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To estimate relative predation rates and identify predators of lepidopteran larvae, we used model caterpillars constructed from plasticine (Leuenberger et al. 2019). Plasticine model caterpillars suffer levels of attack similar to real larvae, and thus provide a useful comparison of predation intensity, causation, and impact across treatments (Howe et al. 2009, Bereczki et al. 2014). We made and deployed 50 light green (08 light green Newplast, Newclay Products, Devon, England) geometrid (inchworm) models in each plot (n = 16) for 6 days (Fig. 2). There is no consistently-timed peak in caterpillar abundance between late May and late July at Hubbard Brook (Lany et al. 2016), so we deployed caterpillars in late June, which was within the breeding season for all migratory birds at our study area and shortly after peak breeding season for resident black-capped chickadees (Poecile atricapillus) and yellow-bellied sapsuckers (Sphyrapicus va rius, Billerman et al. 2020). Accumulated degree days were used to standardize the timing of deployments between years. We obtained daily maximums and minimums for North Woodstock, NH (The Weather Company, LLC 2016). Degree days were calculated beginning on 1 April and included any days with an average temperature ([max + min] / 2) above 10°C (Higley et al. 1986). In 2015, we began deployment on 18 June at 262.5 cumulative degree days, and in 2016 on June 23 at 279.7 cumulative degree days.

Caterpillar models were 25 mm long with a diameter of 3.5 mm and were glued to leaf petioles or next to leaves in life-like typical day time inchworm poses (Howe et al. 2009). Half of the caterpillars (n = 25) in each plot were deployed on hobblebush (Viburnum lantanoides) and half on American beech. All caterpillars were placed between 0.5 and 2 m above ground, with a minimum of 0.5 m horizontal distance between caterpillars. Caterpillars were spread evenly throughout each plot, typically with 7 or 8 caterpillars per 5 × 5 m subplot depending on the availability of host plants. Some caterpillars were placed in the buffer zone surrounding plots if there were not enough locations within the interior plot to deploy all 50 caterpillars. In 2016, we recorded approximate locations of each caterpillar to the nearest 0.25 m within the plot to allow us to account for spatial autocorrelation (Appendix 1). Heights were recorded as one of three categories: 0.5 – 1 m, 1 – 1.5 m, or 1.5 – 2 m. Caterpillar locations were discretely marked so as to not provide obvious search cues for predators and checked every other day for evidence of predation attempts (Bereczki et al. 2014).

Any caterpillars with obvious markings from avian predators were removed and placed in 2 mL microcentrifuge tubes for preservation. If the caterpillar was not found on the plant, the ground surrounding the deployment site was searched for 10 minutes by one person or five minutes by two people. If the caterpillar was still missing after this time, we marked it as ‘missing.’ We continued to briefly check the area on subsequent visits to attempt to recover the caterpillar. All remaining caterpillars were removed after 6 days (Bereczki et al. 2014). Retrieved caterpillars were examined under 1.75× magnification for evidence of predation by birds that could have been missed in the field (Howe et al. 2009).

Bereczki, K., P. Ódor, G. Csóka, Z. Mag, and A. Báldi. 2014. Effects of forest heterogeneity on the efficiency of caterpillar control service provided by birds in temperate oak forests. Forest Ecology and Management 327:96–105.

Billerman, T. S. M., B. K. Keeney, P. G. Rodewald, and T. S. Schulenberg, editors. 2020. Birds of the World. Cornell Laboratory of Ornithology, Ithaca, NY, USA. <https://birdsoftheworld.org/bow/support/citations-and-references>. Accessed 7 Apr 2020.

Higley, L. G., L. P. Pedigo, and K. R. Ostlie. 1986. DEGDAY: a program for calculating degree-days, and assumptions behind the degree-day approach. Environmental Entomology 15:999–1016.

Howe, A., G. L. Lövei, and G. Nachman. 2009. Dummy caterpillars as a simple method to assess predation rates on invertebrates in a tropical agroecosystem. Entomologia Experimentalis et Applicata 131:325–329.

Lany, N. K., M. P. Ayres, E. E. Stange, T. S. Sillett, N. L. Rodenhouse, and R. T. Holmes. 2016. Breeding timed to maximize reproductive success for a migratory songbird: the importance of phenological asynchrony. Oikos 125:656–666.

Leuenberger, W., E. Larsen, J. Leuenberger, and D. Parry. 2019. Predation on plasticine model caterpillars: Engaging high school students using field-based experiential learning & the scientific process. American Biology Teacher 81:334–339.

The Weather Company, LLC. 2016. Weather History for Plymouth, NH | Weather Underground. <https://www.wunderground.com/history/airport/K1P1/2016/4/1/CustomHistory.html?dayend=23&monthend=6&yearend=2016&req_city=&req_state=&req_statename=&reqdb.zip=&reqdb.magic=&reqdb.wmo=>. Accessed 6 Dec 2016.