FRONTISPIECE. Three-striped Warblers (Basileuterus tristriatus) were studied in the northern Andes of Venezuela. Temperate and tropical parulids differ strongly in life histories. Three-striped Warblers have smaller clutches, longer incubation periods, lower nest attentiveness, longer off-bouts, and slower nestling growth rates than most temperate species. Water color by Don Radovich. Published by the Wilson Ornithological Society VOL. 121, NO. 4 December 2009 PAGES 667–914 The Wilson Journal of Ornithology 121(4):667–678, 2009 BREEDING BIOLOGY OF THE THREE-STRIPED WARBLER IN VENEZUELA: A CONTRAST BETWEEN TROPICAL AND TEMPERATE PARULIDS W. ANDREW COX1,3 AND THOMAS E. MARTIN2 ABSTRACT.—We document reproductive life history traits of the Three-striped Warbler (Basileuterus tristriatus) from 146 nests in Venezuela and compare our results to data from the literature for other tropical and temperate parulid species. Mean (6 SE) clutch size was 1.96 6 0.03 eggs (n 5 96) and fresh egg mass was 2.09 6 0.02 g. The incubation period was 15.8 6 0.2 days (n 5 23) and the nestling period was 10.5 6 0.3 days (n 5 12). Males did not incubate and rarely provided food for females during incubation. Females had 57 6 2% (n 5 49) nest attentiveness (% of time on the nest incubating), which caused egg temperature to commonly become cold relative to development. Both adults fed nestlings and feeding rates increased with nestling age. The growth rate constant for nestlings based on mass was K 5 0.490, which is slower than for north temperate warblers. Predation was the primary source of nest failure and only 22% of nests were successful based on a Mayfield daily predation rate of 0.048 6 0.006. Our literature review indicates parulids differ strongly in life histories between temperate and tropical/subtropical sites with species in the tropics having, on average, smaller clutches, longer incubation periods, lower nest attentiveness, longer off-bouts, and longer nestling periods. Received 11 October 2008. Accepted 6 June 2009. Life history strategies often show strong appear to show strong latitudinal patterns in life differences between north temperate versus sub- history traits (Martin et al. 2000, Martin 2002, tropical and tropical sites (Moreau 1944; Lack Auer et al. 2007). The wood-warbler genus 1947; Ricklefs 1976; Martin et al. 2000, 2006, Basileuterus, comprised of 20 species, is a 2007; Martin 2004), although the extent of particularly widespread group distributed from differences varies among phylogenetic groups Argentina to Mexico with records reaching as far (Fierro-Caldero´n and Martin 2007, Martin and north as southern Texas and Arizona (Dunn and Schwabl 2008). Wood-warblers (Parulidae) in- Garrett 1997). One species is endangered (B. clude a diversity of species across latitudes and griseiceps), but most others are common through- out their range and are of low conservation 1 Division of Biological Sciences, University of Missouri, concern (IUCN 2006). Little is known about the 105 Tucker Hall, Columbia, MO 65211, USA. life histories of most species despite their broad 2 USGS, Montana Cooperative Wildlife Research Unit, Avian Studies Program, 205 Natural Science, University of distribution and relative abundance. Basic infor- Montana, Missoula, MT 59812, USA. mation including nest descriptions and clutch size 3 Corresponding author; e-mail: [email protected] is lacking for many species (Curson et al. 1994). 667 668 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 4, December 2009 Reproductive traits including incubation period, calculated following Mayfield (1961, 1975) and nest attentiveness, and nestling growth are Hensler and Nichols (1981). Nesting season described for even fewer members of Basileuterus length was estimated as the middle 90% of nest or other parulid genera (but see Skutch 1954, initiations (exclusion of earliest 5% and latest Ghalambor and Martin 2001, Martin 2002, Auer 5%) following Martin (2007). We used video et al. 2007). The dearth of information from the cameras to measure parental behavior for 6–8 hrs Tropics and the suggestion that Wood-warblers starting at dawn during incubation and nestling may show strong latitudinal patterns make them phases. Nest attentiveness (% of time on the nest an important group to study for improving our incubating) was calculated for each nest as the understanding of latitudinal patterns in life history number of minutes on the nest/total minutes traits. video-monitored. We calculated the incubation We describe the reproductive biology of the period as the number of days that lapsed between Three-striped Warbler (B. tristriatus) in northern the day the last egg was laid and when the first Venezuela. This warbler inhabits the understory egg hatched (Briskie and Sealy 1990). We of mature and second growth forests from 800 to calculated the nestling period as the number of 2,700 m elevation in Costa Rica, Panama, and in days that lapsed from when the first egg hatched the Andes from Venezuela to Bolivia (Hilty until the first nestling fledged. 2003). Nest and clutch sizes have been described Egg temperatures (uC) were measured for B. in both Ecuador and Costa Rica (Greeney et al. tristriatus by inserting thermisters on the first or 2005, Jablonski et al. 2006), but no other second day of incubation into the center of one reproductive traits have been documented. We egg in each nest through a small hole sealed with provide detailed data based on 146 nests in a glue (Weathers and Sullivan 1989). The wire was montane cloud forest in Venezuela during 2002– threaded through the nest and connected to a 2006. We also present a review of the current HOBO Stowaway XTI datalogger (Onset Corpo- literature for all parulids and compare our results ration, Bourne, MA, USA) that recorded temper- to other species throughout North, Central, and atures every 12–24 sec for 5–7 days per nest South America. (Martin et al. 2007, Martin and Schwabl 2008). Ambient temperatures were measured over the METHODS same periods using a shaded probe near the nest. We searched for nests from March to July, We also measured egg temperatures for Red-faced 2002–2006, in Yacambu´ National Park in Lara, Warblers (Cardellina rubrifrons) in northern Venezuela (09u 429 N, 69u 429 W). This moun- Arizona using the same methodology (Martin et tainous park on the northernmost edge of the al. 2007). Andes is characterized by second growth and We searched the literature for life-history data mature tropical forest. The park ranges from 500 for all species in the Parulidae with which to to 2,200 m and our field sites occurred from 1,350 compare our results. We first consulted The Birds to 2,000 m elevation. We located nests via of North America data base (Poole 2005) and systematic and behavioral searches, and moni- supplemented these data with those from other tored them every 2–4 days, except at stage- literature. We calculated weighted means for changing events (laying, hatching, fledging) when clutch sizes, incubation periods (days), and we monitored nests daily or twice daily (Martin nestling periods (days) when multiple mean and Geupel 1993). Nest, egg, and nestling values and sample sizes were provided, or when measurements, and behavioral data were collected only raw data were available. We recorded a following Martin et al. (2000, 2006, 2007) and range of values when means could not be reliably Fierro-Caldero´n and Martin (2007). We measured calculated; these were excluded from analyses egg mass (g) and nestling growth using ACCU- when we compared temperate and tropical/ LAB (Elk Grove, IL, USA) portable electronic subtropical species. scales with an accuracy of 60.001 g during early Statistical Analysis.—Means are reported with incubation (days 0–2) for egg mass and every 61 standard error (SE) for all data and sample other day (starting on day 0 or 1) for nestling sizes reflect numbers of nests sampled. We used growth. Growth rates for non-experimental nests SPSS Version 15.0 (2006) for all statistical tests. were calculated following Remesˇ and Martin We used analysis of variance (ANOVA) to test for (2002), and nest predation and survival rates were temporal changes in nest attentiveness (% time on Cox and Martin N BREEDING BIOLOGY OF A TROPICAL WARBLER 669 FIG. 1. Temporal distribution of nest initiation dates (date the first egg is laid in a nest) for the Three-striped Warbler among weekly (7 day) intervals. the nest) and mean on- and off bouts during from 8 March to 25 June across years (Fig. 1). incubation by separating the stage into three Nests were usually initiated after 10 April (n 5 categories (early, 2–3 days; middle, 5–7 days; 103), although three nests were initiated in March; late, 12–14 days). We used least-significant two of these were from the same individual in difference tests (LSD) to conduct post hoc tests consecutive years based on color-banding. The when ANOVA results were significant (a # 0.05). median date of nest initiations was 16 May (Fig. 1). We used linear regression to test for relationships The nesting season lasted 68 days (Fig. 1). between temporal changes in parental behavior Eggs were white with irregular brown spots. during the nesting stage (e.g., brooding effort, Fresh egg mass (measured between day 0 and day feeding rates). We examined distributions of life- 2 of incubation) was 2.09 6 0.02 g (n 5 90), history trait data for temperate and subtropical/ which represented 17.7% of adult female body tropical warblers using a Shapiro-Wilks test. One mass (11.80 6 0.18 g, n 5 33). Five of 96 or both of the distributions departed from clutches had one egg (5%), one had three eggs normality for most life-history traits, so we used (1%), and the rest had two eggs (94%), yielding non-parametric Mann-Whitney U-tests to test for an average clutch size of 1.96 6 0.03 eggs.