Plumages, Molts, and Structure

Black-capped Petrel has 10 full-length primaries (numbered distally, p1 to p10), 20-21 secondaries (numbered proximally, s1 to s17 or s18, and including 3 tertials, numbered distally, t1 to t3), and 12 rectrices (numbered distally, r1 to r6, on each side of the tail). Petrels are diastataxic (see 6 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. The following is based on descriptions in Howell and Patterson (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ) and Howell (3 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ), along with examination of Macaulay Library images; 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 ) gives specific information on age and sex determination. See Molts for molt and plumage terminology. Sexes show similar appearances in all plumages. Juvenile Plumage is quite definitive-like in appearance but differs in slight characters of flight-feather shape; thus, definitive appearance is achieved following the Second Prebasic Molt.

Natal Down

Present primarily February-May, in the nest burrow. Covered in fine, filamentous gray down.

Juvenile Plumage

Present primarily July (when fresh) to January-April (when worn). Juvenile Plumage is similar to Definitive Basic Plumage except the juvenile flight feathers are uniform in wear, narrower, more tapered, and pointed (outer primaries) or rounded (outer rectrices) at the tips than basic feathers, and lacking "molt clines" (see below and 8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Plumage is fresher in November-May and remiges are typically not molting until May-September. The pale fringing to upperwing coverts form an evenly scaled appearance (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ). Pointed tips to the primary and secondary feathers that can be seen using photo analysis (S. Howell, personal communication).

Formative Plumage

This plumage has not been previously reported in Black-capped Petrel but is present following limited Preformative Molts in other species of Procellariidae (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Examination of Macaulay images indicates that a few scattered to many back feathers (at least) can be replaced well before replacement of primaries during the Second Prebasic Molt, perhaps primarily in October-April, indicating the presence of a Formative Plumage. This molt and plumage appears to occur in most birds but may not occur in all individuals. Most of the feathering including flight feathers are juvenile and become worn at this time of year; formative back feathers are contrastingly fresher and grayer, with broad pale fringing that is usually worn off on juvenile feathers. Other body feathers on the crown, nape, and underparts may also be replaced but harder to detect.

Second Basic Plumage

Present primarily November-October. Protracted Second Prebasic Molt occurs in June-October and during this period individuals can be identified by worn and pointed outer primaries and rectrices, as described under Juvenile Plumage (see right-hand image under Molts). Some individuals may undergo an incomplete molt, resulting in retained juvenile secondaries among s3-s4 and/or in a block among s7-s12, which are significantly narrower and more worn than replaced second-basic secondaries (Figure 188 in 8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Such retained secondaries have not been confirmed in Black-capped Petrel but can be used to identify Second Basic Plumage through the ensuing molt in other species of Pterodroma.

Definitive Basic Plumage

As its English name suggests, the Black-capped Petrel has a clearly defined cap, separated from the dark mantle by a white collar. Dark coloration extends from the cap to eye, and down the sides of the face and around the back of the head, giving an almost a hooded appearance. The brownish-black cap is visually accentuated by the white on the nape. In lighetr forms (see bleow), the cap is restricted to the upper part of the head and separated from the eye by a white supercilium. The conspicuous white “rump” (uppertail coverts) appears to form a broad 'U' shape against the mantle and dark brown tail. In general, upperparts appear brownish-gray to dark or blackish, with the exception of variable white or whitish patches on the forehead, nape, and uppertail coverts. When fresh, upperpart feathers show pale fringes. The uppertail coverts are mostly white, giving these birds their characteristic “white rump” that makes them a “flying field mark” (3 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ) and allowing observers to easily differentiate them from other gadfly petrels in their range; rectrices have dark tips but white bases, contributing to the “white-rumped” appearance. The uppertail can also appear ‘V’-shaped depending on molt. The upperwing is composed of brownish-gray coverts, tertials, primaries, and secondaries can appear blackish or grayish from a distance. The darker coloration of some of the coverts and primaries can give the suggestion of an ‘M’ pattern when feathering is fresh. Individuals in heavy molt can show white patches or a white wing stripe in the upperwing formed by the white bases of secondaries when coverts are missing or growing (see images under Molts).

Underparts are white from chin to under tail, with white and black underwings. A dark brownish to grayish “chest spur” or “neck tab” extends from the mantle to the shoulders and sometimes intrudes upon the white chest. This feature shows great variation among individuals: it is absent in the palest forms but forms a broad patch that looks almost collar-like in the darkest forms. The dark tips of the rectrices are visible from below but not always noticeable in the field. The species has a distinctive black and white underwing pattern; a black ulnar bar formed by varying amounts of black on the marginal and lesser coverts extends into the lesser and median primary coverts. This ulnar bar varies from a thin line in the palest forms to a broad, dark line in the darkest forms. The undersides of the primaries generally have dark webbing but can show white in some individuals. The trailing edge of the underwing is black, this coloration showing from the remiges. In some of the darkest individuals, there is also black in the axillaries and on the sides of the body. Adults of both sexes collected in December had white filoplumes on their crowns, napes, and hind-necks (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Sexes are similar in general appearance; males appear to have more filoplumes (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ).

Black-capped Petrels in Definitive Basic Plumage differ from those in Juvenile Plumage by having less evenly worn plumage due to protracted molts. Pale fringing to the back feathers is present to various degrees relative to plumage wear and does not form an evenly scaled appearance as in Juveniles. Flight feathers are broader and more truncate, the remiges showing "molt clines" reflecting a previous protracted prebasic molt. Primaries become fresher from p1 to p10, secondaries become fresher from s1 to s4 and from s5 and the tertials toward s8-s9, and the outermost secondary (s1) can be noticeably fresher than the innermost primary (p1) as these feathers can be replaced up to 2-3 months apart (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Some individuals may show mixed generations of basic secondaries, as found in other Pterodroma petrels, indicating at least three years of age.

This species is variable in appearance, with wide variations in both size and coloration (see Systematics: Geographic Variation). Two color forms have been described, varying in the amount of dark and white plumage on the face, nape, and collar; these are commonly called “dark” and “light” forms, but discrete intermediate plumages also exist (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ). The nape varies from a strikingly white hind collar in the light form, to one that shows a grayish wash in the dark form, seeming to merge the “cap” with the dark back at times. Dark-form birds tend to show dark or black cheeks and auricular areas, forming a broad black mask that merges with the cap; more extensive dark cap extends farther down on the sides of the head; some dark feathers at the base of the mandible; any white in the face is limited to a white stripe above the lores; posterior ear-coverts mottled blackish or solidly blackish; darker plumage on the nape, reducing or covering the white hind-collar (the hind-neck often shows a grayish wash); larger and more obvious dark collar (chest “spurs”).

Light-form birds are primarily opposite of these patterns, showing substantially reduced dark coloration in these areas: the black cap is smaller and mostly restricted to the top of the head; the dark eye is highlighted by a broad white supercilium; black on the ear-coverts is limited; the white hind-collar is broad and bold; dark chest spurs are smaller and lighter, or absent, depending on wear.

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 ). Black-capped Petrel appears to exhibits a Complex 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 and an absent-to-limited Prefromative Molt but no prealternate molts (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close along with examination of Macaulay Library images, e.g., see those under Plumages).

Limited information has been published on molt in this species, but timing and phenology of molt can be inferred from captured adults, numerous observations at sea, and inferences from closely related taxa such as Bermuda Petrel (see Figure 1, below). 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 ) gives date ranges for molts and Howell and Patteson (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ) discuss molt extensively and comprehensively regarding plumage variation. As suggested in their analysis and by Simons et al. (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ), differences in the timing of molt between dark and light forms of the species likely reflect temporal differences in breeding phenology (see Breeding). This assumption seems corroborated by recent satellite tracking of dark- and light-form petrels captured off Hatteras, North Carolina, US (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ; American Bird Conservancy). Additional information is still needed to better describe molt patterns in all forms of Black-capped Petrel.

Prejuvenile Molt

Occurs primarily in February-May (light light) or April-July (dark form), in the nest. Simons et al. (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) state “The downy plumage of the chick is retained until near fledging and then is shed rapidly in the burrow. Wing and dorsal down are molted first, and some down still remains on the flanks when the chicks depart.”

Preformative Molt

Examination of Macaulay images indicates that some body feathers can be replaced well before initiation of primary replacement during the Second Prebasic Molt; in Procelariidae this has been considered a limited Preformative Molt (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ) that in Black-capped Petrelmay occur primarily in October-March in and December-May in dark-form birds. At least some scattered back feathers can be replaced and probably some crown, nape, and perhaps underpart feathers can also be replaced.

Definitive Prebasic Molt

Complete; occurs entirely at sea. Primaries are replaced from innermost to outermost feathers (p1 to p10), secondaries are replaced bidirectionally from the second tertial and distally from s1 and s5, and rectrices can generally be replaced distally on each side of the tail, with some variation expected (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). In the dark form, breeding adults can begin molt with p1–p2 from mid/late May; all primaries are replaced during June–August, with p9–p10 being replaced around early/mid-August, and as late as 21 August (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Rectrices are replaced between May and July. Body molt is most advanced in late July/early August (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Upperwing greater coverts are replaced rather synchronously about when p3-p5 are being replaced, exposing the white bases to the secondaries.

The Second Prebasic Molt initiates earlier within populations than later prebasic molts, by up to 2 or more months, due to lack of breeding constraints (8 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ), but molt rate may also be slower resulting in completion at about the same time as the Definitive Prebasic Molt. In dark-form birds, the Second Prebasic Molt should be expected in spring of their second calendar year, probably April through July (inferred from the Bermuda Petrel; 4 Brinkley, E. S., and K. Sutherland (2020). Bermuda Petrel (Pterodroma cahow), version 2.0. In Birds of the World (T. S. Schulenberg, B. K. Keeney, and S. M. Billerman, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. Close ). In the light form, analysis of at-sea photographs by Howell and Patteson (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ) showed that wing molt occurs 1–2 months earlier than in the dark form. Additionally, of 10 adult Black-capped Petrels captured at sea between 8–14 May 2019, all five light and intermediate forms were molting some primaries, but none of the five dark forms were (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ).

Molt of innermost primaries occurs during the chick-rearing months for both forms (from March to end of July; see Breeding). Although the molt and breeding schedules may overlap in gadfly petrels (13 Bridge, E. S. (2004). The effects of intense wing molt on diving in alcids and potential influences on the evolution of molt patterns. Journal of Experimental Biology 207:3003–3014. Close ), Black-capped Petrels observed at sea with molting primaries are likely failed breeders or did not attempt to breed that year, including pre-breeding aged birds undergoing their Second-Fourth Prebasic Molts.

Bill and Gape

Bill is stout, with structure typical of Procellariidae in having tubinares at the base of the culmen, containing the nasal passage, and seven to nine distinct horny plates including the maxillary unguis that forms the hook at the tip of the upper mandible. Coloration is deep black, occasionally with slight pinkish or grayish-pink color visible at the base of maxilla and mandible. The gape and tongue are pink.

Iris and Facial Skin

Iris dark brown, often appearing black in the field. Carte (14 Carte, A. (1866). On an undescribed species of petrel from the Blue Mountains of Jamaica. Proceedings of the Zoological Society of London 1:93-95 Close ) described the iris of subspecies caribbaea as "dark hazel."

Legs and Feet

Pink legs. Feet pink proximally but becoming black distally. Distal two-thirds of webs are black but variation exists in the proportion of pink/black in webs and digits. Carte (14 Carte, A. (1866). On an undescribed species of petrel from the Blue Mountains of Jamaica. Proceedings of the Zoological Society of London 1:93-95 Close ) described the tarsi, toes, and nails of subspecies caribbaea as "jet-black," but this was based on museum specimens.

Adult birds collected at sea (summarized in 7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close and 5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) show significant differences in measurements between the sexes, with mass and bill depth being statistically greater in adult males than adult females. Light-form petrels also have significantly greater mass and bill depth than dark-form birds. Males and light-form birds also have longer exposed culmen and wing chord than females and dark-form birds, but small sample sizes prevent conclusions (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ).

Linear Measurements

Howell and Patteson (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ) provide measurements for specimens held at the North Carolina State Museum (56 adults and 4 juveniles). Simons et al. (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) also provide measurements from these specimens, but they did not differentiate between adults and juveniles; therefore, unless mentioned otherwise, measurements summarized here are from data in Howell and Patteson (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close ; adults only). Satgé et al. (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ) provides measurements for 11 adult petrels captured at sea off Cape Hatteras, North Carolina, US, in May 2019.

Total Length

35–46 cm (15 Harrison, P. (1983). Seabirds. An Identification Guide. Croom Helm, Beckenham, UK. Close ).

Bill Length

Exposed culmen mean 32.8 mm (range 28.8–36.5 mm, n = 56). Females average 32.6 mm (range 28.8–34.0 mm, n = 17), and males average 33.0 mm (range 30.1–36.5 mm, n = 39). In field conditions, juveniles appear smaller-billed.

Satgé et al. (16 Satgé, Y. G., E. Rupp, and P. G. R. Jodice (2019). A preliminary report of ongoing research of the ecology of Black-capped Petrel (Pterodroma hasitata) in Sierra de Bahoruco, Dominican Republic – I: GPS tracking of breeding adults. Clemson, South Carolina, USA: South Carolina Cooperative Research Unit, Clemson University. Close ) report bill length (culmen length) in breeding dark-form adults as 32.1 mm (range 30.5–33.4 mm, n = 16). Satgé et al. (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ) measured bill length at 33.8 mm (range 31.4–36.0 mm): females ranged 31.4–36.0 mm (n = 4) and males ranged 31.5–35.3 mm (n = 7).

Bill Depth

Measured at gonys, mean 13.5 mm (range 11.6–15.5 mm, n = 55). The difference between females and males is statistically significant, with females averaging 12.7 mm (range 11.6–13.9 mm, n = 17) and males averaging 14.1 mm (range 12.3–15.5 mm, n = 38). The difference between dark and light forms is also statistically significant, with dark forms averaging 13.3 mm (range 11.6–14.7 mm, n = 43) and light forms averaging 13.8 mm (range 12.5–15.5 mm, n = 9).

Satgé et al. (16 Satgé, Y. G., E. Rupp, and P. G. R. Jodice (2019). A preliminary report of ongoing research of the ecology of Black-capped Petrel (Pterodroma hasitata) in Sierra de Bahoruco, Dominican Republic – I: GPS tracking of breeding adults. Clemson, South Carolina, USA: South Carolina Cooperative Research Unit, Clemson University. Close ) report bill depth in breeding dark-form adults as 13.2 mm (range 12.1–14.4 mm, n = 16). Satgé et al. (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ) measured bill depth at 14.0 mm (range 13.6–14.4 mm): females ranged 13.7–14.4 mm (n = 4) and males ranged 13.6–14.4 mm (n = 7).

Wing Length

Mean unflattened wing chord 292.5 mm (range 268–317 mm, n =50). Females average 290 mm (range 268–305 mm, n = 17); males average 295 mm (range 279–317 mm, n = 33).

Satgé et al. (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ) measured mean wing length at 295.6 mm (range 280­–315 mm): females ranged 292–315 mm (n = 4) and males ranged 280–300 mm (n = 7).

Note that Simons et al. (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) provide “total wing length” at 400 mm (range 375–437 mm, n = 57), but it is unclear how measurements were made. For the same measurement, they also provide data for females (mean 399 mm, range 375–432 mm, n = 17;) and males (mean 400 mm, range 378–437 mm, n = 40).

Tarsus Length

Tarsus length is not reported from collected specimens. Satgé et al. (16 Satgé, Y. G., E. Rupp, and P. G. R. Jodice (2019). A preliminary report of ongoing research of the ecology of Black-capped Petrel (Pterodroma hasitata) in Sierra de Bahoruco, Dominican Republic – I: GPS tracking of breeding adults. Clemson, South Carolina, USA: South Carolina Cooperative Research Unit, Clemson University. Close ) reported tarsus length in breeding dark-form adults at 39.45 mm (range 37.8–41.0 mm, n = 16). Satgé et al. (12 Satgé, Y. G., B. S. Keitt, C. P. Gaskin, J. B. Patteson, and P. G. R. Jodice (2023). Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period. Endangered Species Research 51:183-201. Close ) measured tarsus length at 40.1 mm (range 38.7–41.4 mm, n = 11), which included individuals of both dark- and light-forms.

Mass

Mean 430 g (range 329­–591 g, n = 53). The difference between females and males is statistically significant, with females averaging 410 g (range 329–545 g, n = 16) and males averaging 451 g (range 329–591 g, n = 34). Dark-form birds are generally lighter than light-form ones, and this difference is statistically significant (7 Howell, S. N. G., and J. B. Patteson (2008). Variation in the Black-capped Petrel – one species or more? Alula 14(2):70–83. Close , 5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Dark forms average 421 g (range 347–591 g, n = 40) whereas light forms average 460 g (range 368–557 g, n = 9).

Satgé et al. (16 Satgé, Y. G., E. Rupp, and P. G. R. Jodice (2019). A preliminary report of ongoing research of the ecology of Black-capped Petrel (Pterodroma hasitata) in Sierra de Bahoruco, Dominican Republic – I: GPS tracking of breeding adults. Clemson, South Carolina, USA: South Carolina Cooperative Research Unit, Clemson University. Close ) report that breeding adults (captured at the chick-rearing stage) and adults collected at sea during the breeding months were significantly lighter than adults collected at sea during the non-breeding months (based on data from 5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ): chick-rearing adults had a mean mass of 395 g (range 335–450 g, n = 16), and adults collected during the breeding months at sea had a mean mass of 412 g (range 347–545 g, n = 33); for comparison, adults collected during the non-breeding months had a mean mass of 461 g (range 382–557 g, n = 31).