavities is a long-standing, fundamental question in avian community ecology. The structure of cavity-nesting communities, known as nest webs, includes links between tree species that provide natural holes and bird species that nest in those holes (secondary cavity nesters, SCNs), tree species that provide substrates for cavity excavation and bird species such as woodpeckers that create cavities using those substrates (primary cavity nesters, PCNs), and between PCNs and SCNs. Trzcinski et al. (2022) focus on the latter links and provide the most compelling empirical evidence to date that cavities created by PCNs specifically, as opposed to natural holes or holes generally, limit populations of SCNs. Using data from a long-term study, the authors employ three analyses to separate effects of availability of cavities from environmental factors such as food, habitat features and host tree abundance, while controlling for annual variation and autocorrelation within sites, to isolate the relationship between excavated cavities and SCN numbers. They show that nest density of SCNs is positively related to PCN nest density the previous year, an indicator of availability of excavated cavities, and that the effect of PCNs is stronger when other variables are accounted for. North American coniferous forests such as that studied by Trzcinski et al. (2022) are exceptional in that excavated cavities comprise the vast majority of nesting holes. Whether their findings apply to other systems in which PCNs are a major source of cavities, or to particular PCN-SCN relationships in systems in which excavated cavities account for a much lower proportion of nesting holes remains to be investigated.

Nest preference and ecology of cavity-nesting bees (Hymenoptera: Apoidea) in Punjab, Pakistan

• Artificial nest boxes, an effective tool for nesting and conservation of bees. • Colonization of bees helpful in studying ecology and nesting biology. • The efficacy of nest boxes depends on nesting materials and dimensions of cavities. • Bamboo and drilled wooden log is the most preferred nesting material. • Six bee species along with one parasitic bee did nesting in our nesting materials. Among bees, 85 % are solitary species, most of them are ground-nester and some are cavity-nesting and construct their nests in pre-existing cavities. This work was conducted to evaluate the substrate preference and nest architecture (acceptance, occupation percentage, seasonality and parasitism) of cavity-nesting bees in different substrates. Trap nests offered comprised five different materials (drilled cavities in wood, bamboo, cardboard tubes, plastic soda straws, and mud blocks). These were installed in four districts for two years. The nesting cavities of five different diameters (6, 8, 10, 12 and 14 mm) were provided in each nesting material with an average length of 180 ± 9.92 mm. In all the materials, 5400 nesting cavities were offered, out of which 628 were colonized by bees from two families (Megachilidae and Apidae) and six species ( Megachile cephalotes, M. lanata, M. bicolor, Xylocopa basalis, X. fenestrata and Ceratina smaragdula ), including one parasitic bee ( Euaspis carbonaria ). The bee species differed significantly in occupying five nesting materials. The most preferred diameters were 8 mm and 10 mm, with 52.20% and 29.45% of colonization, respectively. Nesting was done throughout the year except in winter. This study will serve as a baseline for future studies and conservation programs of cavity-nesting bees in Pakistan.

Collapse of Breeding Success in Desert-Dwelling Hornbills Evident Within a Single Decade

Rapid anthropogenic climate change potentially severely reduces avian breeding success. While the consequences of high temperatures and drought are reasonably well-studied within single breeding seasons, their impacts over decadal time scales are less clear. We assessed the effects of air temperature (Tair) and drought on the breeding output of southern yellow-billed hornbills (Tockus leucomelas; hornbills) in the Kalahari Desert over a decade (2008–2019). We aimed to document trends in breeding performance in an arid-zone bird during a time of rapid global warming and identify potential drivers of variation in breeding performance. The breeding output of our study population collapsed during the monitoring period. Comparing the first three seasons (2008–2011) of monitoring to the last three seasons (2016–2019), the mean percentage of nest boxes that were occupied declined from 52% to 12%, nest success from 58% to 17%, and mean fledglings produced per breeding attempt from 1.1 to 0.4. Breeding output was negatively correlated with increasing days on which Tmax (mean maximum daily Tair) exceeded the threshold Tair at which male hornbills show a 50% likelihood of engaging in heat dissipation behavior [i.e., panting (Tthresh; Tair = 34.5°C)] and the occurrence of drought within the breeding season, as well as later dates for entry into the nest cavity (i.e., nest initiation) and fewer days post-hatch, spent incarcerated in the nest by the female parent. The apparent effects of high Tair were present even in non-drought years; of the 115 breeding attempts that were recorded, all 18 attempts that had ≥ 72% days during the attempt on which Tmax > Tthresh failed (equivalent to Tmax during the attempt ≥ 35.7°C). This suggests that global warming was likely the primary driver of the recent, rapid breeding success collapse. Based on current warming trends, the Tmax threshold of 35.7°C, above which no successful breeding attempts were recorded, will be exceeded during the entire hornbill breeding season by approximately 2027 at our study site. Therefore, our findings support the prediction that climate change may drive rapid declines and cause local extinctions despite the absence of direct lethal effects of extreme heat events.

Assessing behavioral sex differences to chemical cues of predation risk while provisioning nestlings in a hole-nesting bird.

Birds can assess nest predation risk and adjust their parental activity accordingly. Risk taking behavior should be related to investment in reproduction as well as to confidence in parenthood that often differ between sexes. In those cases, sexual differences in risk taking behavior may be expected. For example, in blue tits, females invest more time and energy than males in nest-building, egg laying and incubation. Furthermore, confidence in parenthood is supposed to be higher for females, as extrapair paternity is common in this species. Therefore, the reproductive value of nestlings may be higher for females than for males and the former may assume greater risks to ensure nestling growth and maximize their reproductive success. We examined potential sexual differences in the risk assumed by parents in relation to perceived risk of predation inside the nest cavity, where predation risk perception may be higher. We increased perceived predation risk by adding predator chemical cues inside blue tit (Cyanistes caeruleus) nest-boxes, and we tested whether female and male parents differed in the risk assumed when taking care of nestlings. Females and males did not differ in the risk assumed in response to perceived predation risk. However, females reduced time devoted to nest sanitation activities when predator chemical cues were detected inside the nest-box, likely as an anti-predatory strategy to minimize their own risk of predation. Therefore, these results add to the evidence that birds can detect chemical cues of predators inside the nest cavity and suggest that the behavioral response to an increase in risk of predation perceived through olfactory cues is not sex-dependent in blue tit.

Analysis of nest re-use by secondary cavity nesters.

Secondary cavity nesters are birds who are not able to excavate their own cavity for nesting but nest in premade cavities including human made nest boxes. Sometimes these birds will reuse nests left over from other birds in the same year, but this comes with some risks. Old nests can contain ectoparasites that negatively impact reproductive success, and these nests may be more susceptible to predators. To understand the effects of nest re-use on reproductive success, we used citizen science data from Project NestWatch. We analyzed 697 pairs of repeated nest attempts recorded from West Virginia, Pennsylvania, Maryland, and Virginia in 2021. We used contingency tables to determine if there was an association between the success (at least one of the target offspring fledged) or failure (none of the target offspring fledged) of successive nest attempts. Two different contingency tables of this type were made: one for nest re-use by the same species of bird, and one for nest re-used by birds of a different species. The results suggest that nest re-use by birds of the same species were more likely to be successful, while nest re-use by birds of different species had no clear association between success and failure. This difference between inter- and intraspecies nest re-use may be due to the smaller sample size concerning different species.

Life-history traits predict responses of wild bees to climate variation.

Life-history traits, which are physical traits or behaviours that affect growth, survivorship and reproduction, could play an important role in how well organisms respond to environmental change. By looking for trait-based responses within groups, we can gain a mechanistic understanding of why environmental change might favour or penalize certain species over others. We monitored the abundance of at least 154 bee species for 8 consecutive years in a subalpine region of the Rocky Mountains to ask whether bees respond differently to changes in abiotic conditions based on their life-history traits. We found that comb-building cavity nesters and larger bodied bees declined in relative abundance with increasing temperatures, while smaller, soil-nesting bees increased. Further, bees with narrower diet breadths increased in relative abundance with decreased rainfall. Finally, reduced snowpack was associated with reduced relative abundance of bees that overwintered as prepupae whereas bees that overwintered as adults increased in relative abundance, suggesting that overwintering conditions might affect body size, lipid content and overwintering survival. Taken together, our results show how climate change may reshape bee pollinator communities, with bees with certain traits increasing in abundance and others declining, potentially leading to novel plant-pollinator interactions and changes in plant reproduction.

Broadleaf retention benefits to bird diversity in mid-rotation conifer production stands

Retention forestry involves saving important forest structures for flora and fauna during the final felling of a stand, including dead wood and variable amounts of living trees, i.e. green tree retention (GTR). Here we evaluate the long-term effects on avian diversity from GTR by surveying forest birds in 32 mid-rotation stands in southern Sweden, in which broadleaf GTR was present or absent. Complementing the many studies that have assessed GTR in clear-cuts, our results indicated that bird assemblages can also benefit from broadleaf GTR several decades after final felling in conifer dominated production stands. The GTR stands harboured a higher bird abundance and species richness than the control stands without GTR, and also appears to have benefited several important guilds, such as broadleaf-associated birds and cavity nesters. However, variation in the number trees retained, the species composition of retained trees, and their environmental context within the stand (e.g. density and proximity of surrounding production trees), limited our capacity to detect threshold requirements for GTR. In summary, our study provides a “glimpse into the future” as mid-rotation production stands with such old and large retained trees are unusual in today's landscape, but are expected to become more common in the decades to come, in Sweden and many other nations. Our study thereby provides provisional support for the continued and future use of this practice, and indicates that the biodiversity contribution of retention trees continues to occur several decades into the stand’s rotation.

Hatchling vocalizations and beneficial social interactions in subterranean nests of a widespread reptile

Signals are fundamental to communication, and theory suggests signals may evolve to coordinate cooperation on complex tasks. Several recent studies have demonstrated that hatchling turtles vocalize within the subterranean nest cavity, and these vocalizations are hypothesized to promote hatching synchrony and coordinate emergence from subterranean nests (social facilitation hypothesis). Here we test assumptions and predictions of the social facilitation hypothesis in the snapping turtle, Chelydra serpentina, a species with a broad distribution. First, we demonstrate that C. serpentina hatchlings have a vocal repertoire: we identified six types of vocalizations in a simulated nest environment, with one vocalization type occurring before egg pipping and all six types occurring in the 24 h following egg pipping and hatching. We found that Simpson's diversity was greater for vocalizations during the hatching stage compared to the emergence stage and was minimal during the prepipping stage. Second, we manipulated egg burial depth (shallow or deep) and sociality (presence or absence of siblings) in a 2 × 2 factorial design. We found that eggs in the social treatment hatched earlier and lost less mass while emerging from the nest, underlining a likely energetic benefit to hatchlings emerging with siblings versus emerging alone. Third, we tested a subhypothesis of the social facilitation hypothesis, which is that embryos cue hatching in response to hatchling vocalizations. However, vocalization playback to late-stage (prepipping) embryos did not alter pipping date relative to controls. Our combined results provide some support for the social facilitation hypothesis: there are likely energetic benefits to group emergence, embryos in a group hatch earlier, but earlier group hatching is not cued by vocalizations per se. Our study contributes to a growing literature on the adaptive significance of sociality in reptiles and helps disentangle the proximate drivers of vocalizations in hatchling turtles.

Natal philopatry is associated with smaller nest size in a cavity-nesting bird with consequences for nest box temperature

Considerable within-population variation in nest size exists among cavity nesters. We sought to explain this by studying a multi-brooded population of Eastern Bluebirds (Sialia sialis) breeding in nest boxes. We examined seasonal change in nest weights and compared the weights of nests built by immigrant and resident females. We further investigated whether nest weight correlated with maternal condition or breeding success. Nest weight measured after broods fledged was correlated with nest height at the start of incubation. Breeders spent fewer days building and built successively smaller, lighter nests in later nesting attempts. Female bluebirds performed the majority of nest construction. Nests built by immigrant females were significantly larger on average than those built by female recruits hatched on site, and the seasonal decline in nest weight was more pronounced for natally philopatric females. For the first time, we present evidence that the weights of philopatric females’ first nests were significantly positively correlated with the weights of the nests they were raised in, suggesting an effect of natal memory. Contrary to expectation, neither maternal condition nor reproductive success (clutch size, hatching success, brood size, and fledging success) was related to nest weight. To investigate whether smaller nests provided a thermal advantage in summer nest attempts when afternoon box temperatures can exceed 41°C, we measured the temperature within nest boxes using programmable data loggers. Mean daily maximum box temperatures during incubation were significantly positively related to nest weight and significantly negatively related to the volume of free space above the nest. Increased air circulation above the nest likely contributed to cooling the boxes when ambient temperatures were high. Reducing nest size was therefore advantageous, especially in later nesting attempts when ambient temperatures were warmest. Seasonal decline in nest weights and differences between immigrant and natally philopatric females merits further investigation.

Land Cover Analysis and Habitat Identification of Tanimbar Corella (Cacatua Goffiniana) on Tanimbar Islands, Maluku

The Tanimbar Corella (Cacatua goffiniana) is a protected bird species endemic to the Tanimbar Islands (Yamdena and its satellite islands) in the Maluku province of Indonesia. The major threats identified to this species are hunting, illegal trade, and habitat loss. Therefore, this study aims to classify the land cover, distribution, and habitat types occupied by C. goffiniana on the Tanimbar Islands. Classification of land cover was analyzed using a supervised classification method of the Erdas Imagine 2014 software. Direct field observations were conducted to identify the distribution of Tanimbar Corella and its habitat use. The land cover was classified into six classes: forest (54.26 %), open area (20.76%), plantation (14.81%), mangrove (6.89%), settlement (1.85%), and wetland (1.43%). C. goffiniana is distributed on five islands, Yamdena, Selaru, Larat, Sera, and Molu. Furthermore, this species was observed in forest, plantation, and open land habitats. The results identified seventeen nest trees of six species: Canarium Indicum, Pometia pinnata, Instia bijuga, Sterculita foetida, Maranther corymbosa, and Alstonia scholaris, with a range diameter of 40.00-136.71 cm and nest cavity heights of 9.00-34.22 m (n = 17). This research brings new data in three areas: 1) a reassessment of the distribution of C. goffiniana on the Tanimbar Islands; 2) a detailed classification of the land cover concerning habitat types of the Tanimbar Islands; 3) an identification of the tree species utilized by nesting Tanimbar Corellas. Information on preferred habitats and nesting trees is crucial for selecting release sites of confiscated birds to ensure post-release survival.

Nest architecture is linked with ecological success in songbirds

Nests are essential constructions that determine fitness, yet their structure can vary substantially across bird species. While there is evidence supporting a link between nest architecture and the habitat a species occupies, we still ignore what ecological and evolutionary processes are linked to different nest types. Using information on 3175 species of songbirds, we show that—after controlling for latitude and body size—species that build domed nests (i.e. nests with a roof) have smaller ranges, are less likely to colonise urban environments and have potentially higher extinction rates compared to species with open and cavity nests. Domed nests could be a costly specialisation, and we show that these nests take more time to be built, which could restrict breeding opportunities. These diverse strands of evidence suggest that the transition from domed to open nests in passerines could represent an important evolutionary innovation behind the success of the largest bird radiation.

Rural parks as refugia of cavity nesters in an agricultural landscape: Which habitat features are important for cavity dwellers?

Parks as artificial non-forest tree stands that serve many useful functions for people can also act as refuges for specialised species that include, for example, cavity nesters. In 2017, (from March to end of May), using the example of 54 parks in the agricultural landscape of SE Poland, the importance of 9 basic habitat parameters was assessed (tree trunk diameter, health status of the trees, proportion of dead trees, management intensity, distance to the nearest forest, distance to a forest of >10 ha in area, park area, built-up area, area of tree cover surrounding the park), for the occurrence and richness of five cavity nesters. Rural parks serve refugia for cavity nesters in the agricultural landscape, such as Great Spotted and Syrian woodpeckers and secondary cavity nesters: European Starling, Eurasian Nuthatch and Eurasian Wryneck. The park size, as well as the presence of trees with large dimensions, were positively related to the occurrence and richness of most studied species. A small share of scattered built-up areas did not negatively affect the occurrence and richness of cavity nesters, and even positively affected the occurrence of Syrian woodpecker and Eurasian Wryneck. Only significant management intensity of the parks negatively influenced the Eurasian Wryneck occurrence, and richness of secondary cavity nesters and the whole cavity nester assemblage. The protection of parks with the characteristics listed above should also be taken into account when developing park management strategies, as such areas are important for species with greater ecological flexibility, and may support biodiversity in the agricultural landscape. The negative human impact on cavity nesters may be mitigated by the designation of ‘wild zones’ in the parks, which will save ecological valuable trees and at the same time ensure the safety of visitors.

Cavity nesting by a pendant nest–building species, the Bushtit (Psaltriparus minimus)

Plasticity in bird nest placement is relatively understudied compared to many other aspects of breeding biology. We describe an unusual nest of a Bushtit (Psaltriparus minimus) that was placed inside an old woodpecker cavity instead of being attached to the foliage of a tree or shrub. A pair of Bushtits successfully fledged one brood inside this cavity and then immediately constructed a second nest in the same cavity. Concurrent with this second nesting effort, a Tree Swallow (Tachycineta bicolor) actively competed with the Bushtits for the same cavity and was seen nest building in the cavity as well. The apparent rarity of cavity nesting by the Bushtit suggests this nesting effort was serendipitous and perhaps facilitated by the dimensions of the cavity, which were similar to the hanging, pendulous nest this species typically builds.

Ground nesting Capped Wheatear Oenanthe pileata in the Western Cape South Africa

Capped Wheatear Oenanthe pileata is a medium sized passerine that readily inhabits agricultural landscapes. Several Oenanthe species occur worldwide, many of which are considered cavity nesters. Here I present what is to my knowledge the first recorded case of a nest built above ground versus in a rodent tunnel or sheltered under a structure. The wheatear nest was located on the ground in a sheep pasture on the 21st of October 2021 20 km south of Swellendam in the Western Cape, South Africa. No structure or foliage covered the nest. The nest was discovered during construction. The female laid a total of three eggs over the following five days. The eggs were a very pale blue with two having fine dark black ‘scribble’ marks on the shells. The nest failed six days after discovery, presumably trampled by grazing sheep. Despite having failed, this record does suggest a degree of flexibility in the nesting requirements of Capped Wheatears. The ability to exploit novel nesting habitats should be to the advantage of a species inhabiting rapidly changing landscapes.

The Breeding biology of the Cape Parrot Poicephalus robustus in the Eastern Cape province, South Africa

The Cape Parrot Poicephalus robustus is endemic to South Africa where it typically occurs in high-altitude Mistbelt forests. They are listed as Vulnerable internationally with habitat loss being the primary threat to the species. They nest in natural tree hollows in large forest hardwoods which were the target of historical, exploitative harvesting, and which continue to be harvested legally but on a smaller scale. The breeding biology of the species has been described for the central population, but not yet for the southern population, in the Eastern Cape province, where the stronghold of the population resides. There, few nest sites have been located, and the study of the breeding behaviour and biology is a key knowledge gap in the species in need of conservation. This study aims to characterise natural nesting sites in the Eastern Cape, describe breeding behaviour and investigate breeding success during 2017–2021. A total of 43 nesting sites were located of which 20 were occupied. No pairs attempted breeding in 2019 and breeding success was estimated to be 58%. As found in other parts of the range, Cape Parrots in the study area nest in existing hollows predominantly in large, mature, yellowwood Afrocarpus falcatus trees. Parrots also nest in exotic species. They showed no preference for nest orientation and nested as close as 69 m away from their nearest neighbour. Most nest cavities were inaccessible by field researchers and could only be monitored from the ground, but new methods were found that facilitated the inspection of some nests that were unsafe to climb. Nest characteristics and breeding behaviour information gathered in this study provide a practical foundation for the optimisation of the design and installation of more nest boxes in future, to assist in conservation efforts of this threatened species.

Nesting and predatory behaviour of potter wasp, Rhynchium brunneum brunneum (Eumeninae: Vespidae: Hymenoptera) in an urban farm landscape

ABSTRACT Eumenid wasp, Rhynchium brunneum brunneum is a solitary wasp that constructs its nests in hollow cavities provisioning lepidopteran larvae to its broods. The nesting behaviour, biology, prey preference and prey composition of the wasp were studied and molecular characterisation of the prey was done to confirm their identity. The trap occupancy rate by the wasp was 47.51% with 5.82 ± 0.18 cells per trap provisioned with 10.90 ± 1.72 larvae per cell. The egg to adult duration of the wasp lasted for 21.60 ± 2.22 days. The wasp used six different species of lepidopteran larvae as prey viz., Diaphania indica, Maruca vitrata, Parotis atlitalis, Phycita erythrolophia, Spodoptera litura and Sylepta derogata for its developing broods. Three prey species D. indica (Accession No. MN888507.1), M. vitrata (Accession No. MN888506.1) and P. atlitalis (Accession No. MN888512.1) were molecularly characterised. The percent prey composition of D. indica, M. vitrata, P. atlitalis, P. erythrolophia, S. litura and S. derogata were 31.23, 98.17, 10.40, 42.32, 75.85 and 20.10 respectively. Mixed prey composition in the cells were recorded during the months of June to October and January to May. There was a significant difference in the number of live webbings by M. vitrata in the pigeon pea installed with trap nests (1.53 ± 0.72) compared to wasp excluded control plot (4.07 ± 1.35) four weeks after installation. The results suggested that this eumenid wasp be a potential predator of economically important lepidopteran pests. Installation of artificial trap nests amidst crop habitats could help in their conservation and enhance the process of natural biological control of pest insects.

Impacts of purple martin landlord stewardship activities on nest box occupancy

AbstractThe eastern subspecies of purple martins (Progne subis; hereafter martins) nests almost exclusively in human‐made cavity nest boxes. Martin landlords manage nest boxes with varying levels of engagement and methods, but little research has evaluated the effectiveness of management on martin occupancy. In the fall of 2019, based on interviews with 31 martin landlords in Camrose, Alberta, Canada, we compared martin occupancy in nest boxes during 3 years with 8 management practices. Nest boxes whose landlords cleaned nests, removed blowfly larvae, frequently checked nests, removed competitor nests, and added nest material had higher martin occupancy rates than nest boxes without stewardship practices. Our results help affirm and prioritize future martin landlord practices.

Introduced predators and nest competitors shape distribution and breeding performance of seabirds: feral pigeons as a new threat

Petrels are particularly sensitive to predation by introduced species. Many populations have reduced their breeding ranges, currently mainly occupying predator-free sites. Breeding range reduction leads to interspecific competition for nesting sites, which can be detrimental to petrels. Here, we evaluate how the presence of introduced mammals (cats Felis catus and rats Rattus spp.) and potential competitors for nest sites (Cory’s shearwaters Calonectris borealis and feral rock pigeons Columba livia) shape the distribution, breeding density, and breeding performance of Bulwer’s petrel Bulweria bulwerii on Tenerife, the largest and most densely human populated of the Canary Islands. We estimated nest density, assessed the role of nest location and physical characteristics of nests on breeding success, and determined causes of breeding failure by introduced predators and competitors. Nest density was higher in predator-free colonies on marine rocks. Cat presence was the best predictor of nest density, but it was not correlated with either presence or abundance of competitors. Breeding success varied between years and colonies but was not related to nest characteristics. Pigeon competition for nests was the most frequent cause of breeding failure (7.3%), followed by rat predation (6.3%). We also compared petrel and pigeon nest cavities and found considerable overlap in the physical size of nest sites. Our study provides insights into an overlooked impact of the invasive rock pigeon: nest competition with small seabirds. We encourage more research on the effects of pigeons on nest density, as well as disease and pathogen transmission, and vegetation changes within seabird colonies.