In shorebirds, the prevalence of successive clutching and types of associated breeding strategies differ among species, environments and individuals. Although several studies have examined successive clutching behaviour in holarctic species, little research has been conducted in the tropics. To assess the full range of reproductive strategies and better understand breeding constraints in tropical environments, we characterised successive clutching behaviour in 54 and 79 colour-banded Malaysian Plovers Charadrius peronii over two years in the Gulf of Thailand. We also examined monthly changes in clutch size, clutch volume, prey availability and breeding success because temporal variability in breeding conditions can affect the prevalence, timing of, and parental role-division between successive clutches. Short intervals between clutches, successive monogamy, high within-season site fidelity, double-brooding, and complete biparental care were general characteristic of successive clutching behaviour. We did not detect any declines in clutch size, clutch volume, prey availability and reproductive success during the course of the breeding season. For Malaysian Plovers, the stable and progressively favourable prey supply and weather conditions, lack of migration, and intense competition for breeding habitats may have contributed to a breeding system constrained more by habitat availability than by time. In these environments, pairs may retain mates and breed multiple times during the long breeding season.
Shorebirds are an ideal taxon to examine the evolution of mating strategies and variation in parental care behaviour because of their highly variable breeding strategies (Reynolds 1996, Blomqvist et al. 2001, Székely et al. 2006). Part of this variability is a consequence of adaptations to different ecological and physical conditions (Székely & Cuthill 2000). Although numerous studies have focused on the breeding ecology of temperate and arctic shorebirds, more research is needed to understand the full range of variability in shorebird breeding behaviour and to identify the environmental constraints that shape breeding behaviour in tropical species (Thomas et al. 2003).
Successive clutching (re-nesting) occurs when birds lay clutches after failed attempts (‘replacement clutching’) or try to fledge more than one brood in a single season (‘double-brooding’). The prevalence of successive clutches, timing of successive clutches, parental role divisions, and mate or site fidelity between clutches vary both across and within shorebird species (Blomqvist et al. 2001, Andersson 2005). The contrasting environmental conditions in holarctic and tropical areas may lead to differences in successive clutching behaviour between closely related holarctic and tropical shorebirds (Johnsgard 1981, Martin 1996).
A key difference between holarctic and tropical environments is the degree of seasonal variability in shorebird prey abundance. High latitude environments are characterised by a brief burst of high prey availability followed by a progressive decline in productivity (Graul 1976, Pitelka 1979, Breiehagen 1989, Smith et al. 1989, Sandercock et al. 1999). In these types of time-constrained environments, females may exhibit sequential polyandry or may rapidly lay successive clutches (‘multiple-clutching’) during periods of high productivity (Oring & Knudson 1972, Breiehagen 1989). The condition of females breeding at high latitudes may decline later in the breeding season and, as a result, they may be more likely to desert clutches, contribute less to parental care, or produce smaller clutches or eggs than those in the tropics (Rooneem & Robertson 1997, Sandercock et al. 1999). Near the beginning or end of the breeding season there could be cold weather periods and females may also have greater difficulties meeting the higher energetic demands for thermoregulation at higher latitudes and could thus take more time to lay successive clutches (Nilsson & Svensson 1996, Amat et al. 1999b, Amat et al. 2000, Blomqvist et al. 2001).
In contrast to holarctic shorebirds, tropical species may have longer breeding seasons because of extended periods of favourable weather and a more stable prey base (Johnsgard 1981, Martin 1996). Longer breeding seasons could lead to greater replacement clutching (successive clutches after failed attempts) and double-brooding rates (successive clutches after successful attempts) (Dowding et al. 1999). Moreover, female birds that have longer intervals between successive clutches would have more time to build or replenish energy reserves for egg laying.
Shorebirds may have partial or complete uniparental care by either of the sexes, sequential polyandry where the male may care for the first clutch while the female incubates the second clutch (Graul 1976, Erckmann & Wasser 1983, Breiehagen 1989, Blomqvist et al. 2001), or complete biparental care (Lenington 1980, Székely & Cuthill 1999). Many temperate or arctic species may have evolved polygamous mating systems with partial or complete uniparental care because of the relatively short breeding seasons (Graul 1976, Bergstrom 1988). Complete biparental care necessitates longer inter-clutch intervals because successive clutches are usually only laid after the fledge date of the primary clutch (Blomqvist et al. 2001). Nest desertion by one parent is adaptive for the deserting parent if the remaining parent is able to fledge chicks on its own (Amat et al. 1999a, Székely et al. 1999, Johnson et al. 2006). Thus complete biparental care of successive clutches and longer inter-clutch intervals may be favoured in environments where nests and chicks are moderately vulnerable to thermal stress, predators, or attacks from conspecifics, and the cooperation of both adults increases fledging success rates (Erckmann & Wasser 1983, Dale et al. 1996, Reynolds & Székely 1997).
We examined successive clutching in a sedentary shorebird, the Malaysian Plover Charadrius peronii, a threatened species (IUCN redlist) that breeds in the Gulf of Thailand. We conducted behavioural observations and monitored breeding success to describe the successive clutching behaviour of Malaysian Plovers and assess whether food demand, temporal constraints, or parental care requirements may have shaped this aspect of their breeding ecology.
Study area and population
From 15 November 2003 – 25 July 2004 and 10 January – 25 July 2005, we studied plovers along a 108-km section of sandy beaches in the Gulf of Thailand between Bornok Beach (12°00′N, 99°53′E) in Prachuap Khiri Khan Province and Laem Phak Bia (13°03′N, 100°05′E) in Petchburi Province, Thailand. During January and February, Malaysian Plovers began defending 100–300 m long, multi-purpose territories that included an intertidal mudflat foraging area, a sandy beach for nesting, and a shrubby, vegetated area behind the beach that prov