Feeding Preferences and Foraging Behaviour in the Alpine Accentor Prunella Collaris
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Ornis Fennica 83:170–180. 2006 Feeding preferences and foraging behaviour in the Alpine Accentor Prunella collaris Marián Janiga* & Martina Novotná Janiga, M., Institute of High Mountain Biology, University of ilina, SK-05956 Tatranská Javorina 7, Slovak Republic. [email protected] (* Correspondence author) Novotná, M, Institute of High Mountain Biology, University of ilina, SK-05956 Tatranská Javorina 7, Slovak Republic. [email protected] Received 30 November 2005, revised 18 July 2006, accepted 9 August 2006 In flocks of Alpine Accentors (Prunella collaris), we observed the foraging behaviour of birds when they were foraging on a grid containing clumps of seeds. We measured the feeding rate, diet diversity, individual and seasonal feeding preferences and dominance in birds. Producing and scrounging were frequently observed and they often involved ag- gressive interactions. Most birds used both tactics to obtain food. We found that foraging method was not related to dominance. No significant differences in feeding rate and diet diversity were detected between dominant and subordinate birds. The Alpine Accentors showed a strong degree of heterogenity in their food specialisations in different seasons. Calculations of nutritive values of diet showed that birds received relatively more carbo- hydrates in the autumn than in spring or winter. In the “snowy” seasons, the diet contained a relatively high number of lipids. Birds also had significant individual food preferences. 1. Introduction learning ability (Durell 2000), individual food preferences, physiology of a bird (Moon & Ziegler There can be considerable variation in a popula- 1979) and dominance (Flynn & Giraldeau 2001, tion in the way individuals exploit food resources. Johnson et al. 2001, Liker & Barta 2001, 2002). There are several possible mechanisms which may Because the roles of producers and scroungers be responsible for individual differences in the may be exchangeable as a function of food types feeding behaviour of birds. Foraging producer- (Giraldeau & Lefebvre 1986), it seems crucial to scrounger systems have been described in many consider that individual birds are plastic in their bird species (Barnard & Sibley 1981, Giraldeau & feeding preferences (Cueto et al. 2001). Different Lefebvre 1986, Giraldeau et al. 1994). The sys- food types may be preferred by different individu- tems assume that an individual is either engaged in als in a flock of birds (Brown 1969, Giraldeau & searching for its own food (producer) or searching Lefebvre 1985). The existence of individual vari- for joining opportunities (scrounger). Scroungers ability in the selection of food type in birds may in a population can specialize on parasitizing the significantly influence the choice of individuals to food discoveries of producers (Giraldeau & be producers or scroungers. Lefebvre 1986, Flynn & Giraldeau 2001). The Dominance relationships also influence the producer-scrounger relationships are not fixed and use of social foraging tactics (Giraldeau & Beau- may mainly be a result of individual differences in champ 1999). Individuals in many species often Janiga & Novotná: Feeding strategy and dominance in Alpine Accentors 171 behave aggressively during feeding and may form ducer-scrounger system results from conflict-co- dominance hierarchies within foraging flocks. Be- operation among individuals and whether ecologi- cause the dominance rank of an individual may cal conditions on mountain tops play a part in de- crucially affect its success in competition for food, termining the outcome. We also investigated social status may influence an individual’s “deci- whether individual feeding preferences and explo- sion” to play producer or scrounger in ringed indi- ration of potential food (feeding rate) are related to viduals in a foraging group of birds (Barta & the species’ tactic use. In this paper we further Giraldeau 1998). Dominant individuals can dis- present field evidence of strong individual and place subordinates, which gives them priority in seasonal differences in the diversity of diet of accessing food sources, so they mainly play group-feeding Alpine Accentors. scrounger. Subordinates mostly use producer tac- tics. Besides the phenotypic differences of individ- 2. Methods ual birds, the use of alternative foraging tactics, producer or scrounger, depends on environmental 2.1. Locality spatio-temporal conditions, for example time of day (Barta & Giraldeau 2000) or season (Green- We investigated the feeding preferences of Alpine berg 1987). Because producer-scrounger models Accentors during the winter (January–February, can successfully predict the use of foraging tactics wintering birds), spring (March–April, spring ar- in some ground feeding birds (Johnston & Janiga rival in the mountains) and autumn (September– 1995, Giraldeau & Caraco 2000, Mottley & October, moulting, adult and fledged juvenile ag- Giraldeau 2000, Coolen et al. 2001), we used the gregations). The study areas were located in the Alpine Accentor (Prunella collaris Scop.) to in- Tatra and Great Fatra National Parks in the West- vestigate whether individual differences in food ern Carpathians, Slovakia, ranging from 900 m preferences and social hierarchy are related to the a.s.l.(Great Fatra, Malino Brdo ski resort, 960 m producing-scrounging game in a species living in a.s.l, 49°18’N, 19°18’E; wintering area) to 1,700– extreme conditions variable over time. 2,500 m a.s.l. (High Tatra mountain peaks and val- The Alpine Accentor lives in mountainous re- leys: Skalnate lake 1,778 m a.s.l., 49°11’N, gions from western Europe through central Asia to 20°14’E; Solisko peak 1,840 m a.s.l., 49°08’N, Japan, typically breeding well above the treeline at 20°02’E; Tery Cottage 2,015 m a.s.l., 49°10’N, heights of 1,800–4,000 m a.s.l., but even higher in 20°13’E; Krivan peak 2,494 m a.s.l., 49°09’N, the Himalayas where it has been seen at nearly 20°00’E; Rysy peak 2,503 m a.s.l., 49°11’N, 8,000 m on Mount Everest (Cramp 1988, Dyrcz & 20°05’E). Field observations and experiments Janiga 1997). It is a non-migratory species but it were done in the years 1997, 1999, 2000 and 2003. can make considerable local movements during The birds live on mountain tops, well above the winter. Some birds remain in breeding areas in treeline, in a habitat of steep cliffs and grassy winter whereas others become altitudinal migrants meadows strewn with rocks. Over 90% of the feeding near buildings. Birds use different behav- summit area is covered with deep snow in winter ioural schemes in different seasons which may dif- and early spring. The region has the typical climate fer among sites and with respect to weather condi- of high mountain regions: substantial daily tions (Janiga & Romanová 1996, 1997). They changes in temperature and precipitation in spring breed in polygynandrous groups whose size is in- and early summer. Snowfall occurs even in June fluenced by the temporal availability of fertile fe- and July. males (Davies et al. 1995, Heer 1996). In spring, autumn and winter they forage socially and exhibit a dominance hierarchy in which birds compete ag- 2.2. Birds gressively for food and have been shown to use producer-scrounger tactics (Glutz Von Blotzheim Birds were mist-netted or caught with food traps. & Bauer 1985). Adult birds were sexed by the shape of the cloacal The aim of this study was to study how the pro- protuberance (Nakamura 1990, for more details 172 ORNIS FENNICA Vol. 83, 2006 see e.g. Janiga 1992). One-year-old birds were sured for each feeding trial: (1) individual feeding aged by the colouring of the middle and greater preferences in food selection, (2) the ability to find wing-coverts. The minimum age of some birds and change to new food sources in successive tri- was calculated from the day of ringing. Feeding als, (3) dominance status (by recording two or preferences and diversity of diet were studied in 33 more individuals, see below) (4) diversity of diet birds. The individuals were also checked in detail (according to feeding pecks) and (5) feeding rate by video-taping (individual features in the plum- as the number of pecks divided by time spent on age colour and pattern, mainly of throat, primaries, the grid (Liker & Barta 2002). tertials and head, individual characteristics in be- haviour). The roles of producer or scrounger were indentified in 24 birds (4 individuals in 1997, 10 in 2.4. Diet 1999, 2 in 2000, and 8 in 2003). The number of birds studied corresponded to the flock sizes used The species prefers insects in spring and summer in this type of behavioural studies on sparrows whereas in autumn it eats seeds of alpine grasses. (max. 20 birds for producer-scrounger system, Wintering birds often eat garbage in ski areas Barta & Giraldeau 1998) and pigeons (Brown (Cramp 1988). In our experiments we used seeds 1969, Giraldeau & Lefebvre 1985). of the following herbaceous species: white millet Birds were video-taped from distances of ca. (husked) and panicum millet (unhusked) Panicum 2–3 m, usually from the side. Head position was miliaceum, poppy seed Papaver somniferum,sun- visible in every case. Food searching and feeding flower seed Helianthus annuus, buckwheat Fago- were monitored with a portable video camera sy- pyrum aesculentum, flax seed Linum perenne, stem (Panasonic S-VHS.NV MS4). Interrupted wheat Triticum aestivum, canary grass Phalaris video observations lasted from 30 minutes to 10 canariensis, hemp seed Cannabis sativa and cole hours. The number of visits made by each individ- seed Brassica napus. One segment of a plastic ex- ual and the time it stayed at the feeder were ana- perimental dish contained dried flies Musca lysed later in the laboratory. domestica. Three segments were filled with bis- cuits, bread and bacon. Birds mainly eat this type of diet on the terraces of mountain restaurants or 2.3.