Brian J. Karl

The role of introduced predators and competitors in the decline of Kaka (Nestor meridionalis) populations in New Zealand

We investigated the role of introduced predators and competitors in the population decline of kaka, Nestor meridionalis, a previously abundant forest parrot endemic to New Zealand. We provided supplementary food to test if a shortage of high energy food was limiting breeding in kaka. However, because most nesting attempts suffered from predation and we could not establish a non-treatment area, the role of competitors is still unclear. Kaka only bred in years when beech (Nothofagus) seeded. Over 11 years and 20 breeding attempts we recorded only four fledglings surviving to independence. Nine young kaka and four adult females were killed on the nest. We suggest that stoats were predominantly responsible for this predation. Kaka are relatively common on offshore islands without stoats, even in the presence of other predators and competitors, but are scarce on all islands containing stoats. We predict that stoat predation will cause kaka to become extinct on mainland New Zealand unless stoats and/or kaka are managed.

Diet and foraging effort of Adélie penguins in relation to pack-ice conditions in the southern Ross Sea

We investigated the diet and aspects of foraging effort among Adélie penguins (Pygoscelis adeliae) breeding at three colonies on Ross Island, in the southwestern Ross Sea – Capes Royds, Bird and Crozier – during the chick-provisioning period of three austral summers, 1994–1995, 1995–1996 and 1996–1997. During the study period, pack-ice cover differed in waters offshore of these colonies, by colony, seasons and year. Diet differed among colonies only slightly. The fish Pleuragramma antarcticum was the most important prey, especially during years or periods within years when little pack ice was present. With respect to krill, which composed the remainder of diet, juvenile Euphausia crystallorophias were consumed predominantly in a year of heavy pack-ice cover; more adult krill were consumed in 2 years when pack ice was sparse. Foraging trip duration differed by colony, season and year and was related directly to distance from the colony to the nearest pack ice. The amount of food brought to chicks increased as trip duration increased, to a point (2 days), but then decreased as duration increased further (up to 4 days). On the basis of data on mass of parents and of meal sizes to chicks, it appeared that on the longest trips more of the food gathered by parents was used for self maintenance; on the longest trips, parents lost body mass. Successful foraging during chick rearing, the period when adult foraging is most intense, appears to depend on the proximity of pack ice to nesting colonies for this penguin species.

GEOGRAPHIC STRUCTURE OF ADÉLIE PENGUIN POPULATIONS: OVERLAP IN COLONY‐SPECIFIC FORAGING AREAS

In an investigation of the factors leading to geographic structuring among Adelie Penguin (Pygoscelis adeliae) populations, we studied the size and overlap of colony- specific foraging areas within an isolated cluster of colonies. The study area, in the south- western Ross Sea, included one large and three smaller colonies, ranging in size from 3900 to 135 000 nesting pairs, clustered on Ross and Beaufort Islands. We used triangulation of radio signals from transmitters attached to breeding penguins to determine foraging loca- tions and to define colony-specific foraging areas during the chick-provisioning period of four breeding seasons, 1997-2000. Colony populations (nesting pairs) were determined using aerial photography just after egg-laying; reproductive success was estimated by com- paring ground counts of chicks fledged to the number of breeding pairs apparent in aerial photos. Foraging-trip duration, meal size, and adult body mass were estimated using RFID (radio frequency identification) tags and an automated reader and weighbridge. Chick growth was assessed by weekly weighing. We related the following variables to colony size: foraging distance, area, and duration; reproductive success; chick meal size and growth rate; and seasonal variation in adult body mass. We found that penguins foraged closest to their respective colonies, particularly at the smaller colonies. However, as the season pro- gressed, foraging distance, duration, and area increased noticeably, especially at the largest colony. The foraging areas of the smaller colonies overlapped broadly, but very little foraging area overlap existed between the large colony and the smaller colonies, even though the foraging area of the large colony was well within range of the smaller colonies. Instead, the foraging areas of the smaller colonies shifted as that of the large colony grew. Colony size was not related to chick meal size, chick growth, or parental body mass. This differed from the year previous to the study, when foraging trips of the large colony were very long, parents lost mass, and chick meals were smaller. In light of existing data on prey abundance in neritic waters in Antarctica suggesting that krill are relatively evenly distributed and in high abundance in the Southern Ross Sea, we conclude that penguins depleted or changed the availability of their prey, that the degree of alteration was a function of colony size, and that the large colony affected the location (and perhaps ultimately the size) of foraging areas for the smaller colonies. It appears, therefore, that foraging dynamics play a role in the geographic structuring of colonies in this species.

SPATIAL AND TEMPORAL VARIATION OF DIET WITHIN A PRESUMED METAPOPULATION OF ADÉLIE PENGUINS

Abstract We investigated temporal and spatial variability in the diet of chick-provisioning Adélie Penguins (Pygoscelis adeliae) breeding at all colonies within one isolated cluster in the southwestern Ross Sea, Antarctica, 1994–2000. We wished to determine if prey quality explained different population growth and emigration rates among colonies. Diet composition was described both by conventional means (stomach samples) and by analysis of stable isotopes in chick tissues (toenails of individuals killed by skuas [Stercorarius maccormicki]). Diets were similar among the four study colonies compared to the disparity apparent among 14 widely spaced sites around the continent. Calorimetry indicated that fish are more energetically valuable than krill, implying that if diet varied by colony, diet quality could attract recruits and help to explain differential rates of colony growth. However, a multiple-regression analysis indicated that diet varied as a function of year, time within the year, and percent of foraging area covered by sea ice, but not by colony location. Stable isotopes revealed similarity of diet at one colony where conventional sampling was not possible. We confirmed that sea ice importantly affects diet composition of this species in neritic waters, and found that (1) quality of summer diet cannot explain different population growth rates among colonies, and (2) stable isotope analysis of chick tissues (toenails) is a useful tool to synoptically describe diet in this species over a large area. Variación Espacial y Temporal de la Dieta en una Supuesta Metapoblación de Pygoscelis adeliae Resumen. Investigamos la variabilidad temporal y espacial en la dieta de Pygoscelis adeliae que se encontraban aprovisionando a sus polluelos en todas las colonias dentro de un grupo aislado en el mar de Ross sud-occidental, Antártica, entre 1994 y 2000. Deseábamos determinar si la calidad de la presa explicaba las diferentes tasas de crecimiento poblacional y emigración entre colonias. La composición de la dieta fue descrita por medios convencionales (muestras estomacales) y por el análisis de isótopos estables en tejidos de los polluelos (uñas de las patas de los individuos matados por Stercorarius maccormicki). Las dietas fueron similares entre las 4 colonias estudiadas en relación a la disparidad de la dieta evidente entre 14 sitios dispersos a través del continente. Las análisis de calorimetría indicaron que los peces tienen un mayor valor energético que el krill, sugiriendo que si la dieta varía entre colonias, la calidad de la dieta podría atraer a reclutas y ayudaría a explicar los diferentes índices de crecimiento entre colonias. Sin embargo, un análisis de regresión múltiple indicó que la dieta varió en función del año, de la época dentro de un año, y del porcentaje de área de forrajeo cubierta por el hielo del mar, pero no en función de la localización de la colonia. Los isótopos estables revelaron la semejanza de la dieta en una colonia en que no era posible el muestreo convencional. Confirmamos que el hielo en el mar afecta de manera importante la composición de la dieta de esta especie en aguas neríticas, y encontramos que (1) la calidad de la dieta de verano no puede explicar las diferentes tasas de crecimiento poblacional entre colonias, y que (2) el análisis de isótopos estables de los tejidos de polluelos (uñas de las patas) es una herramienta útil para describir, sinópticamente, la dieta en esta especie a través de un área extensa.

Population status and breeding of New Zealand fur seals (Arctocephalus forsteri) in the Nelson‐northern Marlborough region, 1991–94

Abstract The population size, distribution, breeding, and onshore habitats of New Zealand fur seals in the Nelson‐northern Marlborough region, New Zealand, were investigated. Breeding occurs at four relatively new rookeries along the southern shores of Cook Strait: at Stephens Island in the outer Marlborough Sounds, at Archway Islands and Pillar Point near Cape Farewell, and at Tonga Island in Tasman Bay. These rookeries were established in about 1970, 1980, 1988, and 1988, respectively. In 1993–94 about 500 pups were born and the extant population breeding or born at the four rookeries was assessed as 2410. There were also 17 hauling grounds, each with 25 or more seals ashore in winter, and about 50 other sites where lesser numbers hauled out regularly. Comparison with earlier estimates indicates that the summer population increased from about 70 in 1973 to about 1000 in 1994—a sevenfold increase of yearling and older seals. The number of pups produced increased at a mean annual rate of 23% since 1970–71...

Intra-seasonal variation in foraging behavior among Adélie penguins (Pygocelis adeliae) breeding at Cape Hallett, Ross Sea, Antarctica

We investigated intra-seasonal variation in foraging behavior of chick-rearing Adélie penguins, Pygoscelis adeliae, during two consecutive summers at Cape Hallett, northwestern Ross Sea. Although foraging behavior of this species has been extensively studied throughout the broad continental shelf region of the Ross Sea, this is the first study to report foraging behaviors and habitat affiliations among birds occupying continental slope waters. Continental slope habitat supports the greatest abundances of this species throughout its range, but we lack information about how intra-specific competition for prey might affect foraging and at-sea distribution and how these attributes compare with previous Ross Sea studies. Foraging trips increased in both distance and duration as breeding advanced from guard to crèche stage, but foraging dive depth, dive rates, and vertical dive distances travelled per hour decreased. Consistent with previous studies within slope habitats elsewhere in Antarctic waters, Antarctic krill (Euphausia superba) dominated chick meal composition, but fish increased four-fold from guard to crèche stages. Foraging-, focal-, and core areas all doubled during the crèche stage as individuals shifted distribution in a southeasterly direction away from the coast while simultaneously becoming more widely dispersed (i.e., less spatial overlap among individuals). Intra-specific competition for prey among Adélie penguins appears to influence foraging behavior of this species, even in food webs dominated by Antarctic krill.

Assessing pollination and fruit dispersal in Fuchsia excorticata (Onagraceae)

Abstract We assessed the degree of pollen and fruit‐dispersal limitation in the endemic gynodioe‐cious New Zealand tree fuchsia Fuchsia excorticata over several seasons and at 17 sites throughout New Zealand. The flowers were visited mainly by two endemic honeyeaters (bellbirds and tui), and in some cases very frequently by silvereyes, which also occasionally rob nectar from flowers. We confirmed that hermaphrodites account for more than half the plants in all populations, are fully self‐compatible, and can autonomously self in the absence of pollinators (especially in plants with smaller herkogamy). Fruit production in hermaphrodites and (particularly) females was frequently pollen‐limited (mean Pollen Limitation Indices of 0.17 and 0.40, respectively), and was correlated with visual assessments of pollen loads on the stigma, a useful index of pollinator service. A comparison of the proportion of ripe or overripe fruit on branches exposed to birds versus branches enclosed in wire cages showed that uncaged fruit on Kapiti Island is removed almost as soon as it is ripe but on the mainland it persists for much longer. The proportion of ripe or overripe compared to green fruit is therefore an approximate index of dispersal service. Both indices may be useful to managers concerned with measuring the level of mutualism service provided by native birds.