Figure 1.
Schematic diagram showing causes of death of Magellanic penguin chicks.
Starvation and predation killed chicks in all years; rain and heat killed chicks in some years. The overall mean percentages of chicks killed by rain and heat are smaller than the means for starvation and predation, but the variability is higher for rain and heat than for starvation and predation. In 2 years, rain killed more chicks than starvation and predation. Height of the inner arrows is proportional to the means. Height of the outer arrows is proportional to the mean ±1 standard deviation. Days in parentheses under each arrow refer to the range of ages at which a chick is most vulnerable to that cause of death. Means in the arrows do not total the overall mean mortality rate in the rectangle because the overall mean includes unknown and other causes of death. The list on the right indicates ways that climate change will increase the mean and variability of chick mortality by rain and heat. N = 28 years, 3496 chicks.
Figure 2.
Percentages of Magellanic penguin chicks that died from predation, rain, and heat.
(A) Percentages of chicks by year. Predation (solid line) killed chicks in all years; rain (white bars), and heat (gray bars) killed chicks in some years and were sometimes important causes of death. N = 28 years, 3496 chicks. Percentages do not sum to 100 because other causes of death are not shown. (B) By chick age (days). The number of chicks that died from predation (solid line), rain (white bars), and heat (gray bars) divided by the total number of chicks that reached each age. Each chick was counted in each age until that chick died or disappeared. The sample size decreases with age: for 0 days of age, N = 3496 chicks; for 80 days of age, N = 625 chicks.
Figure 3.
Relationship between starvation and fledging in Magellanic penguin chicks.
When a greater percentage of Magellanic penguin chicks starved, a lower percentage fledged (F1,24 = 56.4, P<0.001, R2 = 0.70, N = 26 years, 3250 chicks). The 2 open circles represent 1991 and 1999, when rain killed >40% of chicks each year, and were not included in the regression.
Figure 4.
Storm mortality (observed and predicted) in Magellanic penguin chicks, by nest type, age, and rainfall.
Mortality increased with higher rainfall, but depended nonlinearly on chick age. N = 28 years, 2482 chicks alive during a storm; 206 died of exposure. Top panels: A & C are the observed percentages of chicks that died from age 0 to 55 days for 4 levels of rain. (A) Bush nests: 24 of 44 chicks died in 4 storms with >45 mm rain. 59 of 138 chicks died in 4 storms with 40–45 mm rain. 20 of 47 chicks died in 3 storms with 20–25 mm rain. 40 of 215 chicks died in 14 storms with 10–15 mm rain. (C) Burrow nests: 4 of 10 chicks died in 4 storms with >45 mm rain. 7 of 28 chicks died in 4 storms with 40–45 mm rain. 0 of 16 chicks died in 3 storms with 20–25 mm rain. 6 of 60 chicks died in 14 storms with 10–15 mm rain. Bottom panels: B & D are the predicted probabilities of a chick dying in a storm. Probabilities were calculated from the best logistic regression model (lowest AIC) with age, precipitation, and low temperature standardized plus age squared and interactions. Low temperature and its interactions were held constant for these simulations. (B) Bush nests. (D) Burrow nests.
Figure 5.
Magellanic penguin chick mortality from storms, by age and low temperature.
Mortality increased with lower minimum temperatures, but depended nonlinearly on chick age. N = 28 years, 2482 chicks alive during a storm; 206 died of exposure. Percent of chicks that died from age 0 to 55 days for 3 categories of low temperature for bush and burrow nests combined. 127 of 360 chicks died in 27 storms with low temperature of 1–5°C. 52 of 1058 chicks died in 97 storms with low temperature of 6–10°C. 27 of 1009 chicks died in 100 storms with low temperature of 11–15°C. No chicks died in 7 storms with low temperature >15°C (not shown).
Table 1.
Predictor variables and model AIC values for the probability that a Magellanic penguin chick died in a storm at Punta Tombo, Argentina, 1983–2010.
Table 2.
Partial regression coefficients and robust standard errors for standardized variables in the best model (lowest AIC; Table 1) for the probability that a Magellanic penguin chick died in a storm at Punta Tombo, Argentina, 1983–2010.
Table 3.
Predictor variables and model AIC values for the probability that a Magellanic penguin chick died in a storm at Punta Tombo, Argentina, 1983–2010 for models including nest characteristics.
Figure 6.
Egg laying in Magellanic penguins has become less synchronous.
The laying interval (number of days between the 5th and 95th percentiles of laying dates) of 1st eggs of Magellanic penguins increased between 1983 and 2009 (F1,25 = 12.2, P = 0.002, R2 = 0.33, N = 8033 clutches).
Figure 7.
The percentage of Magellanic penguin chicks likely to die in a storm depended on breeding synchrony.
The solid lines represent the percentages of chicks likely to die in a storm with 40% of chicks hatched within 13 days. The broken lines represent the percentages of chicks likely to die in the same storm if the hatching interval is 27 days. Both curves assume a normal distribution of hatching dates within the interval and probabilities of dying as shown in Fig. 4 for 40 mm of rain. The curves cross at 19 days. Before that, a storm would kill more chicks if the hatch interval is 13 days; after that, a storm would kill more chicks if the hatch interval is 27 days. (A) Bush nests. (B) Burrow nests.