Sex-Specific Parental Care by Incubating Little Auks (Alle Alle)
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Ornis Fennica 86:140148. 2009 Sex-specific parental care by incubating Little Auks (Alle alle) Katarzyna Wojczulanis-Jakubas, Dariusz Jakubas & Lech Stempniewicz K. Wojczulanis-Jakubas, University of Gdañsk, Department of Vertebrate Ecology and Zoology, al. Legionów 9, 80-441 Gdañsk, Poland. E-mail [email protected] (corres- ponding author) D. Jakubas, University of Gdañsk, Department of Vertebrate Ecology and Zoology, al. Legionów 9, 80-441 Gdañsk, Poland. E-mail [email protected] L. Stempniewicz, University of Gdañsk, Department of Vertebrate Ecology and Zoology, al. Legionów 9, 80-441 Gdañsk, Poland. E-mail [email protected] Received 24 March 2009, accepted 11 August 2009 The evolution ofsex-specific reproductive behavior among species with biparental care promotes sexual conflict over care. Such conflict may be less intense in species with long- term pair bonds. We examined sex-specific patterns of care during the incubation period in a monogamous, colonially breeding seabird ofthe high Arctic region, the Little Auk (Alle alle). We recorded time spent by birds ofknown sex in- and outside the nest, and the frequency ofparticular activities (aggressive interactions and collection ofnest material), during four continuous 24-h watches. Males and females shared the incubation duty equally. Both sexes participated in the off-incubation duty behavior with similar fre- quency. However, males attended nest-site territories more than females and were thus more often involved in aggressive interactions and nest-material collection. These results suggest that there were sex-specific patterns of engagement in different forms of parental care during the incubation period. 1. Introduction favors their future breeding success (Mock & Fuijoka 1990, Flower 1995). For many bird species, biparental care is crucial Although both parents have to cooperate dur- for successful breeding (Lack 1968, Gowaty 1996, ing reproduction, sex-specific patterns of parental Sydeman et al. 1996). The participation ofboth care are commonly found. Such sex-specific pat- partners in brood care allows each ofthem to save terns ofparental care reflecta variety ofmale and energy, thereby enabling them to increase their female constraints imposed by physiological, be- own fitness. Particularly, in species with long-ter- havioral and environmental factors, with members m monogamy, such as many seabirds (e.g., del ofeach sex aiming to maximize their own lifetime Hoyo et al. 1996, Gaston & Jones 1998), individu- reproductive success (Trivers 1972). Conse- als are less likely to exploit their partners because quently, understanding sex-specific patterns of pa- maintaining the condition oftheir partner en - rental care is important to comprehend the evolu- hances the fitness ofboth members ofthe pair and tion ofparental strategies. Wojczulanis-Jakubas et al.: Parental care by incubating Little Auks 141 Most studies dealing with sex differences in od, whereas it increased (lower H/L ratio) in parental care have been focused on the chick-rear- males. This difference may indicate sex-specific ing period. While that period has traditionally been differences in parental behavior during incuba- regarded as the most demanding period ofavian tion. reproduction (e.g., Drent & Daan 1980), incuba- To compare sex-specific parental care of incu- tion has been evidenced to be an important compo- bating Little Auks we considered not only the in- nent ofthe reproductive cost, and birds expend a cubation duties but also time spent and behavior considerable amount ofenergy both during egg in - performed during the birds attendance in their ter- cubation in the nest and also during doing parental ritory, but outside the nest chamber. Seven types duties outside the nest, including nest-site defense ofbehavior, performed by birds during territory and maintenance (e.g., Monaghan & Nager 1997, attendance, were as follows: laying down/sitting, Thomson et al. 1998, Reid et al. 2002, Tinbergen walking, preening, sleeping, head-wagging (head & Williams 2002). The behavior ofparents during movements from side to side, performed in pairs, incubation may reflect their earlier investments with unknown behavioral meaning; Evans 1981), and affect their behavior in later stages ofthe aggressive interactions and collection ofnest ma - breeding cycle, and also their future reproduction terial. We paid special attention to the latter two as (e.g., Minguez 1998, Reid et al. 2002, Hanssen et these entail potentially the most stressful and/or al. 2005, Heij et al. 2006). Therefore, knowledge costly behaviors and are directly related to parental on behavioral complexity during the incubation care (guarding, and improving conditions at the period appears crucial for estimating parental in- nest site). Assuming an equal contribution ofthe vestment ofmales and females both at that time parents in incubation duty (Stempniewicz & and also during the whole reproductive season. Jezierski 1987), we hypothesized that males, with Here, we investigated sex-specific patterns of an increased stress level during incubation (Jaku- parental care during the incubation period in the bas et al. 2008), would spend more time and/or Little Auk (Alle alle), a small, planktivorous sea- participate in more aggressive interactions and bird that breeds in rock crevices at coastal Atlantic collecting ofnest material than females, whose areas ofthe High Arctic region (Stempniewicz stress level decreased during incubation. 2001). Like many other seabirds, Little Auks are socially monogamous with negligible sexual di- morphism (Jakubas & Wojczulanis 2007). Both 2. Material and methods partners incubate the single egg and feed the chick, although females tend to cease chick feeding to- 2.1. Study area, field and laboratory work wards the end ofchick rearing, and males exclu - sively take care ofthe young (Stempniewicz 2001, The study was conducted at a breeding colony of Harding et al. 2004). Three studies have examined Little Auks at Ariekammen slopes (77°00 N, sex differences in parental duties during the chick- 15°33 E) in Hornsund, South Spitsbergen in rearing period (Harding et al. 2004, Wojczulanis 2006. For detailed monitoring ofthe time spent in et al. 2006, Welcker et al. 2009), but relatively lit- and outside the nest and behavior performed out- tle is known about the parental activities ofeach side the nest during the incubation period, birds sex throughout the breeding season. To our were caught using mist nets or noose carpets knowledge, the only study focusing on Little Auk (pieces ofthick net with tiny monofilament loops incubation behavior found that both partners con- tied in nooses to capture the birds legs; Wil- tributed to incubation, but the sex ofthe studied liams et al. 2000), spread over the colony surface birds was unknown (Stempniewicz & Jezierski in a restricted sampling patch (hereafter the moni- 1987). Jakubas et al. (2008) demonstrated a differ- tored colony patch). ent pattern ofstress level, as expressed by The monitored colony patch was situated in the heterophil/leucocyte (H/L) ratio changes, in Little central part ofa colony, and the number ofbirds Auk males and females during the incubation peri- present on that patch was comparable with the od. The stress level in females decreased (higher neighboring areas. Before egg-laying, 55 individ- H/L ratio) with the progress ofthe incubation peri - uals were caught and marked individually (distinct 142 ORNIS FENNICA Vol. 86, 2009 color marks, dyed on breast feathers, and a combi- conducted on the 9th,15th,19th, and 27th day after nation ofcolor rings). A small drop ofblood from laying. Time spent inside the nest cavity and in the the brachial vein ofcaught individuals was taken vicinity ofthe nest (expressed further as territory and stored in 1 ml of96% ethanol forlater DNA- attendance) was calculated based on the pres- based sex identification. All birds caught were ence/absence ofmarked individuals on the surface adults (i.e., two years old or older; distinguished ofthe monitored colony patch watched continu - from subadults based on the appearance of flight ously and notied at least every 10 minutes. The ex- feathers and upper-wing coverts; Stempniewicz act time ofbirds entering and exiting nests and/or 2001). departures from and arrivals to the monitored col- The breeding status, partner and location ofthe ony patch were recorded. All occurrences ofag - nest entrances ofthe caught birds were defined gressive interactions and collecting nest material during 22 continuous watches (112 h) carried out were recorded and described in detail. Threaten- during the pre-laying and early incubation periods, ing, attacking and defending, expressed by charac- and during four 24-h continuous watches during teristic postures (upright position, tense body, the incubation period. Social pairs could be easily bristled heads feathers) and/or mutual physical recognized as pair mates. They continuously stay contact, against other individuals were considered close together and copulate frequently with each aggressive interactions. The initiator and the re- other during the pre-laying period, and later on in ceiver ofeach aggressive interaction were re - the season use a shared nest. Extra-pair copula- corded. For occasions ofnest material collecting, tions are easily distinguished from within-pair the type ofitem (pebbles, lichen and moss pieces, ones, as females do not usually accept extra-pair etc.) and the success rate ofits delivery to the nest contacts and perform rejection