DOI: 10.5061/dryad.bd54350
title: Data from: Revisiting the influence of aggressive interactions on the survival of the first-laid egg in crested penguins (genus Eudyptes)

description: Crested penguins (Eudyptes spp.) have evolved a unique form of breeding in
 which the first of two eggs laid is much smaller than the second and has a
 higher likelihood of being lost during egg laying and incubation. In this
 study, we quantified aggressive behaviour in nesting Snares penguins and
 undertook an egg survival analysis to examine which factors influence egg
 loss. During 120 hours of observation of 50 nests, we recorded a total of
 300 aggressive events in which females were repeatedly pecked, bitten and
 beaten. Aggressive events lasted from less than a minute to up to 55
 minutes (mean 4.6 ± 7.4 min). Single males were the aggressor in 75% of
 aggressive events and in 50.7% of aggressive events the aggressor was
 identified as a neighbouring, breeding male. A greater percentage of the
 small first eggs (34%) were lost than the large second eggs (4%). We found
 that egg mortality was influenced by (i) whether the other egg within a
 nest had hatched, (ii) who was present at the nest (father, mother or
 both) and (iii) the average duration of aggressive events on the nest.
 When one egg within a nest had hatched, the other egg had a vastly
 increased mortality risk irrespective of aggression. However, long,
 aggressive events directed towards females after their partners had gone
 foraging, also increased the probability of egg loss. We suggest that the
 prolonged nest attendance by breeding males well beyond egg laying is in
 response to the high frequency of aggressive behaviour during this time.
 Our data show that A‐egg losses occur due to intraspecific aggression in
 this species. Further research is needed to clarify whether aggressive
 behaviour in breeding crested penguins is modulated by elevated
 testosterone levels in the males and whether any reproductive benefits
 accrue to the aggressors.
description: Snares Penguin egg
 survivalThese data describe the
 fate of Snares penguin A-eggs and B-eggs in 50 nests during the 2002
 breeding season. The file has the following columns: Date (date of
 observation): all nests were observed for 4 hours each day to determine
 the status of all eggs in nests and to observe aggressive events; Nest id
 (identification number of each nest); A alive? (the A-egg is alive and
 being incubated = 1; A-egg lost or hatched = 0; A fate (A-egg fate): it
 explains what happened to each egg; B alive? (the B-egg is alive and being
 incubated = 1; B-egg lost or hatched = 0; B fate (B-egg fate): it explains
 what happened to each egg; F present (the female is present at the nest on
 this date = 1; the female is not present = 0); M present (the male is
 present at the nest on this date = 1; the male is not present = 0); Inc
 shift (incubation shift during the course of incubation); day shift (which
 day in the incubation shift); No of attacks (Number of aggressive attacks
 on this nest on this date); Total min (total minutes of all attacks on
 this nest on this date); Mean dur (mean duration of attacks on this nest
 on this date).