Breeding Ecology of the Altamira Oriole in the Lower Rio Grande Valley, Texas

Abstract

During 2002–2003, we studied the breeding ecology of the Altamira Oriole (Icterus gularis), a permanent resident that builds pendulous nests in remnant tracts of Tamaulipan brushland in the Lower Rio Grande Valley, Texas. We found 76 active oriole nests, seven of which were reused for second broods, for a total of 83 nesting attempts. Nearly 20% of the breeding individuals in our sample were subadults (second-year orioles). Using a microvideo camera, we were able to estimate incubation and nestling periods of 12.5 and 15.5 days, respectively. Fifty-nine percent of nests fledged at least one young, with successful nests averaging 2.3 fledglings. Failed nests were all intact, indicating that predators entered through the small opening in the top of the nest. Six nests fledged Bronzed Cowbirds (Molothrus aeneus), although two of these nests produced orioles as well. Vegetation analysis suggested that orioles preferred the tallest trees in the study sites in which to place their nests. A greater number of fallen logs was also a predictor of nest sites, which agrees with previous studies suggesting that orioles prefer open woodlands and edges. Formerly vast, dense forests in the Lower Rio Grande Valley have degraded into open woodlands, perhaps benefiting Altamira Orioles during the last 50 years. However, because of the oriole's preference for tall trees, continued degradation of forested tracts may not be beneficial to this species.

Population status, habitat dependence, and reproductive ecology of Bahama Orioles: a critically endangered synanthropic species

“…), so nests may accumulate in these species from year to year. Other oriole species occasionally reuse nests within the same season (Werner et al 2007), but we did not observe such reuse in our study. All active nests appeared to have been built within the season based on the color of the fibers used to weave nests.…”

“…In 2009, nine of 18 pairs on NA included at least one SY bird and, for two pairs, both individuals were SY birds, indicating that at least some SY males are breeding. This proportion is within the normal range for breeding SY males among oriole species (6–55%; Rising and Flood 1998, Rising and Williams 1999, Flood 2002, Brush and Pleasants 2005, Werner et al 2007). However, the high proportion of oriole pairs with a SY mate on NA compared to MC and SA suggests that oriole density on NA is functionally low, promoting breeding by younger birds.…”

Diverse habitat use during two life stages of the critically endangered Bahama Oriole (Icterus northropi): community structure, foraging, and social interactions

“…Not all avian species will decline with human disturbance, and some may even benefit from resource subsidies and increases in open and edge habitats, including those within anthropogenic areas ( Werner, Hejl & Brush, 2007 ; Kamp et al, 2009 ; Coulombe, Kesler & Gouni, 2011 ). The Bahama Oriole uses anthropogenic areas during the breeding season, where it selects nest sites in the tallest available palm trees ( Price, Lee & Hayes, 2011 ).…”

Nesting Ecology of the Northern Beardlesstyrannulet (Camptostoma Imberbe) in the Lower Rio Grande Valley of Texas, U.S.A.

“…We used a paired, random-plot design to identify features of the vegetation that were more likely to be associated with tyrannulet nests. The center of the 0.04-ha circular non-use plot was located at a random compass direction and a random distance between 20 and 50 m from each nest, to avoid moving into a different habitat (Werner et al 2007). We recorded the number, DBH, and species of small trees (DBH < 15-30 cm), large trees (> 30 cm), and snags (dead trees with DBH > 15 cm and height > 1.4 m), and the number of fallen logs (diameter > 15 cm and length > 3 m).…”

“…Tyrannulets are small and drably colored, and they probably go undetected much of the time, unless the observer knows the unique vocalizations uttered by males and females (Brush 1999, Tenney 2000. There are no published data quantifying lengths of incubation and nestling stages and habitat selection (Werner 2004). The 11 nests found in 1996-1998 (Brush 1999) were the first records of nests in the LRGV since 1940.…”