Back to the Rock: Craveri's Murrelet Rediscovers Alcatraz Island
New fieldwork reveals breeding activity and population estimates for this endangered seabird in the Gulf of California - but nesting success remains fragile
Recovery from the shadows
Long overlooked and hard to study, the Craveri's Murrelet Synthliboramphus craveri is slowly re-emerging as a subject of conservation interest in Mexico's Gulf of California. Endemic to the region and classified as Endangered nationally and Vulnerable by the IUCN, this elusive seabird breeds on remote rocky islands - often in crevices barely large enough to exclude predators. Recent efforts by researchers from Prescott College, summarised in a 2025 Marine Ornithology study, offer the most detailed insight yet into its current breeding status across the Midriff Islands.
The research, spanning over a decade and intensifying since 2017, focused on five key islands: Alcatraz, San Pedro Mártir, San Esteban, Dátil, and Cholludo. Nest searches, camera-trap monitoring, and nocturnal spotlight surveys were used to estimate populations and nesting success. Encouragingly, Alcatraz and San Pedro Mártir showed clear signs of nesting recovery, particularly the latter where rodent eradication occurred in 2007.
Nest success amid environmental pressure
Nest monitoring on Alcatraz Island between 2018 and 2023 revealed average clutch sizes of 1.6 eggs, and a mean hatching success of 1.02 eggs per clutch. However, annual success rates fluctuated - dropping as low as 40% in 2019 before rebounding to 75% in 2023.
At San Pedro Mártir, 17 clutches were found during the 2022/23 season, with a 76% success rate and 65% of laid eggs producing chicks. Most nests were located in deep coastal crevices close to the high-tide line. The lower elevation of these nesting areas, while favoured for concealment, also exposes them to storm surges and seasonal wave activity. The authors note that chick departure occurred typically within 1–3 days of hatching, consistent with earlier observations of precocial behaviour.
San Pedro Mártir's population rebounds post-eradication
One of the most striking findings comes from nocturnal spotlight surveys conducted around San Pedro Mártir in 2022 and 2023. These yielded population estimates ranging from 38 to 99 pairs, suggesting a dramatic recovery since Ship Rats were removed from the island in 2007.
The research team credits this conservation success to improved predator-free conditions and rich marine productivity around the island. Whether this increase came from new recruitment, local survival, or colonisation by a ‘floating' non-breeding population remains unclear. Spotlight counts may also under- or overestimate nesting numbers depending on the murrelets' behaviour and survey conditions.
Rodents still a threat elsewhere
While San Pedro Mártir has seen a resurgence, Alcatraz Island remains compromised by the presence of House Mice. Despite regular sightings of murrelets at sea around San Esteban, little nesting evidence has been found there - likely due to Ship Rat infestations.
Rodents remain a critical limiting factor for this species, which depends on predator-free cavities for successful reproduction. Researchers also documented predator pressure from owls on Alcatraz and observed House Mice entering murrelet nests, though they only fed on already broken eggs. Potential interactions with cavity-sharing lizards such as Chuckwallas are also being investigated.
Next steps for monitoring and conservation
The study highlights the need for continued monitoring, especially in areas where nesting habitat is inaccessible. Camera traps have proved invaluable in determining breeding phenology, showing adult visitation as early as December and chick departures continuing into late April.
More detailed banding and satellite tracking could help clarify individual site fidelity, breeding success, and post-breeding dispersal. Understanding these movements and identifying potential floating populations could be vital for future translocations or island restorations.
With Alcatraz and San Pedro Mártir now confirmed breeding sites, the focus turns to sustaining and expanding these colonies. The authors stress that targeted rodent control, long-term monitoring, and marine protection remain essential tools in reversing the decline of this rare and enigmatic seabird.
August 2025
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