Graham Parker and Kalinka Rexer‐Huber (Parker Conservation, Dunedin, New Zealand) have submitted a draft literature review of methods for estimating population sizes of burrowing petrels (including ACAP-listed Procellaria petrels and Puffinus shearwaters) to last month’s meeting of the Conservation Services Programme (CSP) of New Zealand’s Department of Conservation.

The report’s Executive Summary follows:

“Robust population estimates are needed for conservation management of burrowing petrel populations.  Estimates of population size for burrowing petrels are often obtained by extrapolation of burrow surveys to a population- or island-wide scale.   However, extrapolation will also extrapolate bias or error, giving rise to potentially large error bounds reflecting imprecise estimates of population size.  This hinders species risk assessment and limits the ability to detect trends in population size over time.   We review methods for estimating the breeding population size of burrowing petrels by extrapolation from surveys, focusing in particular on the error associated with population estimates of the larger Procellaria petrels.  Sources of error in extrapolation of survey data are divided into five key areas: (1) uncertainty of burrow contents, (2) timing, (3) burrow detection probability, (4) availability bias and (5) observer bias.  We reviewed 87 relevant studies.  Of these, 45 published and unpublished studies deal specifically with quantitative surveys of burrowing petrels.  The review highlights that there is no single-best method for minimising error levels in population estimates.  Rather, the most accurate and precise studies are those designed according to the specifics of the study resources, species and site, and we discuss a range of the factors that are important to consider.  To produce an accurate and precise population estimate from burrow counts, it is important to determine burrow contents and to distinguish between breeding and non-breeding birds.  If a proportion of occupants are missed, further error is introduced to the population estimate, so it can be valuable to check occupant detection probability.  The timing of burrow occupancy checks can help avoid assumptions about what proportion of breeding birds has not yet laid or has already failed.  Extrapolation errors occur when the area sampled is not representative of the area that the samples are extrapolated to.  If sampling sites are not representative, or if some part of a petrel’s burrowing range is not accessible/available to sample, this availability bias can affect extrapolation.  Burrow detection rates can also affect the accuracy of extrapolation, so the assumption that every burrow in the sampled area was detected should be checked.  Whether planar map area or true surface area is used for extrapolation can be a further source of error.  Observers may differ in their ability to detect burrows or burrow contents and this observer bias should be tested for.  Several key points are relevant to all studies: the need for a good pilot study to minimise error sources in the main survey; the need for sufficient time to cover enough ground while including contingency for weather; and the need to document burrowing petrel survey methods in enough depth to be repeatable.”

Black Petrel, photograph by David Boyle

Click here for a visual presentation on the literature review.

Reference:

Parker, G.C. and Rexer-Huber, K. 2015.  Literature Review of Methods for Estimating Population Size of Burrowing Petrels based on Extrapolations from Surveys.  Department of Conservation, Conservation Services Programme Objective 7, Project POP2014-02.  Dunedin: Parker Conservation.  28 pp.

John Cooper, ACAP Information Officer, 11 July 2015

Last month the General Assembly of the United Nations (UNGA) adopted without a vote a resolution (A/69/L.65) to develop an international legally-binding instrument under the UN Convention on the Law of the Sea (UNCLOS) on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction (“high seas”) (click here).

The UNGA agreed to establish, prior to holding an intergovernmental conference, a preparatory committee, open to all States Members of the United Nations, members of the specialized agencies and parties to the Convention, with others invited as observers in accordance with past practice of the United Nations, to make substantive recommendations to the General Assembly on the elements of a draft text of an international legally-binding instrument under the Convention.  The preparatory committee is to start its work in 2016 by holding sessions from 28 March to 8 April and from 29 August to 12 September to draft text for the proposed instrument.

Negotiations  are to address “the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction, in particular, together and as a whole, marine genetic resources, including questions on the sharing of benefits, measures such as area-based management tools, including marine protected areas, environmental impact assessments and capacity-building and the transfer of marine technology.”

Juvenile Wandering Albatross at sea 

John Cooper, ACAP Information Officer, 10 July 2015

In December 2014 a photographic survey of Black browed Thalassarche melanophris and Grey-headed T. chrysostoma Albatrosses was undertaken around the South Atlantic island of South Georgia (Islas Georgias del Sur)*.  Because the breeding colonies are mainly located on steep coastal headlands and sea cliffs it was not possible to gain access from the land so a vessel was used to support a two-person team to photograph the colonies from the water.

A report on the survey is precised here:

“At the end of the 14-day trip, more than 1,000 photos had been taken including close up shots and perspectives at 12 locations.  Using the photographs as a guide, images of discrete colonies or groups of birds were ‘stitched’ together.  Some colonies lacked clearly defined boundaries due to the complexities of terrain and so landscape features such as ridges and spurs were used to define counting areas.  The location of each individual albatross was highlighted on the computer screen by superimposing a coloured dot on each bird, and these dots were then counted.

After the total number of birds in each colony was counted, the numbers of breeding pairs were corrected for diurnal variation and for nest failure between the date of laying and the date each colony was censused [sic].  More than 15,000 black-browed and 16,000 grey-headed albatross were recorded but unfortunately this still signifies a considerable decline since the previous survey in 2004.  For the black-browed albatross this represents around a 20% decline in the population but for grey-headed it is more than a 40% decline.”

Black-browed Albatross, photograph by Oli Yates

Click here to access the original report in full.

Relevant Literature:

Poncet, S., Robertson, G. Phillips, R.A., Lawton, K., Phalan, B., Trathan, P.N. & Croxall, J.P. 2006.  Status and distribution of wandering, black-browed and grey-headed albatrosses breeding at South Georgia.  Polar Biology 29: 772-781.

John Cooper, ACAP Information Officer, 09 July 2015

*A dispute exists between the Governments of Argentina and the United Kingdom of Great Britain and Northern Ireland concerning sovereignty over the Falkland Islands (Islas Malvinas), South Georgia and the South Sandwich Islands (Islas Georgias del Sur y Islas Sandwich del Sur) and the surrounding maritime areas.

Graham Parker (Parker Conservation, Dunedin, New Zealand) and colleagues have submitted a draft report to last month’s meeting of the Conservation Services Programme (CSP) of New Zealand’s Department of Conservation on a survey of ACAP-listed Grey Petrels Procellaria cinerea on Campbell Island.

The report’s abstract follows:

“Populations of grey petrels have declined due to both incidental capture in commercial fisheries and predation by introduced mammals at breeding sites.  In the New Zealand region grey petrels breed only on Campbell and Antipodes islands.  Rats were successfully eradicated from Campbell Island in 2001.  To investigate if the grey petrel population had expanded since the rat eradication, we defined the population’s spatial extent and produced the first quantitative population estimate on Campbell Island and surrounding islets.  We found no clear increase in the number of grey petrels breeding on Campbell Island relative to a historic, non-quantitative population estimate.  However, two of the four colonies we found are either recently established or previously went unidentified.  We estimated 90 pairs of breeding grey petrels from the four colonies located.  This underestimates the breeding population since work was conducted during the mid chick-rearing stage.  There may be grey petrels breeding on the off-shore islands that we could not survey, but if so, the number there would not significantly increase the island-wide population estimate.  The Campbell Island grey petrel breeding population remains small.  Our study provides a baseline for future population estimates of grey petrels on Campbell Island.”

A Grey Petrel in its burrow, photograph by Peter Ryan 

Click here to view a presentation on the above report.

With thanks to Barry Baker.

Reference:

Parker, G.C., Rexer-Huber, K. & Thompson, D. 2015.  Are Grey Petrels Returning to Campbell Island? Survey and Census 14 years after Rodent Eradication.  Report to the Department of Conservation.  Dunedin: Parker Conservation.  18 pp.

John Cooper, ACAP Information Officer, 08 July 2015