Ginger A. Rebstock

Following the fish: penguins and productivity in the South Atlantic

We tested four predictions for central-place foragers provisioning offspring along a gradient in primary production spanning 1000 km of coastline in Argentina, using male Magellanic Penguins (Spheniscus magellanicus). Three of the predictions were supported. (1) Foraging trip distances corresponded with the production gradient; penguins swam shorter distances (mean maximum distance: 60–110 km) at the southern colonies where production is higher and prey species aggregate nearshore, and longer distances (143–242 km) at the northern colonies where production is lower and prey species aggregate at offshore fronts. Within these broad regions, foraging locations coincided with tidal mixing fronts or high chlorophyll concentrations. (2) Foraging trips followed a pattern of intermediate speed and meandering when outbound (32% of locations at sea), slow meandering movements within the foraging areas (45%), and very fast and direct returns to the colony (23%). Regardless of how far they went, penguins spent the mo...

Climate change increases reproductive failure in Magellanic penguins.

Climate change is causing more frequent and intense storms, and climate models predict this trend will continue, potentially affecting wildlife populations. Since 1960 the number of days with >20 mm of rain increased near Punta Tombo, Argentina. Between 1983 and 2010 we followed 3496 known-age Magellanic penguin (Spheniscus magellanicus) chicks at Punta Tombo to determine how weather impacted their survival. In two years, rain was the most common cause of death killing 50% and 43% of chicks. In 26 years starvation killed the most chicks. Starvation and predation were present in all years. Chicks died in storms in 13 of 28 years and in 16 of 233 storms. Storm mortality was additive; there was no relationship between the number of chicks killed in storms and the numbers that starved (P = 0.75) or that were eaten (P = 0.39). However, when more chicks died in storms, fewer chicks fledged (P = 0.05, R 2 = 0.14). More chicks died when rainfall was higher and air temperature lower. Most chicks died from storms when they were 9–23 days old; the oldest chick killed in a storm was 41 days old. Storms with heavier rainfall killed older chicks as well as more chicks. Chicks up to 70 days old were killed by heat. Burrow nests mitigated storm mortality (N = 1063). The age span of chicks in the colony at any given time increased because the synchrony of egg laying decreased since 1983, lengthening the time when chicks are vulnerable to storms. Climate change that increases the frequency and intensity of storms results in more reproductive failure of Magellanic penguins, a pattern likely to apply to many species breeding in the region. Climate variability has already lowered reproductive success of Magellanic penguins and is likely undermining the resilience of many other species.

Long-term change and stability in the California Current System: lessons from CalCOFI and other long-term data sets

Abstract The California Current System (CCS) is a highly variable system, both spatially and temporally, that is strongly affected by low-frequency climatic fluctuations. This paper reviews evidence for long-term (decadal-scale) change in the physics and biology of the CCS over the last 50–100 years, as well as evidence for stability in planktonic community structure and long-term persistence of populations. Increases in water temperature, thermocline depth and stratification in the CCS have been accompanied by changes in populations of kelp, diatoms, foraminifera, radiolarians, intertidal invertebrates, zooplankton, fish and seabirds. However, there is also evidence for stability in assemblages of larval fish, calanoid copepods and radiolarians. Statistical averaging (the portfolio effect) may explain some aspects of stability in assemblages. Advection of planktonic populations may account for rapid recovery of biomass and dominance structure following perturbations such as strong El Nino events. Planktonic populations in the CCS may be adapted to large-scale biotic and abiotic variability, through a combination of advection of populations and life history traits. Several lessons may be learned from the California Cooperative Oceanic Fisheries Investigations and other long-term data sets: (1) long time series are needed to understand the dynamics of the ecosystem; (2) life histories are important determinants of species responses to environmental forcing, even in the plankton; and (3) the CCS is simultaneously variable and stable, and these properties are not necessarily in conflict.

WHY PENGUIN EGGSHELLS ARE THICK

Abstract Like most other penguin species, Magellanic Penguins (Spheniscus magellanicus) are large-bodied birds that incubate their eggs for a prolonged period on hard substrates with little nesting material—all circumstances that could lead to high rates of egg breakage. However, Magellanic Penguin eggs at Punta Tombo, Argentina are seldom broken. From 1984 to 2001, only 2.6% of 10,023 eggs in our study areas broke or cracked. Most of those were broken in unusual or catastrophic events, mainly penguin fights and rainstorms. Low breakage rates appear to be attributable to thick eggshells. Shells of Magellanic Penguin eggs averaged 0.81 mm without the egg membranes—at least 56% thicker than expected for bird eggs of similar mass. The calcium required for those thick eggshells cannot be supplied by normal food intake because females lay eggs during a fasting period. It is also unlikely that sufficient skeletal calcium can be mobilized. An alternative potential calcium source is mollusk shells. To determine whether female penguins were selectively ingesting calcium to form thick eggshells, we examined stomach contents of birds during the egg period (settlement, egg laying, and early incubation) and the post-egg period (late incubation and chick rearing). Both females and males were more likely to have mollusk shells in their stomachs during the egg period than during the post-egg period. However, females were much more likely than males to have shells in their stomachs during the egg period, whereas the proportions of males and females with mollusk shells did not differ in the post-egg period. Selective ingestion of mollusk shells by Magellanic Penguins, resulting in thick eggshells, appears to be an adaptive response that reduces egg breakage.

Parental Behavior Controls Incubation Period and Asynchrony of Hatching in Magellanic Penguins

Abstract. In many species of birds, periods of incubation of eggs within a clutch depend on the order in which the eggs were laid and determine whether the eggs hatch asynchronously or on the same day. Magellanic Penguins (Spheniscus magellanicus) lay two eggs 4 days apart that hatch 2 days apart; first eggs take 41 days to hatch, and second eggs take 39 days. We tested whether temperatures of the two eggs differ and whether delayed onset of incubation caused this pattern. First eggs were cooler than second eggs during their first few days (P < 0.001). First eggs averaged 23.4 ± 0.3 °C in the first 24–48 hours after they were laid. Second eggs averaged 27.9 ± 0.3 °C, warm enough for development. Egg temperature did not stabilize (33.9 °C) until eggs were about 18 days old. We swapped first and second eggs of different nests to determine if parental behavior caused the differences in temperatures and incubation periods. First eggs treated as second eggs developed as fast as control second eggs, and second eggs treated as first eggs developed nearly as slowly (40 days) as control first eggs. First eggs that were stored in a cooler until second eggs were laid took 2 days longer to hatch than control first eggs. Parental incubation behavior explained why the incubation period of second eggs was shorter than that of first eggs and controlled asynchrony of hatching, which affects chick growth and survival.

Intraclutch Egg-Size Dimorphism in Magellanic Penguins (Spheniscus magellanicus): Adaptation, Constraint, or Noise?

ABSTRACT. Many species of birds lay clutches that include eggs of varying sizes. Smaller eggs laid late in a clutch may facilitate brood reduction when there is insufficient food, whereas larger eggs may offset the disadvantage of late-hatching chicks when hatching is asynchronous. Alternatively, egg size may not be adaptive but may reflect energetic constraints on females. Magellanic Penguins (Spheniscus magellanicus) usually lay clutches of two eggs that are similar in size. In 5.1% of clutches (n = 7,085; 1983–2006), the volume of the smaller egg was <88.8% of the volume of the larger egg. We wondered whether this was possibly an adaptive trait. We found that laying a dimorphic clutch was costly and not adaptive. Eggs in dimorphic clutches failed to hatch 30% of the time, even if the eggs were larger than average. Eggs in normal clutches failed to hatch only 8% of the time. When both eggs hatched, no chicks fledged from 68% of dimorphic clutches, whereas no chicks fledged from 62% of normal clutches (G = 8.2, P = 0.02). Laying a dimorphic clutch is not a trait; females that laid a dimorphic clutch did not always lay dimorphic clutches and commonly laid eggs of similar size in other years. We did not find evidence of a constraint on females, in terms of body condition, age, laying date, persistence of the mate, or environmental conditions inferred from mean annual reproductive success. Dimorphic clutches are not adaptive and appear to be noise in the system.

Repeated observations of a Cape Gannet Morus capensis on the coast of Patagonia, Argentina

1 Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA, and the Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA 2 Biologia y Manejo de Recursos Acuaticos, Centro Nacional Patagonico – CONICET, Boulevard Brown 2915, Puerto Madryn, Chubut, Argentina 3 Centro Universitario Leonardo da Vinci, Rodovia BR 470, Km 71, N° 1040, Santa Catarina, Brazil 4 Universidad Nacional de la Patagonia San Juan Bosco, Boulevard Brown 3700, Puerto Madryn, Argentina * Corresponding author, e-mail: gar@u.washington.edu