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Conspecific and Interspecific Nest Reuse by Wood Thrush (Hylocichla mustelina)
Sonya Richmond, Erica Nol, Margaret Campbell, and Dawn Burke

Northeastern Naturalist, Volume 14, Issue 4 (2007): 629–636

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2007 NORTHEASTERN NATURALIST 14(4):629–636 Conspecifi c and Interspecifi c Nest Reuse by Wood Thrush (Hylocichla mustelina) Sonya Richmond1,*, Erica Nol2, Margaret Campbell3, and Dawn Burke4 Abstract - We report one instance of conspecifi c nest reuse by Hylocichla mustelina (Wood Thrush) within the same breeding season, two instances of conspecifi c nest reuse in subsequent breeding seasons, and two instances of Wood Thrushes reusing nests originally constructed by Pheucticus ludovicianus (Rose-breasted Grosbeaks) during a three-year study in Ontario. Rates of nest reuse were higher than previously reported for Wood Thrush, with conspecifi c nest reuse accounting for 8–12% of the observed nesting activity, and interspecifi c nest reuse accounting for 8–9%. Nest reuse occurred following periods of colder minimum temperatures or greater precipitation than in other years. We suggest that instances of nest reuse within and between breeding seasons may occur in response to time or energy constraints on females resulting from unusual weather conditions. Documenting instances of nest reuse behaviour contributes to our understanding of some of the constraints experienced during breeding and may shed light on factors affecting annual reproductive success. Introduction Nest reuse is reportedly uncommon in passerines with open-cup nests, both within and between breeding seasons, and most such accounts describe birds reusing previously successful nests built by conspecifi cs (Cavitt et al. 1999, but see Curson et al. 1996, Marshall et al. 2001). Nest reuse could be a strategy to minimize the amount of energy spent on nest construction (Cavitt et al. 1999), to reduce competition for limited nest sites (Curson et al. 1996), or to maximize short-term chances of nest survival by choosing sites which were previously successful (Styrsky 2005). Consistent, but infrequent, nest reuse has previously been reported for Hylocichla mustelina Gmelin (Wood Thrush), an open-cup nesting Neotropical migratory passerine. During a nineteen-year study in a small deciduous woodlot in Delaware, three out of 389 Wood Thrush nests (0.8%) were reused in the same breeding season by their original occupants (Roth et al. 1996). Friesen et al. (1999) reported two instances of nest reuse within the same breeding season (1.3%) as well as two occurrences of nest reuse in subsequent years (1.9%). All nests successfully fl edged host young during both nesting attempts. 1Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, ON, M5S 3B3, Canada. 2Watershed Ecosystems Graduate Program, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada. 3Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada. 4Southern Science and Information Unit, Ontario Ministry of Natural Resources, 659 Exeter Road, London, ON, N6E 1L3, Canada. *Corresponding author - sonya.richmond@utoronto.ca. 630 Northeastern Naturalist Vol. 14, No. 4 The purpose of this study was to document instances of conspecifi c and interspecifi c nest reuse in Wood Thrushes nesting in a deciduous woodlot in Ontario. To our knowledge, no instances of interspecifi c nest reuse have been previously reported for Wood Thrushes. While this was not an experimental study, we also discuss our observations in light of unusual weather conditions, which suggest that nest reuse may be a response to time or energy constraints experienced by females resulting from stressful conditions. Methods Between 2003 and 2005, we monitored sixty-four Wood Thrush nests and sixteen Pheucticus ludovicianus Linnaeus (Rose-breasted Grosbeak) nests in a 29.4-ha deciduous woodlot located near Keene, ON, Canada (44°15'N; 78°07'W). Dominant canopy species in the study site included Acer saccharum Marsh. (sugar maple), Fraxinus americana Linnaeus (white ash), Ostrya virginiana Mill. (ironwood), Thuja occidentalis Linnaeus (eastern white cedar), and Tilia americana Linnaeus (basswood). The surrounding landscape was predominantly agricultural, consisting of a mixture of row crops, hay fi elds, old fi elds, pastures, and scattered small housing developments (Phillips et al. 2004). Nest searching and monitoring were undertaken between May and August in each year to obtain estimates of nest success for Wood Thrushes and Rose-breasted Grosbeaks. When we located a nest, we attached a directional fl ag to a nearby tree containing the species code, a unique alphanumeric identifi er for the nest, and a detailed description of the nest’s location. We did not remove nest fl ags between breeding seasons, and in many cases, they were still legible 1–2 years after they were initially placed, making positive identifi cation of nest-reuse events possible. We used a modifi ed version of the spot-mapping technique described in Bibby et al. (1992) to collect information on territory placement and pairing status for all territorial males of each focal species. We marked nest locations and territories using global positioning system (GPS) units (Garmin GPS 12XL) and plotted them on a map of the study site. We classifi ed active nests as fi rst or second nest attempts based on time during the breeding season and observed nest initiation and failure dates within each territory. Unless previous, unsuccessful nests had been found and monitored for a particular Wood Thrush pair, nests found with eggs or young on or prior to June 19th were considered fi rst nest attempts (Roth et al. 1996). Nests located after June 19th were considered to be second nest attempts, as all pairs in the study site established territories early in the season (e.g., late May) during all years in the study. We monitored nests every four or fi ve days throughout the breeding season using a mirror attached to a telescoping pole. We calculated clutch size, date of nest initiation (day when the fi rst egg was laid), and nest-reuse status for each nest. We obtained values for daily minimum temperatures and total 2007 S. Richmond, E. Nol, M. Campbell, and D. Burke 631 monthly precipitation for May, June, and July of each year from Environment Canada for the study area. We tested clutch size, nest-initiation date, temperature, and precipitation data for normality, and the non-parametric Kruskal-Wallis statistic was used to test for between-year differences in each of the four variables. For variables that showed signifi cant between-year differences, we used the Nemenyi test (Zar 1999) to make post-hoc comparisons. Results In this study, we report one instance of conspecifi c nest reuse by a Wood Thrush within the same breeding season, two instances of conspecifi c nest reuse in subsequent breeding seasons, and two instances of Wood Thrushes reusing nests originally constructed by Rose-breasted Grosbeaks. One instance of interspecifi c nest reuse occurred within the same breeding season, and the other occurred in subsequent breeding seasons. In the second case, the nest, which was originally built by a Rose-breasted Grosbeak in 2003 and reused by a Wood Thrush in 2004, was reused a third time in 2005 by Turdus migratorius Linnaeus (American Robin). Nest reuse did not appear to be linked to previous successes in those nests (Table 1), nor to changes in Wood Thrush demographics (Table 2) or habitat characteristics during the course of the study. In 2003, one of 16 Wood Thrush pairs (6%) chose to reuse an existing Wood Thrush nest instead of constructing a new one (Table 1). The instance of nest reuse occurred in early July, suggesting that conspecific nest reuse accounted for 1 of 8 second nest attempts (12%). In 2004, one of 17 Wood Thrush pairs chose to reuse a previously constructed Rose-breasted Table 1. Conspecifi c and interspecifi c nest reuse within and between breeding seasons by Wood Thrush in 2003, 2004, and 2005. Nest no. / species Year 1st egg day Outcome Original nests 1 / Wood Thrush 2003 June* Failed 2 / Wood Thrush 2004 May 23 Success 3 / Wood Thrush 2004 May 20 Failed 4 / Rose-breasted Grosbeak 2004 May 19 Failed 5 / Rose-breasted Grosbeak 2004 May 18 Success 1st nest reuse 1 / Wood Thrush 2003 July 2 Failed 2 / Wood Thrush 2005 June 2 Success 3 / Wood Thrush 2005 June 15 Success 4 / Wood Thrush 2005 May 26 Failed 5 / Wood Thrush 2004 July 22 Success 2nd nest reuse 4 / American Robin 2005 May 12 Failed *The original Wood Thrush nest constructed in 2003 was observed with 2 host eggs on June 20th and was depredated on the next visit, prohibiting calculation of an exact nest-initiation date. 632 Northeastern Naturalist Vol. 14, No. 4 Grosbeak nest (6%). This nest-reuse event occurred in late July, suggesting it accounted for 1 of 11 second nest attempts (9%). In 2005, two of 17 Wood Thrush pairs used conspecific nests constructed the previous year (12%). Based on nest-initiation dates and territorial information, one instance probably accounted for 1 of 13 first nest attempts (8%), and the other probably accounted for 1 of 8 second nest attempts (12%). In 2005, one Wood Thrush pair chose to reuse a Rose-breasted Grosbeak nest constructed the previous year (6%), which accounted for 1 of 13 (8%) first nest attempts. Combining intra-and interspecific instances of nest reuse, 16% of Wood Thrushes reused nests during their first attempt in 2005. None of the nests that were reused appeared to have undergone substantial reconstruction efforts prior to reuse as there did not appear to be fresh nesting material in the walls or linings of these nests. In 2004, mean minimum temperature during June (9.7 ºC) was significantly colder than in previous and subsequent years (2003: 11.2 ºC, 2005: 12.6 ºC; H = 6.52, p = 0.04; Fig. 1a). Mean minimum temperatures for July (2003: 14.4 ºC , 2004: 14.0 ºC, 2005: 13.2 ºC) did not differ significantly between years (H =1.89, p = 0.39). The one instance of nest reuse observed in 2004 occurred at the end of July (Table 1), following a period of unusually cold weather during June and a heavy rainstorm in the middle of July. In 2005, mean minimum temperature during May (1.9 ºC) was significantly colder than in previous years (2003: 6.3 ºC, 2004: 7.1 ºC; H = 22.39, p < 0.001; Fig. 1a). All three instances of nest reuse observed in 2005 occurred at the end of May or the beginning of June, following this period of unusually cold weather (Table 1). Mean precipitation per day did not significantly differ between years for May, June, or July (p >> 0.05), probably due to high levels of variation associated with the data (Fig. 1b). However, the total precipitation for July 2004 was considerably greater than in other months and years during this study. This variance is partially due to a heavy rainstorm on July 14, 2004, during which 239.8 mm of rain fell over the course of a single day. Mean nest-initiation date (measured as mean 1st egg day) for first Wood Thrush nests was slightly later in 2005 than in previous years (H = 5.85, p = 0.053), but the difference was not statistically significant (Fig. 2a). The earliest recorded 1st egg day for 2005 (May 23rd) occurred nine days Table 2. Number of active Wood Thrush pairs and nests monitored during 2003, 2004, and 2005. Year 2003 2004 2005 Number of pairs 16 17 17 Number of 1st nests 9 15 13 Number of 2nd nests 8 11 8 Total number of nests 17 26 21 2007 S. Richmond, E. Nol, M. Campbell, and D. Burke 633 after the first recorded date in 2003 and seven days after the first recorded date in 2004. Mean clutch size for first nests tended to be smaller in 2005 than in previous years, but the difference was not significant (H = 6.44, p = 0.09; Fig. 2b). Discussion Nest reuse in Wood Thrushes occurred at a much higher rate in 2005 than in previous years. In each case, nest reuse occurred following unusual weather conditions. In 2004, the instance of interspecific nest reuse occurred at the very end of the breeding season, following a two-day period of extremely heavy rainfall in late July. In 2005, all instances of nest reuse occurred in late May and early June, towards the end of the first nesting cycle, following a month of colder-than-usual temperatures. In all cases, nest Figure 1. Mean minimum temperature (ºC) (± SD) during May, June, and July for 2003, 2004, and 2005 (a). Total precipitation (mm) during May, June, and July for 2003, 2004, and 2005 (b). 634 Northeastern Naturalist Vol. 14, No. 4 reuse occurred when time and energy constraints resulting from unusual weather conditions could have influenced the amount of resources female Wood Thrushes could expend on egg and nest production. Smaller mean clutch sizes and later nest-initiation dates for first nests in 2005 also suggested that energetic constraints may have been influencing breeding success by limiting the amount of energy available for egg production. Our observations of Wood Thrush behaviour also suggested that breeding pairs spent more time feeding than usual, and that the duration of male singing appeared to be much reduced (S. Richmond, pers. observ.). Nest construction is estimated to take 3–6 days (Roth et al. 1996), which roughly corresponds to the delay in the average nest-initiation date that was observed for first nests in 2005. We suggest that food was limited and extra energy was required for metabolic functions due to colder-than-usual spring temperatures. This hypothesis is consistent with the observations of Powell and Rangen (2000), who found that Figure 2. (a) Mean nest initiation date (± SD.) (measured as 1st egg day, day 1 = January 1) for fi rst Wood Thrush nests during 2003, 2004, and 2005. (b) Mean clutch size (± SD.) for fi rst Wood Thrush nests in 2003, 2004, and 2005. 2007 S. Richmond, E. Nol, M. Campbell, and D. Burke 635 Wood Thrush nest size varied with changes in temperature and possible time constraints imposed by the end of the breeding season. Therefore, we propose that reuse of existing nests may have been one strategy to minimize the amount of time and energy spent on reproduction. While instances of conspecific nest reuse have been reported both within and between breeding seasons, interspecific nest reuse has not previously been documented for Wood Thrushes. We suggest that Wood Thrushes may have selected Rose-breasted Grosbeak nests as sites for re-nesting because they coexisted in the same habitat, the nests were of approximately the same size and shape, and they may have been able to maintain more of their structural integrity than Wood Thrush nests. The only other species with a similar-sized nest in the same habitat was the American Robin. While we did not observe any instances of Wood Thrushes using American Robin nests, an American Robin in 2005 used a nest that had been built by a Rose-breasted Grosbeak and then reused by a Wood Thrush in 2004. In this study, not all nests that were reused successfully fledged young during the first use. While this is not usually the case in passerines, Marshall et al. (2001) have reported the reuse of a failed Dumetella carolinensis Linnaeus (Gray Catbird) nest. This nest was built by conspecifics the previous year, and both nesting attempts failed. Reuse of previously unsuccessful nests does not support the hypothesis that nest reuse is a strategy to reduce short-term chances of nest predation. It is also unlikely that reuse of existing nests was a strategy to reduce competition for limited nest sites because suitable sites appeared to be abundant and the amount of available habitat did not change during the course of the study. As a result, we suggest that time and energy constraints resulting from unusual weather conditions are the most likely cause of the observed instances of nest reuse by Wood Thrushes in this study. We suggest that nest reuse is a consistent, but infrequent part of Wood Thrush nesting strategy, and that it can be influenced by weather conditions. If more instances of nest reuse are documented in the future, and more detailed behavioural observations are recorded, it may be possible to better understand how stressful conditions such as unusual weather patterns can alter nesting strategies by Wood Thrushes. Acknowledgments We would like to thank the Natural Science and Engineering Research Council of Canada, the Ontario Ministry of Natural Resources, and Environment Canada’s Science Horizons Youth Program for partial funding of this research. We would also like to thank the landowners for their permission to conduct this research on their property, and to thank Sandi Schmitter, Natalie Charland, Kerri Pigeon, Jerome Ptigny, Sean Male, Janine McCleod, Jessica Plourde, and Christine Baljko for their assistance in the fi eld. 636 Northeastern Naturalist Vol. 14, No. 4 Literature Cited Bibby, C.J., N.D. Burgess, and D.A. Hill. 1992. Bird Census Techniques. Academic Press, London, UK. Cavitt, J.F., A.T. Pearse, and T.A. Miller. 1999. Brown Thrasher nest reuse: A timesaving resource, protection from search-strategy predators, or cues for nest-site selection. Condor 101:859–862. Curson, D.R., C.B. Goguen, and N.E. Mathews. 1996. Nest-site reuse in the Western Wood-Pewee. Wilson Bulletin 108:378–380. Friesen, L.E., V.E. Wyatt, and M.D. Cadman. 1999. Nest reuse by Wood Thrushes and Rose-breasted Grosbeaks. Wilson Bulletin 111:132–133. Marshall, J.S., P.A.R. Glover, K.A. Becchi, and L.W. VanDruff. 2001. Nest reuse by a Gray Catbird. Wilson Bulletin 113:837–338. Phillips, J., E. Nol, D. Burke, and W. Dunford. 2004. Impacts of housing developments on Wood Thrush nesting success in hardwood forest fragments. Condor 107:97–106. Powell, L.A., and K.A. Ranger. 2000. Variation in Wood Thrush nest dimensions and construction. North American Bird Bander 25:89–96. Roth, R.R., M.S. Johnson, and T.J. Underwood. 1996. Wood Thrush (Hylocichla mustelina). In A. Poole and F. Gill (Eds.). The Birds of North America, No. 246. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, DC. Styrsky, J.N. 2005. Infl uence of predation on nest-site reuse by an open-cup nesting neotropical passerine. Condor 107:133–137. Zar, J.H. 1999. Biostatistical Analysis, 4th Edition. Prentice Hall, Upper Saddle River, NJ. 663 pp.