Plumages, Molts, and Structure

Markham's Storm-Petrel has 10 full-length primaries (numbered distally, p1 to p10), 12 secondaries (numbered proximally, s1 to s9, and including 3 tertials, numbered distally, t1 to t3), and 12 rectrices (numbered distally, r1 to r6, on each side of the tail). Storm-petrels are diastataxic (see 4 Bostwick, K. S., and M. J. Brady (2002). Phylogenetic analysis of wing feather taxis in birds: macroevolutionary patterns of genetic drift? Auk 119(4):943–954. Close ) indicating that a secondary has been lost evolutionarily between what we now term s4 and s5. No geographic variation in appearance has been reported (see Systematics). The following is based on descriptions in Murphy (1 Murphy, R. C. (1936) Oceanic birds of South America. Volume 2. American Museum of Natural History, New York, NY, USA. Close ), Blake (5 Blake, E. R. (1977). Manual of Neotropical Birds. Volume 1. Spheniscidae (Penguins) to Laridae (Gulls and Allies). University of Chicago Press, Chicago, IL, USA. Close ), Jaramillo (6 Jaramillo, A. (2003). A Field Guide to the Birds of Chile Including the Antarctic Peninsula, the Falkland Islands and South Georgia. Christopher Helm, London, UK. Close ), Brooke (2 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), Howell (3 Howell, S. N. G. (2012) Petrels, albatrosses, and storm-petrels of North America. Princeton University Press, Princeton, New Jersey. Close ), and Harrison et al. (7 Harrison, P., M. Perrow, and H. Larsson (2021). Seabirds: The New Identification Guide. Lynx Edicions, Barcelona, Spain. Close ), along with examination of Macaulay Library images; see Pyle (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ) for specific information on ageing other Hydrobates storm-petrels. See Molts for molt and plumage terminology. Sexes show similar appearances in all plumages. Definitive appearance is assumed at the Second Basic Plumage.

Natal Down

Occurs in the natal crevices, primarily in April-September in northern breeding populations and January-April in southern breeding populations. Natal down is thick and pale to dark, gray to brownish gray (see image below).

Juvenile (First Basic) Plumage

Present primarily in September (when fresh) to July (when worn) in northern breeding populations and March (when fresh) to November (when worn) in southern breeding populations, at sea, until the Second Prebasic Molt has begun, assuming no Preformative Molt occurs (see Molts). Similar to Definitive Basic Plumage but grayish in tone when fresh (and adults of the same population are worn), the greater coverts often with narrow white margins not present in basic feathers (cf. ML284866031). Juvenile Plumage becomes much browner with wear of juvenile feathers. Juvenile outer primaries and rectrices average narrower and slightly more tapered at the tips than basic feathers, and become increasingly brownish and abraded through wear. Juvenile remiges are grown synchronously at the natal site and are consistent in wear, not showing 'molt clines' of basic plumage (see below).

Definitive Basic Plumage

Appears to be present primarily in March (when fresh) to January (when worn) in northern breeding populations and October (when fresh) to March (when worn) in southern breeding populations. Sooty black above, shading to blackish brown on the underparts; the head, neck and mantle have a plumbeous gloss in fresh plumage. The median and greater wing coverts, longer scapulars, and tertials are paler, more gray brown, forming a distinct diagonal bar across the extended upperwing, broadest at the carpal joint. The distal uppertail coverts may be paler than the back, creating slight contrast with the blackish tail. In fresh plumage, the subscapulars have narrow whitish edges. The underwing is blackish gray with a slight silvery sheen when fresh (cf. ML179939671) and brownish when worn (see below). Flight feathers and primary coverts are almost black; the bases of the primary shafts are white this color in the outer primaries usually visible beyond the primary coverts. When worn, the upperparts appear tricolored, with brownish back and lesser coverts, paler wing band with wear, and blackish flight feathers; the underparts also become browner with wear.

Definitive Basic Plumage distinguished from Juvenile Plumage by having broader slightly more truncated, relatively fresher, and blacker outer primaries and rectrices. Following complete molts, "molt clines" are visible among primaries reflecting molt sequence (see Molts), primaries becoming darker and fresher distally, and the outermost secondary (s1) is usually visibly darker and fresher than the innermost primary (p1) due to a lag in the timing of replacement (see8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ).

Molt and plumage terminology follows Humphrey and Parkes (9 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. The Auk 76(1):1–31. Close ) as modified by Howell et al. (10 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close ). Markham's Storm-Petrel may exhibit a Simple Basic Strategy (cf. 10 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close , 11 Howell, S. N. G. (2010). Peterson Reference Guide to Molt in North American Birds. Houghton Mifflin Harcourt, Boston, Massachusetts, USA. Close ), including complete prebasic molts but no inserted preformative or prealternate molts, as in other storm-petrels (12 Cramp, S., and K. E. L. Simmons, Editors (1977). The Birds of the Western Palearctic. Volume 1. Ostrich to Ducks. Oxford University Press, Oxford, UK. Close , 8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close , 13 Howell, S. N. G. (2012). Petrels, Albatrosses & Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ); however, a limited inserted preformative molt of up to a few body feathers could occur; study needed.

Prejuvenile (First Prebasic) Molt

Complete, in the nest burrow. Pin feathers in the primaries and rectrices appear and begin growing at about day 25-30. After 60 days chicks may have almost or fully developed flight feathers. At least 90-100 days after hatching body feathering may be completely developed except up to 10% of the natal down may remain, especially on the belly, flanks, back, and head (see images under Breeding: Young Birds).. Fledglings are often found with remnants of down on the head (cf. ML284866031, ML196728091).

Second and Definitive Prebasic Molts

Complete. In northern breeding populations (colonies of Paracas, Arica, and Quiuña), molt is initiated between December-January and is completed in April-May (3 Howell, S. N. G. (2012) Petrels, albatrosses, and storm-petrels of North America. Princeton University Press, Princeton, New Jersey. Close ; see images below). Definitive Prebasic Molt in southern breeding populations may be expected to occur in June-October. Timing of flight-feather replacement during the Second Prebasic Molt likely begins earlier due to lack of breeding constraints, as in other storm-petrels (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ), perhaps September to March in northern breeding populations (3 Howell, S. N. G. (2012) Petrels, albatrosses, and storm-petrels of North America. Princeton University Press, Princeton, New Jersey. Close ; see images below) and April-September in southern breeding populations. As in other storm-petrels, primary molt proceeds distally from p1 to p10; secondary molt proceeds proximally from s1, proximally from s5, and bidirectionally from the second tertial (t2), and rectrices generally molt distally on each side of the tail (r1 to r6) with some variation possible. Molt of secondaries typically commences when primary molt has reached p5-p7. Molt of most to all body feathers appears to occur within the time frame of primary molt.

The following is based on descriptions in Murphy (1 Murphy, R. C. (1936) Oceanic birds of South America. Volume 2. American Museum of Natural History, New York, NY, USA. Close ) along with examination of Macaulay Library images.

Bill

The bill is relatively long for a storm-petrel and hooked with prominent tubinares at the base of the culmen. At all ages the bill is black.

Iris and Facial Skin

At all ages the iris is dark brown.

Tarsi and Toes

At all ages the legs and feet are slate gray to blackish, with black claws. Older breeding tubenoses often acquire worn claws after years of digging burrows, which can assist with age determination (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ).

Linear Measurements

Total Length

210-240 mm. Wingspan ca. 530 mm (5 Blake, E. R. (1977). Manual of Neotropical Birds. Volume 1. Spheniscidae (Penguins) to Laridae (Gulls and Allies). University of Chicago Press, Chicago, IL, USA. Close ).

Measurements below come from Murphy (1 Murphy, R. C. (1936) Oceanic birds of South America. Volume 2. American Museum of Natural History, New York, NY, USA. Close ), and include overall range, female mean (n = 5), and male mean (n = 6).

Wing Length

Range 163-181 mm; female mean 169.8 mm, male mean 172.7 mm.

Tail Length

Range 87-97 mm; female mean 89.4 mm, male mean 92.7 mm.

Culmen Length

Range 16.8-19 mm; female mean 18.1 mm, male mean 18 mm.

Tarsus Length

Range 23-25 mm; female mean 24.2 mm, male mean 23.9 mm.

Middle Toe and Claw

Range 23-25 mm; female mean 25.1 mm, male mean 25.6 mm.

Mass

Mean 53.1 g (n = 40; 14 Dunning, J. B., Jr. (2008). CRC Handbook of Avian Body Masses. Second edition. CRC Press, Boca Raton, FL, USA. Close ).