Ornis Hungarica (2009) 17-18: 33-45. Do mating opportunities influence within- season dispersal in Penduline Tits? ORSOLYA KISS AND ISTVÁN SZENTIRMAI Kiss, O. and Szentirmai, I. 2009. Do mating opportunities influence within-season dispersal in Penduline Tits? – Ornis Hung. 17-18: 33-45. Abstract To find better mating opportunities may be one of the reasons why birds disperse from one population to another, although evidence is scarce to prove this proposition. Penduline Tit is a highly suitable model species to clarify this question, since both males and females may have several mates during a single breeding season. We followed the dispersal of Penduline Tits in a system consisting of six popula- tions. Our study provided evidence for short distance within-season breeding dispersal in Penduline Tit between our study sites. Both the rate of immigration and emigration showed a strong seasonal pattern, which may be related to the fluctuation in mating opportunities. The number of immigrating males increases with the number of unmated females in the population, i.e. mating opportunities of males. Furthermore, the number of unmated males (mating opportunities of females) in the population increased with the number of immigrating males. Our results thus indicate a relationship between dispersal behaviour and mating opportunities in Penduline Tits. Further stud- ies are needed to distinguish between cause and effect. Keywords: dispersal, Remiz pendulinus, mating system, mating opportunities Összefoglalás A szaporodási időszakon belüli diszperzió egyik lehetséges oka, hogy az egyedek az optimális szaporodási feltételek érdekében vándorolnak át az egyik populációból a másikba, bár kevés bizonyíték támasztja alá ezt a feltételezést. A függőcinege különösen alkalmas a fenti kérdés tisztázására, mivel egy egyednek több egymást követő párja is lehet egy költési időszakon belül. Vizsgálatunkban egy hat populációból álló rendszerben követtük nyomon a függőcinegék diszperzióját. Eredményeink bizonyították szaporodási időszakon belüli disz- perzió meglétét a vizsgált populációk között. Mind a bevándorlás, mind a kivándorlás mértéke jelentős szezonális mintázatot mutatott, amely összefüggésben lehet a párosodási esélyek változásával. A bevándorló hímek száma nőtt a populációban lévő párnélküli tojók számával. Ugyanakkor a párnélküli hímek száma (tojók párbaállási esé- lyei) is nőtt a populációba történő hím bevándorlással. Eredményeink szerint a függőcinegénél összefüggés lehet a diszperziós viselkedés és a pártalálási esélyek között. Az ok-okozati összefüggések megállapításához azonban további vizsgálatokra van szükség. Kulcsszavak: diszperzió, Remiz pendulinus, szaporodási rendszer, párosodási esélyek Kiss, O., Department of Ecology, University of Szeged, Középfasor 52, H-6726 Szeged, Hungary, e-mail: orsi_ [email protected]; Szentirmai, I., Őrség National Park Directorate, Siskaszer 26a, H-9941 Őriszentpéter, Hun- gary, e-mail: [email protected] 1. Introduction sites (Greenwood 1980). Dispersal plays an important role in source-sink dynamics Dispersal is one of the most fundamental (Clobert et al. 2001), in gene-flow between and a well studied population functions. populations (Neigel & Avise 1993), in ad- During natal dispersal, young individuals aptation to changing environmental condi- move from their birth place to their breed- tions (Ronce 2007) and in the population ing site, while during breeding dispersal regulation of many bird and mammal spe- they move between successive breeding cies (Greenwood 1980). It may enhance sur- 34 Ornis Hungarica 17–18 (2009) vival chances of small population (Brown of depleted resources and the possibility of & Kodric 1977), for example by decreas- fast renesting. He found that predation is the ing inbreeding depression (Greenwood & most likely explanation, because moving to Harvey 1982) or by reducing the effect of new territories before renesting can reduce environmental stochasticity on population the probability of nesting failure caused by dynamics. In Indigo Bunting (Passerina predators. In line with this explanation Gre- cyanea) for instance, dispersal can affect ig-Smith (1982) showed that pairs of Sto- effective population size (Payne & Payne nechats (Saxicola torquata) moved further 1993). However, in some circumstances if they renested after predation. Supporting high levels of dispersal may increase the a role for avoidance of depleted resources risk of global extinction (Molofsky & Ferdy Greig-Smith (1982) found that pairs that 2005). Most studies focused on natal disper- raised large broods moved greater distances sal and showed that it is more extensive than than did pairs whose broods were small. breeding dispersal (Greenwood & Harvey The Penduline Tit (Remiz pendulinus) is 1982). Many fewer studies have addressed a small passerine bird (body mass 9-10g) is breeding dispersal; nevertheless, several one of the handful species in which within- factors have been shown to influence it. For season breeding dispersal is common. The instance breeding dispersal between years is appearance and disappearance of adult indi- more extensive among females than among viduals in a population can be observed all males in birds, and this pattern may be ex- over the breeding season from early April to plained by their mating system (Greenwood early August (I. Szentirmai, R.E. van Dijk, 1980, Greenwood & Harvey 1982, Liu & T. Székely, unpublished data). In Penduline Zhang 2008). In the resource-defence mat- Tits either the male or the female deserts the ing system of most birds, where males in- clutch during the egg-laying phase, and pa- vest more energy in competing for resources rental care is provided by a single parent. in order to attract females, males are less Additionally, 30-40% of clutches is deserted likely to disperse than females. Paradis et by both parents and doomed to failure (Pers- al. (1998) showed that migrant species dis- son & Öhrström 1989, Szentirmai 2007). perse further than resident ones, and species After desertion, males and females search living in wet habitats disperse further than for new partners and may remate up to six those living in dry habitats, which could be times during a breeding season and produce explained by the greater patchiness of wet multiple broods. habitats in space and/or time. Dispersal may play an important role Within-season breeding dispersal is the in the breeding system of Penduline Tits. least known form of dispersal, although its Emigration of deserting individuals may role could be very similar to between-sea- decrease the number of available partners son dispersal. One reason for the lack of stu- in one subpopulation, but these individuals dies of within-season dispersal is that it is could provide a source of new partners in not extensive in most species (Greenwood the subpopulations to which they immigrate. & Harvey 1982). Jackson (1989) examined Through mating opportunities dispersal may three hypotheses in Prairie Warblers (Dend- influence the payoffs of desertion and even- roica discolor) to explain within season dis- tually parental care strategies (Székely et al. persal: avoidance of predation, avoidance 2000). Orsolya Kiss and István Szentirmai 35 Through operational sex ratio, dispersal to Fehértó. Fertő is very close to Fehértó, but can also affect the viability of populations. we treated them as distinct populations, since If there are not enough unmated individuals they were separated by a main road and we in the population due to the lack of disper- did not observe regular movements of Pen- sal, deserters will have a lower chance of duline Tits between them. Population of Pen- finding a new mate and this can reduce the duline Tit consists of 20 pairs in Fertő and 15 reproductive success of these individuals. pairs in Csaj-tó. Maty-ér is 3 km long rowing The objective of this study was to collect course and fishing area where 25 pairs breed evidence for the existence of breeding dis- regularly. Madarász-tó is a small fishpond persal in Penduline Tits between our study system (200 ha) with extensive reedbeds and populations and to investigate the relation- willow trees, but it supports only two pairs ship between mating opportunities and dis- of Penduline Tits. Kisszéksós-tó is a lake persal behaviour. We hypothesised first that (30 ha) almost completely covered with reed disappearing Penduline Tits continue breed- where five pairs of Penduline Tits breed. The ing in a different population and that new- exact population size was known, beacuse coming individuals come from other popu- we estimated all Penduline Tits in our study lations. Second, we assumed that attractive population by regular counts throughout the males have better mating opportunities and breeding season. therefore are less likely to emigrate. Third, At each study site males were caught us- we hypothesised that emigration will be high ing mist-nets and using song playback at when mating opportunities are low, and low their first nest, and were individually col- when mating opportunities are high. Finally, our-ringed. Females were caught either to- we predicted that immigration will influence gether with their mate or during incubation the operational sex ratio of the population, in the nest, using a purpose-designed net. and through this breeding system. We measured their wing length and took pictures of the masks of males. The area of the mask was measured from photographs 2. Methods (see details in Kingma et al. 2008). Dur- ing the study we examined 563 nests