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San Benito's project methods

The field work is carried out during the whole breeding season, from early December to early March. This timing of the field work guarantees an almost full coverage the elephant seals breeding season. We observed frequent movements of males between the three islands of the San Benitos group. Therefore, we carry out the field work on all three islands, or, at least on the two (west and central) that shelter more than 90% of the population. Together, these islands present a wide variation in female density and harem size (from few females to more than four hundreds), increasing the opportunity to examine the effect of demographic variation on mating success distribution.

Field work is carried out daily, during the whole span of the daylight (elephant seals behavior and activity are similar during day and night). All breeding males and as much female as possible are marked by numbered cattle tags deployed in their rear flippers and by writing names or codes on their back and flanks using hair dye or bleach. Dye and bleach marks last for the whole breeding season. A full census of the study area is carried out daily to record the presence and status of marked males and count females. Data will is collected using hand-held computers and custom designed software. Behavioral observations are carried out during standard periods of two-hours length. Aggressive and reproductive interactions is recorder recorded using an all-occurrences sampling norm, and a continuous recording norm. To estimate breeding effort male time budgets are calculated from data collected using a scan sampling protocol, with 5 minutes intervals.

To study the effects of the topography of the breeding beaches on mating tactics GIS-grade GPS receivers, with post-processing and differential correction of positional data (MSTAR software, Magellan Corporation), is: one ProMarkX receiver fitted with a multipath resistant aerial and connected to a laptop computer as base station, and two ProMarkX receivers as rovers. The same instruments are to study the spatial structure of harems, and to estimate female density and harem crowding. Navigation-grade GPS receivers are used to store the GPS position of marked males during the census. These receivers has proven to be effective in the collection of spatial data with enough accuracy to measure gross male movements. A significant problem of the collection of socio-spatial information is to be able to measure the position of individuals and social units without affecting their behavior. Starting from 2003 we used, with excellent results, a laser-based system, the LASER LOCATOR rangefinder (Leica), that includes an electronic compass, and permits to obtain 3D position (with 1 m accuracy) from the distance without any disturbance to the animals. The rangefinder is connected to a computer running a custom designed software that stores the positional data together with attributes (like time, social unit, identity) and permits the real time mapping of the positions. The Laser locator is used to map social units, males and females at regular, 5 minutes, interval during observation periods. Moreover, it is used as much as possible for general mapping duties, to reduce the invasiveness of field work protocol.

To study the effect of the physical environment on male mating tactics we measure the microclimate of the breeding beaches and estimate the effects of tide variation on female spatial distribution, inside and outside harems. Tide levels and timing are calculated from tide table of Cedros Island with an harmonic interpolation procedure. Micro-climate data is collected by automatic data loggers placed on the breeding beaches. A total of 15 data loggers (Hobo, Onset Computer Corporation) with air temperature, soil temperature and humidity sensors are deployed in the study area. A weather station (Micro Station, Onset), fitted with a wind speed/direction sensor and a solar radiation sensor is placed on vantage point the main study areas.

Samples are collected to study the genetic paternities, following a protocol already used for a study on southern elephant seals. Skin samples (few grams in weight) are taken from the rear flippers of elephant seals using ear notchers or from the rump using biopsy heads (ø = 4 mm) mounted on a 1.6 metres pole. In all cases sampling is accomplished by surprise without any kind of restraint or immobilization, and results in a modest and short term pain for the animal. Samples are preserved in pure ethanol until DNA extraction and analysis, which is accomplished by standard protocols.

Our field work protocol is compliant to the Animal Behaviour Guidelines for the treatment of animals in behavioural research and teaching (Animal Behaviour 63: 195-199, 2002; http://www.academicpress.com/anbehav) and the Canadian Council on Animal Care guidelines for the care and use of research animals (http://www.ccac.ca/).