Southern Giant Petrel Macronectes giganteus Nest Attendance Patterns under Extreme Weather Conditions Author(s): Uwe Horst Schulz, Lucas Krüger and Maria Virginia Petry Source: Zoological Science, 31(8):501-506. 2014. Published By: Zoological Society of Japan DOI: URL:

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ZOOLOGICAL SCIENCE 31: 501–506 (2014)

¤ 2014 Zoological Society of Japan

Southern Giant Petrel Macronectes giganteus Nest Attendance Patterns Under Extreme Weather Conditions Uwe Horst Schulz1, Lucas Krüger2,4, and Maria Virginia Petry2,3* 1

Laboratório de Ecologia de Peixes, Universidade do Vale do Rio dos Sinos, Av. Unisinos, 950 CEP 93022-00, São Leopoldo, Rio Grande do Sul, Brazil 2 Laboratório de Ornitologia e Animais Marinhos, Universidade do Vale do Rio dos Sinos, Av. Unisinos, 950 CEP 93022-00, São Leopoldo, Rio Grande do Sul, Brazil 3 Instituto Nacional de Ciência e Tecnologia Antártico de Pesquisas Ambientais – INCT-APA, Instituto de Biologia, Centro de Ciências da Saúde (CCS) Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil 4 IMAR-CMA Marine and Environmental Research Centre, Department of Life Sciences, University of Coimbra, Coimbra, Portugal

Differences in nest attendance between genders in seabirds may be related to morphological differences. Southern giant petrel is a dimorphic species with gender-specific foraging behavior. The objective of this study was to investigate sex-related differences in nest attendance during the breeding period of southern giant petrels by presence/absence patterns of both sexes during incubation and compare use of the colony after nest failure. Fourteen birds were tagged with digitally coded radio-transmitters in a colony at Elephant Island, Antarctica, in the beginning of 2009/2010 breeding season. Females were present during 18 periods (min. 3 days, max. 9 days) and males only in five periods (min. 2 days, max. 13 days). The difference in mean number of radio signals per day between females (4330; s.e. 313.5) and males (2691; s.e. 248.6) was highly significant (t = 4.3; d.f. = 199; P < 0.001; Fig. 4). As consequence of the severe weather conditions that year, all tagged birds failed to reproduce. After abandonment of the nests, the presence of both genders decreased drastically, although the tagged individuals stayed in the area. Under severe weather conditions female Southern Giant Petrels continue breeding while males abandon the nest earlier. Key words:

breeding behavior, foraging ecology, radiotransmitters, telemetry, climate change

INTRODUCTION Colonial seabirds are exposed to high intra-specific competition on their foraging grounds (Balance et al., 2009; Burke and Montevecchi, 2009). Such competition is reduced between males and females by differences in morphology, foraging areas, foraging efficiency, or foraging strategies (Gonzaléz-Solís, 2004; Gladbach et al., 2009; Quintana et al., 2011). Generally, one sex is larger and heavier, which allows sexes to explore different niches (Gonzaléz-Solís, 2004; Pinaud and Weimerskirch, 2007). Usually males are larger and heavier than females but many species show reversed sexual dimorphism with larger females, for instance booby species (i.e., Weimerskirch et al., 2009; Lormee et al., 2005; Taylor et al., 2011; Castillo-Guerrero and Mellink, 2011). In species with sex size dimorphism differences in nest attendance, provision frequency and duration of foraging trips between genders can be expected. Gender-related differences in foraging behavior and nest attendance have * Corresponding author. Tel. : +55-51-3591-1122 R. 2243; Fax : +55-51-3590-8289; E-mail: [email protected] doi:10.2108/zs130135

been reported for species such as cormorants (Kato et al., 1999), albatrosses (Weimerskirch et al., 1993; Phillips et al., 2004), and boobies (Weimerskirch et al., 2006, 2009). Small seabirds with negligible sexual dimorphism have shown disparities in foraging behavior only under low food availability, which seems to indicate that more expressive morphological differences will more profoundly influence the nest attendance and reproduction investment between males and females (Pinaud and Weimerskirch, 2007; Quillfeldt et al., 2007; Gladbach et al., 2009). Southern giant petrel Macronectes giganteus (Gmelin, 1978) is a long-lived seabird species that uses the temperate and the cold waters of the southern oceans (Onley and Scofield, 2007; Patterson et al., 2008; Techow et al., 2010). The species forages in shallow and productive waters near the shelf during the breeding season (Copello et al., 2011) and is frequently associated with trawler and longline fishing vessels (Copello and Quintana, 2009). The northern giant petrel Macronectes halli (Mathews, 1912) is a congeneric species whose ecology, morphology and distribution is very similar to the southern species (González-Solís et al., 2000ab; González-Solís, 2004; González-Solís et al., 2008). Both species exhibit accentuated size dimorphism. Males are up to 20% heavier than females. Sex-related differences in foraging and incubation shifts duration have been


U. H. Schulz et al.

observed for northern giant petrels (González-Sólis et al., 2000a). Such differences have consequences on foraging strategies, foraging areas and food resources used by each sex (Gonzáles-Sólis et al., 2000a, b; Gonzáles-Sólis, 2004). Females were encountered more frequently in pelagic habitats than males and fed more often on marine prey. Males made shorter foraging trips than females, principally feeding on penguin and seal carrion on the beaches close to the breeding sites. Nonetheless, sexual segregation is slightly higher for northern giant petrels, except in areas where they overlap with southern giant petrels (Gonzáles-Sólis et al., 2000a, b, 2004; Gonzáles-Sólis et al., 2008). Nest attendance patterns of the southern giant petrel and the influence of climatic factors on breeding behavior are poorly investigated. This study aims to compare nest attendance between genders in a colony in high Antarctic latitudes during a breeding season with extreme climatic conditions. MATERIALS AND METHODS Study area The study was conducted at Stinker Point on Elephant Island (Fig. 1), South Shetlands. Ninety-five percent of the island is under permanent ice cover. All colonies of penguins and other seabirds are concentrated on the remaining 5%, which can be ice free in the Antarctic summer. Mean annual temperature is −2°C and mean summer temperature is 1°C. Even in the austral summer snowstorms and low visibility due to fog are frequent. The 2009/2010 breeding season was an extremely cold austral summer in the South Shetlands, with the monthly average temperature below historical average temperature recorded for the same period (INPE 2010). Southern giant petrel occurs at two locations. One is called North Plateau and the other is South Plateau. The North Plateau colony is subdivided in several breeding groups. The total estimated abundance of giant petrel was 931 breeding pairs in 2009/2010 summer. Tagging Digitally coded transmitters (LOTEK; type MCTF-3A weight 16 g) were used for tagging individuals. Burst rate was set to 5 s, expected transmitter life 641 d. The tagging procedure extended for seven days, due to the weather conditions with temperatures at −5°C and gust winds of up to 60 km/h. We tagged seven females and seven males on nine nests, of which five were occupied by couples (Table 1). Considering a mean weight of 5 kg for adult petrels, transmitter weight fell well below the recommended 3% maximum mass- relative-to-bodyweight (Phillips et al., 2003). All individuals were tagged while sitting on the nest. One leg was gently extended usually without securing the body of the bird. The transmitter, glued on a piece of soft foam, was attached to the tarsus-metatarsus by 3M Silver tape, with the whip antenna extending in the direction of the foot (Fig. 2A, B). Three individuals had to be secured, two males and one female, by holding the body. When these individuals were released after tagging, they escaped flying. The two males returned to the nest after less than two minutes, the female after four. The radio signals were registered by an automatic listening station (ALS) which consisted of a SRX 400 receiver with data logger function (LOTEK, Canada) equipped with a standard omnidirectional whip antenna Fig. 1. at a distance of approximately 100 m from the colony. Time partition of the receiver was set to 30 minutes to Point.

optimize data logger memory capacity of 524,288 bytes. The power was supplied by the internal batteries of the receiver, which were automatically recharged in a 12 hours rhythm by the electric generator of the research unit. The experimental setup was designed to record presence of tagged individuals. Precise position fixes were not possible. Birds sitting on or beside the nest produced the same signal. Birds were tagged in two different colonies. The tracking period extended from 3 December 2009 to 10 February 2010. Between 7 January and 10 February the equipment was left unattended. During this period power was supplied by a 300 Ah truck battery. Data from the ALS was downloaded in three days intervals. During the absence of the research team data accumulated approximately for one month in the internal receiver memory. The raw data obtained from the data logger were filtered, which eliminated error codes and false presence data of inexistent codes. The incubation period and the period when the birds abandoned the Table 1. Tagging date, last day of incubation period, date of last registered signal, digital transmitter code, gender and nest number of tagged individuals. Note that nest numbers 1, 3, 5, and 14 were occupied by one tagged parent only. Tagged 4-Dec-09 4-Dec-09 4-Dec-98 6-Dec-09 4-Dec-09 5-Dec-09 3-Dec-09 5-Dec-09 3-Dec-09 5-Dec-09 3-Dec-09 4-Dec-09 6-Dec-09 9-Dec-09

Incubation Last signal Code Female Male Nest period until – 16-Jan-10 14-Dec-09 31-Dec-09 21-Dec-09 30-Dec-09 21-Dec-09 3-Jan-10 18-Dec-09 17-Dec-09 23-Jan-10 27-Dec-09 – –

10-Feb-10 10-Feb-10 10-Feb-10 7-Feb-10 9-Feb-10 6-Feb-10 10-Feb-10 8-Feb-10 10-Feb-10 10-Feb-10 10-Feb-19 10-Feb-10 9-Feb-10 7-Feb-10

102 103 105 114 101 104 107 106 108 109 110 112 111 113


1 3 5 14 2 2 7 7 8 8 10 10 11 11

Elephant Island, Antarctica. The circle indicates the study area Stinker


Southern giant petrel nest attendance nests were defined for each individual by visual examination of the presence/absence pattern (Fig. 3). In a second step, the mean number of received signals per day for females and males was compared by Student-T test. The same procedure was applied for the period the birds abandoned the nests. Three individuals that abandoned the nest within two days after tagging (102-male, 111male, 113-female) were excluded from the T-test. To document the weather anomaly of the 2009 breeding season, geo-referenced satellite data of water temperature, ice cover, and wind speed of a circle with a radius of 200 km around Elephant Island were downloaded from the Coastwatch Browser (NOAA 2013). For each variable, 1000 random points were extracted from

an average image including October, November, and December 2009, which was the beginning of the breeding season of the experimental period. The means of these 1000 random points per variable were compared by Student-T test with the means of 1000 equally extracted values of the same variables for the comparison period October, November, and December of the years 2000 to 2008. Statistical analysis was conducted at SPSS 18.0. Significance level in all tests was set to P < 0.05. The dispersion measure is the standard error (s.e.). Satellite images were processed with Arc Gis 10.0.

Fig. 2. (A) Southern giant petrel leg tagged with radiotransmitter and (B) a view of one individual at the colony.

Fig. 3.

RESULTS The breeding individuals produced distinct presence/absence patterns (Fig. 3). Several switches of attendance were recorded. When one gender is present the other tends to be absent (nest 2, 7, 8, 10; Fig. 3). Although females were present during 18 periods (min. 3 days, max. 9 days) and males only five periods (min. 2, max. 13 days). All nests were abandoned during the study period and no chicks hatched. The first nest abandoned was nest 8 on 17 December, the last nest 10 on 23 January. The attendance pattern of codes 110 (female) and 112 (male; Fig. 3) show that the male ceased breeding on 27 December. On this date, a switch in nest attendance occurred. The departing male was regis-

Nest attendance periods of tagged southern giant petrel. Codes on the right refer to individuals of Table 1. F = female; M = male.


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tered a final time at 12:30 h and the arriving female at 12.36 hours. From then on, the female remained for a period of eight days on the nest and left for four. She left and returned three times, with decreasing periods of nest attendance until the nest was abandoned ultimately on 23 January. The female of nest 2 abandoned the nest after male desertion, while the male of nest 7 skipped after the female, and was the male that remained the longest. Both the genders seemed to have left the nest at similar times in nests 8 and 11. The females of nest 3 (code 103) and nest 10 (code 110) were the last to abandon the nest (Fig. 3). During the incubation period a total of 756,590 radio signals were registered by the ALS, of which 549,350 were produced by the presence of females and 207,240 by males. The difference in mean number of signals per day between females (mean = 4330; s.e. = 313.5) and males (mean = 2691; s.e. = 248.6) is highly significant (t = 4.3; d.f. = 199; P < 0.001; Fig. 4). After abandonment of the nests, the presence of both genders decreased drastically, although the tagged individuals stayed in the area, resulting in a daily mean of 19.1 (s.e. = 2.1) signals per female and 19.0 (s.e. = 2.7) per male (Fig. 4). This small difference is not significant (t = 0.036; d.f. = 277; P = 0.97). At the beginning of the breeding season in October,

November and December 2009 the mean sea surface temperature was significantly lower (t = 30.83, d.f. = 999, P < 0.001), sea ice cover (t = 14.06, d.f. = 999, P < 0.001) and wind speed (t = 20.26, d.f. = 999, P < 0.001) significantly higher than the means of the corresponding months between the years 2000 and 2008 (Fig. 5). DISCUSSION Three birds abandoned their nests (21%), probably as a consequence of handling during the tagging procedure. All three birds were held during the tagging procedure. De Villiers et al. (2006) documented high stress levels in congeneric northern giant petrels when disturbed. Many recent studies using telemetry devices on free ranging sea birds do not report any effects of the method: Shaffer et al. (2005) on albatrosses, Trebelco et al. (2008) on northern and southern petrels, Weimerskirch et al. (2009) on blue footed and brown boobies, Phillips et al. (2003) on albatrosses and petrels. This may lead to the assumption that tagging effects in general may be neglected. Our study showed that at least under severe climatic conditions, handling may add additional stress that can lead to abandonment of the nest. All other tagged individuals initially continued breeding and abandoned the nests later. No chicks hatched in nests

Fig. 4. Female – male presence during incubation period (A) and after nest abandonment (B). Error bars are standard errors. Please note different scales.

Fig. 5. Comparison of the mean sea surface temperature, mean sea surface ice cover and mean wind speed in October, November and December of the years 2000–2008 and of the corresponding months in 2009.


Southern giant petrel nest attendance

where one or both parents were tagged. Most probably the extreme weather conditions of the 2009/2010 austral summer, as documented by the low sea surface temperature, high ice cover and high wind speeds, caused the reproductive failures. Heavy snowfall and gusts of winds of 90 km/h occurred frequently at the beginning of the tracking period. Snow cover on the island extended until mid December. When the research team returned on 13 February, census data showed that only 5.8% of 931 pairs successfully raised a fledge. Contrary to González-Solís (2000b), who stated that northern giant petrel M. halli males remain slightly longer on nests than females, which spent more time on longer foraging trips, the southern giant petrels males from Stinker Point spent less time in nest than females, as shown by the higher numbers of female attendance periods and the significantly higher mean number of received signals per day. It may be assumed that the tagged females emitted these signals when sitting on the nest. This assumption was supported by occasional visual observations and by the nest attendance pattern of Fig. 3, which shows little overlap in female and male presence. The more expressive presence of females in our study is the result of female insistence not to abandon the nest. For example the female of nest 10 continued attending the nest almost one month after abandonment by the male. These results indicate a higher breeding effort in females while larger males may trade off reproduction success effort in favor of own survival. When the females finally abandoned the nest the mean number of signals per day decreased from over 4000 to 19.1, indicating the same presence as males in the colony. Long-lived species such as southern giant petrels make numerous breeding attempts during their up to 30 years life cycle (ATCM30 2007). A failed breeding attempt may only have a low influence on the lifetime reproduction success. These trade-offs were measured in handicapping studies with other marine bird species. Bijleveld and Mullers (2009) showed, that handicapped Cape gannets (Morus capensis) doubled their foraging trip duration and reduced the time invested in nest attendance. The unhandicapped control partners did only partially compensate the lower feeding efficiency by increasing their nest attendance and trip duration. As a consequence chick growth was slower and mortality higher than in the control group. Thick billed murres (Uria lomvia) compensated the impairment of a handicapped partner, producing the same fledging rates as the controls (Paredes et al., 2005). However, Antarctic petrel (Thalassoica antarctica) did not compensate for a handicapped partner and chick mortality increased significantly (Seather et al., 1993). Apparently compensation behavior is species specific. The decision whether to allocate effort on chick rearing or on parental survival may highly depend on food availability. When a bird is unable to satisfy the energy demands necessary for attending the nest and survival, it will probably abort breeding (Weimerskirch, 1995; Weimerskirch et al., 2001). The unusual harsh weather conditions of the austral summer 2009/2010 probably caused a shortage of food supplies that drove male southern giant petrels of the present study to a trade-off decision, to increase individual mortality risk by continuing breeding, or to augment survival probabil-

ity by abandoning the nest. Further studies are scheduled to investigate the nest attendance behavior under more favorable conditions. ACKNOWLEDGMENTS The project received funding from INCT-APA (CNPq Processo n°574018/2008-5), FAPERJ (E-26/170.023/2008), WCS (Wildlife Conservation Society) and was supported by the Ministry of Environment, Ministry of Science and Tecnology and the Department of Marine Resources (SECIRM). We wish to thank the staff of Lotek Wireless Inc. for the fast processing of the transmitter order.

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Southern giant Petrel Macronectes giganteus nest attendance patterns under extreme weather conditions.

Differences in nest attendance between genders in seabirds may be related to morphological differences. Southern giant petrel is a dimorphic species w...
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