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«Yuri Vladimir Albores-Barajas Division of environmental and evolutionary biology Institute of Biomedical and Life Sciences University of Glasgow ...»

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The effects of human disturbance and climatic

condition on breeding Cassin’s auklets

Yuri Vladimir Albores-Barajas

Division of environmental and evolutionary biology

Institute of Biomedical and Life Sciences

University of Glasgow

Thesis submitted in candidature for the degree of Doctor of

Philosophy to the University of Glasgow, September 2007

©Yuri V. Albores-Barajas 2007


I declare that this thesis is my own work and no part of the work submitted

here has been submitted as part of any previous examination. Supervision by R. W. Furness has helped develop ideas throughout the thesis.

II Summary Human disturbance has been observed to have effects on wildlife.

These effects can be either positive or negative, depending on the study species; however, most of the research done to date has demonstrated negative effects that are reflective in the behaviour and reproductive biology of the organisms. I focused on Cassin’s auklet, a burrow-nester species to study the effects of increasing tourism on the islands along the peninsula of Baja California, Mexico. I also studied the effects of adverse climatological conditions on breeding success of this species.

First, using some biometrics of the individuals captured, I tested a method for aging Cassin’s auklet based on the iris colour. My results corroborate what was proposed before, juveniles have a dark-brown iris that shades into a complete white as they become adults. I also used morphometrics to determine the sex of the individual. When making intra-pair comparisons, it is possible to estimate the sex of the individual based on bill measurements. In 100% of the cases, individuals were correctly sexed using bill depth and width, as corroborated with DNA analysis.

Second, using distance as a measure of disturbance, I looked onto the effects of people walking around the island. In general, breeding success was lower in those sites closer to the path or the village; older and more experienced individuals represented the vast majority of the burrows further away from the disturbance source. After that, using an experimental approach, I manipulated the amount of disturbance received by the chicks III and recorded growth rate, as well as fledging weight, that may influence the possibility of survival for the chicks. I found that at the early stages of development, chicks grew at the same rate; however, chicks in the experimental groups reached a lower peak weight, compared to chick in the control group, and once fully feathered, chicks in the experimental group had a higher rate of weight loss, fledging lighter and earlier than control chicks.

I also had the opportunity to explore the effects of adverse climatic conditions on breeding success. My results show that under a warming of the upper layer of the ocean, as was registered in 2005, Cassin’s auklets struggle to maintain a good body condition and, although attempting to breed, abandon the nest later on, to guarantee survival and another attempt to breed the following season should the condition improve. Breeding success decreased from nearly 70% in 2004 to less than 10% in 2005. Body condition was also lower in 2005, with a slight improvement the following year.

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I am most thankful to my supervisor Bob Furness, whose guidance helped me develop the ideas and research presented on this thesis. Pat Monaghan and David Houston for the advises during the meetings we had.

To Jenny Gill for discussing with me all the ethic issues about human disturbance. Kate Griffiths for helping me with the sexing of Cassin’s auklets.

Shaye Wolf for inviting me to work with her and for introducing me to the Cassin’s auklets. Grupo de Ecologia y Conservacion de Islas for introducing me to the Mexican Pacific islands and for granting me permission to do research on the island. Pescadores Nacionales de Abulon for all their logistical support; without them I would have lived only on lobster and abalone during my stay on San Benito.

To my friends in Glasgow, Gume Osorio, Liliana D’Alba, Maria Bogdanova, Jan Lindstrom, Pep Arcos, SinYeon Kim, Pierre Bize, Kampanat Tharapoom, Gustavo Quinonez, MiRan Kim, Jon Crane, Leandro Bugoni, Federico and Claudia Ruiz for making these years in Glasgow so nice and memorable.

To all my family; my wife Cecilia Soldatini for all her love, support, encouragement and advises during the final stages of this project. My parents, brothers and Nico for supporting me in this adventure.

Finally, to the Cassin’s auklets, for being such amazing birds This PhD was funded by CONACYT, Mexico.

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1.1 San Benito Islands The San Benito Islands are located in the west of the Peninsula of Baja California c. 65 km west of Point Eugenia, (28° 18’ 30” N; 115° 34’ 00” W). They comprise three islands (East, Middle and West) with an area of 195, 104 and 548 ha respectively, with a maximum altitude of 200 metres above sea level (m asl) (UNEP, 2003). The mean annual temperature is 22.6 °C, and the precipitation ranges from 15.4 mm to

244.1 mm per year, with a mean of 163.8 mm (Crosswhite et al., 1982, INEGI, 2006). These Sonoran desert islands are low in biodiversity but high in endemism, including at least eight endemic plant species (Junak and Philbrick, 2000). They have no native terrestrial mammals.

Figure 1.1 Geographical location of the San Benito Islands

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The vegetation of the islands is categorised as mainly Vizcaino desertscrub and maritime desert scrub (Junak and Philbrick, 2000); this is mainly because the lack of fresh water, and soil conditions, are not appropriate for agriculture or cattle raising. This limits the presence of humans to temporary settlements, mainly fishermen or tourists (INEGI, 2006). The dominant plant community of the islands is maritime desert scrub, consisting of shrubs and perennials Agave sebastiana (Greene), Atriplex barclayana (Benth.), Euphorbia misera (Benth.), Frankenia palmeri (I.M. Johnst.), Lycium brevipes (Benth.), L. californicum (Nutt.), Malva pacifica (M.F. Ray), Suaeda moquinii (Greene) and two species of cacti, as well as winter annuals, Cryptantha spp., Eschscholzia ramose (Greene), Hemizonia streetsii (A. Gray) and Perityle emoryi (Torr.) (Junak and Philbrick, 2000).

The San Benito Islands are an important seabird nesting site, with 12 species breeding in large numbers (Boswell, 1978). The islands hold the southernmost breeding colony of Cassin’s auklet (Ptychoramphus aleuticus), with an estimated population of 30,000 individuals (Manuwal and Thoresen, 1993); it is also the northernmost breeding site for Craveri’s murrelet (Synthlyboramphus hypoleucus) and one of two breeding sites in the Pacific for Heermann’s gull (Larus heermanii) (Moran and Lindsay, 1951). Due to their large numbers, seabirds probably play an important role in terms of nutrient input to the islands (Anderson and Polis, 1999).

Introductions of alien animals to islands may have devastating effects, especially in areas with no native predators, where local fauna

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may not have developed appropriate defence behaviour (AlvarezCastaneda and Ortega-Rubio, 2003). European rabbits Oryctolagus cuniculus were introduced to the San Benito Islands during the early 1990s and have caused significant damage to the vegetation (Donlan et al., 2000), and they also compete for burrows with the burrowing seabird species. On West San Benito Island, rabbits were introduced in 1991;

goats Capra hircus and donkeys Equus asinus have had a discontinuous presence since 1948 (Junak and Philbrick, 2000). At the beginning of the study, a few donkeys (5 in total) were present on West San Benito Island.

On East San Benito Island, rabbits were introduced between 1995 and 1996; rabbits were abundant by March 1996 (Donlan et al., 2000).

There is no history of goats or donkeys being present on East San Benito.

Given the small numbers of donkeys (one to five) and goats present on West San Benito, both historically (Moran and Lindsay, 1951) and just prior to the study, rabbits were considered the primary vertebrate herbivore on both islands. However, rabbits were recently eradicated from all three islands, with the last few individuals eradicated early in 2001 (Aguirre-Munoz et al., 2003).

1.2 Cassin’s auklet (Ptychoramphus aleuticus) 1.2.1 Description Cassin’s auklet is one of the most widely distributed of the Pacific alcids, and one of the best studied. It has an overall length of approximately 23 cm, and weighs between 159 and 200 g. It is dark grey

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on the upper parts, fading to paler grey below and whitish on the belly.

Legs are bluish, with black claws. Juveniles have a brown iris that fades into white as they grow to adults. Two subspecies have been identified, the northern and larger P. a. aleuticus and the southern, smaller, P.a.

australis (Nettleship, 1996). The latter is the form that is found on the San Benito Islands, and this subspecies is the smallest of all the Auklets (Manuwal, 1974b).

1.2.2 Distribution and habitat Cassin’s auklets can be found on the east coast of the Pacific. The largest colony is located in Triangle Island, British Columbia, with a total of 1,100,000 breeding individuals (Manuwal and Thoresen, 1993). In Mexico, the population is calculated to be around 40,000 individuals, most of them breeding in San Benito Islands (~30,000 individuals) (Manuwal and Thoresen, 1993).

Cassin’s Auklets nest on small offshore islands that are far from human activities and other mammals. They spend their life on the open sea along the edge of the continental shelf and are rarely seen on the mainland (Manuwal and Thoresen, 1993). They come ashore only during the nesting season, from late December to late May in the San Benito Islands. Even then, they arrive on the colony well after dark and, unless they are incubating eggs or brooding small chicks, return to sea before dawn.

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Figure 1.2 Cassin’s auklet range and main colonies.

1.2.3 Feeding Cassin’s Auklets spend the daylight hours resting and feeding on the open ocean. The auklets are pursuit divers, feeding on small oil-rich crustaceans such as copepods and euphausids that can be caught in the top 30 m of the sea. In spring and early summer, the auklets feed on larval or juvenile fish, which are also rich in oil and very abundant (Nettleship, 1996). Once captured, the prey is stored in a subgular pouch if the auklet is feeding a chick.

Food for Cassin’s auklets is especially plentiful and available along continental shelf edges where upwelling currents carry nutrients to the surface. In most places, this shelf edge is only 20 to 30 km offshore; so

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the auklets do not have to fly far when they carry food home to the chick (Manuwal and Thoresen, 1993, Abraham and Sydeman, 2006).

As Cassin’s auklets dive, the preferred habitats are highly productive regions such as the subpolar areas or the boundaries where currents meet, as in these places there are dense prey aggregations that allow the birds to meet their energetic requirements (Piatt et al., 1990, Hodum et al., 1998).

1.2.4 Breeding In addition to being better protected from many predators, birds nesting in burrows or rock crevices are apparently subjected to less environmental extremes than birds nesting on the ground surface, which are exposed to direct sunlight, rain, wind and other factors (Manuwal, 1974a).

Following on this point, temperature of the nest site is very important for the reproductive success of the birds, as it provides a stable and relatively warm environment that minimises the heat loss of the birds and also minimises heat loss between the bird (brood patch) and the egg (Manuwal, 1979).

Cassin’s auklets breed from middle Baja California Peninsula to the Aleutian Islands in Alaska. They nest in either natural cavities, such as rock crevices or in burrows excavated in soft soil or sod. If breeding adults are successful, the burrow is used repeatedly year after year by the same pair (Manuwal and Thoresen, 1993). They lay one egg and incubation takes an average of 40 days to hatch (Manuwal, 1974b). Both parents

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incubate for approximately 24 h before they are substituted by the partner.

When the egg hatches, the parents will stay in the burrow until the chick is capable of thermoregulation, after that, they will leave the chick alone during the day and will return to the burrow at night to feed the chick (Albores-Barajas pers. obs.). When the chick has reached approximately adult size and is fully feathered, the parents will stop bringing food, and the chick will leave the burrow after a couple of days (Morbey et al., 1999).

The average length of the nestling period is 40 days, but it can vary latitudinally depending on the length of season of food availability (Morbey and Ydenberg, 1997).

Cassin’s auklets are the only Alcid known to lay a second clutch.

Around 90% of birds in Triangle Island, British Columbia relayed after the first egg was removed (Hipfner et al., 2004), but they don’t usually in natural conditions lay a second clutch after successful rearing of the first.

Only the southern subspecies (P.a. australis) lays a second clutch after a successful fledging (S. Wolf pers. comm.). This happens mainly for early breeders that lay the first egg in early January and incubate the egg for 40 days and attend for another 35-40 days until the chick fledges. They still have enough time to lay a second brood during mid-April. It has been noticed that mainly older and more experienced females lay eggs early in the season (Hipfner et al., 2004). Cassin’s Auklets can start breeding as young as two years old, this being dependent on the resources available (Pyle, 2001).

The breeding season in San Benito Island starts in early January, much sooner than the other populations of Cassin’s auklet, as conditions

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