Intraclutch Egg-Size Variation in Magellanic Penguins

Rafferty, Nicole E.; Boersma, P. Dee; Rebstock, Ginger A.

doi:10.1650/7688.1

Cited by 12 publications

(17 citation statements)

References 41 publications

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“…After tagging penguins, we checked nests of tagged penguins 20 times during the first breeding season to determine reproductive success (number of chicks fledged per nest with eggs). All tagged penguins were breeding adults of unknown age, but at least 4 yr old because females do not lay eggs until they are 4 (Rafferty et al 2005) and males first breed at 6 to 7 yrs (Williams and Boersma 1995). We used bill measurements of each pair to determine sex, with larger‐billed birds being males.…”

Section: Methodsmentioning

confidence: 99%

Effects of double bands on Magellanic Penguins

Boersma

Rebstock

2010

Journal of Field Ornithology

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Banding penguins is controversial because bands can alter the survival, reproduction, and behavior of marked individuals. The effects of bands are not consistent among band types and, although stainless steel is thought to be better than other materials, tests of the long‐term impact of bands on tag‐loss rates and the reproduction and survival of individuals are needed. We tested three types of external tags on Magellanic Penguins (Spheniscus magellanicus) to measure band effects and tag‐loss rates. In 1993, we double‐tagged 300 penguins with aluminum flipper bands, stainless‐steel flipper bands, or small (2 mm × 10 mm) metal tags attached to foot webbing. We searched for double‐tagged birds for 13 of 15 yrs (1994–2008). Aluminum bands deformed, caused feather wear, injured and killed some penguins, and were lost more often than stainless‐steel bands or web tags. During the first 2 yrs of our study, at least nine penguins lost one aluminum band (N= 71 penguins resighted), but no penguins lost a stainless‐steel band (N= 84) or a web tag (N= 88). During the next 13 yrs, five penguins lost one of their two web tags (N= 89), but none lost a stainless‐steel band (N= 84). Females laid eggs of similar size before they carried a band and in the year following tagging (P= 0.09). The type of tags a female carried did not significantly change egg size (P > 0.22). During the first breeding season after tagging, penguins with aluminum bands had lower reproductive success than penguins with stainless‐steel bands or web‐tags (P= 0.04). The annual survival of females with two stainless‐steel bands was lower (0.79) than that of males with two stainless‐steel bands or males and females with two web‐tags (0.87). Aluminum bands injured Magellanic Penguins, were lost at high rates, and should not be used. Double stainless‐steel bands had no apparent effects on adult male Magellanic Penguins, but reduced survival rates of adult females. A single stainless‐steel band would likely have less impact than two bands, and our results suggest that the impact of a single band would be difficult to measure.

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Section: Methodsmentioning

confidence: 99%

Effects of double bands on Magellanic Penguins

Boersma

Rebstock

2010

Journal of Field Ornithology

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“…To estimate narrowsense heritability (h 2 ; ratio of additive genetic variance to total phenotypic variance) of the 4 structural traits for individual offspring sexes, we compared the size of parents to the adult size of their offspring using parent-offspring regression. Only rarely do Magellanic Penguins breed before or at 4 yr of age (Rafferty et al 2005). We used only parents whose chicks fledged in any year from 1983 to 2005, to allow offspring time to return to the colony and be resighted.…”

Section: Heritabilities and Phenotypic And Genetic Correlationsmentioning

confidence: 99%

Natural selection on morphology varies among years and by sex in Magellanic Penguins (Spheniscus magellanicus)

Koehn

Hard

Akst

et al. 2016

The Auk

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“…We collected eggshells after the chick had hatched, when the shell is expected to be thinner (Handrich 1989, Thompson & Goldie 1990, Blom & Lilja 2004). Rafferty et al. (2005) found first eggs had significantly greater volume than second eggs in Magellanic Penguins, using a sample size of over 400 nests, but the mean difference was small, about 2%, and was probably not biologically significant.…”

Section: Discussionmentioning

confidence: 79%

“…We measured incubation period, eggshell thickness and egg‐pore density in Magellanic Penguin Spheniscus magellanicus eggs to determine whether these variables could predict the patterns of their incubation periods and whether female age might modify egg pore number. Magellanic Penguins lay two eggs of similar size approximately 4 days apart which hatch 2 days apart on average (Boersma & Stokes 1995, Rafferty et al. 2005).…”

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Magellanic Penguin eggshell pores: does number matter?

Boersma

Rebstock

2009

Ibis

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Most penguin species lay two eggs 3–4 days apart that hatch 1–2 days apart. Hypotheses to explain the shorter incubation period for the second egg include differences in porosity of the eggshells. Eggs with more or larger pores and/or thinner shells have higher gas exchange rates and faster embryonic development. We used eggshells from hatchling Magellanic Penguins Spheniscus magellanicus to test whether eggshell thickness and pore density affect incubation period. We expected: (i) second eggs to have thinner shells and/or more pores than first eggs; (ii) eggs to have thinner shells and/or more pores if they were laid by older females, later in the season, or in burrow nests (more humid than open nests under bushes). We found no support for these hypotheses. Egg pores and shell thickness were not related to incubation period. Eggs from the same clutch were similar in eggshell thickness and pore density. Female age, laying date and nest type were poor predictors of eggshell thickness and pore density. Egg pores, we conclude, have little explanatory power for differences in incubation time of eggs in Magellanic Penguins, and suggest that synchronous onset of incubation matters.

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Intraclutch Egg-Size Variation in Magellanic Penguins

Cited by 12 publications

References 41 publications

Effects of double bands on Magellanic Penguins

Effects of double bands on Magellanic Penguins

Natural selection on morphology varies among years and by sex in Magellanic Penguins (Spheniscus magellanicus)

Magellanic Penguin eggshell pores: does number matter?

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