Band-rumped Storm-Petrel vs Wedge-rumped Storm-Petrel

In short

The Wedge-rumped Storm-Petrel (Hydrobates tethys) and the Band-rumped Storm-Petrel (Hydrobates castro) are both members of the Hydrobatinae subfamily, yet they possess distinct features that aid in identification. The Wedge-rumped Storm-Petrel is generally characterized by its wedge-shaped tail and darker underparts, whereas the Band-rumped Storm-Petrel has a more prominent band on its rump, lighter underparts, and different foraging behaviors.

Identification tips

1. Birds of the World Similar-Species Diagnostics:

2. The Wedge-rumped Storm-Petrel is noted for having a wedge-shaped tail and darker underparts. In contrast, the Band-rumped Storm-Petrel features a distinct band across its rump and lighter underparts. These differences are critical for field identification as highlighted in the Birds of the World sources.

3. AI Field Diagnostics:

4. Size and Shape: Look for the overall body shape; the Wedge-rumped appears more robust and compact, while the Band-rumped is slender and elongated.
5. Plumage: The dark underparts of the Wedge-rumped Storm-Petrel can make it blend into the ocean, whereas the lighter underparts of the Band-rumped make it stand out more against the water.
6. Flight Behavior: Observe the flight patterns; the Wedge-rumped often dips and flutters erratically, while the Band-rumped may glide more smoothly and consistently.
7. Breeding Behavior: If observed near their breeding colonies, note the timing; Band-rumped Storm-Petrels are more active at dusk and dawn, while Wedge-rumped Storm-Petrels may be seen throughout the day.
8. Rump Band: The most striking field mark is the dark band on the Band-rumped’s rump, which is absent in the Wedge-rumped Storm-Petrel. This can be a useful feature to note when the birds are in flight.

By focusing on these key differences, birdwatchers will have a better chance of accurately identifying these two closely related storm-petrel species in the field.

Size

Both species are similar in size, generally measuring around 25-30 cm in length with a wingspan of approximately 60-70 cm. However, the Wedge-rumped Storm-Petrel tends to have a slightly more robust body compared to the Band-rumped Storm-Petrel, which can appear more slender in flight.

Plumage

• Wedge-rumped Storm-Petrel: This species displays a darker overall plumage with a distinctive wedge-shaped tail. The underparts are generally darker, which can blend with oceanic waters, making them less visible.
• Band-rumped Storm-Petrel: In contrast, the Band-rumped Storm-Petrel has lighter underparts and a notable dark band across the rump. Its plumage is less uniform, with a more pronounced contrast between the upper and underparts.

Behaviour

• Wedge-rumped Storm-Petrel: Known for its agile flight, it often forages in a more erratic manner, frequently dipping and fluttering over the water's surface to catch small marine organisms.
• Band-rumped Storm-Petrel: This species tends to be more nocturnal, returning to land only after dark to feed its young. During the day, it can often be seen flying in a more stable, steady manner, gliding gracefully over the ocean.

Habitat

Both species prefer remote oceanic environments, but their breeding habitats differ. The Wedge-rumped Storm-Petrel typically breeds on rocky islands in the Mediterranean and Atlantic regions, whereas the Band-rumped Storm-Petrel breeds on various islands across the North Atlantic, including the Azores and Galápagos Islands.

Voice

While both species are generally quiet at sea, the Band-rumped Storm-Petrel is known to emit a variety of soft cooing sounds during the breeding season, particularly when calling from the nesting burrows. The Wedge-rumped Storm-Petrel's vocalizations are less documented but are similarly subtle, often characterized by low, muffled calls.