Depredation Of Artificial Nests Research Articles

Effects of Edge Habitat and Nest Characteristics on Depredation of Artificial Nests in Fragmented Australian Tropical Rainforest

Variation in nest predation levels associated with rainforest fragmentation (edge effects) was assessed in Australia's Wet Tropics bioregion. Artificial nests were placed in the forest understorey at seven edge sites where continuous forest adjoined pasture, seven interiors (about 1 km from the edge), and six linear riparian forest remnants (50–100 m wide) that were connected to continuous forest. Four nest types were also compared, representing different combinations of two factors; height (ground, shrub) and shape (open, domed). At each site, four nests of each type, containing one quail egg and two model plasticine eggs, were interspersed about 15 m apart within a 160 m transect during September–October 2001. Predators were identified from marks on the plasticine eggs. The overall depredation rate was 66.5% of 320 nests' contents damaged over a three-day period. Large rodents, especially the rat Uromys caudimaculatus, and birds, especially the spotted catbird Ailuroedus melanotis, were the main predators. Mammals comprised 56.5% and birds 31.0% of predators, with 12.5% of unknown identity. The depredation rate did not vary among site-types, or between open and domed nests, and there were no statistically significant interactions. Nest height strongly affected depredation rates by particular types of predator; depredation rates by mammals were highest at ground nests, whereas attacks by birds were most frequent at shrub nests. These effects counterbalanced so that overall there was little net effect of nest height. Mammals accounted for 78.4% of depredated ground nests and birds for at least 47.4% of shrub nests (and possibly up to 70.1%). The main predators were species characteristic of rainforest, rather than habitat generalists, open-country or edge specialists. For birds that nest in the tropical rainforest understorey of the study region, it is unlikely that edges and linear remnants presently function as ecological population sinks due to mortality associated with increased nest predation.

Effects of Nest-Site Selection on Depredation of Artificial Nests

We compared depredation of artificial arboreal nests between nests placed at nest sites used by birds in the previous season (actual nests) and those located at random nest sites (random nests) on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from May to July 1987. Ninety-eight (65%) actual nests and 109 (73%) random nests were disturbed by predators. The number of actual and random nests disturbed did not differ (P = 0.74) from expected. Fate (undisturbed vs. disturbed by predators) of actual and random nests was not related (P > 0.05) to time of nest placement during the study or to plot age, nest height, nesting substrate, and woody stem densities at ground level or at nest height. Because nesting substrate and, hence, degree of nest conspicuousness varies among bird species in nature, we suggest that results obtained from studies of predation on artificial nests be used with caution. J. WILDL. MANAGE. 53(1):21-25 Depredation of artificial avian nests may vary with time of placement, age of plot, height of nests above ground, extent of forest fragmentation, and degree of concealment provided by vegetation surrounding nest sites (Sugden and Beyersbergen 1986, Yahner and Cypher 1987, Yahner and Scott 1988). In artificial nest studies, nests typically are placed at random nest sites selected by the investigator, e.g., in the nearest tree or shrub species (Yahner and Scott 1988). However, whether or not depredation of artificial nests placed at random nest sites differs from that of artificial nests placed at nest sites selected by birds is unknown. If artificial nests at these 2 types of nest sites differ in susceptibility to predation, then caution would be advis d when interpreting results obtained from artificial nests placed at random and extrapolati g to depredation of avian nests in nature. Our objectives were to compare depredation rates between artificial nests placed at random ne t sites to those placed at nest sites used by birds in the preceding breeding season, and determine if depredation of nests at these 2 types of nest sites is related to time of nest placement uring the breeding season or to plot age, nest height, nesting substrate, and woody stem densiti at ground level or at nest height. We thank J. L. Bauer for field assistance and T. E. Morrell for reviewing the manuscript. Funding for this research was provided by the I Present address: Box 175, Spangler, PA 15775. This content downloaded from 207.46.13.33 on Sat, 26 Nov 2016 04:10:49 UTC All use subject to http://about.jstor.org/terms 22 DEPREDATION ON ARTIFICIAL NESTS * Yahner and Voytko J. Wildl. Manage. 53(1):1989 Pennsylvania Agricultural Experiment Station and the Max McGraw Wildlife Foundation. This is Journal Series Paper 7826 of the Agricultural Experiment Station, The Pennsylvania State University, University Park.

Effects of Forest Fragmentation on Depredation of Artificial Nests

Depredation on artificial ground and arboreal (1.5 m above ground) nests was studied in mature (uncut) forest stands on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from May to August 1986. Predation was evaluated in mature stands with zero, 25, and 50% zones of the surrounding forest fragmented by clearcutting. Nest depredation was highest in the 50% zone and least in the zero percent zone; more arboreal nests than ground nests were disturbed. American crows (Corvus brachyrhynchos) were major predators on nests in the 50% zone, and crows and blue jays (Cyanocitta cristata) caused most nest disturbances in the 25% zone. Our results suggest that fragmentation of surrounding mature forest stands may negatively impact avian nesting success, especially when the principal nest predators are corvids. Predation in fragmented forests may have a greater effect on nesting success of birds nesting above ground than on those nesting at ground level. J. WILDL. MANAGE. 52(1):158-161 Forest fragmentation, or the cutting of remaining natural forest into progressively smaller patches (Harris 1980), negatively impacts abundance and distribution of insectivorous passerines in the eastern United States (Whitcomb et al. 1981). Because forest fragmentation results in greater edge (Ranney et al. 1981) and predators select edges for foraging (Gates and Gysel 1978, Chasko and Gates 1982), predation on avian nests could increase with extensive forest fragmentation (Noss 1983). However, with the exception of a study dealing with predation on artificial nests in woodlots of various sizes (Wilcove 1985), the influence of forest fragmentation on nest predation is not well documented. Clearcutting forest to improve ruffed grouse habitat at the Barrens Grouse Habitat Management Study Area (BGMA) in central Pennsylvania provides suitable nesting habitat for a variety of avian species that nest ?2 m from the ground (Yahner 1986b, Yahner and Cypher 1987). The BGMA contains a sector with no forest fragmentation (zero clearcutting) and sectors with 2 intensities of forest fragmentation (25 and 50% clearcutting) that provided an opportunity to examine the relationship between nest depredation and forest fragmentation. Our objective was to compare depredation on artificial ground and arboreal nests placed in mature forest stands surrounded by uncut forest and 2 intensities of forest fragmentation at the BGMA. We thank R. A. Voytko and R. W. Bond for field assistance. Funding for this study was provided by the Max McGraw Wildlife Foundation and the Pennsylvania Agricultural Experiment Station. W. A. Creed, R. G. Eckstein, and M. J. Lacki reviewed the manuscript. This is Journal Series Paper 7565 of the Agricultural Experiment Station, The Pennsylvania State University, University Park.