SPECIES

Pink-footed Shearwater Ardenna creatopus Scientific name definitions

Ryan D. Carle, Valentina Colodro, Jonathan Felis, Joshua Adams, and Peter J. Hodum
Version: 2.0 — Published April 9, 2022

Demography and Populations

Introduction

Many demographic parameters are unknown, such as age at first breeding, survivorship, and life span. As of 2022, the best estimates of the breeding population are 114,777 breeding pairs (range 40,757–209,971) on Isla Mocha, and 10,000–15,000 breeding pairs on the Juan Fernández Islands, for an overall population of 50,757–224,971 breeding pairs (Oikonos, unpublished data). Overall population trends are unknown. Reproductive parameters such as burrow occupancy, hatching success, and fledging success have been monitored in long-term studies at all breeding islands.

Measures of Breeding Activity

Age at First Breeding, Intervals Between Breeding

No information.

Clutch Size and Number of Clutches per Season

Clutch size is 1 egg. No evidence of double or replacement clutches.

Annual and Lifetime Reproductive Success

Reproductive success here is defined as the proportion of total eggs laid that produced young that left the nest (i.e., the number of active nests that produced fledged young because this species has a 1-egg clutch). In long-term monitoring plots on Isla Robinson Crusoe, reproductive success across three colonies averaged 0.67 ± 0.13 SD chicks fledged per pair (range 0.44–0.80, 6 years) (Oikonos, unpublished data). Among individual breeding colonies on Isla Robinson Crusoe, the maximum annual reproductive success was 0.95 and the minimum was 0.16 chicks fledged per pair (Oikonos, unpublished data). At Isla Santa Clara, average annual reproductive success was 0.71 ± 0.04 SD chicks fledged per pair (range 0.65–0.75, 5 years) (Oikonos, unpublished data). At Isla Mocha, annual reproductive success across 5 colonies averaged 0.74 ± 0.08 SD chicks fledged per pair (range 0.62–0.86, 9 years) (Oikonos, unpublished data). Among individual breeding colonies on Isla Mocha, the maximum annual reproductive success was 0.94 chicks fledged per pair and the minimum was 0.53 (Oikonos, unpublished data).

Annual burrow occupancy (the proportion of viable burrows that were occupied in a given year) differs by location and year. At colonies on Isla Robinson Crusoe, mean occupancy rate was: Piedra Agujereada, 0.64 ± 0.11 SD (range 0.52–0.72, years 2014–2016); Reserva Comunitaria, 0.48 ± 0.08 SD (range 0.43–0.58, years 2005–2007); and Tierras Blancas, 0.61 ± 0.01 SD (range 0.60–0.62, years 2015–2016) (37). Annual burrow occupancy at colonies on Isla Santa Clara was: Cerro Alto, 0.55 ± 0.11 SD (range 0.36–0.69, years 2002–2008, 2011); Refugio, 0.67± 0.10 SD (range 0.52–0.89, years 2002–2009, 2011, 2014–2016); and Volcán, 0.57 ± 0.11 SD (range 0.42–0.73, years 2002–2009, 2011, 2014–2016 (37). Average burrow occupancy over 5 colonies on Isla Mocha was 0.75 ± 0.10 SD (range 0.65–0.95, 9 years) (Oikonos, unpublished data).

Annual hatching success (the proportion of eggs laid that hatched) also varies by colony and year. At colonies on Isla Robinson Crusoe, mean (± SD) hatching success was 0.82 ± 0.11 at Piedra Agujereada colony (range 0.74–0.90, years 2014–2016); 0.81 ± 0.08 at Reserva Comunitaria colony (range 0.75–0.86, years 2005–2007); and 0.76 ± 0.07 at Tierras Blancas colony (range 0.75–0.76, years 2015–2016) (37). Annual hatching success on colonies on Isla Santa Clara was 0.75 ± 0.20 at Cerro Alto colony (range 0.50–1.00, years 2002–2008, 2011); 0.82 ± 0.12 at Refugio colony (range 0.69–0.98, years 2002–2009, 2011, 2014–2016); and 0.83 ± 0.11 at Volcán colony (range 0.68–0.97, years 2002–2009, 2011, 2014–2016) (37). On Isla Mocha, annual hatching success averaged across 5 colonies was 0.85 ± 0.03 (9 years) (Oikonos, unpublished data).

No information on lifetime reproductive success.

Number of Broods Normally Reared per Season

One.

Life Span and Survivorship

No information.

Disease and Body Parasites

No information.

Causes of Mortality

Exposure

Adults, chicks, and/or eggs may die when burrows collapse or are crushed, causing suffocation from burial. Chicks and eggs may also die from exposure or parental abandonment after damage to a burrow. Damage to burrows from erosion is especially an issue on Isla Santa Clara where the native vegetation was nearly completely destroyed by introduced European rabbit (Oryctolagus cuniculus; 71), and has not recovered. On Isla Robinson Crusoe, approximately 50% of surveyed burrows at the Piedra Agujereada colony had structural damage from trampling by cattle (Bos taurus; 36). Other colonies on Isla Robinson Crusoe do not have cattle present and have had lower rates of burrow damage (A. Gladics and PJH, unpublished data).

Depredation

No population-level information; see Behavior: Predation for a summary of known predators.

Disease

No information.

Direct Human Impacts

Human-caused mortality primarily occurs from capture as fisheries bycatch, with thousands of birds killed per year worldwide (reviewed in 29, 16; see Fisheries Bycatch in Effects of Human Activity: Conservation and Management). Chicks are also harvested by human residents on Isla Mocha, though the scale of mortality is difficult to quantify (33; see Hunting and Trapping in Effects of Human Activity: Conservation and Management). Mortality from fallout from light attraction also occurs on Isla Robinson Crusoe and Isla Mocha (72, 73). Between 2012 and 2018, 226 grounded fledglings were recorded at the town of San Juan Bautista, Isla Robinson Crusoe, with a maximum of 43 individuals per season (73). There have been periodic fallout events of up to 80 birds on Isla Mocha (73; see Light Pollution under Effects of Human Activity: Conservation and Management).

Population Spatial Metrics

In breeding colonies, nest burrows may be clustered, with approximately 0.5 m distance between burrow entrances at higher densities, or spread with > 1 m between burrow entrances at lower densities (RDC). Burrows tend to be more clustered in what is presumed to be higher quality nesting habitat (RDC). Quantitative measurements on distances between nest burrows are not available.

Individual Distance

Burrow densities were measured in 10-m-radius plots at colonies in the Juan Fernández Islands in 2018. In breeding colonies on Isla Robinson Crusoe, mean burrow densities (burrows per m2) were 0.035 ± 0.034 SD at Puerto Frances; 0.041 ± 0.048 SD at Piedra Agujereada; and 0.055 ± 0.059 SD at Vaquería (Oikonos, unpublished data). In colonies on Isla Santa Clara, mean burrow densities (burrows per m2) were 0.085 ± 0.013 SD at Refugio; 0.032 ± 0.019 SD at Volcán; and 0.102 ± 0.059 SD at Cerro Alto (Oikonos, unpublished data). At Isla Mocha, Guicking et al. (33) reported burrow densities of up to 0.40 burrows per m2 in highest density areas, but few to no burrows in other areas. Other studies across Isla Mocha found averages (burrows per m2) in suitable habitat of 0.036 ± 0.09 SD (35) and 0.009 ± 0.005 SD (Oikonos, unpublished data).

Territory Size

No defended territories; see Individual Distance, above.

Home Range Size

Not calculated, but see Movement section for approximate at-sea range for breeding birds.

Population Status

Numbers

As of 2022, the best estimates of the breeding population are 114,777 breeding pairs (range 40,757–209,971) on Isla Mocha, and 10,000–15,000 breeding pairs on the Juan Fernández Islands, for an overall population of 50,757–224,971 breeding pairs (Oikonos, unpublished data).

In 2016, data were collected for a population survey of Isla Mocha, with the goal of estimating breeding population based on modeling burrow densities in suitable habitat. Preliminary model results indicated a burrow count of 151,421 (range 63,967–238,875) (Oikonos, unpublished data). Application of a burrow occupancy factor of 0.758 ± 0.121 SD (based on 9 years of reproductive monitoring in high-density burrow areas) resulted in a population estimate of 114,777 breeding pairs (range 40,757–209,971), or 229,554 breeding individuals (range 81,514–419,942) (Oikonos, unpublished data). On the Juan Fernández Islands, island-wide burrow counts in 2016 indicated 10,055 burrows on Isla Robinson Crusoe and 5,944 on Isla Santa Clara, for a total of 15,999 burrows across the archipelago (Oikonos, unpublished data). Application of a burrow occupancy factor to these burrow counts resulted in a total Juan Fernández breeding population estimate of approximately 10,000–15,000 pairs (Oikonos, unpublished data). On the Juan Fernández Islands, burrow occupancy varied depending on year the method used to quantify it (Oikonos, unpublished data). The low range Juan Fernández population estimate here (approximately 10,000 pairs) is based on a burrow occupancy factor of 0.63 for Isla Robinson Crusoe and 0.73 for Isla Santa Clara, based on monitoring of reproductive plots in areas with high burrow densities from 2014–2016 (Oikonos, unpublished data). The high range (approximately 15,000 pairs) is based on an occupancy factor of 0.89 for Isla Robinson Crusoe and 0.99 for Isla Santa Clara, based on burrow occupancy measured in 2022 using a method in which every sixth burrow counted was checked in a series of standardized monitoring plots covering both high- and low-burrow density areas (Oikonos, unpublished data).

Previous estimates of breeding pairs on Isla Mocha were 42,095 (74), approximately 25,000 (34), 13,000–17,000 (4) and 19,380 (75, 76). 74 and 34 both used rough extrapolations of burrow density from limited sampling to estimate the population; 74 additionally used estimates of local chick harvest. 4 did not specify their methodology. The 19,380 breeding pairs estimate for Isla Mocha has been most widely used in conservation assessments (75, 76). That estimate was based on sampling burrow densities in transects and modeling burrow density in suitable habitat, resulting in an estimate of a minimum of 27,156 burrows island-wide (35). That burrow count estimate (35) was multiplied by a burrow occupancy factor from long-term reproductive monitoring, resulting in an estimate of 19,380 pairs (75, 76). The 2016 study indicating a larger breeding population on Isla Mocha (Oikonos, unpublished data) differed from 35 in sampling and modeling methodology; more habitat was considered "suitable" for breeding based the 2016 study's model results, with the result of a greater overall burrow and population estimate (Oikonos, unpublished data).

Previous breeding population estimates from the Juan Fernández Islands were 2,750 breeding pairs (4, based on a personal communication with PJH), and 8,602 pairs on the Juan Fernández Islands (5,076 pairs on Isla Robinson Crusoe, 3,526 pairs on Isla Santa Clara ) (75, 76). The most current breeding population estimate of 10,000–15,000 pairs on Juan Fernández (Oikonos, unpublished data) is larger than the previous estimate of 8,602 because of a more comprehensive burrow count on Isla Robinson Crusoe and an increase in burrow occupancy on Isla Santa Clara after rabbit eradication in 2003 (75,76).

The estimate of a larger population at Isla Mocha than previously thought is supported by at-sea survey results in waters off the West Coast of North America, where there were peak numbers of approximately 130,000 individuals offshore of central California, and more than 400,000 offshore of southern California during 1975–1983 (these were extrapolated abundances; 40). These at-sea estimates also include nonbreeding birds (e.g., juveniles and potentially a “floating population” of reproductively mature birds that are excluded from breeding by competition for nest sites; 40).

Trends

Given the uncertainty in population estimates, overall population trends are unknown. However, burrow occupancy rates remained similar on Isla Mocha from 2010 to 2019 (Oikonos, unpublished data). Island-wide surveys of Isla Robinson Crusoe and Isla Santa Clara showed a 4% increase in the number of burrows for areas surveyed in both 2002–2003 and 2016 (Oikonos, unpublished data). On Isla Santa Clara, the breeding population increased by an estimated 813 pairs between 2002–2003 and 2016, due to increased burrow occupancy after the eradication of European rabbit (Oikonos, unpublished data). On Isla Robinson Crusoe, trends in burrow occupancy appear flat from 2014–2021, based on monitoring at three colonies (Oikonos, unpublished data).

Population Regulation

No information.

Recommended Citation

Carle, R. D., V. Colodro, J. Felis, J. Adams, and P. J. Hodum (2022). Pink-footed Shearwater (Ardenna creatopus), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.pifshe.02