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1 This article was downloaded by: On: 11 August 2009 Access details: Access Details: Free Access Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Bird Study Publication details, including instructions for authors and subscription information: Polygyny in Spanish Pied Flycatchers Ficedula hypoleuca J. Potti a ; S. Montalvo a a Departamento de Biologic Animal, Universidad Alca de Henares, Madrid, Spain Online Publication Date: 01 March 1993 To cite this Article Potti, J. and Montalvo, S.(1993)'Polygyny in Spanish Pied Flycatchers Ficedula hypoleuca',bird Study,40:1,31 37 To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Bird Study (1993) 40, Polygyny in Spanish Pied Flycatchers Ficedula hypoleuca J. POTTI and S. MONTALVO Departamento de Biologic Animal, Universidad Alcalá de Henares, Madrid, Spain Downloaded At: 08:44 11 August 2009 Polygyny was studied for 4 years in a central Spanish montane population of Pied Flycatchers. The frequency of Polygyny was low (4.4%) and limited to two females per male. Bigamous males only differed from monogamous males in that they were older. Secondary females had a lower reproductive success and their surviving nestlings were smaller and undernourished, probably due to the absence of the male during most of the early nestling period. Primary and secondary nests were separated by short distances, which makes it hard to explain the mating system by male 'cheating' or female female aggression. Secondary females were mainly young inexperienced birds which might not otherwise have bred in their first potential breeding season. The mating system of the Pied Flycatcher Ficedula hypoleuca has been a subject of much interest since first described by von Haartman. 1 Successive polygamy (usually bigyny =1 male: 2 females) and polyterritoriality have been recently intergrated in a variety of hypotheses which try to explain male and female polygamous mating behaviour. 2-7 Of these hypotheses, that of 'male deception' proposed by Alatalo et al. 2'4 has elicited much attention, in addition to an experimental test. 7 Under the male deception hypothesis males try to hide their mated status by establishing secondary territories some distance from their primary nest site. Females attracted to secondary territories are presumably unaware of the male's status and are 'deceived' into accepting as a partner a male that is already mated. Recent work has questioned the general validity of the deception hypothesis as the only explanation for the evolution of polygyny in this and other species. 7' $ Mate retention, 5 female female aggression,' distinctive male behaviour by already mated males' and costs of mate searching in females 10 have been shown to be plausible or complementary alternatives to the male deception hypothesis. Furthermore, it has been pointed out that the mating system of a species may vary across the geographical range, depending on ecological conditions such as habitat type, breeding density, abundance of competitors for nest sites, etc. 6' 11 However, until now all work on the Pied Flycatcher mating system has been done in central and northern Europe, and no data are available on the frequency or consequences of polygyny in southern populations. In this paper we analyse data collected in a population study of Pied Flycatchers in central Spain Although these data do not allow any formal test of the deception hypothesis, they are of interest in the context of predictions of the hypotheses outlined above and the possibility of geographical variation in the mating system. MATERIALS AND METHODS A population of Pied Flycatchers breeding in a montane deciduous oakwood (Quercus pyrenaica) about 80 km northeast of Madrid has been studied since Starting in 1986 (females) or 1987 (males), nearly all breeding birds were captured at their nests while incubating (females) or feeding nestlings (both sexes), in the latter case with the device of Stutchbury and Robertson. 16 Upon capture all birds were given a metal ring and an individual 31

3 32 J. Potti and S. Mantalvo combination of colour rings, aged, 13' I7 measured and weighed. Condition indices were computed for each bird as the residuals from the population regression of weight on cubed tarsus-length. A polygynous male was defined as a male which was captured and/or individually identified while feeding nestlings in more than one nestbox. In practice, only bigynous matings occurred, primary and secondary females being defined by the respective laying dates of the first egg in each clutch. Breeding phenology and performance (clutch size, hatching success and fledging success) were routinely recorded for all nests. Arrival dates of males were intensively studied in 1988 and ' 14 Territory quality was computed for each year as the proportion of previous years, since 1985 onwards, a particular nestbox was occupied by Pied Flycatchers in relation to those that were available, i.e. not occupied by other species (Parus spp, Sitta europaea). From 1986 onwards for females and from 1987 onwards for males, breeding experience was quantified by the number of previous years that a bird has bred in the area. All nestlings were ringed and measured when 13 days old in 1987 to Mean weight, wing-length, tarsus-length and condition index (analogous to that for adults; see above) were calculated for each brood. Nearly all reproductive variables showed significant yearly variation; therefore, variables were standardized when necessary by subtracting individual values from the yearly means. In 1990, unusually heavy predation by weasels (Mustela nivalis) precluded the capture (although not the individual identification) of many males. Hence, all data analysed in this paper refer to the period for females and for males. Nestling feeding frequencies by the parents were quantified in the 1988 breeding season by quietly sitting some distance from the nest and counting the number of male and female feeding visits during 20-min periods. For the purpose of the analysis, feeding frequencies were divided in three periods of nestling age; early (0-5 days from hatching), middle (6-10 days) and late (from 11 days old and onwards). The nestlings fledged around the 17th day of life (range days). All statistical tests' $ are 2-tailed. Means are given with one standard error. RESULTS Frequency of polygyny Between 1987 and 1990, 12 cases of bigyny were recorded, making up 4.4% of all known matings (n = 274). Characteristics of the bigamous males Bigamous males were significantly older than monogamous males (Mann Whitney U- test = 482.5, n = 169, 10; P = 0.01). When the analysis was restricted to old males (> 2 years old), bigamous males still tended to be older than monogamous adult males (U = 342, n = 112,9; P = 0.052), the respective mean ages being 2.7±0.17 and 2.4±0.006 years. Between-male comparisons of morphological features (wing-length, tarsus-length, weight, condition), secondary sexual characteristics (mantle colour, 19 white patch area on the males' foreheads 13), arrival date and territory quality of the primary nestbox of the bigamous males were thus restricted to adult monogamous males. There were no significant differences in colour, size (tarsus- and wing-length), weight, condition or white patch area between the two male classes (Mann Whitney U-test, in all P? 0.20). Nestbox quality tended to vary with pairing status (Kruskal Wallis test, H = 5.23, df = 2, P = 0.07). Primary nestboxes did not differ significantly from secondary nestboxes (respective medians 0.59 and 0.29, ranges , U = 70.5, n = 10,10; P = 0.12) although they were of significantly better quality than the boxes occupied by monogamous females (median 0.25, range , U = 702.5, n = 237,10; P = 0.03). Overall, nestboxes occupied by primary females were better than the remainder of the occupied nestboxes (U = 732, n = 247,10; P = 0.055). Although bigamous males tended to arrive earlier (mean arrival date 7 May), than monogamous males (mean 10 May), the difference was not significant (U = 434.5, n = 96,7; P = 0.20). Characteristics of polygynously-mated females and their broods Secondary females, by definition, lay their first egg later than primary females mated to the

4 same male. The interval between the first egg dates for the two females ranged from 2 to 15 days (mean 8.7±1.4 days, n = 11) and was not shorter when the nests were farther apart (Fig. 1). Of the secondary females, 70% (n = 10) lacked previous breeding experience, the difference being significant in relation to experience rate of primary females (77.8%, n = 8, Fisher's exact P = 0.025). Since female Pied Flycatchers, unlike many males, start breeding in their first year of life, secondary females tended to be younger (mean age 1.25±0.16) than monogamous and primary females considered together (1.77±0.07), but the difference was not significant (U = 848, n = 162,8; P = 0.11). Primary and monogamous females did not differ in any of the variables examined, except in nestbox quality (see above). Secondary females returned at a lower rate (36%) than primary (80%) or monogamous (57%) females, but the difference did not reach statistical significance (x 2 = 4.07, df = 2, P = 0.13). Neither were there differences in breeding dispersal distances between returning primary and secondary females (respective median distances, 189 m (n = 7) and 337 m (n = 5); U = '14, P > 0.20). Breeding success in the Pied Flycatcher declines with the progression of the breeding season, 4' 20 which may confound comparisons of breeding performance between groups of females. To control for breeding phenology, the group of secondary females was compared only with those females breeding at the same time (Table 1). There were no differences in either clutch size, incubation period or number of eggs hatched although hatching success was, surprisingly, higher in secondary females than in the monogamous and primary females grouped together. However, performance in all other variables, including recruitment to the breeding population, was significantly lower in secondary nests. Nestlings in secondary nests were undernourished and their development slower than that of nestlings in primary and monogamous nests. The nests of secondary females were usually not far from the nestboxes occupied by primary females (range m, median 25 m, Fig. 1), although secondary nests were significantly farther away from the primary female's nestbox than the nearest nestbox available in Polygyny in Pied Flycatchers 33 any direction (Wilcoxori s test for matched pairs, T = 10, n = 11, P < 0.05). Although this result could give support to the idea that males defend nestboxes separated some distance from the primary nestbox in order to hide their pairing status, 2 there were no differences in the distances between the nestbox of primary females and the nearest monogamous female compared with the distances between primary and secondary nestboxes (U = 55, n = 10,10; P > 0.20). Further, the nests of the monogamous females compared were also further from the nearest occupied nestbox than from the nearest empty nestbox (T = 4, n = 11, P < 0.02). That is, primary and secondary nests were not more widely separated than nearby nests of monogamous pairs. N T 16 v 14 R * * -g n 10.* u 4 iu ^ w 2 x ó 0 _J ^ Distance (m) Figure 1. Distances between primary and secondary nests of each bigamous male and differences in laying dates of their females (Spearman rank correlation r, = 0.13, n.s.). Parental feeding frequency in primary and secondary nests Previous findings 3 point to the lack of male attendance as the major cause of partial or total nest failure in secondary broods, since the females rear their broods almost unaided. This was confirmed by our data on feeding frequencies per nestling in primary and secondary nests in 1988 (Fig. 2) Bigamous males rarely visited their secondary nests while they were rearing their primary brood. Only after the fledging of the former did the bigamous males help the secondary female to feed the nestlings, but by that time brood reduction had

5 34 J. Potti and S. Montalvo Table 1. Mean values±s.e. (n) adjusted reproductive variables and mean nestling measurements for concurrently laying females. Breeding variables, but not no. of recruits or nestling measurements, varied annually and were therefore standardized around a mean = 0. Differences were tested with Mann-Whitney 2-tailed tests (LI values) Monogamous and primary females Secondary females U P Clutch size 0.05±0.05 (233) -0.42±0.25 (11) No. hatched eggs -0.03±0.07 (211) -0.04±0.24 (11) Hatching success -0.01±0.01(211) 0.08±0.03 (11) No. fledglings 0.10±0.11(163) -1.66±0.40 (11) Fledgling success 0.02±0.02 (163) -0.33±0.08 (11) Relative success* 0.01±0.02 (163) -0.23±0.09 (11) No. recruitst 0.82±0.09 (96) 0.00±0.00 (6) Nestlings tarsus-length 19.58±0.04 (144) 19.19±0.15 (9) Nestlings wing-length 49.70±0.32 (143) 45.47±0.72 (9) Nestlings weight 14.73±0.08 (144) 13.34±0.43 (9) Nestlings condition 0.05±0.07 (144) -1.04±0.37 (9) *No. fledged/clutch size. t Nestlings fledged in 1987 and 1988, recorded breeding until Downloaded At: 08:44 11 August 2009 usually already occurred. However, one bigamous male was observed alternating his feeding visits between his two broods in In this case, the nestboxes were contiguous (25 m apart), and the laying dates of the two females separated by only 2 days. Feeding visits/ nestling DISCUSSION The results of this study on polygyny in Spanish Pied Flycatchers show many similarities and some differences with previous work on central European and Scandinavian populations. 2-4,21 Old age of polygamous males and Feeding visits/ nestling Secondary nests Nestling period Figure 2. Male and female feeding frequencies (±s. e.) to the primary and secondary nests in 1988 (n = 5 20-min periods in each nestling period class, for each mating category). Panel a for the same age period in each nest. Panel b: irrespective of the nestling periods, on concurrent dates. It can be seen that males preferentially feed their primary nestlings (early period in panel a) when there are nestlings in both nests (panel b). In all cases, primary nestlings had fledged by the time the secondary nestlings were in the late period.

6 the low prospects of successful breeding among secondary females are two features of our population that appear to be typical. At variance with the most previous work, however, is the close proximity of the nestboxes of bigamous males. Males of this species are considered a classic example of polyterritorial polygyny,' but in this study only 3 out of 11 bigamous males had their nestboxes separated by distances greater than 100 m. The situation in our population is thus somewhat reminiscent of the behaviour of polygynous Collared Flycatchers Ficedula albicollisl' 2 (which attract females to nearby holes) or, at least, of a mixture of both the monoterritorial and polyterritorial male strategies. Our results do not, therefore, lend support to the hypothesis of male 'cheating' as the explanation of polygyny in this species, although deception cannot be ruled out with our scanty evidence. It is more difficult to judge from our data the relevance of female female aggression for the evolution of polyterritorial polygyny. 9 Certainly, it is difficult to see how aggression could have played an important role in nest spacing in our study, as in 8 of 11 cases primary and secondary females were separated by distances of less than than 50 m. However, female aggression levels decrease through the nesting cycle 9 and hence may have been important in preventing early bigamous matings. This should be important for primary females as it would ensure exclusive male help in the feeding of the nestlings if the delay is substantial We have circumstantial evidence that female aggression may play a role in nest spacing during the nest building period (J. Potti and S. Montalvo, unpub. obs.). This behaviour is not always effective (or present), since some secondary females settled very quickly after the primary female. Our observations of some primary and secondary females looking at the interior of each other's nestbox while the other female was temporarily absent (captured by us), suggest that some females 'know something' about their mate's activities. However, these observations are not serious challenges to either the deception or the aggression hypotheses, as the crucial knowledge about the partner status should be gained by secondary females before pairing. After laying, secondary females cannot afford a renesting attempt without losing even more of their low pros- Polygyny in Pied Flycatchers 35 pects of successful breeding.' More studies on mate assessment by female Pied Flycatchers are necessary before any firm conclusions on female behaviour can be drawn. 23 In common with other studies, only a small fraction of all males succeeded in attracting more than one female, and these tended to be older males. Old males arrive early in spring and occupy the best territories, 13,21,24,25 many of them defending more nestboxes than later arriving males. 13 ' 24 This may give them a mating advantage by virtue of the higher number and quality of the nestboxes possessed, the greater area defended, 26 and the higher chance of being visited more often by prospecting females. It is interesting that these males attracted their primary females to the best nextboxes in the area, suggesting that male Pied Flycatchers are more prone to attract a second female when they already possess a high quality nestbox. Adult females are first attracted to these nestboxes but, unlike other studies, 2''' 8 we have not observed any reduction in reproductive performance in primary as compared to monogamous nests. This is probably due to the fact that bigamous males fed their primary brood as often as monogamous males did. Male help was substantially reduced at secondary nests, which in the year when we had data on feeding frequency lagged behind the primary nests by 7-14 days. This means that secondary females only obtained significant help after the primary nestlings had fledged, and this was reflected in brood reduction and poor nestling development and condition of surviving nestlings. Primary females may suffer from lack of male attendance after fledging of the primary brood, but the importance of post-fledging parental care is not known. Also, primary females may obtain less male help when both nests of a bigamous male are more synchronized and thus in a similar developmental stage2' Our results highlight an often neglected aspect of polygyny in the Pied Flycatcher: the breeding experience of the females involved. Young and inexperienced females seem to be in more danger of occupying secondary nests than older, experienced females. As noted in several studies, 2-5,7,13,21 late females are in a hurry to establish a pair bond and perhaps their lack of breeding experience makes them more prone to make 'wrong' decisions about

7 36 J. Potti and S. Montalvo the male's status. As stated above, young Pied Flycatchers arrive later in spring than adult birds and many birds (more males than females) do not breed in their first potential breeding season We suggest that secondary females are mainly 'recruited' from the pool of inexperienced females, many of which would not otherwise breed in their first potential breeding season. Unpaired males are always available elsewhere, but females may only search a restricted area which is probably limited by search costs. 1o,32 These costs, in combination with routes of entry into the nestbox area, 7 male polyterritoriality and deception, female aggression and previous experience of mating behaviour, will determine the pairing decisions made by females. The relative contribution of each of these factors in shaping the polygynous mating system of the Pied Flycatcher is unknown. ACKNOWLEDGMENTS We thank D. Blanco for help with data collection and D. G. Harper for commenting on the text and improving the English. The study was made under a grant from the Spanish CAICYT (project PB CO2-02). REFERENCES 1. von Haartman, K. (1951) Successive polygamy. Behaviour, 3, Alatalo, R.V., Carlson, A., Lundberg, A. & Ulfstrand, S. (1981) The conflict between male polygamy and female monogamy: The case of the pied flycatcher Ficedula hypoleuca. Am. Nat. 117, Alatalo, R.V., Lundberg, A. & Stahlbrandt, K. (1982) Why do pied flycatcher females mate with already-mated males? Anim. Behay. 30, Alatalo, R.V. & Lundberg, A. (1984) Polyterritorial polygyny in the pied flycatcher Ficedula hypoleuca-evidence for the deception hypothesis. Ann. Zool. Fennici, 21, Slagsvold, T. & Lifjeld, J.T. (1986) Mate retention and male polyterritoriality in the pied flycatcher. Behay. Ecol. Sociobiol. 19, Slagsvold, T. & Lifjeld, J.T. (1988) Why are some birds polyterritorial? Ibis, 130, Stenmark, G., Slagsvold, T. & Lifjeld, J.T. (1988) Polygyny in the pied flycatcher Ficedula hypoleuca: a test of the deception hypothesis. Anim. Behay. 36, Temrin, H. & Arak, A. (1989) Polyterritoriality and deception in passerine birds. Trends Ecol. Evol. 4, Breiehagen, T. & Slagsvold, T. (1988) Male polyterritoriality and female-female aggression in pied flycatchers, Ficedula hypoleuca. Anim. Behay. 36, Slagsvold, T., Lifjeld, J.T., Stenmark, G. & Breiehagen, T. (1988) On the cost of searching for a mate in female pied flycatchers Ficedula hypoleuca. Anim. Behay. 36, Alatalo, R.V., Lundberg, A. & Ulfstrand, S. (1985) Habitat selection in the pied flycatcher Ficedula hypoleuca. In Habitat Selection in Birds (Ed. M.L. Cody). Academic Press, London, pp Potti, J. & Montalvo, S. (1990) Ocupación de areas con nidales por el papamoscas cerrojillo (Ficedula hypoleuca). Ardeola, 37, Potti, J. & Montalvo, S. (1991a) Male arrival and female mate choice in the pied flycatcher Ficedula hypoleuca in central Spain. Ornis Scand. 22, Potti, J. & Montalvo, S. (1991b) Male colour variation in Spanish pied flycatchers Ficedula hypoleuca. Ibis, 133, Potti, J. & Montalvo, S. (1991c) Return rate, age at first breeding and natal dispersal of pied flycatchers in central Spain. Ardea, 79, Stutchbury, B.J. & Robertson, R.J. (1986) A simple trap for catching birds in nestboxes. J. Field Ornithol. 57, Karlsson, L., Persson, K. & Walinder, G. (1986) Ageing and sexing in pied flycatcher Ficedula hypoleuca. Var Fagelviirld, 45, (In Swedish, with English summary). 18. Siegel, S. (1970) Estadística no paramétrica. Ed. Trillas, México. 19. Drost, R. (1936) Uber das Brutkleid mannlicher Trauerfliegenfange, Muscicapa hypoleuca. Vogelzug, 6, Kallander, H. (1975) Breeding data for the pied flycatcher Ficedula hypoleuca in southernmost Sweden. Ornis Fennica, 52, Askenmo, C.E.H. (1984) Polygyny and nest site selection in the pied flycatcher. Anim. Behay. 32, Pinxten, R. & Eens, M. (1990) Polygyny in the European Starling: Effect on female reproductive success. Anim. Behay. 40, Dale, S., Amundsen, T., Lifjeld, J.T. & Slagsvold, T. (1990) Mate sampling behaviour of female pied flycatchers-evidence for active mate choice. Behay. Ecol. Sociobiol. 27, Slagsvold, T. & Lifjeld, J.T. (1988) Plumage colour and sexual selection in the pied flycatcher Ficedula hypoleuca. Anim. Behay. 36, Alatalo, R.V., Lundberg, A. & Stahlbrandt, K.

8 Polygyny in Pied Flycatchers 37 (1984) Female mate choice in the pied flycatcher Ficedula hypoleuca. Behay. Ecol. Sociobiol. 14, Dale, S. & Slagsvold, T. (1990) Random settlement of female pied flycatchers Ficedula hypoleuca: significance of male territory size. Anim. Behay. 39, Lifjeld, J.T. & Slagsvold, T. (1990) Manipulations of male parental investment in polygynous pied flycatchers Ficedula hypoleuca. Behay. Ecol. 1, Sternberg, H. (1989) Pied Flycatcher. In: Lifetime Reproduction in Birds (Ed. I. Newton). Academic Press, London, pp Nyholm, N.E.I. (1986) Birth area fidelity and age at first breeding in a northern population of pied flycatcher Ficedula hypoleuca. Ornis Scand. 17, von Haartman, L. (1985) The biological significance of the nuptial plumage of the male pied flycatcher. Proc. 18th Int. Om. Congress 1982, Harvey, P.H., Stenning, M.J. & Campbell, B. (1985) Individual variation in seasonal breeding success of pied flycatchers (Ficedula hypoleuca). J. Anim. Ecol. 54, Alatalo, R.V., Carlson, A. & Lundberg, A. (1988) The search cost in mate choice of the pied flycatcher. Anim. Behay. 36, (MS received 15 April 1991; revised MS accepted 13 October 1991)