Monteiro's Storm-petrel Hydrobates monteiroi


Justification of Red List Category
This species is listed as Vulnerable as it has a very small population which is restricted to breeding on few small islets. It is therefore highly susceptible to stochastic events, and remains at risk of mammalian introductions and avian and reptile predators.

Population justification
The population was estimated at 300 pairs in 1999 (Bolton et al. 2008). Recently, the Praia islet population size was updated to 178 breeding pairs, resulting in a global population size estimated at 328-378 pairs (Oliveira et al. 2016). Although the estimate for the population other than Praia islet is now a decade old, the population is not thought to have declined since. The Praia population increased in response to the installation of artificial nest boxes. Thus, the population is best placed in the band 250-999 mature individuals. This equates to 375-1,499 individuals in total, rounded here to 350-1,500 individuals.

Trend justification
Although there is no trend data, the population is suspected to be stable. The population may have even increased since the last known population estimate in 1999 owing to an increase in annual productivity following the installation of nest boxes (Bolton et al. 2008, Bried et al. 2009).

Distribution and population

The species breeds on three islets (Praia, Baixo and Baleia) situated off Graciosa Island, and other two very small islets (Alagoa) located off Flores Island Azores, Portugal. Breeding is suspected on further islets (including some stacks off Corvo Island) in the Azores, but proof is still lacking (Bolton et al. 2008, J. Bried in litt. 2010, Oliveira et al. 2016). It is thought to remain in the vicinity of the Azores during the non-breeding season, a suggestion which is supported by the analysis of carbon isotopes (Bolton et al. 2008). Although unlikely to occur elsewhere, identification amongst Madeiran Storm-petrel H. castro is difficult (W. Bourne in litt. 2012). The total population size was estimated at 250-300 pairs in 1999 (Bolton et al. 2008). Recently, the Praia islet population size was updated to 178 breeding pairs, resulting in a global population size estimated at 328-378 pairs (Oliveira et al. 2016). Accounts from the 16th and 17th centuries of a small black and white seabird, which appear to match the breeding cycle of this species, indicate that it may have once been far more abundant (Bolton et al. 2008); however, there are no recent trend data. 


This species breeds during summer; females lay eggs between early May (perhaps late April) and early July, incubating a single egg until as late as early August, with the first chicks hatching in early June and the latest chicks fledging in early October (Bolton et al. 2008, J. Bried and N.V. Neves in litt.). Its diet is poorly known, but thought to consist of small fish and squid, and it generally feeds on prey of a higher trophic level than H. castro (Bolton et al. 2008).


The two known breeding islets are currently free of introduced mammalian predators. They are, however, only 1km offshore of the inhabited island of Graciosa, and the large number of summer tourists to one of the islets means the introduction of rodents is a possibility (Bolton et al. 2008, Oliveira et al. 2016). Further to this, a cargo ship containing livestock ran aground on one of the breeding islets in 2000, leading to concerns over pollution and rodents escaping ashore (Bolton et al. 2008). Madeiran Wall Lizards, introduced to the Azores in the 19th Century, have been noted predating large chicks on Praia Islet (Neves et al. 2017). The predation appears to be a recent behavioural change and may currently only be carried out by a few individuals. As the majority of the global population of Monteiro's Storm-petrel breed on the islet, as such, this novel source of chick predation has the potential to cause significant declines (Oliveiro et al. 2016, Neves et al. 2017). High predation rates of adults by the native Northern Long-eared Owl Asio otus have been reported, which, given the small global population of H. monteiroi, may prevent population expansion (Bolton et al. 2008). However, this natural predation is unlikely to drive significant declines. Inter-specific competition for natural nesting cavities with Cory’s Shearwaters is known to result in increased mortality for the smaller petrel species (Bried and Neves 2015), the impact of this has not been evaluated (Oliveira et al. 2016). There has, however, been a six-fold increase in the number of nesting attempts using artificial nests on Praia Islet between 2000 and 2011, with the number of attempts made in natural nests not changing over the same period (Bried and Neves 2015). Further to this, overall breeding success between 2000 and 2007 was significantly higher in artificial nests (Bried and Neves 2015). This will likely reduce the impact of competition for nesting cavities, as the artificial nests cannot be excavated by Cory’s Shearwaters (Bried and Neves 2015).

Light pollution is likely to disorient a small number of fledglings each year, though this has not been documented for Monteiro's Storm-petrel as yet (Oliveiro et al. 2016) and the colonies are not adjacent to areas of considerable light pollution. Hence, the current threat is unlikely to exceed a negligible impact. Both of the known breeding islets lie within 2 km of the main shipping route for large passenger ferries and container ships docking on Graciosa, which can potentially cause disturbance, habitat degradation and mortality. Historically, this species was heavily hunted for food, with early 16th and 17th century accounts from the Azores of a small black and white seabird that was killed nightly by the thousands (Bolton et al. 2008). This threat, however, is highly unlikely to return on this scale.

Conservation actions

Conservation Actions Underway
Bern Convention Appendix II. Praia and Baixo islets are Special Protected Areas and natural reserves (Baixo Islet Natural Reserve and Praia Islet Natural Reserve). In 2008, both islets together with Baleia Islet were included in the Graciosa Natural Park, a fact which provides them with regional legal protection (Oliveira et al. 2016). Recent work to reduce interspecific competition for nest cavities with rabbits and other larger procellariiform species through the installation of nest boxes has met with considerable success, leading to a large increase in annual productivity (Bolton et al. 2008). Nest boxes had higher productivity than natural nest sites, probably due to the greater degree of protection they provided from inclement weather and interspecific competition for nest space (Bried et al. 2009). Data from a MRR ringing study is being analysed, with preliminary results suggesting annual survival is high (F. Jiguet in litt. 2010). The Species Action Plan for the Monteiro's Storm-petrel is on preparation under the project LIFE EuroSAP (LIFE PRE/UK/002) and must be due by 2018.

Conservation Actions Proposed Obtain an up-to-date population census. Continue constructing artificial nest-sites. Consider (re-)introducing the species to other islets in the Azores, reducing the potential impact of rodents being introduced to one of the current breeding islets. Monitor the breeding islets for rodent introductions. Assess predation by other potential predators including gulls and reptiles (particularly Madeira Lizard Teira dugesii). Control Madeira Lizards.


This species is a medium-sized, stocky storm-petrel with quite broad wings and square tail. Feet do not project beyond tail in flight. The species has a more prominent diagonal wing bar than that of the Madeiran Storm-petrel Hydrobates castro (Robb and Mullarney 2008), although such wing markings in storm-petrels vary with age and season.


Text account compilers
Moreno, R., Stuart, A., Symes, A., Anderson, O., Derhé, M., Fjagesund, T., Calvert, R., Hermes, C., Martin, R., Ashpole, J, Miller, E.

Olivera, N., Bried, J., Robert, A., Jiguet, F., Bourne, W., Bolton, M.

Recommended citation
BirdLife International (2020) Species factsheet: Hydrobates monteiroi. Downloaded from on 23/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from on 23/10/2020.