A Survey of Population Size and Parasitism of Gray Vireos in the Los Piños Mountains Jaclyn N. Andberg Niles H. Brinton
Jan 16, 2016
A Survey of Population Size and Parasitism of Gray Vireos in the Los Piños MountainsJaclyn N. Andberg
Niles H. Brinton
Introduction Little is known about the population densities and
effects of brood parasitism on the Gray Vireo in New Mexico
The Gray Vireo is A Species of Conservation Concern (USFWS 2002) Listed as Threatened in the State of New Mexico (New
Mexico Game and Fish 2008) Frequently parasitized by the Brown-Headed Cowbird
Increased knowledge of this species will Aid in improved wildlife management of the Sevilleta
National Wildlife Refuge (SNWR) Improve our understanding of biotic interactions between
SNWR and surrounding rangeland
Gray Vireo (Vireo vicinior) Small, insectivorous passerine with
gray plumage Inhabits low-elevation piñon (Pinus
spp.)-juniper (Juniperus spp.) woodlands in the southwestern United States
Cup-shaped nests suspended in fork branches
Egg dates: 20th April -2nd Aug (but usually late May)
Clutch size: 2 – 4 eggs Incubation period: 12-14 days Nestling period: 13-14 days Parasitized nests are often abandoned
Brown-headed Cowbird (Molothrus ater) Stocky, brood parasite from the
family Icteridae (blackbirds) Forages for ground seeds and
grains, grasshoppers and beetles in open grasslands
“nests” in trees from surrounding habitats
Energy spent on egg production rather than parental care
Can lay up to 3 dozen eggs in one breeding season
Lay eggs in the nests of over 220 bird species
Clutch size: 1-7 eggs Incubation period: 10-12 days Nestling period: 8-13 days
Species Distribution
Objectives
1) Determine population density of the Gray Vireo by surveying suitable sample habitats located within the SNWR
2) Monitor nests in order to determine a) nest success of parasitized versus non-parasitized nests b) productivity of breeding Gray Vireo pairs
3) Determine the effects of brood parasitism on reproductive success by comparing sites based on proximity to heavily utilized rangeland
Methods Two study sites based on
habitat suitability and proximity to actively grazed rangeland
Sampling of two sites alternates daily
Territories are identified and nests are located
Sepultura Flats
Northern Piños Mountains
Methods
300 m² grid points at each study site
60 points surveyed per site
~546 Ha. Sites (1,350 acres)
Surveying begins around 7:00 am
Methods
Song playback is used at each point
Gray Vireos are detected by sight and sound
Individuals are recorded and observed for nest building/tending behavior in order to locate nests
MethodsIf nests are not immediately located, territories are returned to for further observation
Extend-A-Vue mirrors are used to observe out-of-reach nests
Nests are monitored every 3-4 days
Census Results 1.50 Vireos / 40 Ha
Previous research found density range of 0.2 - 0.9 Vireos / 40 Ha
Found 41 individuals
12 mated pairs
7 nests (3 parasitized, 4 depredated)
Northern Piños Mountains
1.83 Vireos / 40 Ha
25 individuals 6 unknown individuals 9 known pairs
4 nests
N
Northern Piños Nest Data
No nests produced vireo fledglings
2 out of 4 nests were parasitized, then abandoned
2 non-parasitized nests were depredated
Sepultura Flats
1.17 Vireos / 40 Ha
16 individuals 10 unknown individuals 3 known pairs
3 nests
map
Sepultura Nest Data
1 nest was parasitized (with an unhatched cowbird egg)
This nest was successful
2 out of 3 nests were depredated, but not parasitized
Discussion
1.50 Vireos / 40 Ha There were 5 mated pairs
for which no nest was ever located
Cowbird parasitism was observed at both sites
Not enough nests were found to perform statistical analyses
Discussion Every nest that was not
predated upon was either parasitized or abandoned
Parasitism commonly leads to nest abandonment
The only successful nest was parasitized
Nests were all found in trees very close to arroyos
Drought
Food source availability Reproductive habits Productivity was very low
during this breeding season (0.29 young / territory)
Literature: 0.7 – 3.0 young / territory
Future Research Expand sample areas
and produce multi-year data set
Determine if nest-arroyo proximity is significant
Use cameras to determine nest predators
Cowbird trapping
Drought effects Were vireos pairing
normally? Were vireos nesting
normally? Is productivity higher in
years with more precipitation?
Literature Cited Martin, Thomas E., and Geupel, Geoffrey R. Nest-Monitoring Plots: Methods for
Locating Nests and Monitoring Success. Journal of Field Ornithology: 64(4). 1993. pp 507-519.
Mayfield, Harald. F. Suggestions for Calculating Nest Success. The Wilson Bulletin: 87(4). 1975. pp. 456-466.
Pierce, Leland J., Gray Vireo (Vireo vicinior) Recovery Plan. New Mexico Department of Game and Fish. May 3, 2007.
Rothstein, S. I., Verner, J., and Steven, E. Radio-Tracking Confirms a Unique Diurnal Pattern of Spatial Occurrence in the Parasitic Brown-headed Cowbird. Ecology: 65(1). 1984. pp. 77-78.
Stake, Mike M., and Garber, Gail. Gray Vireo Monitoring in Northwestern and Southeastern New Mexico. Proceedings of the New Mexico Department of Game and Fish Gray Vireo Symposium, April 2008. pp 11-13.
Acknowledgements Kathy Granillo Scott Collins Jennifer Johnson Fellow REU students Sevilleta Interns