Brood Parasitism, Nest Predation, and Season-Long Reproductive Success of a Tropical Island Endemic

Abstract

The Puerto Rican Vireo (Vireo latimeri) is a single-island endemic resident on Puerto Rico. The Shiny Cowbird (Molothrus bonariensis), a generalist brood parasite native to South America, arrived on the island in 1955 and has established itself as a breeding resident. To determine the impact of the exotic cowbird on vireo reproductive success, I studied the demography of marked Puerto Rican Vireos in Guinica Forest, Puerto Rico, in 1990-1993. Vireo breeding season length varied among years (69-106 days), apparently influenced by rainfall. The primary causes of reproductive failure were nest parasitism and nest predation. Cowbirds parasitized 73-83% of vireo nests. Parasitism reduced the number of vireos fledged per successful nest by 82%, primarily through decreased hatching success and fledging success. Vireos did not abandon nests in response to cowbird egglaying, but frequently deserted if cowbirds removed host eggs. Native avian predators and exotic mammalian predators together caused the demise of about 70% of all nest attempts. As a result, daily nest survival rate was low (0.93 tO .Ol), and only 13-19% of nests tledged vireo or cowbird young. Pairs renested after failure and attempted to raise second broods. Females in this population attempted two to six nests per season and fledged an average of 1.33 vireos in 1991 and 0.24 vireos in 1993. The combination of restricted breeding season, high predation and parasitism rates, large impact of parasitism on reproductive output, and low seasonal fecundity of females suggests that, despite high survival rates, the Puerto Rican Vireo is in danger of extirpation from portions of its range.

Teste do efeito de borda na predação de ninhos naturais e artificiais no Cerrado

“…MARINI, dados não publicados). A taxa de parasitismo da borda da reserva é considerada baixa em relação a outros locais da região Neotropical onde pode atingir entre 65 e 83% dos ninhos (WOODWORTH 1997, MERMOZ & REBOREDA 1998 Os dados obtidos nesse trabalho permitem concluir que as taxas de predação de ninhos naturais e artificiais, assim como de parasitos de ninho e a abundância relativa de duas espécies de predadores não foram significativamente diferentes entre a borda e interior. Porém não se sabe se essas atuais taxas de predação são normais para a região ou se ainda não houve tempo suficiente de resposta às mudanças dos efeitos de borda na Estação Ecológica de Águas Emendadas.…”

Occupancy dynamics in human‐modified landscapes in a tropical island: implications for conservation design

“…Increasing cover might provide greater foraging resources (e.g. arthropods) and potential nesting substrates (Woodworth, 1997).…”

Threats from introduced birds to native birds

“…Brood parasitism Causal Potentially Woodworth (1997) ( Table S1). There was some strong evidence for a lack of competition in interactions with the Common Myna (Parsons et al 2006;Lowe et al 2011;Borowske et al 2012), Common Starling (Williamson and Gray 1975;Vierling 1998) and Mute Swan (Conover and Kania 1994).…”

“…The Shiny Cowbird (Molothrus bonariensis) was introduced to the island of Puerto Rico in c. 1955 and was recorded parasitising 17 native species, including a single-island endemic, the Puerto Rican Vireo (Vireo latimeri) (Woodworth 1997, and references cited therein) ( Table 1; see 'Evidence for threats involving introduced species', below).…”

“…The Shiny Cowbird was introduced to Puerto Rico in 1955 (Woodworth 1997). It parasitised up to 83% of the nests of the Puerto Rican Vireo, which reduced the fledging rate by 82% and potentially threatened to reduce the range of the Vireo (Woodworth 1997).…”