<em>Jacqueline Hulina, Morgan Lauf, and Susan Lewis, Ph.D.
Department of Life Sciences, Carroll University
Waukesha, Wisconsin</em>

<strong>Introduction:</strong>
Understanding courtship and breeding behaviors is critical to the management of wild and captive species facing population declines.  Gentoo penguins (<em>Pygoscelies papua</em>) are listed as declining and approaching threatened status by the IUCN (Birdlife International, 2010).  Establishing a captive environment that promotes breeding while minimizing intraspecific conflict is critical in zoos.

Gentoo penguins form monogamous pairs that breed only once per year (Roscoe, 2008), producing an average of two eggs per nest. Extensive parental care, including incubation, food provisioning, and nest defense, allows for chicks to survive in a harsh environment.  Parental care may even extend past fledging, as adult Gentoo penguins have been observed to offer food to chicks that have dispersed and then returned to their original colony (Polito &amp; Trivelpiece, 2008).

There is disagreement among researchers about the relative amount of time and energy invested by male and female Gentoo penguins in courtship/nesting behaviors.  Polito and Trivelpiece (2008) noted a higher level of female parental investment in post-copulation behavior.  Further, females have been shown to lose more biomass during chick rearing compared to males, suggesting that post-copulation parental investment is not equal between the sexes (Lescroël, 2009).  On the other hand, some studies show that males and females invest equal proportions of time incubating eggs (Croxall, 1982; Davis, 1989), leading other researchers to suggest that parental investment between males and females is nearly equivalent (Bingham, 2008).

The Milwaukee County Zoo successfully bred Gentoo penguins for the first time in 2010-11, with two pairs producing chicks in the 2010-11 breeding season.  The objectives of this study were to: a) monitor courtship and breeding behaviors of males and females during the second breeding season, b) compare the behavior of birds that were successful breeders in 2010-11 to those that were unsuccessful, and c) investigate factors influencing aggression during courtship and breeding.  We predicted that the amount of time invested in courtship/nesting behaviors would differ between genders.  We expected an increase in the amount of time invested in courtship/nesting behavior as they entered the breeding period and a correlation between increased courtship/nesting behaviors with breeding success.  We also predicted that the frequency of aggressive behaviors would increase throughout the courtship/nesting period, with a higher amount of aggressive behaviors shown by females.

<strong>Methods:</strong>
We investigated the behavior of captive Gentoo penguins at the Milwaukee County Zoo.  The exhibit contains eight Gentoo penguins (<em>Pygoscelies papua</em>) and twelve rockhopper penguins (<em>Eudyptes chrysocome</em>).  Three male/female adult pairs were observed (Table 1).  In the 2010-11 season, two pairs produced chicks (Oscar &amp; Daphne, Felix &amp; Olive). Due to a medical situation, the remaining male (Marvin) was kept at the Animal Health Center and thus was not present in the exhibit during the 2010-11 courtship period.  The remaining female (Fiona) did not appear to assist in chick rearing in 2010-11.  Marvin was returned to the enclosure after the chicks were hatched.  The other two Gentoo penguins in the enclosure were chicks from the previous year that had not yet reached sexual maturity, and thus were not considered in the study.  All penguins were marked with individually-recognizable combinations of colored bands.

The exhibit was well suited for penguin nesting with multiple flat rock surfaces at varying heights around the perimeter.  The rock surfaces surround a pool with a rock column in the center that forms a bridge to the perimeter rocks (Figure 1).  The center rock blocked a portion of the underwater section of the enclosure from observation, but rarely affected data collection.  The enclosure was kept at 7.2°C – 10°C.  Observations were made from the public viewing area and observers moved to follow the focal animal during each observation session.  In October, zoo keepers placed small inner tubes at sites that had been used for nesting in the 2010-2011 breeding season and brought small rocks into the enclosure for nesting materials.  Enrichment items (ex. sprinkler, rubber ball, stuffed octopus, and partially deflated inner tubes) were placed in the enclosure at various times.  Interactions with enrichment items were taken into account in the ethogram.

The Gentoos were observed prior to data collection using an ethogram from a study of captive Humboldt penguins (Merritt &amp; King, 1987).  After the initial observation period, the Humboldt ethogram was adapted for the captive Gentoo penguins by grouping individual behaviors based on the needs of this study and revising definitions as needed.  For example, seven aggressive behaviors from the Humboldt ethogram were grouped into four categories based on whether the behavior involved physical contact and if the behavior was directed toward a member of the same or different species.  The final ethogram (Appendix A) was designed to include a broad variety of behaviors to account for changes in behavior from the norm as Gentoos entered the courtship period.

To compare the relative time invested in courtship/nesting behaviors, a combination of all-occurrences sampling and focal animal sampling was used (Martin &amp; Bateson, 2007).  One individual was observed at a time over a 30-minute period, recording all behaviors from the ethogram except for aggression at 15-second intervals.  Because aggressive behavior occurred in discrete and conspicuous bouts, all occurrences of aggressive behaviors were recorded during the full observation period.  Each penguin was observed for two 20-minute sessions and nine 30-minute sessions.  Some observation sessions were disturbed by the entrance of a zoo keeper to clean the enclosure or to feed the penguins.  In the majority of cases, this altered observed behavior.  Since feeding time was scheduled around the same time of day, observation sessions were rotated so that each observation session was subject to the same potential disruption.

Observations were conducted from October 1st to November 19th, 2011 between 1:00 – 4:00 pm on Mondays and between 8:00 am – 12:00 pm on Saturdays.  This reduced potential bias from behavioral changes at scheduled feeding times.  One observer collected data on the male while the other collected data on the female at the same time so that any introduced situational bias (ex. the entrance of a zoo keeper to the enclosure) would be the same for each sex.  Data collection was standardized on two occasions to ensure 85% or better inter-observer reliability.<img class="alignright size-large wp-image-2807" title="penguin" src="http://aecetia.net/gws/aazk/wp-content/uploads/penguin-1024x518.jpg" alt="penguin" width="512" height="259" />

The average frequency of each non-aggressive behavior was calculated for individuals and aggregated for all females versus all males.  The average occurrence of aggressive behaviors was calculated for each day and graphed to assess any change in frequency over time.  Means are presented +/- one standard deviation.

<strong>Results:</strong>
Two pairs formed during the courtship/nesting period (Oscar &amp; Daphne; Olive &amp; Felix).  The other male (Marvin) and female (Fiona) displayed courtship/nesting behaviors, but did not appear to preferentially direct such behaviors toward any particular individual.  On average, males had a slightly higher percent of time invested in courtship/nesting behaviors (pairing: 0.7 +/- 5.8%; nesting: 25.5 +/- 32.5%) compared to females (pairing: 0.2 +/- 0.8%; nesting: 21.0 +/- 32.8%; Figure 2), although the time budgets were highly variable between days.  Nest guarding behaviors stayed relatively…

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