Cropland edge, forest succession, and landscape affect shrubland bird nest predation

Abstract

The effects of habitat edges on nest survival of shrubland birds, many of which have experienced significant declines in the eastern United States, have not been thoroughly studied. In 2007 and 2008, we collected data on nests of 5 shrubland passerine species in 12 early successional forest patches in North Carolina, USA. We used model selection methods to assess the effect of distance to cropland and mature forest edge on nest predation rates and additionally accounted for temporal trends, nest stage, vegetation structure, and landscape context. For nests of all species combined, nest predation decreased with increasing distance to cropland edge, by nearly 50% at 250 m from the cropland edge. Nest predation of all species combined also was higher in patches with taller saplings and less understory vegetation, especially in the second year of our study when trees were 4–6 m tall. Predation of field sparrow (Spizella pusilla) nests was lower in landscapes with higher agricultural landcover. Nest predation risk for shrubland birds appears to be greater near agricultural edges than mature forest edges, and natural forest succession may drive patterns of local extirpation of shrubland birds in early successional forest patches. Thus, we suggest that habitat patches managed for shrubland bird populations should be considerably large or wide (>250 m) when adjacent to crop fields and maintained in structurally diverse early seral stages. © 2011 The Wildlife Society.

Linking landscape composition to predator‐specific nest predation requires examining multiple landscape scales

“…Indeed, contrasting results among other studies offer no clear pattern of agriculture's impact on nest predation (e.g. Benson et al., ; Robinson et al., ; Shake et al., ; Tewksbury et al., , ). Taken collectively, our results reveal that no land cover type positively or negatively impacted predation by all predators, further illustrating the intricacy of predator–habitat relationships and the benefits of assessing predator‐specific patterns whenever able.…”

“…We chose these buffer sizes primarily because they have been used in previous studies to relate landscape features to nest survival or predation (e.g. Boulet, Darveau, & Bélanger, ; Chapa‐Vargas & Robinson, ; Lyons et al., ; Shake et al., ; Winter, Johnson, Shaffer, Donovan, & Svedarsky, ) and because we wanted to illustrate how composition at these previously used scales might vary in their relationship with different nest predator species (e.g. squirrels relative to Cooper's hawks; Mannan & Boal, ; Sheperd & Swihart, ).…”

“…Yet, studies have found both higher and lower predation rates in agricultural landscapes (e.g. Benson, Brown, & Bednarz, 2010;Robinson, Thompson, Donovan, Whitehead, & Faaborg, 1995;Shake, Moorman, & Burchell, 2011;Tewksbury, Hejl, & Martin, 1998). Likewise, despite developed landscapes supporting greater densities of nest predators (e.g.…”

The Influence of Different Cover Types on American Robin Nest Success in Organic Agroecosystems

“…It is possible that the linear woodlands in which many nests are embedded serve as corridors and edges for nest predators [40] while the agricultural matrix may limit the activity of the predator community [39]. For example, predation of Field Sparrow (Spizella pusilla) nests in North Carolina was lower when a greater percentage of the landscape was dedicated to agricultural production [39], though individual crops were not identified. In our study sties, wheat may provide cover and thus recruit predators, decreasing daily survival rate.…”

“…At the end of the nesting season, we estimated the percent coverage of each land use and land cover (Table 1) within 50 meters of each nest, a distance beyond the average observed foraging distance [32]; visually estimating, in the field, percent cover while standing at each nest site. In order to associate daily survival rate to organic farm management we selected model parameters associated with local land use and land cover patterns (Table 1) by reviewing published literature from American Robin and both woodland and agroecosystem biodiversity conservation [20,[37][38][39][40]. multicollinearity.…”