Comparison Of Breeding Strategies In Two Sympatric Tropical Birds

The diversity of life history and evolutionary strategies are the focus of study in evolutionary ecology.Many existing views and tests on evolution of life history are based on the northern temperate system,while information on life history characteristics of tropical birds is poorly known.Birds devote a lot of energy and cost to breeding offspring in the course of their lives,and focus their evolution on the reproductive phase,thus reproduction is the core content of life history research in birds.However,nest predation is the main cause of bird breeding failure.Therefore,nest predation enables breeding birds to evolve a series of anti-nest predation strategies throughout various stages of reproduction.This study was designed to mark and track common tailorbird(Orthotomus sutorius)and rufescent prinia(Prinia rufescens)individuals,compare the characteristics of life history in the two sympatric tropical birds during the breeding period,explore the mechanism of their coexistence in the same region,explain the causes of nest failure through predator types and predation patterns and the anti-nest-predator adaptation strategies adopted by birds.The main results and conclusions of the present study are as follows:1.Tailorbird and prinia had similar breeding behavior,building a unique leaf nest,breeding from the beginning of March to the end of September.They were nesting at the foot of the mountains,which in the border of forest and farmland,but there was differentiation in nest leaves and nest-site microenvironment,so as to reduce competition for coexistence: Tailorbirds prefer nesting in secondary forest habitat at the foot of the mountains,and using more leaves of Sterculia nobilis,while prinias prefer nesting in grassy areas at the foot of the mountains,and using more leaves of Ficus macrophylla.2.There was significant difference in the clutch size between the two related birds(P= 0.041),indicating that different laying and incubation strategies were adopted.Tailorbirds laid more eggs and more frequent return to the nest,that was,more activities outside the nest;prinias laid less eggs and less frequent return to nest,but there was significant difference for nestprotecting behavior in prinias,when someone approached the nest,it would constantly jump and give out strong warning calls,while the tailorbird showed nothing.Both two bird species can try multiple brooding under successful reproduction up to three clutches within one year.The ratio of multiple brooding by tailorbirds was 17.9% and by prinias was 23.7%.There was no significant difference in the ratio of multiple brooding between the two groups(P= 0.411).3.The reproductive success rates of tailorbird and prinia were only 44.7% and 44.2%,with no significant difference(P= 0.094).Nest predation and human disturbance were the main factors affecting the breeding success of the two bird species.The predation rate of tailorbirds and prinias were 36.5% and 38.0%,there was no significant difference in predation rate.Snake were identified by video recording as the most common nest predators(72.2%),while the rest were bird predators,including the Greater Coucal(Centropus sinensis),Indochinese Green Magpie(Cissa hypoleuca)and White-winged Magpie(Urocissa whiteheadi).All the snake predation events took place at night,and the snakes could prey on the artificial nests with only eggs inside.Bird predation occur during the daytime,and magpies may carry off chicks from both species to feed their own chicks.4.Tailorbirds and prinias had high level of mate retention and nest site fidelity during within year and between years.Nest predation did not affect the change of territory between each breeding attempt,nor did it affect how far it dispersal,that was,nest predation did not force the parents to build a nest over a greater distance;both birds followed the same pattern of dispersal during within year and between years,that was,re-nesting in the old territory.5.We compared the multiple breeding behaviors of the two birds and their influencing factors in detail.The results showed that both of tailorbirds and prinias have strong reproductive ability and they can breed four clutches under the condition of nest failure(i.e.,predation).The incidence of re-nest of tailorbirds was 46.0%,the interval of egg laying was 6-91 days;and the incidence of re-nest of prinias was 49.1%,the interval of egg laying was 20-96 days.A total of 50% of two bird individuals changed the number of brooding in two years,and there were no difference in the quality of multiple brooding females compared with single brooding females(P= 0.821;P= 0.423).Tailorbird's clutch size and the quality of eggs did not change between multiple brooding(P= 0.438),while the clutch size of prinias was decreasing(P= 0.025),showing a different multiple breeding strategies in egg-laying behavior.There were significant differences in the probability of re-nest under nest predation and successful reproduction(P= 0.003;P= 0.038),the probability of re-nest under predatory conditions was greater than in successful breeding nests,suggesting that nest predation can promote multiple reproduction of birds.In conclusion,the two species of tropical birds,common tailorbirds and rufescent prinias,have achieved coexistence by differentiation through nest leaves and nest site microhabitats.They have the life history characteristics and strategies for long breeding time,leaf nest camouflage,high predation pressure,low reproductive success rate,high loyalty to mating and nest site,rapid reproduction,short single reproduction time and multiple brooding.