Grassland bird nest ecology and survival in upland habitat buffers near wooded edges

Abstract

Upland habitat buffers (i.e., strips of noncrop, herbaceous vegetation) that are established adjacent to wooded fencerows offer landowners an economical option to provide wildlife benefits within intensive agricultural landscapes. However, being located near a wooded edge may increase grassland bird vulnerability to edge effects through reduced nest survival. We examined nesting bird communities in field margins adjacent to wooded field edges with no buffer (i.e., control), narrow (approx. 10-m) buffers, and wide (approx. 30-m) buffers in an intensive agricultural system in the Lower Mississippi Alluvial Valley, United States. Dickcissel (Spiza americana) and red-winged blackbird (Agelaius phoeniceus) accounted for 97% of nests. Nest density was >7 times greater in wide buffers than in narrow. We modeled nest survival in Program MARK as a function of time (yr and season), nest-site, and local vegetation characteristics. Nest survival was influenced by among-and within-season temporal effects and local vegetation structure, but not by buffer width. Nest success varied substantially between years and within seasons for dickcissel (12.9% and 19.1% early in the seasons of 2003 and 2004, respectively), but not for red-winged blackbird (15.1%). Overall nest-success estimates were similar to noncrop, herbaceous strips elsewhere in the United States, though whether or not these estimates represent population sinks remains uncertain. Based on this research, we advocate integrating upland habitat buffers within intensive agricultural landscapes and emphasize the use of wide buffers when grassland-nesting birds are a conservation priority. ß 2011 The Wildlife Society.

Assessment of variation of nest survival for grassland birds due to method of nest discovery

“…proximity to edge). Period survival estimates were lower than previous research on Dickcissels in the region based on structured searches in Clay County, Mississippi (27.9%; Adams et al 2013), and the Mississippi Alluvial Valley (12.9% and 19.1%; Conover et al 2011). However, Conover et al (2011 derived estimates based on a 20-day nesting cycle, and the initiation dates used for both studies were earlier than our data, which could account for differences in survival estimates.…”

“…Commonly, nests are constructed by females in dense grass, forbs, or low woody vegetation, usually with overhead vegetative cover (Blankspoor 1970, Temple 2002. Dickcissels are a good model species to compare nest survey methods for grassland birds because previous research on this species has successfully located nests with all three search methods (Jensen & Finck 2004, Conover et al 2011, Sousa 2012.…”

Effects of measuring nestling condition on nest success in the dickcissel (Spiza americana)

“…Snakes may be attracted to nest sites by activity of adults and nestlings (Stake et al ), and although the handling of nestlings agitated adults during our study, we strived to minimize the duration of our banding visits and did not infer predation of nests from snakes after banding (i.e., nest found empty and intact prior to the earliest potential fledge date; Thompson and Burhans ). Finally, the overall nest predation rate observed in our study (73.8%, or 83.6% when including fire ants) was at the middle‐ to lower end of the range reported in other dickcissel studies (range = 76–94% [Churchwell et al ; Conover et al , ]), and this may have reduced the effects of observers on nest predation relative to other studies.…”

“…Similarly, nest site characteristics could influence nest survival rates (Martin et al ), which may potentially confound testing of observer effects in our study. For dickcissels, these include nest height (Conover et al ), grass coverage, and vegetation density (Winter , Conover et al ). To assess nests for these potential confounding variables, we measured nest‐site vegetation after nesting attempts were completed, including nest height measured from the ground to the base of each cup, grass coverage averaged from five 0.25‐m 2 frames (Daubenmire ) positioned around each nest (Winter ), and visual obstruction measured with a Robel pole (Robel et al ) at nest sites.…”

Improving distance sampling: accounting for covariates and non‐independency between sampled sites

“…). Conover, Burger & Lindner () showed that field buffers increased nesting activities along field margins for a range of birds, including indigo buntings. In contrast, Riddle & Moorman () showed that implementing field borders had no beneficial effect on nesting success of indigo buntings.…”