On the nest site characteristics of the 'dusky' orange-crowned warbler (Vermivora celata sordida) endemic to Santa Catalina Island

This study focuses on the nest site of a poorly known endemic subspecies of orange-crowned warbler (Vermivora celata sordida). The research took place during 2006 on Santa Catalina Island, part of the Channel Island archipelago in Southern California. As one of the first detailed descriptions of the nest site characteristics of this subspecies, this study has revealed that nest placement is highly variable, particularly when compared to mainland populations. Nest height on Catalina ranges from ground to 5m, whereas mainland subspecies nest predominately on or close to the ground. This research also provides an extremely comprehensive analysis of materials used in nest construction and reveals surprising plasticity in the types and amounts of materials used. Measurements of the nest site uncovered a significant preference to place the nest in the North-East part of the substrate, which was highly correlated with the slope of the terrain. There were no relationships between nest site characteristics and nest success in terms of fledge/fail, although 2006 was an extremely poor year in terms of reproductive success, with a Mayfield estimate of 0.17. It was found, however, that nests under a less dense canopy were active for a longer number of days, as were nests which had a higher level of concealment from below. This is an interesting outcome, as the concealment of a nest from below is not a measurement which is considered in most studies of nest sites. There was very little difference in nest site characteristics between the xeric and mesic ecotypes, apart from the lower canopy cover above nests found on the xeric plot. Interestingly, nesting success was higher in the xeric habitat when compared with the mesic. Detailed microclimatic measurements were obtained for both nesting sites, before incubation, and for random points. It was found that nests were placed at a location in the substrate which provided lower maximum temperatures when compared to random points within the same substrate. Temperature within the nest was higher than just outside, indicating that the nest structure has an insulative function. Furthermore, it was found that grasses and dense plant matter incorporated into the nest structure provided a higher level of insulation. Nests which experienced higher maximum temperatures were active for a longer number of days, which may have been related to canopy cover, as mentioned above. Two nests were particularly interesting, as warmer temperatures within the nest were experienced throughout the night, but cooler temperatures during the day, when compared with just outside the nest. This study has revealed several interesting characteristics of the nesting site of this poorly understood subspecies and provides a platform for possible future research in this area.

Level dc:type.qualificationlevel

MSc(R)

Grantor dc:publisher.institution

University of Glasgow

Year dc:date.issued

2008

Author dc:creator

• Montag, Hannah

• QH301 Biology
• QL Zoology

Language dc:language

en