An Overlooked Cost for the Velvety Plumage of Owls: Entanglement In

An Overlooked Cost for the Velvety Plumage of Owls: Entanglement in Adhesive Vegetation Author(s) :Airam Rodríguez, Felipe Siverio, Rubén Barone, Beneharo Rodríguez, and Juan J. Negro Source: The Wilson Journal of Ornithology, 121(2):439-441. 2009. Published By: The Wilson Ornithological Society DOI: 10.1676/08-086.1 URL: http://www.bioone.org/doi/full/10.1676/08-086.1

BioOne (www.bioone.org) is a a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.

BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Short Communications

The Wilson Journal of Ornithology 121(2):406–411, 2009

American Robin Seet Calls: Aerial Alarm or a Contact Call?

E. Natasha Vanderhoff1,2,3 and Perri K. Eason1

ABSTRACT.—The literature regarding the seet call respond appropriately for a specific kind of of the American Robin (Turdus migratorius) is unclear threat (Evans et al. 1993, Evans 2002). For as anecdotal accounts indicate it is an aerial alarm. A example, Steller’s Jay (Cyanocitta stelleri) more recent, comprehensive account indicates it is most likely a contact call. We examined the meaning give a wah call when mobbing ground pred- of seet calls through observations and a playback ex- ators and a high-pitched call when hawks are periment, both of which support the aerial alarm func- seen (Hope 1980), both of which elicit a dif- tion of the call. Robins only gave seet calls to aerial ferent response. We investigated whether the predators and many engaged in skygazing, a behavior American Robin (Turdus migratorius) has a previously unreported for robins. Robins engaged in three anti-predator behaviors, skygazing, alert, and distinctive aerial alarm call given for aerial scanning for significantly more time after hearing an predators and examined conspecifics’ re- alarm compared to hearing a control. American Rob- sponse to that call. ins, like many other birds, probably evolved this call Previous research on robin alarm calls fo- to avoid detection by aerial predators and to warn con- cused on those given in response to terrestrial specifics. Received 14 July 2008. Accepted 14 Decem- predators, and these calls have been clearly ber 2008. characterized (Shedd 1982, Gottfried et al. 1985). Robins give two types of terrestrial Birds use a variety of calls to communicate alarm calls, yeeps and chucks. However, rob- and can readily comprehend and discriminate ins also have numerous aerial predators with between calls in their repertoire. However, it accipiters (Cooper’s Hawk [Accipiter cooper- often takes years for scientists to fully under- ii] and Sharp-shinned Hawk [A. striatus]) be- stand the context and meaning of many calls. ing particularly important predators (Roth and The study of avian communication has Lima 2003, Roth et al. 2006) and, according- evolved from largely observational accounts ly, an aerial alarm might provide a strong se- to hypothesis-driven experimentation, often lective advantage. Currently there are conflict- with aid of technology, which has allowed sci- ing reports in the literature concerning wheth- entists to discern the meaning of many birds’ er or not robins have an aerial alarm. Two calls (Baptista and Gaunt 1994). Alarm calls anecdotal reports from the 1950’s suggested may be particularly important communica- that robins give a seet call in the presence of tions, as they may allow birds to warn con- aerial predators and that robins become ‘‘rig- specifics and escape predation, and potentially id’’ when they hear that call (Jackson 1952, have an immediate effect on fitness (Klump Hailman 1959). The seet call is higher pitched and Shalter 1984). Many birds have alarm and longer in duration than other alarm calls calls and, in some species, different kinds of in the robin’s repertoire (Fig. 1) and it sounds alarms are given for different types of threats similar to the call of Cedar Waxwings (Bom- (Marler 2004). Some species give distinctive bycilla cedrorum); robins often have bouts of alarms for ground and aerial predators, a re- seet calls, during which they repeatedly give finement that allows conspecifics to gain this vocalization. Two later studies assumed much more information from the alarm and the robin seet call was an aerial alarm and used it in investigations of hawks’ perception 1 Department of Biology, University of Louisville, of alarm calls (Brown 1982, Jones and Hill Louisville, KY 40299, USA. 2001). A recent review of robin behavior and 2 Current address: Francis Marion University, P. O. Box 100547, Florence, SC 29501, USA. ecology by Sallabanks and James (1999) sug- 3 Corresponding author; e-mail: gested this call might be used as a contact call [email protected] between males and females, and between par- 406 SHORT COMMUNICATIONS 407

FIG. 1. Spectrogram of American Robin alarm calls. ents and young; however, they did not men- of calls/min). We also calculated the average tion its possible use as an aerial alarm. duration, and minimum and maximum fre- Our goal was to clarify the meaning of the quencies of a single seet call. American Robin seet call and conspecifics’ re- We collected data on the occurrences of sponses to the call. We first examined the con- seet calls on 31 days between 26 May and 21 text of the call, recording whether we could September 2006 to test if seet calls were given see a terrestrial or aerial predator when a robin solely in the presence of aerial predators. We gave seet calls, and then recorded the calls for noted when we heard a seet call and recorded description and analysis. We also noted the whether we observed a raptor or terrestrial behavior of conspecifics in response to the predator when the alarm was given. We com- calls. Finally, we compared the responses of pared the proportion of calls given in the pres- robins to recorded calls and a control of ence of aerial predators versus terrestrial pred- white-noise in a playback experiment. ators with Chi-square. We also noted during this observational study when robins dis- METHODS played one anti-predator behavior not previ- We conducted our study from 25 May to 25 ously reported in this species, skygazing. Sky- November 2006 at two public parks in Lou- gazing behavior was defined by the following isville, Kentucky: Joe Creason Park (27.5 ha; postural change: robin froze, squatted low to 38Њ 12Ј N, 85Њ 42Ј W) and George Rogers the ground with its neck bent towards its back Clark Park (18.6 ha; 38Њ 12Ј N, 85Њ 42Ј W). and beak pointing skyward. Individuals hear- Both parks contain forested patches and open ing seet calls as well as individuals giving seet grassy areas with scattered trees. We recorded calls displayed this behavior. six bouts of seet calls during spring 2006 us- We conducted a short playback experiment ing a Sennheiser ME 62 directional micro- in which we played recorded seet calls to 10 phone connected to a Sony TCM-5000 EV re- adult robins and a control (white noise) to an corder. Recordings were made within 3 m of additional 10 adult robins while they were for- the vocalizing robin and, in all instances, a aging on the ground. We performed these raptor (Accipiter spp.) was seen in the area playbacks only when no terrestrial or aerial immediately prior to or during recording. We predators were visible in the area and when analyzed these calls using Raven bioacoustic no robins had been giving any alarm calls for software (Cornell Laboratory of Ornithology at least 30 min. The seet call playback con- 2003) and recorded the following: length of sisted of three seet calls played over 15 sec, the calling bout, number of calls within a which represented a short bout and a conser- bout, inter-call interval, and call rate (number vative test of robins’ responsiveness to this 408 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

FIG. 2. Spectrogram of American Robin seet call bout. call. We also recorded white-noise, broad We heard robin seet calls on 29 of 31 ob- band noise at a constant frequency, for 15 sec servation days. We observed solitary robins as a control. We observed robins for 2 min and those in ﬂocks emitting seet calls. How- after playing either white noise or the seet ever, on most occasions we observed calling calls. We noted whether or not the focal bird birds after the initial vocalizations and were stopped foraging during these observations unable to tell if the bird was alone at the time and whether the bird performed any of three the alarm was initially given. We saw an aerial anti-predator behaviors. These behaviors in- predator (accipiter hawk) on 16 of the 29 oc- cluded standing alert, scanning, and skygaz- casions. There were many terrestrial predators ing. Robins standing alert froze in an erect at the parks where we conducted our study, position; scanning birds also stood in place but we did not hear robins give the seet call but turned their heads rapidly from left to in response to any terrestrial predator (␹2 ϭ right, appearing to scan the area. We per- 22.0952, P Ͻ 0. 0001). We also saw robins formed a Chi-square test to compare the pro- skygazing in the vicinity of a robin delivering portion of robins that stopped foraging after a seet call on 16 of the 29 days. This behavior hearing a seet call versus after hearing white- was not observed in response to terrestrial noise. We used MANOVA to compare the predators or the terrestrial alarm calls, yeeps robins’ behaviors after playbacks between the and chucks. two treatments. SAS (SAS Institute Inc. 2003) The behavior of robins hearing white-noise was used for all statistical tests and data are in the playback experiments differed strongly reported as means Ϯ SE. from that of robins hearing seet calls. No robins stopped foraging after a playback of white- RESULTS noise; in contrast, all robins stopped foraging The call bouts of American Robins giving when they heard the seet call (␹2 ϭ 20.0, P Ͻ seets lasted on average 186 Ϯ 49.9 sec (range 0.0001). Most robins stopped foraging almost 23–315), and the average number of calls giv- immediately upon hearing the call; the aver- en within a bout was 38.8 Ϯ 12.3. The interval age time between hearing the call and stop- between calls was 5.5 Ϯ 1.1 sec (range 1–33) ping foraging was 2.6 Ϯ 0.8 sec, and values and, on average, robins gave 11.4 Ϯ 2.9 seet for this lag time ranged from 1 to 8 sec. Rob- calls/min. Individual seet calls lasted Ͻ1 sec ins often engaged in one of the three anti- (0.424 Ϯ 0.010, n ϭ 130) and had a minimum predator behaviors we recorded; 90% scanned frequency of 7306.6 Ϯ 38.5 Hz and a maxi- the sky, 80% stood alert, and 50% engaged in mum frequency of 9012.3 Ϯ 67.6 Hz (n ϭ skygazing. Robins hearing playbacks of seet 130; Fig. 2). calls engaged in these behaviors for signiﬁ- SHORT COMMUNICATIONS 409

ϭ ϭ FIG. 3. American Robins spend significantly more time scanning (ANOVA, F1,18 6.14, P 0.0234), alert ϭ ϭ ϭ ϭ (ANOVA, F1,18 7.12, P 0.0156), and skygazing (ANOVA, F1,18 5.51, P 0.0306) after hearing a playback of a seet call as compared to white- noise. cantly more time than did individuals hearing however, no robin gave a seet call after hear- ϭ ϭ white-noise (Wilk’s Lamba F3,16 8.14, P ing the seet playback. It is easy to see how 0.0016; Fig. 3). these calls might have been classified as contact calls, especially considering that an aerial DISCUSSION predator is often not visible when robins are Our investigation supports the early obser- calling. An accipiter was only visible to us in vational accounts reporting the American our observations on about half of the days we Robin seet call is an aerial alarm. Seet calls heard robins engaging in seet call bouts, most were only given in response to aerial preda- likely because we failed to see the raptor as it tors, and robins altered their behavior upon flew between patches of trees. hearing playbacks of the call. They also en- Numerous birds have developed high- gaged in a novel anti-predator behavior, sky- pitched alarm calls in response to aerial pred- gazing, which presumably allows the robin to ators including Wood Thrush (Hylocichla scan the sky for danger. A more appropriate mustelina) (Saunders 1961), Tufted Titmouse test of the function of skygazing would be to (Baelophus bicolor) (Morse 1970), Bank compare behaviors after hearing all three call Swallow (Riparia riparia) (Windsor and Em- types, seets, yeeps, and chucks. We did not test lem 1974), Black-capped Chickadee (Poecile this function of skygazing, but preliminary re- atricapillus) (Ficken and Witkin 1977), and sults from playbacks of chuck calls (not re- Rufous-backed Robin (Turdus rufopalliatus) ported here) and observational data support our findings that skygazing occurs only in re- (Grabowski 1979). High-pitched calls, like sponse to seet calls. Future work should be robin seet calls, are difficult for predators to conducted to understand the exact conditions localize (Marler 1955, 2004; Brown 1982; that elicit this behavioral response, i.e., wheth- Jones and Hill 2001). It is likely these calls er robins skygaze more or less often when the evolved as warnings for birds other than the risk of predation is higher. predator, unlike the robin’s other mobbing The bouts we recorded lasted ϳ3 min on calls (Shedd 1982, Gottfried et al. 1985). Two average, but we often heard robins giving seet generally recognized explanations for evolu- calls for longer durations. Several robins in tion of warning calls are reciprocal altruism different areas of the park could be heard giv- and kin selection (Klump and Shalter 1984). ing seet calls for extended periods of time, The cost of giving a call must be low relative Ͼ30 min on one occasion. It was difficult to to the benefit gained by receivers for recip- discern if robins in one area called after hear- rocal altruism to evolve, and signalers must ing a robin calling in another area of the park; have a high probability of encountering one 410 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 another repeatedly (Trivers 1971, Axelrod and izations in birds. Zeitschrift Tierpsychologia 59: Hamilton 1981). Seet calls likely have a rel- 338–350. atively low cost for the signaler given they CORNELL LABORATORY OF ORNITHOLOGY. 2003. Raven Pro 1.3 Bioacoustic Software. Cornell University, can not be easily distinguished by predators. Ithaca, New York, USA. Seet calls may therefore fit the criteria for evo- EVANS, C. S. 2002. Cracking the code: communication lution through reciprocal altruism. Seet calls and cognition in birds. Pages 315–322 in The cog- may have also evolved through kin selection. nitive animal (M. Bekoff, C. Allen, and G. M. Our study was conducted after the breeding Burghardt, Editors). MIT Press, Cambridge, Mas- season, during a time when juveniles were in- sachusetts, USA. dependent from their parents. The relatedness EVANS, C. S., L. EVANS, AND P. M ARLER. 1993. On the of individuals in a foraging flock is unknown meaning of alarm calls: functional reference in an avian vocal system. Animal Behaviour 46:23–38. for robins (Sallabanks and James 1999); how- FICKEN,M.S.AND S. R. WITKIN. 1977. Responses of ever, it is likely that some flock mates may be Black-capped Chickadee flocks to predators. Auk related, leading to benefits for kin when an 94:156–157. individual gives alarm calls. Another possi- GOTTFRIED, B. M., K. ANDREWS, AND M. HAUG. 1985. bility to explain evolution of seet calls in rob- Breeding robins and nest predators: effect of pred- ins is that the confusing nature of the calls acts ator type and defense strategy on initial vocali- to increase an individual’s direct fitness, i.e., zation patterns. Wilson Bulletin 97:183–190. GRABOWSKI, G. L. 1979. Vocalizations of the Rufous- emitting seet calls directly deters predators by backed Thrush (Turdus rufopalliatus) in Guerrero, minimizing their ability to locate and capture Mexico. Condor 81:409–416. the individual emitting the call. HAILMAN, J. P. 1959. An avian predator alarm of the Our data do not allow us to discriminate American Robin. Journal of Field Ornithology 30: among these mechanisms, but they are test- 46–47. able. If alarms are given when robins are for- HOPE, S. 1980. Call form in relation to function in the aging alone, it would suggest the calls have Steller’s Jay. American Naturalist 116:788–820. JACKSON, M. 1952. A warning call of the American direct fitness benefits. If calls are only emitted Robin, Turdus migratorius. Auk 69:466. in flocks, it is likely they evolved, at least in JONES,K.J.AND W. L. HILL. 2001. Auditory percep- part, to warn kin or other conspecifics. It tion of hawks and owls for passerine alarm calls. would be necessary to track whether robins Ethology 107:717–726. emit these calls more often in the presence of KLUMP,G.M.AND M. D. SHALTER. 1984. Acoustic dependent young than in their absence to dis- behaviour of birds and mammals in the predator criminate between these two possibilities. context. Zeitschrift Tierpsychologia 66:189–226. MARLER, P. 1955. Characteristics of some animal calls. Testing these predictions will lead to a better Nature 176:6–8. understanding of how these important signals MARLER, P. 2004. Bird calls: a cornucopia for com- evolved in the American Robin. munication. Pages 132–177 in Nature’s music, the science of birdsong (P. Marler and H Slabbekoorn, ACKNOWLEDGMENTS Editors). Elsevier Academic Press, London, Unit- ed Kingdom. We thank Louisville Metro Parks for allowing us to MORSE, D. H. 1970. Ecological aspects of some mixed- conduct our study at Joe Creason and George Rogers species foraging flocks of birds. Ecological Mono- Clark parks. We also thank Catherine Byers, Chadwick graphs 40:119–168. Hanna, Tom Pelletier, and anonymous reviewers for ROTH II, T. C. AND S. L. LIMA. 2003. Hunting behavior helpful comments on the manuscript. This investiga- and the diet of Cooper’s Hawk: an urban view of tion was funded by a small grant to ENV from the the small-bird-in-winter paradigm. Condor 105: University of Louisville, Biology Graduate Student 474–483. Organization. ROTH II, T. C., S. L. LIMA, AND W. E. VETTER. 2006. Determinants of predation risk in small wintering LITERATURE CITED birds: the hawk’s perspective. Behavioral Ecology and Sociobiology 60:195–204. AXELROD,R.AND W. D. H AMILTON. 1981. The evolu- SALLABANKS,R.AND F. C. JAMES. 1999. American rob- tion of cooperation. Science 211:1390–1396. in (Turdus migratorius). The birds of North Amer- BAPTISTA,L.F.AND S. L. L. GAUNT. 1994. Advances ica. Number 462. in studies of avian sound communication. Condor SAS INSTITUTE INC. 2003. SAS system Version 9.1 for 96:817–830. Windows. SAS Institute Inc., Cary, North Caro- BROWN, C. H. 1982. Ventroloquial and locating vocal- lina, USA. SHORT COMMUNICATIONS 411

SAUNDERS, A. A. 1961. The songs and calls of the TRIVERS, R. L. 1971. The evolution of reciprocal altru- Wood Thrush. Auk 78:595–606. ism. Quarterly Review of Biology 46:35–57. SHEDD, D. H. 1982. Seasonal variation and function of WINDSOR,D.AND S. T. EMLEM. 1975. Predator-prey mobbing and related antipredator behaviors of the interactions of adult and preﬂedgling Bank Swal- American Robin (Turdus migratorius). Auk 99: lows and American Kestrels. Condor 77:359– 342–346. 361.

The Wilson Journal of Ornithology 121(2):411–415, 2009

Habitat Selection of Least Flycatchers Includes Deciduous Regeneration in Pine Plantations

Andrea M. Geboers1,2 and Erica Nol1

ABSTRACT.—Least Flycatchers (Empidonax min- North American songbirds: Yellow Warbler imus) are socially monogamous birds that exhibit clus- (Dendroica petechia; Clark and Robertson tered nesting behavior. We examined the potential in- 1979), Henslow’s Sparrow (Ammodramus fluence of forest structure in habitat selection, and formation of Least Flycatcher clusters within a habitat henslowii; Cully and Michaels 2000), Logger- type not previously studied in this species: red pine head Shrike (Lanius ludovicianus; Etterson (Pinus resinosa) plantations. We documented 10% less 2003), Baird’s Sparrow (Ammodramus bair- understory vegetation, 13% greater canopy cover, and dii; Ahlering et al. 2006), and Cerulean War- 30% more deciduous trees in occupied than in adja- bler (Dendroica cerulea; Roth and Islam cent, unoccupied, yet available habitat in 12 clusters 2007). Clustered breeding may occur in some in pine plantations. Well developed canopy cover and species for competitive exclusion, predator deciduous foliage appear to provide visual cues for Least Flycatchers when selecting habitat for breeding. defense, use of patchy resources, or from so- Received 3 July 2008. Accepted 10 December 2008. cial factors including increased potential for extra-pair copulations (reviewed in Tarof and Ratcliffe 2004). These hypotheses have been examined with mixed results to explain clus- Studies of clustered nest patterns in birds tered nesting behavior of Least Flycatchers have focused on both ecological and social (Empidonax minimus) (Sherry and Holmes factors that might promote this apparent so- 1985, Perry and Andersen 2003, Tarof and ciality (Ward and Schlossberg 2004, Tarof et Ratcliffe 2004, Tarof et al. 2005). al. 2005, Ahlering et al. 2006). Conspecific Least Flycatcher clusters occur within a patch attraction is a social behavior that may influ- of apparently homogeneous forest habitat while ence settlement patterns whereby individuals other areas within the same patch are left un- are attracted to the presence of other individ- occupied (Breckenridge 1956, Perry and An- uals of the same species and subsequently es- dersen 2003). All previously reported studies in- tablish adjacent territories (Stamps 1988). volving clustering behavior of Least Flycatchers Conspecific attraction may be a cue to (per- have been conducted in predominately decidu- ceived) habitat quality (VanHorne 1983); ous forests. Our objective in this study was to however, preference for a particular habitat identify breeding habitat characteristics of Least may also be cued by vegetation structure (Hil- Flycatchers in red pine (Pinus resinosa) plan- deń 1965, Sherry and Holmes 1985). tations. Studying different habitat types used by Clustered nesting in all-purpose territories Least Flycatchers may further our understanding has been observed in at least five species of of habitat selection and links to clustering behavior in this species. 1 Biology Department, Trent University, Peterbor- METHODS ough, ON K9J 7B8, Canada. 2 Corresponding author; e-mail: Study Area.—We studied Least Flycatchers [email protected] at Ganaraska Forest (44Њ 5Ј N, 78Њ 30Ј W) 30 412 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 km south of Peterborough, Ontario, Canada clusters, n ϭ 12). A 5 ϫ 10 m rectangular plot (hereafter, the Forest) from late May to mid- was established centrally within occupied ar- July 2007. The Forest is a 4,280-ha tract com- eas. All vegetation plots in unoccupied areas prised of ϳ50% pine plantation and 50% were Ͼ50 m from the delineated cluster mixed hardwoods in contiguous patches. Pine boundary to preclude any possibility of cluster plantations are predominately red pine. The boundary discrepancy. Vegetation plots be- mixed hardwood forests are predominately tween 50 and 100 m from cluster boundaries sugar maple (Acer saccharum), American should represent unused, but available habitat beech (Fagus grandifolia), red oak (Quercus (Jones 2001) because all feeding and nesting rubra), and white birch (Betula papyrifera). occur within their respective territories (i.e., The red pine plantation stands are 25 to 70 all-purpose territories). years of age and have been managed using Vegetation characteristics sampled in occu- row thinning and subsequent selective thin- pied and unoccupied areas included percent liv- ning every 10–15 years (S. McMullen, Gan- ing ground cover, bare soil, stone, leaf litter, and araska Region Conservation Authority, pers. coarse woody debris (CWD). Vertical layers, comm.), which promotes the growth of decid- based on height and diameter at breast height uous trees. The predominant sapling species (dbh) (1.2 m) categories, were estimated using are red oak and black cherry (Prunus seroti- percent cover, regeneration (0.5–1.3 m tall and na), and ground cover is largely poison ivy Ͻ2.5 cm dbh), saplings (Ͼ1.3 m in height and (Toxicodendron radicans). The terrain is gen- Ͻ2.5 cm dbh), understory (Ͼ2.5 m tall and erally undulating to hilly and is underlain by Ն2.5 but Ͻ8 cm dbh), and sub-canopy (10–20 glacial-fluvial deposits, primarily of sand or m tall and Ն8 cm dbh). Canopy cover was mea- sandy-loam texture (Tedford 1978). sured using a Model-C densiometer (Lemmon Mapping Clusters.—Observations were 1956). The tallest tree in each plot was mea- made in areas within the Forest where Least sured with a clinometer (Korning and Thomsen Flycatchers were nesting. We chose 12 red 1994), and basal area was estimated using a fac- pine plantations in which to map clusters tor-2 prism sweep (Arsenault et al. 2006). All based on presence of two or more calling trees (Ն8 cm dbh) and saplings, dead or alive, males within ϳ75 m of conspecifics. Conser- within each plot were identified to species. vative estimates indicate 12 clusters were oc- Statistical Analysis.—Tests for normality cupied by 2–7 territorial males with a mean and homogeneity of variance were performed density of 3.6 males/ha. Delineation of cluster on the data. Square-root or arcsine were used boundaries was conducted between 25 and 30 when data did not meet these assumptions. All June from 0600 to 1100 hrs EDT. We walked tests were performed using an alpha of 0.05. the perimeter of the cluster from an arbitrary We compared habitat characteristics be- starting point within each chosen area of tween occupied and unoccupied areas using known Least Flycatcher location. We stopped Student’s t-test for all variables except number every 50 m to perform a 2-min point count of trees where the unequal variance t-test was survey to listen for calling males and to record used because, even with transformation, this the location using a Global Positioning Sys- variable was not normally distributed. Bon- tem (GPS) (Garmin GPS 12, Garmin Inter- ferroni corrections were not used to minimize national Inc., Olathe, KS, USA.). The Least the probability of Type II error (Moran 2003). Flycatcher has a distinctive song, chebec, Tree (Ն8 cm dbh) species counts were com- which males sing frequently during the breed- bined into two groups: coniferous (including ing period, up to 60 times/min (MacQueen red pine, white pine [Pinus strobus]), and de- 1950) making them easy to distinguish and ciduous (black cherry, red oak, white oak locate. GPS locations were plotted and con- [Quercus alba], white birch, American beech, nected to form polygons. and sugar maple), and compared between oc- Habitat Characteristic Measurements.—We cupied and unoccupied areas using a two- compared forest vegetation characteristics in tailed Fisher’s exact test. Means and Ϯ SE are occupied areas (inside clusters, n ϭ 12) with presented as untransformed values. All statis- adjacent unoccupied, but available areas with- tical analyses were performed with STATIS- in the same plantation forest patch (outside TICA (Version 7.0; StatSoft Inc. 2004). SHORT COMMUNICATIONS 413

FIG. 1. The proportion of all trees (deciduous and coniferous) inside and outside Least Flycatcher clusters in south-central Ontario red pine plantations, 2007. Sample size ϭ 12 vegetation plots both inside and outside of clusters.

RESULTS DISCUSSION Occupied areas (inside clusters) had more, We report the first use of pine plantations 15/44 (34%), deciduous trees (Ն8 cm dbh) by Least Flycatchers for nesting. Our study than unoccupied areas (outside the clusters) suggests that regenerating deciduous trees, as where only 1/23 (4%) were deciduous (Fish- a result of tree thinning operations, attract er’s exact test, P ϭ 0.007; Fig. 1). Canopy Least Flycatchers. More deciduous and total cover and number of trees Ն8 cm dbh were number of trees inside Least Flycatcher clus- significantly greater inside versus outside the ters resulted in greater canopy cover than in clusters (Table 1). The amount of understory red pine plantation sites adjacent and outside vegetation was marginally significant with these clusters. The greater canopy cover sup- greater mean understory cover outside than pressed growth of understory vegetation in- inside clusters. side the clusters. Other studies also report

TABLE 1. Habitat variables inside and outside Least Flycatcher clusters in red pine plantations in south- central Ontario, 2007. Statistical signiﬁcance was ascertained using a t-test for all variables. All sample sizes include 12 clusters and 12 areas outside clusters.

Inside clusters Outside clusters

Vegetation variable Mean Ϯ SE Mean Ϯ SE P Live ground cover, % 36.3 Ϯ 6.7 44.8 Ϯ 6.2 0.358 Leaf litter, % 44.0 Ϯ 6.9 40.8 Ϯ 6.2 0.732 Coarse wood debris, % 9.3 Ϯ 1.5 9.4 Ϯ 2.7 0.967 Regeneration cover, % 6.3 Ϯ 1.5 20.1 Ϯ 7.4 0.086 Sapling cover, % 8.2 Ϯ 1.5 8.5 Ϯ 3.1 0.912 Understory cover, % 8.2 Ϯ 3.6 18.8 Ϯ 3.6 0.052 Sub-canopy cover, % 32.9 Ϯ 8.6 37.9 Ϯ 5.9 0.637 Canopy cover, % 84.2 Ϯ 2.8 71.3 Ϯ 5.3 0.042 Basal area, m2/ha 21.3 Ϯ 1.1 20.3 Ϯ 1.9 0.853 Tallest tree, m 21.1 Ϯ 1.0 21.8 Ϯ 1.0 0.640 Mean number of trees/plot 3.7 Ϯ 0.7 1.9 Ϯ 0.2 0.046 414 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

Least Flycatcher occupancy was associated establishing territories. However, a full decid- with a well-developed canopy (DellaSala and uous canopy may not provide an explanation Rabe 1987, Darveau et al. 1992, Perry and for clustered breeding. Andersen 2003) and a relatively open under- Several alternate hypotheses for aggregat- story (Breckenridge 1956, Johnston 1971, ing behavior in Least Flycatchers have been Sherry and Holmes 1985). Certain structural proposed. Clustering during breeding may and compositional features of a forest, such as have (1) a predator deterrence effect through a minimum required canopy cover, appear to mobbing and alarm calls (Perry and Andersen provide visual cues in Least Flycatcher habitat 2003), (2) a means of competitive exclusion selection. of American Redstarts (Setophaga ruticilla) Clustering was not associated with differ- (Sherry and Holmes 1988), or (3) may be in ences in forest structure in other studies ex- response to female pursuit of extra-pair cop- amining the habitat hypothesis (Sherry and ulations and formation of hidden leks (Tarof Holmes 1985, Tarof and Ratcliffe 2004). This et al. 2005). No study has reported conclusive does not imply that habitat selection cues and consistent results to explain clustering, based on structure of vegetation are not used but most studies have found some evidence by Least Flycatchers when choosing where to related to these hypotheses. Least Flycatchers settle. The predominately deciduous forests in may benefit in several ways from clustering these studies may have a homogeneous, well- behavior; each benefit may be acting syner- developed canopy cover which flycatchers gistically to promote and/or maintain the be- may use to form clusters without apparent havior. Our study suggests a necessary pre- preference for habitat features within these cursor to formation of Least Flycatcher clus- forests. Relatively dense canopy cover includ- ters is a deciduous habitat component. ing deciduous foliage may be important for Least Flycatcher foraging. Least Flycatchers ACKNOWLEDGMENTS use a hovering tactic to glean prey from fo- We are grateful to the Oak Ridges Moraine Foun- liage and may need an open sub-canopy to dation and Environment Canada for funding this proj- detect prey movements in the denser main ect. Our appreciation is also expressed to Brendan canopy (Robinson and Holmes 1982). Rogers Hickie for valuable comments, and to Paul Woodward, (1985) reported Least Flycatchers use decid- Donna Tozzi, Myles Falconer, and Ben Walters for uous foliage for foraging more than Pinus spp. field assistance. when compared to the proportion of tree spe- LITERATURE CITED cies available. Habitat selection has fitness consequences ARSENAULT, E. J., R. J. HALL,R.S.SKAKUN,E.H. and high quality habitats are preferred to in- HOGG, AND M. MICHAELIAN. 2006. Pages 1–6 in crease fitness (Johnson 2007). Cues used as Characterizing aspen dieback severity using mul- indicators of high quality habitat may include tidate landsat data in western Canadian forests. Eleventh Forest Service Remote Sensing Appli- vegetation (Hildeń 1965), presence of conspe- cations Conference, Salt Lake City, Utah, USA. cifics (Stamps 1988, Ward and Schlossberg AHLERING,M.A.,D.H.JOHNSON, AND J. FAABORG. 2004), or both. Several studies have found that 2006. Conspecific attraction in a grassland bird, Least Flycatchers respond to song of conspe- the Baird’s Sparrow. Journal of Field Ornithology cifics during settlement (Mills et al. 2006, 77:365–371. Fletcher 2007), but the first individual to ar- BETTS, M. G., A. S. HADLEY,N.RODENHOUSE, AND J. J. NOCERA. 2008. Social information trumps veg- rive and begin singing in an appropriate hab- etation structure in breeding-site selection by a itat must be cued by something other than migrant songbird. Proceedings of the Royal So- conspecific attraction (Roth and Islam 2007, ciety of London Series B 275:2257–2263. but see Betts et al. 2008). Least Flycatchers BRECKENRIDGE, W. J. 1956. Measurements of the hab- may be stimulated to settle in habitats, includ- itat niche of the Least Flycatcher. Wilson Bulletin ing red pine plantations, with a relatively 68:47–51. closed canopy due to presence of deciduous CLARK,K.L.AND R. J. ROBERTSON. 1979. Spatial and temporal multi-species nesting aggregations in trees. This may be a basic, yet essential, com- birds as anti-parasite and anti-predator defenses. ponent of Least Flycatcher habitat defining the Behavioral Ecology and Sociobiology 5:359–371. innate cue used by the first males arriving and CULLY,J.F.AND H. L. MICHAELS. 2000. Henslow’s SHORT COMMUNICATIONS 415

Sparrow habitat associations on Kansas tallgrass ROBINSON,S.K.AND R. T. HOLMES. 1982. Foraging prairie. Wilson Bulletin 112:115–123. behavior of forest birds: the relationships among DARVEAU, M., J. L. DESGRANGES, AND G. GAUTHIER. search tactics, diet, and habitat structure. Ecology 1992. Habitat use by three breeding insectivorous 63:1918–1931. birds in declining maple forests. Condor 94:72–82. ROGERS, C. M. 1985. Foraging success and tree species DELLASALA,D.A.AND D. L. RABE. 1987. Response use in the Least Flycatcher. Auk 102:613–620. of Least Flycatchers Empidonax minimus to forest ROTH,K.L.AND K. ISLAM. 2007. Do Cerulean War- disturbances. Biological Conservation 41:291– blers (Dendroica cerulea) exhibit clustered terri- 299. toriality? American Midland Naturalist 157:345– ETTERSON, M. A. 2003. Conspecific attraction in Log- 355. gerhead Shrikes: implications for habitat conser- SHERRY,T.W.AND R. T. HOLMES. 1985. Dispersion vation and reintroduction. Biological Conserva- patterns and habitat responses of birds in northern tion 114:119–205. hardwoods forests. Pages 283–309 in Habitat se- FLETCHER, R. J. 2007. Species interactions and popu- lection in birds (M. L. Cody, Editor). Academic lation density mediate the use of social cues for habitat selection. Journal of Animal Ecology 76: Press, San Diego, California, USA. 598–606. SHERRY,T.W.AND R. T. HOLMES. 1988. Habitat selec- HILDE´ N, O. 1965. Habitat selection in birds. Annales tion by breeding American Redstarts in response Zoologici Fennici 2:53–75. to a dominant competitor, the Least Flycatcher. JOHNSON, M. D. 2007. Measuring habitat quality: a re- Auk 105:350–364. view. Condor 109:489–504. STAMPS, J. A. 1988. Conspecific attraction and aggre- JOHNSTON, D. W. 1971. Niche relationships among gation in territorial species. American Naturalist some deciduous forest flycatchers. Auk 88:796– 131:329–347. 804. STATSOFT INC. 2004. Statistica for Windows 7.0. Stat- JONES, J. 2001. Habitat selection studies in avian ecol- soft Inc., Tulsa, Oklahoma, USA. ogy: a critical review. Auk 118:557–562. TAROF,S.A.AND L. M. RATCLIFFE. 2004. Habitat char- KORNING,J.AND K. THOMSEN. 1994. A new method acteristics and nest predation do not explain clus- for measuring tree height in tropical rain forest. tered breeding in Least Flycatchers (Empidonax Journal of Vegetation Science 5:139–140. minimus). Auk 121:877–893. LEMMON, P. E. 1956. A spherical densiometer for es- TAROF, S. A., L. M. RATCLIFFE,M.M.KASUMOVIC, timating forest overstory density. Forest Science AND P. T. B OAG. 2005. Are Least Flycatcher (Em- 2:314–320. pidonax minimus) clusters hidden leks? Behavior- MACQUEEN, P. M. 1950. Territory and song in the al Ecology 16:207–217. Least Flycatcher. Wilson Bulletin 62:194–205. TEDFORD, J. A. 1978. Ganaraska Forest Study. Ganar- MILLS, A. M., J. D. RISING, AND D. A. JACKSON. 2006. Conspecific attraction during establishment of aska Region Conservation Authority. Ontario Least Flycatcher clusters. Journal of Field Orni- Ministry of Natural Resources, Peterborough, On- thology 77:34–38. tario, Canada. MORAN, M. D. 2003. Arguments for rejecting the se- VANHORNE, B. 1983. Density as a misleading indicator quential Bonferroni in ecological studies. Oikos of habitat quality. Journal of Wildlife Manage- 100:403–405. ment 47:893–901. PERRY,E.F.AND D. E. ANDERSEN. 2003. Advantages WARD,M.P.AND S. SCHLOSSBERG. 2004. Conspecific of clustered nesting for Least Flycatchers in north- attraction and the conservation of territorial song- central Minnesota. Condor 105:756–770. birds. Conservation Biology 18:519–525. 416 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

The Wilson Journal of Ornithology 121(2):416–421, 2009

Nocturnal Predation of Females on Nests: An Important Source of Mortality for Golden-cheeked Warblers?

Jennifer L. Reidy,1,5 Mike M. Stake,2,4 and Frank R. Thompson III3

ABSTRACT.—We monitored 124 female Golden- can be an unreliable method to identify nest cheeked Warblers (Dendroica chrysoparia)at133 fate, cause of nest failure, or identity of a nests with video cameras from 1997–2002 and 2005– predator (Thompson et al. 1999). 2006 at two study areas in central Texas, USA. Six adult females were depredated by snakes in 781 cam- Video surveillance has recently been shown era-monitored intervals when females were on the nest to be an effective and reliable method to iden- at night and exposed to possible nocturnal predation. tify and evaluate the importance of nest pred- Daily nest survival was 0.971 (95% CI: 0.959–0.980) ators (Thompson 2007). The main groups of and daily adult female predation while nesting was nest predators identified from these studies 0.008 (95% CI: 0.003–0.017). We estimated that were sciurids, corvids, raptors, and snakes. 14.6% of breeding females were depredated on the nest during the breeding season based on the observed Adult mortality was only observed in two survival rates and assuming females whose first nest studies using video surveillance to monitor was unsuccessful and which survived attempted a sec- songbirds—a thirteen-lined ground squirrel ond nesting attempt. Females were captured 75% of (Spermophilus tridecemlineatus) depredated the times they were on the nest at the time of a noc- one Chestnut-collared Longspur (Calcarius turnal nest predation by a snake. Predation of nesting ornatus) female (Pietz and Granfors 2000) females is potentially an important source of mortality and rat snakes (Elaphe spp.) depredated three for Golden-cheeked Warblers, and warrants further investigation. Received 7 June 2008. Accepted 30 August Golden-cheeked Warbler (Dendroica chryso- 2008. paria) females (Stake et al. 2004). The potential for snake predation of incubating females has long been speculated (Laskey 1946, Ma- Survival of migrant songbirds is generally han 1956), but this phenomenon has rarely thought to be high during the breeding season been documented (Plummer 1977, Blem 1979, (Sillett and Holmes 2002); however, there is Carter 1992). We believe snakes pose the little direct evidence of the frequency or greatest risk of depredating adult songbirds at sources of adult mortality during this period. the nest because they are the only group Documenting any predation event on the nest known to be significant nocturnal predators, is difficult (Pettingill 1976) and adult mortal- at least in some habitats (Hensley and Smith ity is usually inferred from remains left at the 1986, Stake and Cimprich 2003, Stake et al. nest (Sherry and Holmes 1997, Flaspohler et 2004, Reidy et al. 2008), large enough to kill al. 2001). Often evidence suggests that adults and consume adult songbirds. were killed in defense of the nest or circum- We monitored Golden-cheeked Warbler stantially, and were not the intended victim nests with video cameras and report on causes (Fendley 1980, Quinn 1985, King 1999). In- and rates of nest mortality, and identity of nest terpretation of evidence at the nest, however, predators elsewhere (Stake et al. 2004, Reidy et al. 2008). Our objective in this study is to 1 Department of Fisheries and Wildlife Sciences, report on the extent of adult mortality at the University of Missouri, Columbia, MO 65211, USA. nest and discuss its potential implications. 2 Division of Biological Sciences, University of Golden-cheeked Warblers, a federally endan- Missouri, Columbia, MO 65211, USA. gered species, are endemic breeders in central 3 Northern Research Station, U.S. Forest Service, Texas with strict nesting habitat requirements University of Missouri, Columbia, MO 65211, USA. (Ladd and Gass 1999). The requisite mixed 4 Current address: Hawks Aloft, P. O. Box 10028, Albuquerque, NM 87184, USA. mature Ashe juniper (Juniperus ashei) and 5 Corresponding author; e-mail: oak (Quercus spp.) woodlands in which they [email protected] nest are currently being heavily fragmented SHORT COMMUNICATIONS 417 and developed in historically important parts val and as 0 if all nest contents were de- of the breeding range (USDI 1992). stroyed. We fit a model with covariates for date, date2, and date3 to account for potentially METHODS non-linear effects of date (Grant et al. 2005, Study Area.—We monitored nests of Gold- Reidy 2007). We ignored other potential tem- en-cheeked Warblers at Fort Hood Military poral covariates such as nest stage or year be- Reservation, Texas, USA (30Њ 10Ј N, 97Њ 45Ј cause there was not much support for them in W) from 1997 to 2002 and in 2005, and in previous analyses examining factors affecting Austin, Texas (30Њ 23Ј N, 97Њ 34Ј W) from Golden-cheeked Warbler nest survival (Stake 2005 to 2006. Fort Hood (Bell and Coryell 2003, Peak 2007, Reidy 2007). We estimated counties) is a large, active military base in a daily nest survival with the above model for rural landscape with discrete patches of Gold- median nest interval observed in the study en-cheeked Warbler habitat separated by open (Shaffer and Thompson 2007). valleys leased for cattle grazing. Austin (Trav- We similarly estimated female daily surviv- is County) is a large and growing city with al with a logistic exposure model; we coded historically large amounts of contiguous survival as 1 if the female survived the over- breeding habitat currently being fragmented night observation interval and as 0 if she was by human development. depredated. We fit a constant survival (inter- Field Methods.—We mapped territories of cept only) model because there were too few banded and unbanded adults from March to mortality events to model as a function of co- May to establish pairing and nesting status of variates. We only included observations from males, and to narrow the nest-searching area. the days females sleep on the nest because We searched for nests from March to June, that is when they are potentially exposed to typically using adult behavioral cues to locate predation (nest days 3–21). We estimated fe- nests. We placed miniature video cameras male daily predation as 1 Ϫ daily survival. with infra-red illumination (Fuhrman Diver- We estimated total loss of adult females sified Inc., Seabrook, TX, USA) that allowed during the breeding season due to predation continuous monitoring at as many nests as on the nest based on daily nest survival, daily possible during the incubation and nestling female mortality, and number of nesting at- stages, prioritizing nests in the incubation tempts. If daily nest survival is assumed con- stage. Video cameras were attached by a 20-m stant, the proportion of nests surviving to any long cable to a video recorder and battery given day of the nest cycle can be estimated ϭ k placed as far from the nest as possible. We as pk s , where pk is the proportion of nests monitored nests daily using a monitor that surviving to day k and s is the daily survival plugged into the video recorder and did not estimate. If the daily mortality of females on approach the nest while it was active after the the nest is defined as m and is also assumed camera was installed. We recorded standard constant for nest days 3–21 (assuming the fe- monitoring information daily including nest male begins incubating the penultimate egg of contents and identified nest predators to the a typical 4-egg clutch, Pulich 1976), the pro- lowest possible taxa when we concluded a portion of females lost to predation during the ϭ⌺ k ϫ predation event had occurred. We used band- first nest attempt is: F1 kϭ3–21 (s m). If ing and territory status, and nest success in- we assume females which were successful in formation to establish the number of females their first nesting attempt do not re-nest and we monitored with video cameras (several fe- that all females whose first attempt failed and males were monitored with video cameras which survived re-nest, the proportion of fe- during more than one nesting attempt). Ad- males lost to predation during a second nest- ϭ Ϫ 25 Ϫ ϫ ditional monitoring details are available in ing attempt is: F2 (1 p F1) F1, Stake et al. (2004) and Reidy et al. (2008). where p25 is the proportion of females which Data Analyses.—We estimated daily sur- were successful during their first attempt and vival of nests with a logistic exposure model F1 is the proportion of females which died on (Shaffer 2004) in SAS 9.1 (SAS Institute their first attempt. The total proportion of 2004). We coded survival as 1 if at least one nesting females dying due to predation on the ϭ ϩ egg or nestling in the nest survived the inter- nest, FT, can be estimated as: FT F1 F2. 418 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

TABLE 1. Video camera-monitored nests of Golden-cheeked Warblers at Fort Hood, Texas, USA from 1997 to 2002 and 2005, and in Austin, Texas, USA, in 2005 and 2006. Most years had Ն4 nests with cameras during days 3–21 of the nest cycle and produced at least one snake predation of a female attending the nest.

Number of nests Number of nests Number of female monitored with monitored during mortalities (number cameras (total days 3–21 (total of females Year Site observation days) observation days) monitored) 1997 Fort Hood 1 (13) 1 (10) 0 (1) 1998 Fort Hood 2 (36) 2 (28) 0 (2) 1999 Fort Hood 2 (21) 2 (16) 0 (2) 2000 Fort Hood 6 (40) 4 (28) 1 (6) 2001 Fort Hood 30 (292) 26 (198) 0 (29) 2002 Fort Hood 24 (189) 15 (125) 2 (20) 2005 Fort Hood 7 (68) 6 (32) 0 (7) 2005 Austin 18 (174) 13 (100) 1 (16) 2006 Austin 43 (364) 31 (244) 2 (41)

Females rarely made a third nesting attempt If females spent one less or one more night at after two failures and we recorded no instanc- the nest (all else being equal), these totals es of double brooding (J. L. Reidy, pers. obs.). would be 14.0 or 15.2%, respectively. All predations of females were nocturnal, RESULTS occurring between 2103 and 2352 hrs CDT We monitored 133 nests (61 in Austin and from 18 April to 9 May in Austin, and be- 72 on Fort Hood) representing 124 females tween 0022 and 0448 hrs from 23 April to 17 with video cameras for an effective sample May at Fort Hood. All nest predations by size of 1,197 nest monitoring intervals (Table snakes (n ϭ 21) were nocturnal but one, oc- 1). We recorded 43 nest predations on video; curring between 2001 and 2352 hrs from 18 however, 11 of these were considered suc- April to 19 May in Austin and between 2037 cessful because Ն1 host young fledged despite and 0448 hrs from 23 April to 10 June at Fort a nest predation event. Rat snakes were the Hood. One additional nest predation by a leading predator at both sites, depredating 21 snake occurred at 1024 hrs at Fort Hood. nests. Texas rat snakes (Elaphe obsoleta lind- Snakes were not deterred by Golden- heimeri) and a Great Plains rat snake (E. gut- cheeked Warblers nesting in the canopy. Nests tata emoryi) depredated 20 and 1 nests, re- with depredated females were on average 5.2 spectively. We recorded females being cap- m(n ϭ 6; range ϭ 4.2 to 6.1 m) above ground tured and consumed during six of these nest and 1.8 m from the main trunk (n ϭ 6; range predations, three at each site. We identified ϭ 0.3 to 4.5 m) on trees with a diameter at Texas rat snakes as the predator at five adult breast height averaging 23 cm (n ϭ 6; range predation events and a Great Plains rat snake ϭ 12 to 43 cm). Nests were in Ashe junipers, at one. which are characterized by rough, peeling Daily nest survival was 0.971 (95% CI: bark. 0.959–0.980). We observed six predations of Four of the total snake nest predations females by snakes over 781 observation days (19%) were in the incubation stage and 17 during nest days 3–21, resulting in a daily fe- (81%) in the nestling stage. Two of four male predation rate of 0.008 (95% CI: 0.003– (50%) snake nest predations during the incu- 0.017). We estimated 0.103 (or 10.3%) of bation stage resulted in predation of the fe- breeding females were depredated during their male. Of the remaining two, the female was first nesting attempt. If all surviving females present at one and left the nest 3 min prior to with failed nests re-nested (42% of initial pop- the snake appearing at the nest (this was the ulation), we estimated 0.043 (or 4.3%) of one diurnal snake predation), and at the other breeding females were depredated during their nest, the female abandoned the nest just after second nesting attempt. Total losses of breed- sunset, several hrs before the snake predation. ing females to predation amounted to 14.6%. A Mourning Dove (Zenaida macroura) nest SHORT COMMUNICATIONS 419 located just below this nest was depredated identified Texas rat snakes as the most fre- the same night suggesting the female may quent predator, responsible for 18 of 48 nest have flushed from and possibly abandoned the predation events (Stake and Cimprich 2003). nest due to the presence of a predator below However, no nest predation by a snake result- her. Four of 17 (23%) snake nest predations ed in depredation of an adult. Black-capped during the nestling stage resulted in predation Vireos nest in shrubs and the nesting substrate of the female and occurred while the nestlings is likely not as stable or sturdy as that of were young (Յ5 days old) and in need of Golden-cheeked Warblers. Adults spending brooding. Eleven (65%) snake nest predations the night at the nest in shrubs would more occurred late in the nestling stage when fe- likely be alerted to an approaching predator. males were no longer brooding. Four of these Little is known about adult survival for nest predation events caused at least one nest- Golden-cheeked Warblers, particularly fe- ling to prematurely fledge (‘force-fledge’) and males, and we cautiously speculate about pos- two nests had already fledged young prior to sible implications on population dynamics. the snake predation event. Females were pre- Pairing success is commonly used as an in- sent but escaped the remaining two (12%) dicator of habitat quality with presence of un- snake nest predations. Both nests contained 5- paired males suggesting low habitat quality or 6-day old nestlings. The female was brood- (Gibbs and Faaborg 1990, Bayne and Hobson ing at one nest and left the nest as the snake 2001). Golden-cheeked Warbler pairing suc- appeared in view. This predation event oc- cess is generally high (often Ն90%) for ter- curred about 30 min after sunset while the fe- ritorial males at sites considered to be high- male was still alert. She peered below the nest quality habitat (Jette´ et al. 1998; Becker 2006; 3 min prior to the snake appearing on camera Peak 2006; J. L. Reidy, unpubl. data), while and flew off the nest as the snake approached. lower quality habitat in Austin had low (20– The female at the other nest was sleeping on 33%) pairing success (Becker 2005, 2006). the rim of the nest and was actually pushed Pairing success was also lower for second- off the nest by the snake as it investigated the year males than older males at Fort Hood (Jet- nestlings. The snake lurched after the falling te´ et al. 1998). These observations of differ- female, but when it returned to view at the ential pairing success are indicative of a pop- nest seconds later, it did not appear to have ulation with a lower number of females than caught the female. This female was not seen males, and we suggest female-biased mortal- returning to the nest. Females were preyed ity during the breeding season may be a con- upon during 29% (6/21) of the total snake nest tributing factor. Better estimates of adult and predations, 67% (6/9) of the times they were juvenile survival for males and females, pair- present during the nest predation, and 75% (6/ ing success, and existence and extent of po- 8) of the nocturnal nest predations for which tential non-territorial, or ‘‘floater’’ males the female was at the nest. (Bayne and Hobson 2001) are necessary to examine if predation on adult females during DISCUSSION the breeding season affects long-term stability Snakes consumed females attending the of Golden-cheeked Warbler populations. nest during the majority of nest predation Predation of adult females at the nest may events for which females were present, a find- partially explain the skewed adult survival ing no other study has reported for a songbird. rates and sex-ratios exhibited by many song- Predation by snakes on female Golden- birds. Wood Thrush (Hylocichla mustelina) cheeked Warblers attending the nest likely females had lower survival rates than males represents an important source of mortality during the breeding season (Powell et al. during the breeding season for this species. 2000, Coulter 2005). Survival was also lower Rat snakes are well-known tree climbers (Ten- for Black-throated Blue Warbler (Dendroica nant 1998) and would not be deterred from caerulescens) females than males during the climbing trees with rough bark (Mullin and breeding season (Sillett and Holmes 2002) Cooper 2002) such as Ashe juniper. A study and Ovenbird (Seiurus aurocapillus) females documenting nest predators of Black-capped had lower annual survival estimates than Vireos (Vireo atricapillus) at Fort Hood also males (Bayne and Hobson 2002). Many mi- 420 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 grant songbird populations exhibit male-bi- LITERATURE CITED ased sex-ratios during the breeding season BAYNE,E.M.AND K. A. HOBSON. 2001. Effects of (Gibbs and Faaborg 1990, Villard et al. 1993, habitat fragmentation on pairing success of Ov- Van Horn et al. 1995). Migrant songbird pop- enbirds: importance of male age and floater be- ulations can be more sensitive to changes in havior. Auk 118:380–388. adult survival than juvenile or nest survival BAYNE,E.M.AND K. A. HOBSON. 2002. Annual sur- (Noon and Sauer 1992, Donovan and Thomp- vival of adult American Redstarts and Ovenbirds son 2001). The loss of substantial numbers of in the southern boreal forest. Wilson Bulletin 114: 358–367. breeding females to predators simultaneous to BECKER, H. M. 2005. 2005 Golden-cheeked Warbler nest failure may be calamitous, especially for Dendroica chrysoparia and Black-capped Vireo an endangered species. Extinction risk for en- Vireo atricapillus monitoring program. Pages 4– dangered species is greater for populations 11 in Balcones Canyonlands Preserve Annual Re- with male-biased sex-ratios (Donald 2007) port 2004–2005. City of Austin, Texas, USA. BECKER, H. M. 2006. 2006 Golden-cheeked Warbler and for small, isolated populations experienc- Dendroica chrysoparia and Black-capped Vireo ing recent habitat fragmentation (Dale 2001). Vireo atricapillus monitoring program. Pages 3– Songbirds nesting in climates hospitable to 11 in Balcones Canyonlands Preserve Annual Re- snakes, particularly those exhibiting nocturnal port 2005–2006. City of Austin, Texas, USA. foraging patterns such as rat snakes, may be BLEM, C. R. 1979. Predation of black rat snakes on a particularly vulnerable to predation while on Bank Swallow colony. Wilson Bulletin 91:135– 137. the nest (Carter et al. 2007). Open-cup nesters CARTER, G. M., M. L. LEGARE,D.R.BREININGER, AND may have more opportunity to escape than D. M. ODDY. 2007. Nocturnal nest predation: a cavity nesters, but species which nest on stur- potential obstacle to recovery of a Florida Scrub- dy substrates, such as Golden-cheeked War- Jay population. Journal of Field Ornithology 78: blers, or on the ground, may not detect a pred- 390–394. CARTER, W. A. 1992. Black-and-white Warbler nest ator in time to escape, especially during the failure in Pontotoc County, Oklahoma. Bulletin of night. We suspect more nesting studies using the Oklahoma Ornithological Society 25:22–23. time-lapse video surveillance in geographic COULTER, S. C. 2005. Effects of forest management on regions with nocturnal snakes will reveal ad- Wood Thrushes in the Atchafalaya Basin, Loui- ditional predation on incubating and brooding siana. Thesis. University of Arkansas, Fayette- adult songbirds. We believe adult mortality ville, USA. DALE, S. 2001. Female-biased dispersal, low female during the breeding season warrants further recruitment, unpaired males, and the extinction of investigation for other species and ecosys- small and isolated bird populations. Oikos 92: tems. 344–356. DONALD, P. F. 2007. Adult sex ratios in wild bird populations. Ibis 149:671–692. ACKNOWLEDGMENTS DONOVAN,T.M.AND F. R. THOMPSON III. 2001. Mod- eling the ecological trap hypothesis: a habitat and We thank John Cornelius and the Department of the demographic analysis for migrant birds. Ecologi- Army, Fort Hood and Tim Hayden and the Army En- cal Applications 11:871–882. gineer Research and Development Center for funding FENDLEY, T. T. 1980. Incubating Wood Duck and and other support. Richard Aracil, Kyla Ercit, Mark Hooded Merganser hens killed by black rat Faherty, Nicole Flood, Allen Graber, Carter Mullen, snakes. Wilson Bulletin 92:526–527. Charles Pekins, Scott Stollery, Diane Tracy, Maria FLASPOHLER, D. J., S. A. TEMPLE, AND R. N. ROSEN- Elena Tolle, and Michael Wickens provided field as- FIELD. 2001. Species-specific edge effects on nest sistance. We are grateful to biologists with The Nature success and breeding bird density in a forested Conservancy and the City of Austin for assistance and landscape. Ecological Applications 11:32–46. support. We thank the U.S. Forest Service Northern GIBBS,J.P.AND J. FAABORG. 1990. Estimating the vi- Research Station and the Missouri Cooperative Fish ability of Ovenbird and Kentucky Warbler popu- and Wildlife Research Unit (U.S. Geological Survey, lations in forest fragments. Conservation Biology Missouri Department of Conservation, University of 4:193–196. Missouri, and U.S. Fish and Wildlife Service) for their GRANT, T. A., T. L. SHAFFER,E.M.MADDEN, AND P. J . support. Information included in this manuscript does PIETZ. 2005. Time-specific variation in passerine not necessarily reflect the position or policy of the U.S. nest survival: new insights into old questions. Auk Government or The Nature Conservancy, and no of- 122:661–672. ficial endorsement should be inferred. HENSLEY,R.C.AND K. G. SMITH. 1986. Eastern Blue- SHORT COMMUNICATIONS 421

bird responses to nocturnal black rat snake nest snake predation in a colony. Wilson Bulletin 97: predation. Wilson Bulletin 98:602–603. 233–234. JETTE´ , L. A., T. J. HAYDEN, AND J. D. CORNELIUS. 1998. REIDY, J. L. 2007. Golden-cheeked Warbler nest suc- Demographics of the Golden-cheeked Warbler cess and nest predators in urban and rural land- (Dendroica chrysoparia) on Fort Hood, Texas. scapes. Thesis. University of Missouri, Columbia, U.S. Army Construction Engineering Research USA. Laboratories Technical Report 98/52. Champaign, REIDY, J. L., M. M. STAKE, AND F. R. THOMPSON III. Illinois, USA. 2008. Golden-cheeked Warbler nest mortality and KING, D. I. 1999. Mortality of an adult Veery incurred predators in urban and rural landscapes. Condor during defense of nestlings. Wilson Bulletin 111: 110:458–466. 576–77. SAS INSTITUTE. 2004. The SAS system for Windows. LADD,C.AND L. GASS. 1999. Golden-cheeked Warbler Version 9.1. SAS Institute Inc., Cary, North Car- (Dendroica chrysoparia). The birds of North olina, USA. America. Number 420. SHAFFER, T. L. 2004. A unified approach to analyzing LASKEY, A. R. 1946. Snake depredations at bird nests. nest success. Auk 121:526–540. Wilson Bulletin 58:217–218. SHAFFER,T.L.AND F. R. THOMPSON III. 2007. Making MAHAN, H. D. 1956. Nocturnal predation on Song meaningful estimates of nest survival with model- Sparrow eggs by milksnake. Wilson Bulletin 68: based methods. Studies in Avian Biology 34:84– 245. 95. MULLIN,S.J.AND R. J. COOPER. 2002. Barking up the SHERRY,T.W.AND R. T. HOLMES. 1997. American wrong tree: climbing performance of rat snakes Redstart (Setophaga ruticilla). The birds of North and its implications for depredation of avian nests. America. Number 277. Canadian Journal of Zoology 80:591–595. SILLETT,T.S.AND R. T. HOLMES. 2002. Variation in NOON,B.R.AND J. R. SAUER. 1992. Population models survivorship of a migratory songbird throughout for passerine birds: structure, parameterization, its annual cycle. Journal of Animal Ecology 71: and analysis. Pages 441–464 in Wildlife 2001: 296–308. Populations (D. R. McCullough and R. H. Barrett, STAKE, M. M. 2003. Golden-cheeked Warbler nest pre- Editors). Elsevier Applied Science, New York, dation. Thesis. University of Missouri, Columbia, USA. USA. PEAK, R. G. 2006. Demography of the Golden-cheeked STAKE,M.M.AND D. A. CIMPRICH. 2003. Using video Warbler on Fort Hood, Texas, 2006. Pages 72–94 to monitor predation at Black-capped Vireo nests. in Endangered species monitoring and manage- Condor 105:348–357. ment at Fort Hood, Texas: 2006 annual report. The STAKE, M. M., J. FAABORG, AND F. R . T HOMPSON III. Nature Conservancy, Fort Hood Project, Fort 2004. Video identification of predators at Golden- Hood, Texas, USA. cheeked Warblers nests. Journal of Field Orni- PEAK, R. G. 2007. Forest edges negatively affect Gold- thology 75:337–344. en-cheeked Warbler nest survival. Condor 109: 628–637. TENNANT, A. 1998. A field guide to Texas snakes. Gulf Publishing Company, Houston, Texas, USA. PETTINGILL JR., O. S. 1976. Observed acts of predation on birds in northern Lower Michigan. Living Bird THOMPSON III, F. R. 2007. Factors affecting nest pre- 15:33–41. dation on forest songbirds in North America. Ibis PIETZ,P.J.AND D. A. GRANFORS. 2000. Identifying 149:98–109. predators and fates of grassland passerine nests THOMPSON III, F. R., W. DIJAK, AND D. E. BURHANS. using miniature video cameras. Journal of Wildlife 1999. Video identification of predators at songbird Management 64:71–87. nests in old fields. Auk 116:259–264. PLUMMER, M. V. 1977. Predation by black rat snakes U.S. DEPARTMENT OF INTERIOR (USDI). 1992. Golden- in Bank Swallow colonies. Southwestern Natural- cheeked Warbler (Dendroica chrysoparia) recov- ist 22:147–148. ery plan. USDI, Fish and Wildlife Service, Al- POWELL, L. A., J. D. LANG,M.J.CONROY, AND D. G. buquerque, New Mexico, USA. KREMENTZ. 2000. Effects of forest management on VAN HORN,M.A.,R.M.GENTRY, AND J. FAABORG. density, survival, and population growth of Wood 1995. Patterns of Ovenbird (Seiurus aurocapillus) Thrushes. Journal of Wildlife Management 64:11– pairing success in Missouri forest tracts. Auk 112: 23. 98–106. PULICH, W. M. 1976. The Golden-cheeked Warbler: a VILLARD, M.-A., P. R. MARTIN, AND C. G. DRUMMOND. bioecological study. Texas Parks and Wildlife De- 1993. Habitat fragmentation and pairing success partment, Austin, USA. in the Ovenbird (Seiurus aurocapillus). Auk 110: QUINN, J. S. 1985. Caspian Terns respond to rattle- 759–768. 422 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

The Wilson Journal of Ornithology 121(2):422–423, 2009

Depredation of Black-throated Blue Warbler Nestlings by an Introduced Slug (Arionidae)

Traynor G. Biasiolli1

ABSTRACT.—Black-throated Blue Warblers (Den- disintegrated, and the three nestlings were on droica caerulescens) are subject to nest predation by the ground underneath the nest. The nest had a variety of avian and mammalian species. I present apparently been damaged by heavy rains the evidence that slugs (Gastropoda: Mollusca) can also function as nest predators. On two occasions, slugs previous day, and the nestlings had fallen were observed feeding on 6–7 day-old nestling Black- through the nest bottom. The nestlings were 7 throated Blue Warblers at Hubbard Brook Experimen- days of age and too young for independent tal Forest, New Hampshire, USA. This is apparently movement (Black-throated Blue Warbler nest- the first report documenting that slugs can function as lings generally fledge 9 days after hatching; avian nest predators. Received 22 February 2008. Ac- Holmes et al. 2005). All nestlings were still cepted 25 December 2008. alive, although a slug was attached to each bird. One slug was attached to the upper wing of a nestling, while the other two slugs were Black-throated Blue Warblers (Dendroica each attached to the underside of a nestling caerulescens) are shrub-nesting Nearctic-neo- wing. The nestlings were likely weakened due tropical migrant passerines. These warblers to their poor ability to thermoregulate. How- are subject to nest predation by a wide variety ever, they were sufficiently strong to beg ac- of mammals and birds, including red squirrels tively for food, and showed no evidence of (Tamiasciurus hudsonicus), eastern chip- injury other than lesions where the slugs were munks (Tamias striatus), Blue Jays (Cyano- attached. Both parents were nearby, attempt- citta cristata), and Sharp-shinned Hawks (Ac- ing to feed the nestlings. The field assistant at cipiter striatus) (Holmes et al. 2005). Slugs the site decided to remove the slugs, and re- are rarely but consistently noted in or on placed the nestlings in the remnants of the Black-throated Blue Warbler nests at a study nest. None of the nestlings were observed dur- site in New Hampshire, USA (R. T. Holmes, ing the subsequent nest check 2 days later, and unpubl. data). However, no evidence exists to the adults had begun building a replacement indicate that slugs can function as avian nest nest. The principal cause of apparent nestling predators. I present evidence that, at least in mortality is unclear. rare instances, slugs will feed on nestling A second observation occurred on 4 August Black-throated Blue Warblers. 2006 at a second study area within Hubbard Brook, ϳ5 km from the site of the first ob- OBSERVATIONS servation. As I approached a nest during a Observations were made during summer routine nest check, I observed a slug inside 2006 at the Hubbard Brook Experimental For- the nest actively feeding on a nestling. All est (43Њ 56Ј N, 71Њ 45Ј W), a 3,160-ha reserve four nestlings in the nest had suffered severe within the White Mountain National Forest. disfiguration, and three had died by the time Black-throated Blue Warblers have been in- I arrived. The remaining live nestling was tensively studied at Hubbard Brook and more weakly attempting to beg for food, despite its than 2,900 nests have been monitored since injuries. The slug was feeding on a nestling 1986 (Holmes et al. 2005). which had already died, and I did not observe On 24 June 2006, during a routine nest a slug feeding on the remaining live nestling. check, a field technician found a nest that had The pattern of disfigurement found on all nestlings was inconsistent with damage previously 1 223 Cooksboro Road, Troy, NY 12182, USA; observed in depredated nests at Hubbard e-mail: [email protected] Brook (R. T. Holmes, N. L. Rodenhouse, and SHORT COMMUNICATIONS 423

T. S. Sillett; pers. comm.), suggesting the slug consume animal matter. However, the preda- was the sole source of damage to the nest- tion events described may represent unusual lings. Specifically, all four nestlings had suf- circumstances. The nestlings in the first inci- fered the complete loss of at least one eye, dent had fallen from their nest onto the and two nestlings, including the live nestling, ground. Slugs were much more likely to en- had suffered damage to their bills. Eyes were counter the nestlings outside of the nest, and cleanly removed rather than partially pecked the adults may have been less able or willing or chewed, and no scratches or cuts were ev- to dislodge slugs from their young on the ident near the eyes. Damage to the nestlings’ ground. In the second instance, the male had bills was extensive with approximately two- abandoned the nest and the task of nest de- thirds of the upper mandible consumed on the fense was left to the female. Previous obser- live nestling. I observed no scratches or cuts vations of this nest indicated the female was near the bills, which would be consistent with extraordinarily wary, and may have been too evidence of an avian or mammalian predator. skittish or inattentive to attack or drive off the The nest was still being attended by the fe- slug. It is likely that when slugs encounter male, although the male had deserted. Male nests during the nestling stage, adults will suc- Black-throated Blue Warblers frequently cessfully repel slugs, and slugs may only abandon nests after late July, but females can function as nest predators under atypical cir- typically raise late-season young without male cumstances. assistance when food levels are sufficient, as they were in late July 2006 (Holmes et al. ACKNOWLEDGMENTS 2005; R. T. Holmes, unpubl. data). Thus, it is My research was supported by a grant from the U.S. unlikely the nestlings had been weakened or National Science Foundation to R. T. Holmes, N. L. died due to starvation prior to being consumed Rodenhouse, and T. S. Sillett and a U.S. Department by the slug. of Agriculture McIntire-Stinnis grant to the University of Vermont. I thank the Hubbard Brook Experimental DISCUSSION Forest of the U.S. Department of Agriculture’s North- The slugs observed in both instances were east Research Station for support and cooperation. This manuscript benefited from comments of T. S. Sillett, members of the genus Arion (Arionidae), pre- A. M. Strong, M. H. Cline, W. S. Schwenk, N. G. sumably the same species. This genus is na- Perlut, S. J. K. Frey, and N. J. Zalik, as well as two tive to Europe, but many Arion species have anonymous referees. K. P. Hotopp, T. A. Pearce, and successfully established populations in North G. L. Bernon provided valuable assistance with slug America (Chichester and Getz 1973). The identification. slugs observed were most likely A. subfuscus, which has been previously documented at LITERATURE CITED Hubbard Brook (Strayer et al. 1986; T. A. BOYCOTT, A. E. 1934. The habitats of land Mollusca Pearce, pers. comm.). in Britain. Journal of Ecology 22:1–38. A thorough search of the ornithological and CHICHESTER,L.F.AND L. L. GETZ. 1973. The terrestrial malacological literature revealed no prior ev- slugs of northeastern North America. Sterkiana idence of slugs feeding on birds, nor on other 51:11–42. HOLMES, R. T., N. L. RODENHOUSE, AND T. S. SILLETT. live vertebrate prey. Most terrestrial slugs, in- 2005. Black-throated Blue Warbler (Dendroica cluding Arionidae, feed primarily on plant and caerulescens). The birds of North America. Num- fungal matter (South 1992). However, Arion ber 87. consume a wide variety of food items, includ- SOUTH, A. 1992. Terrestrial slugs: biology, ecology, ing food of animal origin such as mammal and and control. Chapman and Hall, London, United bird carcasses, dead invertebrates, and con- Kingdom. specifics (Boycott 1934, South 1992). STRAYER, D., D. H. PLETSCHER,S.P.HAMBURG, AND S. C. NODVIN. 1986. The effects of forest disturbance It is perhaps surprising that slugs have not on land gastropod communities in northern New been previously documented as nest predators England. Canadian Journal of Zoology 64:2094– given their wide dietary breadth and ability to 2098. 424 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

The Wilson Journal of Ornithology 121(2):424–426, 2009

Nest Sharing between an American Robin and a Northern Cardinal

Paul W. Govoni,1,2 Keith S. Summerville,1,4 and Muir D. Eaton3

ABSTRACT.—Mixed-clutch nest sharing was ob- erally rejecting Brown-headed Cowbird eggs served between an American Robin (Turdus migrato- (but see Lowther 1981), and have not been rius) and a Northern Cardinal (Cardinalis cardinalis) observed to exhibit intraspecific cooperative in Saylor Township, Polk County, Iowa in May 2007. The nest contained three American Robin eggs and brood care (Sallabanks and James 1999). two Northern Cardinal eggs, but only American Robin Examples of interspecific nest sharing, young were fledged successfully. This was not a case where eggs from both species are present in of brood parasitism, as both females were observed the nest and/or cared for by both species, are alternating incubation of the nest. Competition for de- less commonly documented, but not absent sirable nest sites might be a possible cause for this type from the literature (e.g., Cohen 1899, Atkins of interspecific behavior. Received 17 July 2008. Ac- cepted 15 October 2008. 1916, Bleitz 1956, Crowell et al. 1982). One example of this phenomenon documented a clutch of 17 larger and nine smaller eggs be- Both intra- and interspecific interactions ing jointly incubated by a female Greater among birds can have significant influences Scaup (Aythya marila) and a female Lesser on nesting success. For example, brood shar- Scaup (A. affinis) on Great Slave Lake (Four- ing, brood parasitism, nest usurpation, and in- nier and Hines 1996). The eggs were posi- terspecific feeding have been documented tioned in the nest so both females could sit among passerines (Payne 1977). Nest usur- side by side, in contact with each other, and pation is often restricted to species with en- incubate all of the eggs simultaneously (Four- closed or cavity nests (Lindell 1996), but oth- nier and Hines 1996). Mixed clutches have er interactions have been observed across a also resulted in mixed broods; during a 10- variety of cup-nesting species (e.g., Payne year field investigation of cavity nesting spe- 1977, Shy 1982, McNair 1984). Brood para- cies, Robinson et al. (2005) observed fledg- sitism of Northern Cardinal (Cardinalis car- lings of both Red-breasted Nuthatches (Sitta dinalis) is known to occur, mainly from canadensis) and Mountain Chickadees (Poe- Brown-headed Cowbirds (Molothrus ater) cile gambeli) after adults of both species had (Halkin and Linville 1999). Intraspecific exhibited parental behavior at a single nest. brood sharing has also been observed between We report a case of interspecific nest sharing two female Northern Cardinals, and was attrib- and brood care by a pair of Northern Cardi- uted to fertilization of both by the same male nals and a pair of American Robins. (Rice 1969). Cardinals have also exhibited intraspecific cooperative breeding behavior OBSERVATIONS among unrelated individuals (Halkin and Lin- On 3 May 2007, PWG observed an Amer- ville 1999), as well as an instance of feeding ican Robin in a nest constructed ϳ1 m above of American Robin (Turdus migratorius) ground level in a 2-m tall Sunkist Arborvitae young (Shy 1982). American Robins, how- (Thula occidentalis ‘‘Sunkist’’). The evergreen ever, are less tolerant of nest violations, gen- was in a suburban development, 2 m from a house and adjacent to a raised wooden deck. 1 Department of Environmental Science, Drake Uni- The nest was partially sheltered by these versity, Des Moines, IA 50311, USA. structures. The surrounding neighborhood 2 Current address: 5800 NE 6th Street, Des Moines, lacked mature trees or much shrub cover. On IA 50313, USA. 4 May 2007, a female Northern Cardinal was 3 Department of Biology, Drake University, Des Moines, IA 50311, USA. observed using the same nest. These two birds 4 Corresponding author; e-mail: changed their respective occupation of the [email protected] nest frequently and, while each was away SHORT COMMUNICATIONS 425

FIG. 1. American Robin and Northern Cardinal eggs incubated in the same nest. from the nest, were observed in close prox- turned to the nest and found the robin there, imity to a conspecific male. These males were the cardinal would stand on the back of the presumed to be the mates of each female, robin and scratch and kick until the robin fled which was confirmed for the cardinal by sub- the nest. During this time, it was also common sequent observations. to observe the male cardinal bringing food to Examination of the nest on 5 May 2007 re- the female while she sat on the nest. vealed three robin eggs and two cardinal eggs A fledgling appeared in the nest on 14 May (Fig. 1). The nest was monitored ad hoc over 2007, and both females continued to share the next week to document incubation. Reg- nest time, with the male cardinal continuing ular shifting of females on the nest continued to feed the female while she roosted on the during this period, however, the distance be- nest. A second fledgling was present in the tween the females and the nest continually de- nest on 16 May 2007. From this point for- creased. Quite often, the female cardinal ward, the cardinals were no longer seen at the would return to the nest to find the robin on nest. Subsequent inspection of the nest re- the eggs and perch several centimeters away vealed only the two fledglings and remains of on a limb. As time progressed, it was common a single cardinal egg on the ground directly to see both the female cardinal and the female beneath the nest. The two fledglings continued robin in the nest at the same time. This prac- to develop under parental care of the robin, tice appeared to cease when the female car- only, and were recognizable as juvenile Amer- dinal began to display aggressive behaviors ican Robins on 22 May 2007. The juveniles toward the robin. If the female cardinal re- eventually forayed onto the deck from the nest 426 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 and in a matter of days were no longer seen LITERATURE CITED in the area, as was true of the parents. ATKINS, E. 1916. A nestful. Condor 38:201–202. DISCUSSION BLEITZ, D. 1956. Eggs of the California Quail in the The nesting strategy that uses the active nest of a Spotted Towhee. Condor 58:77–78. COHEN, D. A. 1899. Nesting and other habits of the takeover of a nest site of one species by a Oregon Towhee. Condor 1:61–63. different species for egg laying and incubation CROWELL, D. K., C. C. CARPENTER, AND D. G. HUFF- is known as nest usurpation or nest piracy. MAN. 1982. Nest-sharing by a Lark Sparrow. Auk This particular behavior is not in agreement 99:591–592. with the popular belief that coexisting species FILLIATER, T. S., R. BREITWISCH, AND P. M . N EALEN. have divergent nest placement (Lindell 1996). 1994. Predation on Northern Cardinal nests: does However, studies have also concluded that choice of nest site matter? Condor 96:761–768. FOURNIER,M.A.AND J. E. HINES. 1996. Nest sharing convergence upon a nest site by more than by a Lesser Scaup and a Greater Scaup. Wilson one species is evidence of interspecific com- Bulletin 108:380–381. petition for nesting sites (Lindell 1996). The HALKIN,S.L.AND S. U. LINVILLE. 1999. Northern Car- nesting behavior we observed demonstrates a dinal (Cardinalis cardinalis). The birds of North single nest site can be suitable for more than America. Number 440. one species. Whether the cardinal pair ob- LINDELL, C. 1996. Patterns of nest usurpation: when served in this instance was two juvenile birds should species converge on nest niches? Condor with little nesting experience or was compet- 98:464–473. LOWTHER, P. E. 1981. American Robin rears Brown- itively inferior to the robin pair are unresolved headed Cowbird. Journal of Field Ornithology 52: questions. The aggressive nature of this par- 145–147. ticular observation suggests the value of nest- MCNAIR, D. B. 1984. Reuse of other species’ nests by ing sites in suburban habitats is worth pro- Lark Sparrows. Southwestern Naturalist 29:506– tracted physical confrontation. The Northern 509. Cardinal may use an aggressive re-nesting PAYNE, R. B. 1977. The ecology of brood parasitism strategy in response to high levels of nest pre- in birds. Annual Reviews of Ecological Systems 8:1–28. dation (Filliater et al. 1994), and the selective RICE, O. O. 1969. Record of female Cardinals sharing pressures that affect the evolution of nest site nest. Wilson Bulletin 81:216. selection require further research for both spe- ROBINSON, P. A., A. R. NORRIS, AND K. MARTIN. 2005. cies. Interspecific nest sharing by Red-breasted Nut- hatch and Mountain Chickadee. Wilson Bulletin ACKNOWLEDGMENTS 117:400–402. We thank C. E. Braun, M. M. Robbins, and two SALLABANKS,R.AND F. C . J AMES. 1999. American anonymous reviewers for constructive comments on Robin (Turdus migratorius). The birds of North this note that greatly improved the manuscript. S. K. America. Number 462. Govoni contributed observations to our own and thus SHY, M. M. 1982. Interspecific feeding among some expanded our understanding of the nesting behavior of birds: a review. Journal of Field Ornithology 53: these two species. 370–393. SHORT COMMUNICATIONS 427

The Wilson Journal of Ornithology 121(2):427–429, 2009

Misdirected Parental Care by a Male Eastern Towhee at a Wood Thrush Nest

Kelly M. Schaeffer,1,3 William P. Brown,2 and W. Gregory Shriver1

ABSTRACT.—Misdirected parental care, or care di- We report the first case of Wood Thrush nest- rected toward unrelated young, has been recorded for lings in a nest parasitized by the Brown-head- many bird species. The Wood Thrush (Hylocichla mus- ed Cowbird (Molothrus ater) being fed by a telina) is not known to practice this behavior or allow other species to attend to its young. We observed a male Eastern Towhee. Wood Thrush nest with three Wood Thrush nestlings Wood Thrush nests were located and mon- and one Brown-headed Cowbird (Molothrus ater) nest- itored during the 2006 field season as part of ling being attended by a male Eastern Towhee (Pipilo a long-term study of Wood Thrush breeding erythrophthalmus). The towhee fed the young of both ecology in the 15-ha University of Delaware species in the nest for at least 5 days and was subse- Woods (UDW) in Newark, Delaware (Brown quently observed feeding a Wood Thrush fledgling. The towhee also participated in nest maintenance and and Roth 2002, 2009). Individually color- defense. The proximate cause of towhee attendance at banded adults were associated with each nest the Wood Thrush nest remains unknown, but begging and assumed to be the social parents of young calls from the nestlings may have stimulated the be- Wood Thrushes in the nest. An 80-mm spot- havior. Received 28 June 2008. Accepted 3 November ting scope was used to conduct observations 2008. from a blind approximately 15 m from the nest for at least 1 hr/day for each of eight nests in a separate observational study (Schaeffer Misdirected parental care is intra- or inter- 2007). It was during these nest observations specific care directed toward the young of an that KMS discovered a male Eastern Towhee unrelated bird (Shy 1982, Price et al. 1983). feeding Wood Thrush nestlings and a Brown- Misdirected parental care differs from inter- headed Cowbird nestling in a Wood Thrush specific feeding, which also may include an nest (Fig. 1). adult of one species feeding an adult of another species (Boix-Hinzen 1997). Misdirect- OBSERVATIONS ed parental care has been described several The Wood Thrush nest of interest was dis- times for the Eastern Towhee (Pipilo erythro- covered on 25 May 2006, ϳ4.5 m above- phthalmus), but Wood Thrushes (Hylocichla ground in a shadbush (Amelanchier spp.), and mustelina) are not known to exhibit this be- contained three Wood Thrush eggs and two havior or cooperate as recipients of the be- Brown-headed Cowbird eggs. Three thrushes havior in the wild. Skutch (1961) reported an and one cowbird hatched and survived to adult male Wood Thrush helped feed nestlings fledge. of several different species in an aviary. Shy We observed the male Eastern Towhee car- (1982) reported four occurrences of the East- rying food near the Wood Thrush nest during ern Towhee feeding young of other species, the first nest observation period for this nest including Field Sparrow (Spizella pusilla), on 14 June 2006, when the young were 8 days Northern Mockingbird (Mimus polyglottos), of age. The towhee did not approach the nest and House Finch (Carpodacus mexicanus). while the female was brooding, but remained on a branch 10–15 cm distant. The young 1 Department of Entomology and Wildlife Ecology, thrushes were gaping while being brooded and 250 Townsend Hall, University of Delaware, Newark, the cowbird was begging loudly; these behav- DE 19716, USA. iors appeared to be directed at the towhee be- 2 254 East Walnut Street, Kutztown, PA 19530, USA. cause all young were facing in his direction. 3 Corresponding author; e-mail: Once the female Wood Thrush left the nest, [email protected] the towhee approached the rim and fed one 428 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

FIG. 1. Female Wood Thrush brooding her begging young as a male Eastern Towhee approaches the nest with food. Photograph by M. E. Zuefle and W. P. Brown, 2006. young before quickly departing. The Wood the nest several times, remaining ϳ5 cm from Thrush parents did not react to the presence the rim, while the female was brooding on 16 of the towhee. It is likely the towhee had been June. She did not react to his presence, but the feeding the nestlings before 14 June based on towhee did not try to feed the young. How- the insistent begging behavior of the young at ever, when the towhee approached the nest on the approach of the towhee, the indifferent be- 17 June while the female was brooding, he havior of the Wood Thrush nest owners, and attempted to feed one of the nestlings. In re- the rather direct route the towhee took to the sponse, the female Wood Thrush leaned over nest. the rim and pecked at him. The towhee quick- The towhee participated in feeding and sev- ly flew from the nest tree, but remained in the eral other aspects of nest activity during the area and returned with food as soon as the six subsequent 1-hr observation periods from female had left the nest. The towhee made 15 June to 20 June. We removed the Wood eight successful feeding trips while the Wood Thrush nestlings for banding on 15 June, and Thrush parents made seven trips collectively the towhee called agitatedly while in close during the 1-hr observation period on 17 June. proximity to the Wood Thrush parents, which Both the towhee and female Wood Thrush fed also were scolding. The towhee was observed the young on 19 June. The male Wood Thrush removing fecal sacs from the nest on 16 June. did not complete any feeding trips during this The towhee continued to take part in nest de- 1-hr observation period, but remained in the fense on 17 June, responding to the presence area singing almost continuously. The Eastern of a Great Horned Owl (Bubo virginianus) Towhee averaged 3.6 feeding trips/hr com- ϳ90 m from the nest. The towhee stood on pared to the parents’ combined 5.2 (2.6/adult) the rim of the nest calling, while two Wood trips/hr for all observations. Thrushes, presumably the nest owners, scold- The young fledged on the morning of 20 ed near the owl. June, and the towhee was observed feeding a The Wood Thrush parents seldom reacted Wood Thrush fledgling in the nest tree, ϳ3m to the presence of the towhee over the course from the nest and 5 m above ground. The to- of our observations. The towhee approached whee was observed in the same area as the SHORT COMMUNICATIONS 429

fledglings until 30 June, after which the fledg- local towhee nests. Yoerg and O’Halloran lings were not observed in the area of the nest. (1991) and Dro´z˙dz˙ et al. (2004) reiterated the The towhee was not observed feeding fledg- potential importance of begging sounds, as lings except for 20 June, but heavy cover pre- well as proximity to nests of other species, as cluded our efforts to successfully observe the a stimulus for misdirected parental care. fledglings being fed. Shy (1982) reported that only 11 of 95 cases (12%) of misdirected parental care in- DISCUSSION volved the feeding of both nestlings and fledg- We observed misdirected parental care be- lings. Part of this rarity may be due to the havior by the male Eastern Towhee over a 7- difficulty of observing fledglings when they day period, including the first day the young are being fed. The presumed rarity of misdi- fledged. Digital photographs of the towhee rected parental care also may be due to the with food in his bill were taken near the nest lack of systematic nest observations beyond on 18 June 2006 (Fig. 1). To our knowledge, recording the contents of the nest. this is the first report of Wood Thrushes being the recipient of misdirected parental care in ACKNOWLEDGMENTS the wild. We thank Vanessa Shiavi for help in the field and Wood Thrushes fledged at 12.3 days of age, M. E. Zuefle for photography. KMS was supported by on average, during the 2006 field season. The the University of Delaware Undergraduate Research young attended by the towhee fledged at 13 Program and Science Scholars Program. days of age, suggesting the misdirected parental care did not affect nest success. LITERATURE CITED The circumstances that led the male Eastern BOIX-HINZEN, C. 1997. Note on misdirected feeding Towhee to attend the Wood Thrush nest were behaviour. Lanioturdus 30:26–28. unclear, as the breeding status of the towhee BROWN,W.P.AND R. R. ROTH. 2002. Temporal pat- was not known. Shy (1982) described eight terns of fitness and survival in the Wood Thrush. different categories that might stimulate mis- Ecology 83:958–969. directed parental care. These include the pos- BROWN,W.P.AND R. R. ROTH. 2004. Juvenile survival sibility that: (1) the bird practicing misdirect- and recruitment of Wood Thrushes Hylocichla mustelina in a forest fragment. Journal of Avian ed parental care was raising a mixed clutch, Biology 35:316–326. (2) the original nest of the bird was destroyed, BROWN,W.P.AND R. R. ROTH. 2009. Age-specific re- (3) the nest of another species was close to production and survival of individually marked that of the bird performing the behavior, (4) Wood Thrushes, Hylocichla mustelina. Ecology the calls of nestlings stimulated the misdi- 90: In press. ´ ˙ ˙ rected parental care, (5) orphaned birds were DROZDZ, R., M. HROMADA, AND P. T YRANOWSKI. 2004. Interspecific feeding of Great Grey Shrike (Lanius adopted temporarily or permanently, (6) a excubitor) fledgling by adult Yellowhammers male fed another species while his mate in- (Emberiza citronella). Biological Letters 41:185– cubated, (7) finding a mateless bird, or being 187. mateless itself, a bird joined a pair with PRICE, T., S. MILLINGTON, AND P. G RANT. 1983. Helping young, or (8) reasons different from those giv- at the nest in Darwin’s Finches as misdirected pa- en above. rental care. Auk 100:192–194. SCHAEFFER, K. 2007. The effects of Brown-headed The Brown-headed Cowbird regularly par- Cowbird parasitism on the parental feeding rates asitizes both Wood Thrush and Eastern To- of Wood Thrush. Undergraduate Research Schol- whee nests and the familiar sounds of a beg- ars Poster Session. University of Delaware, New- ging cowbird, or of nestlings in general, may ark, USA. have been the stimulus that triggered the to- SHY, M. M. 1982. Interspecific feeding among some whee’s feeding efforts. Brown-headed Cow- birds: a review. Journal of Field Ornithology 53: bird parasitism was particularly heavy at 370–393. SKUTCH, A. F. 1961. Helpers among birds. Condor 63: UDW during 2006 (12 of 15 nests; Brown and 198–226. Roth [2004] report annual rates of parasitism YOERG,S.I.AND J. O’HALLORAN. 1991. Dipper nest- at UDW); the same may have been true for lings fed by a Gray Wagtail. Auk 108:427–429. 430 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

The Wilson Journal of Ornithology 121(2):430–434, 2009

Brood Rearing Ecology of King Eiders on the North Slope of Alaska

Laura M. Phillips1,4,5 and Abby N. Powell2,3

ABSTRACT.—We examined King Eider (Somateria Estimates of duckling survival for water- spectabilis) brood survival in the Kuparak oil field in fowl species suggest that survival rates are northern Alaska in 2002 and 2003 by monitoring hens lower from hatching to fledging than during with broods using radiotelemetry. We observed complete brood loss in eight of 10 broods. Broods survived later life stages, and variation in survival is less than 2 weeks on average, and most mortality oc- linked to recruitment (Mendenhall and Milne curred within 10 days of hatch. Distance hens traveled 1985, Johnson et al. 1992). Duckling mortality overland did not affect brood survival. Apparent King has been attributed to predation, adverse Eider brood survival in our study area was lower than weather, starvation, and disease (Johnson et al. reported for eider species in other areas. We recom- 1992). Identifying mortality at different life mend future studies examine if higher densities of predators in oil fields reduces King Eider duckling sur- history stages is important for developing vival. Received 26 September 2008. Accepted 18 Jan- conservation plans for King Eiders. We ex- uary 2009. amined survival of King Eider ducklings on the North Slope of Alaska and examined survival in relation to distance traveled over land. Declines in the North American population of King Eiders (Somateria spectabilis) have in- METHODS creased interest in the status and ecology of this Study Area.—We trapped female King Ei- species (Dickson et al. 1997, Gratto-Trevor et ders on nests in 2002 and 2003 at the Kuparuk al. 1998, Suydam et al. 2000). King Eiders are oil field (70Њ 20Ј N, 149Њ 45Ј W) between the circumpolar breeders that nest primarily along Colville and Kuparuk rivers on the North the margins of freshwater ponds and lakes on Slope of Alaska. The site was characterized the arctic tundra (Suydam 2000). King Eider fe- by numerous thaw lakes, ponds, and basins males leave the nest after hatch with their brood (Anderson et al. 1999). and move over land among tundra ponds (Berg- Capture and Telemetry.—We searched ac- man et al. 1977). Some waterfowl studies hy- cessible areas in the Kuparuk oil field for nest- pothesize that distance traveled over land may ing King Eiders during each summer, 2002 reduce duckling survival by increasing risk of and 2003. We candled and floated eggs from mortality due to predation or exposure (Rotella nests to assess incubation stage and estimate and Ratti 1992, Seymore and Jackson 1996), hatch date (Weller 1956). We monitored nests while other studies suggest a positive correlation at least once per week. (Yerkes 2000, Mehl and Alisauskas 2007) or no We captured hens on nests about 1 week effect (Wayland and McNicol 1994, Dzus and prior to hatch using hand-carried mist nets Clark 1997). (Bacon and Evrard 1990) or bow-net traps (Sayler 1962). We originally planned to trap 1 Department of Biology and Wildlife, 211 Irving 1 20 randomly selected hens each year but, due Building, University of Alaska, Fairbanks, AK 99775, USA. to low nest success we attempted to trap any 2 U.S. Geological Survey, Alaska Cooperative Fish female still on a nest 1 week prior to predicted and Wildlife Research Unit, P. O. Box 757020, Uni- hatch date. We captured 12 females in 2002, versity of Alaska, Fairbanks, AK 99775, USA. clipped feathers on their upper back between 3 Institute of Arctic Biology, P. O. Box 757000, Uni- their wings, and attached 8-g VHF transmit- versity of Alaska, Fairbanks, AK 99775, USA. ters (Telonics Inc., Mesa, AZ, USA) to the 4 Current address: Center for Resources, Science, area using epoxy. We attached 10-g VHF an- and Learning, Denali National Park and Preserve, P. O. Box 9, Denali National Park, AK 99755, USA. chor transmitters using a suture technique 5 Corresponding author; e-mail: (Pietz et al. 1995) to 12 hens in 2003 to reduce laura[email protected] transmitter loss. We checked nests daily after SHORT COMMUNICATIONS 431

TABLE 1. King Eider radio-tracking at Kuparuk, Alaska, 2002–2003.

2002 2003 Total Females radio-marked 12 12 24 Radio-marked females that failed to hatch eggs 5 3 8 Radio-marked females that lost radio tag 3 0 3 Females radio-tracked 4 6 10 Radio-marked females that lost broods prior to ﬁrst relocation 0 3 3

capture to document departure of broods. We to still have a brood if ducklings of the ap- did not flush hens from nests during these propriate age tended to follow her rather than checks. We checked nests for number of alternate hens when disturbed. We calculated hatched eggs when females departed the nest daily survival estimates for broods using the area following hatch. We assumed initial Mayfield method and assigned exposure days brood size was equal to the number of hatched for complete brood loss equal to 50% of the shell membranes (Girard 1939). All methods last observation interval (Mayfield 1961, and handling of birds were approved by the 1975, Johnson 1979). Survival to 30 days was University of Alaska Institutional Animal calculated by raising the daily survival rate to Care and Use Committee (IACUC # 02-10). the power of 30. We located hens after hatch every 2–5 days We used linear regression to test whether until ducklings were 30 days of age or until the number of days a brood survived was af- we observed a female without a brood on two fected by distances traveled over land and if consecutive tracking sessions. We tracked distances traveled per day varied with duck- marked hens by vehicle, foot, and aircraft. Ae- ling age. Data from both years were pooled in rial telemetry flights were used weekly when all analyses due to small sample sizes. We weather permitted to locate hens not found performed all statistical analyses using SAS from the ground. Transmitters had a range of software (SAS Institute 1990); means Ϯ SE at least 1 km from the ground and up to 10 are presented. Results were considered signif- km from the air. We recorded location infor- icant at ␣ϭ0.05. mation using Global Positioning System (GPS) units and aerial photos. We used aerial RESULTS photos to record locations when we were not Four of 12 hens captured in 2002 were suc- able to get exact GPS locations or did not cessfully radio-tracked with broods, five failed want to disturb hens with broods. We later re- to hatch eggs, and three prematurely lost their turned to these locations to obtain locations radio transmitters prior to first relocation after using GPS or inferred locations using Arc- hatch (Table 1). Six of 12 hens captured in View. We also recorded brood size, number of 2003 were successfully radio-tracked, three hens and ducklings if broods had formed failed to hatch eggs, and three lost broods pri- cre`ches, and predators observed. or to first relocation after hatch (Table 1). We Analysis.—We plotted movements of fe- relocated marked hens with broods 5.6 Ϯ 1.4 males using ArcView 3.2 Geographic Infor- times (n ϭ 10, range ϭ 1–14). mation System (GIS) (ESRI 1998). We cal- Average brood size at hatch was 4.2 Ϯ 0.4 culated straight line distances between re-ob- ducklings (n ϭ 10, range ϭ 2–6). We observations and mean bearing of movement served complete brood loss in eight of 10 paths using Animal Movement extension broods (80%). Broods survived an average of (Hooge and Eichenlaub 1997) in ArcView. 13.4 Ϯ 3.1 days (n ϭ 10, range ϭ 2–31). Most We considered survival of a brood as at least brood loss (5 of 8, 62.5%) occurred within the one duckling surviving to 30 days of age first 10 days after hatch (Table 2). The daily when King Eider ducklings closely resemble survival estimates for broods was 0.855 Ϯ adults in size and mortality from predation is 0.026, and estimated survival over 30 days negligible (Mehl and Alisauskas 2007). We was 10.3% (95% CI: 2.0–49.3). We observed considered a marked hen observed in a cre`che the depredation of a King Eider chick from a 432 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

TABLE 2. Number of King Eider ducklings ob- DISCUSSION served in broods of radio-tracked females at Kuparuk, We offer the first description of survival of Alaska, 2002–2003. All females experienced complete King Eider broods in Alaska. We observed brood loss within the first 2 weeks after hatch. lower apparent survival of broods (20%) than Age (days) observed for King Eiders breeding at Karrak ID # Hatch 1–5 5–10 10–15 Lake in Nunavut, Canada (35%, Mehl and Al- KIEI02 4 0 isauskas 2007). Apparent survival of King Ei- KIEI06 5 3 0 der broods at Kuparuk was also lower than KIEI17 3 0 reported for related eider species in Alaska. KIEI29 6 3 0 Half (49%) of all Spectacled Eider (Flint and KIEI68 4410Grand 1997) and 73% of all Common Eider KIEI70 5510(S. mollissima) females (Flint et al. 1998) on KIEI87 3 3 0 KIEI95 4330the Yukon-Kuskokwim Delta lost their broods within 30 days of hatch. Our calculation of apparent survival of broods does not include an estimate of varia- tracked brood by a Glaucous Gull (Larus hy- tion in the data. Given our small sample size perboreus) and witnessed two unsuccessful at- and probable variation among years, we tacks on radio-tracked broods, including one by two Parasitic Jaegers (Stercorarius para- would assume this variation to be significant. siticus) and another by a Glaucous Gull. Mayfield estimates of survival for King Eider Average daily movement rate of hens with broods at Kuparuk, while low, show large broods was 507.4 Ϯ 68.7 m/day (n ϭ 56; confidence intervals that overlap with survival range ϭ 0–2,376 m). Longer daily movement estimates for broods at Karrak Lake (31%, rates did not affect the number of days a brood 95% CI: 13–50%; Mehl and Alisauskas 2007). ϭ ϭ Gull predation has been identified as a pri- survived (F1,8 0.10, P 0.76). Distance traveled per day by hens with broods did not mary cause of eider duckling mortality (Men- ϭ ϭ denhall and Milne 1985, Mehl and Alisauskas vary with duckling age (F1,54 0.90, P 0.35). Hens did not appear to travel in a par- 2007). Glaucous Gulls nest across Alaska’s ticular general direction with ducklings after Arctic Coastal Plain; studies have indicated hatch. Four hens moved east, three north, two their populations may be more concentrated south, and one west. near coastal villages and areas of industrial Cre`che formation was not extensive; we development such as Kuparuk and Prudhoe rarely observed cre`ches of King Eiders on the Bay (Noel et al. 2006). Other potential pred- study area and only observed two marked ators of ducklings at Kuparuk included Para- hens with broods in cre`ches. The hens that sitic Jaeger, Common Raven (Corvus corax), joined cre`ches were the only females in our and arctic fox (Alopex lagopus). The popula- study to successfully raise young to 30 days tion of predators in Alaskan oil fields has in- of age. One marked hen hatched five duck- creased since development, most likely due to lings, but was later observed with three King greater access to food from anthropogenic and three Spectacled (S. fischeri) Eider chicks. sources such as landfills and garbage dump- We first observed her in a cre`che when her sters, and shelter for nesting and denning sites chicks were 9 days of age. We later observed (National Research Council 2003). this hen in a cre`che of up to 40 hens and 12 We did not observe extensive cre`che for- young. We believe some of these ducklings mation at Kuparuk similar to Mehl and Ali- were still associated with the marked hen sauskas (2007) at Karrak Lake; however, the based on their behavior. We observed the sec- only hens in our study that successfully raised ond successful hen in a small cre`che with one ducklings joined other females with broods. other hen when her chicks were 18 days of Cre`che formation may increase duckling sur- age; each had a brood of two ducklings. The vival by females jointly caring for young and two broods were discernable by their different by larger brood sizes diluting the risk of pre- ages with the marked hen having smaller, dation (Eadie et al. 1988). younger ducklings. King Eider brood survival did not improve SHORT COMMUNICATIONS 433 with greater distance travelled over land in the or firm names in this publication is for descriptive pur- Kuparak area in contrast to the findings of poses only and does not imply endorsement by the Mehl and Alisauskas (2007) at Karrak Lake. U.S. Government. We hypothesize the contrasting results of LITERATURE CITED these two studies may be partially explained ANDERSON, B. A., C. B. JOHNSON,B.A.COOPER,L.N. by habitat composition of the study areas. The SMITH, AND A. A. STICKNEY. 1999. Habitat asso- Karrak Lake site is a large lake with many ciations of nesting Spectacled Eiders on the Arctic islands, while Kuparuk is characterized by Coastal Plain of Alaska. Pages 27–32 in Behavior small ponds and wetland complexes. Mehl and ecology of sea ducks (R. I. Goudie, M. R. and Alisauskas (2007) hypothesized that Peterson, and G. J. Robertson, Editors). Occasion- movement of broods to smaller ponds from al Paper Number 100. Canadian Wildlife Service, the main nesting areas at Karrak Lake im- Ottawa, Ontario, Canada. BACON,B.R.AND J. O. EVRARD. 1990. Horizontal mist proved survival by providing better foraging, nets for capturing upland nesting ducks. North lower gull densities, and more shelter from American Bird Bander 15:18–19. winds. Movements from nesting locations at BERGMAN, R. D., R. L. HOWARD,K.F.ABRAHAM, AND Kuparuk would not yield the same benefits be- M. W. WELLER. 1977. Water birds and their wet- cause nesting already occurs on small ponds. land resources in relation to oil development at We had little evidence to suggest broods not Storkersen Point, Alaska. Resource Publication 129. USDI, Fish and Wildlife Service, Washing- re-observed with hens were adopted, because ton D.C., USA. cre`che formation was limited in the study area DICKSON, D. L., R. C. COTTER,J.E.HINES, AND M. F. and we did not observe hens with an unusu- KAY. 1997. Distribution and abundance of King ally large number of ducklings. Our analysis Eiders in the western Canadian arctic. Pages 29– of brood survival underestimated mortality by 39 in King and Common eiders of the western censoring broods from the analysis that were Canadian arctic (D. L. Dickson, Editor). Occa- sional Paper Number 94. Canadian Wildlife Ser- not re-observed after hatch, but our observa- vice, Ottawa, Ontario, Canada. tions of King Eider broods at Kuparuk suggest DZUS,E.H.AND R. G. CLARK. 1997. Overland travel, that survival of broods may be low. Our find- food abundance, and wetland use by Mallards: re- ings should be useful for developing a com- lationships with offspring survival. Wilson Bul- prehensive investigation of King Eider surviv- letin 109:504–515. al as more King Eider nesting habitat across EADIE, J . M . , F. P. K EHOE, AND T. D . N UDDS. 1988. Pre- northern Alaska is leased for resource devel- hatch and post-hatch brood amalgamation in North American Anatidae: a review of hypothe- opment. We encourage additional study of ses. Canadian Journal of Zoology 66:1709–1721. King Eider survival on the North Slope of ESRI. 1998. ArcView GIS Version 3.2. Environmental Alaska especially near areas of resource de- Research Institute Inc., Redlands, California, USA. velopment where survival of ducklings may FLINT,P.L.AND J. B. GRAND. 1997. Survival of Spec- be depressed by artificially inflated predator tacled Eider adult females and ducklings during populations. brood rearing. Journal of Wildlife Management 61: 217–221. ACKNOWLEDGMENTS FLINT, P. L., C. L. MORAN, AND J. L. SCHAMBER. 1998. Survival of Common Eider Somateria mollissima Financial support for this research was provided by adult females and ducklings during brood rearing. the Coastal Marine Institute and Minerals Management Wildfowl 49:103–109. Service. Additional support was provided by GIRARD, G. L. 1939. Notes on the life history of the ConocoPhillips, Alaska Inc., the North Slope Borough, Shoveler. Transactions of the North American U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Conference 4:364–371. Wildlife Research Unit, University of Alaska Foun- GRATTO-TREVOR, C. L., V. H. JOHNSTON, AND S. T. PEP- dation Angus Gavin grant, and the U.S. Fish and Wild- PER. 1998. Changes in shorebird and eider abun- life Service. We acknowledge the valuable suggestions dance in the Rasmussen Lowlands, N. W. T. Wil- and assistance provided by Chuck Monnett, Jeff Glea- son Bulletin 110:316–325. son, Betty Anderson, Philip Martin, Catherine Rea, HOOGE,P.N.AND B. EICHENLAUB. 1997. Animal move- Anne Lazenby, Leigh McDaniel, Justin Harth, Robert ment extension to ArcView. Version 1.1. USDI, Suydam, and Declan Troy. We thank Eric Duran, Lori Geological Survey, Alaska Science Center, Anchor- Guildehaus, Ben Soiseth, and Rebecca Bentzen for age, USA. http://www.absc.usgs.gov/glba/gistools field assistance. Carol McIntyre, Nora Rojek, and two (accessed 30 January 2005). anonymous reviewers provided helpful reviews of ear- JOHNSON, D. H. 1979. Estimating nest success: the May- lier drafts of the manuscript. Any use of trade, product, field method and an alternative. Auk 96:651–661. 434 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

JOHNSON, D. H., J. D. NICHOLS, AND M. D. SCHWARTZ. ROTELLA,J.J.AND J. T. RATTI. 1992. Mallard brood 1992. Population dynamics of breeding waterfowl. movements and wetland selection in southwestern Pages 446–475 in Ecology and management of Manitoba. Journal of Wildlife Management 56: breeding waterfowl (B. D. J. Batt, A. D. Afton, 508–515. M. G. Anderson, C. D. Ankney, D. H. Johnson, SAS INSTITUTE. 1990. SAS user’s guide: statistics. Version J. A. Kadlec, and G. L. Krapu, Editors). Univer- 8. SAS Institute Inc., Cary, North Carolina, USA. sity of Minnesota Press, Minneapolis, USA. SAYLER, J. W. 1962. A bow-net trap for ducks. Journal MAYFIELD, H. F. 1961. Nesting success calculated from of Wildlife Management 26:219–221. exposure. Wilson Bulletin 73:255–261. SEYMORE,N.AND W. J ACKSON. 1996. Habitat-related MAYFIELD, H. F. 1975. Suggestions for calculating nest variation in movements and fledging success of success. Wilson Bulletin. 87:456–466. American Black Duck broods in northeastern MEHL,K.R.AND R. T. ALISAUSKAS. 2007. King Eider Nova Scotia. Canadian Journal of Zoology 74: (Somateria spectabilis) brood ecology: correlates 1158–1164. of duckling survival. Auk 124:606–618. SUYDAM, R. S. 2000. King Eider (Somateria specta- MENDENHALL,V.M.AND H. MILNE. 1985. Factors af- bilis). The birds of North America. Number 491. fecting duckling survival of eiders Somateria mol- SUYDAM, R. S., D. L. DICKSON,J.B.FADELY, AND L. lissima in northeast Scotland. Ibis 127:148–158. T. Q UAKENBUSH. 2000. Population declines of NATIONAL RESEARCH COUNCIL. 2003. Cumulative en- King and Common eiders of the Beaufort Sea. vironmental effects of oil and gas activities on Condor 102:219–222. Alaska’s North Slope. National Academies Press, WAYLAND,M.AND D. K. MCNICOL. 1994. Movements Washington D.C., USA. and survival of Common Goldeneye broods near NOEL, L. E., S. R. JOHNSON, AND W. J. GAZEY. 2006. Sudbury, Ontario, Canada. Canadian Journal of Oilfield development and Glaucous Gull (Larus Zoology 72:1252–1259. hyperboreus) distribution and abundance in cen- WELLER, M. W. 1956. A simple field candler for wa- tral Alaskan Beaufort Sea lagoons, 1970–2001. terfowl eggs. Journal of Wildlife Management 20: Arctic 59:65–78. 111–113. PIETZ, P. J., D. A. BRANDT,G.L.KRAPU, AND D. A. YERKES, T. 2000. Influence of female age and body BUHL. 1995. Modified transmitter attachment condition on brood and duckling survival, number method for adult ducks. Journal of Field Orni- of surviving ducklings, and brood movements in thology 66:408–417. Redheads. Condor 102:926–929.

The Wilson Journal of Ornithology 121(2):434–439, 2009

Diet Composition of Wintering Wilson’s Snipe

Jon T. McCloskey,1,2 Jonathan E. Thompson,1,3 and Bart M. Ballard1,4

ABSTRACT.—We examined diet composition of consumed by snipe and during spring represented ap- Wilson’s Snipe (Gallinago delicata)(n ϭ 372) col- proximately the same proportion of the diet as earth- lected along the central Gulf Coast of Texas based worms. Plant foods consisted almost entirely of seeds solely on upper digestive tract contents. Food items and comprised 9.7–26.8% of the diet throughout the included 11 invertebrate orders, one invertebrate class, non-breeding period. Wilson’s Snipe consumed dipter- and eight plant genera. Oligochaetes were the predom- an larvae more often during spring than fall (P ϭ inant food throughout the non-breeding period, but 0.056). Female snipe consumed crustaceans during snipe consumed fewer (P ϭ 0.021) earthworms in spring (14.8%), while only trace amounts were found spring than in fall. Aquatic insects were frequently in the diet of male snipe. Differences in the diet of Wilson’s Snipe between males and females were probably related to differences in habitat use as well as 1 Caesar Kleberg Wildlife Research Institute, MSC 218, Texas A&M University–Kingsville, Kingsville, availability of invertebrates throughout the non-breed- TX 78363, USA. ing period. Received 5 March 2008. Accepted 7 Sep- 2 Current address: BioDiversity Research Institute, tember 2008. 19 Flaggy Meadow Road, Gorham, ME 04038, USA. 3 Current address: Ducks Unlimited Canada, #200, 10720-178 Street, Edmonton, AB T5S 1J3, Canada. 4 Corresponding author; e-mail: Studies of Wilson’s Snipe (Gallinago deli- [email protected] cata) suggest that animal foods are a signifi- SHORT COMMUNICATIONS 435 cant portion of their winter diet (Erickson low rice fields, mud flats (i.e., recently disked 1941, Whitehead 1965, White and Harris fallow rice fields), drained impoundments, and 1966, Owens 1967, Booth 1968, Jirovec 1971, coastal marshes. Vegetation communities and Tuck 1972). Most studies suggest aquatic in- land use practices associated with the study sects and mollusks are the primary animal area were described by McCloskey (1999). foods consumed by snipe and discount the im- We collected Wilson’s Snipe (n ϭ 372) by portance of earthworms (Oligochaeta). Owens shooting, systematically alternating between (1967) found earthworms in 50% of the birds habitat types throughout the non-breeding pe- he collected in wet cattle pastures in Louisi- riod. We typically collected four birds per day ana, but they accounted for only 21.6% of the allocated throughout the day. We examined total animal volume in the diet. Previous stud- diet composition by analyzing the contents of ies stimulated debate over the importance of the upper digestive tract (UDT) (i.e., esopha- plant foods in the diet of wintering Wilson’s gus and proventriculus). Each specimen was Snipe. Whitehead (1965), Owens (1967), and injected with 2–3 ml of 80% ethanol into their Booth (1968) found the dry mass of plant ma- UDT immediately after collection to prevent terials comprised ϳ41, 50, and 62% of the post-mortem digestion of food items. The diet of wintering snipe, respectively. In con- UDT contents were subsequently placed into trast, White and Harris (1966) and Jirovec individually labeled nalgene bottles contain- (1971) reported that plant foods accounted for ing 80% ethanol (Swanson and Bartonek Յ20% of the dry mass in the diet. 1970). Food items were sorted, classified, and Inconsistencies between these studies and dried to constant mass at 80Њ C to quantify the conclusion that earthworms are relatively percent occurrence and aggregate percent dry unimportant in the diet of wintering snipe mass of foods consumed during each season. probably occurred because they included giz- We separated the non-breeding period into zard contents in diet composition analysis. three seasons based on molt intensity of col- This approach biases diet composition toward lected individuals. A fall molting period was hard food items (i.e., plant foods or hard an- delineated as 6 October–13 November 1997, imal parts) because the grinding action of the a non-molting winter period was delineated as gizzard quickly renders soft foods (e.g., earth- 14 November 1997–4 February 1998, and a worms) unrecognizable (Rundle 1982). This spring molting period was 5 February–10 bias can be avoided by examining only the April 1998. contents of the esophagus and proventriculus We used Kruskal-Wallis one-way ANOVA (Swanson and Bartonek 1970, Reinecke and (PROC NPAR1WAY; SAS Institute Inc. Owen 1980, Rundle 1982). 1999) to investigate seasonal variation in diet Snipe have long bills with a prehensile tip of males and females. We used Dunn’s Mul- used to probe moist soils in search of inver- tiple Comparisons Test (SAS Institute Inc. tebrates (Arnold 1994). Winter habitats used 1999) to examine any seasonal differences. by Wilson’s Snipe typically have wet ground We used Mann-Whitney U-tests to compare (i.e., wet pastures, plowed and fallow rice diets between males and females within each fields, and coastal marshes) (Arnold 1994), season. and soil moisture is a primary variable regu- lating earthworm abundance and distribution RESULTS (Curry 1998). Our objective was to quantify Sixteen of 39 females and 16 of 30 males the diet of wintering Wilson’s Snipe based contained food in their upper digestive tract solely on examination of upper digestive tract during fall. Only 19 of 95 females and 11 of contents. 64 males contained food in their UDT in winter. The proportion of birds with ingesta in- METHODS creased in spring with 26 of 86 females and We conducted this study in the rice prairies 17 of 58 males containing food in their UDT. and coastal marshes along the central Gulf Proportions of male and female snipe contain- Coast of Texas from October 1997 through ing food were highest throughout spring mi- April 1998. Collection sites included five dif- gration (16 Mar–10 Apr), with 21 of 41 fe- ferent habitat types: harvested rice fields, fal- males and 11 of 17 males containing food in 436 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 their UDT. Diets of Wilson’s Snipe included (i.e., Gastropoda and Pelecypoda), one south- foods from 11 invertebrate families, one in- ern cricket frog (Acris gryllus gryllus), and vertebrate class, one vertebrate species, and unidentified invertebrate parts (Table 1). Only eight plant genera (Table 1). Snipe fed pri- females consumed Hydracarina with the ma- marily on animal foods, which represented jority being consumed during fall and winter. Ͼ73% of the dry mass of the diet throughout Females consumed mollusks during all sea- the non-breeding period (Table 1). Ninety-one sons, while males consumed gastropods and percent of all snipe that contained food in pelecypods mostly during spring (Table 1). their UDT consumed animal foods. Plant foods represented Յ26.8% of the diet Oligochaetes (earthworms) were the primary and were detected in Յ62.5% of male and fe- food item of Wilson’s Snipe, representing from male Wilson’s Snipe throughout the non-breed- 33.1 to 67.3% of the dry mass of the diet over ing period (Table 1). Seeds, particularly those of the entire non-breeding period (Table 1). There Cyperus spp., Eleocharis spp., and Polygonum were seasonal differences in Oligochaete con- spp. were the most frequently consumed plant sumption (H ϭ 6.08, df ϭ 2, P ϭ 0.048). The foods (Table 1). Polygonum spp. was consumed diet of male and female snipe contained similar almost exclusively by females and mostly dur- proportions of Oligochaetes during fall and ing fall and winter (H ϭ 7.534, df ϭ 2, P ϭ spring but, during winter, earthworms comprised 0.023). Male snipe consumed only trace 63.4% of the total food mass of males, com- amounts of Polygonum and only during fall (Ta- pared to only 38.3% for females (Table 1). Ol- ble 1). Plant parts (i.e., stems and leaves) were igochaetes comprised a greater proportion of the not considered food items because they usually diet of both males and females during fall than comprised only a trace of the total plant dry during spring (P ϭ 0.021). mass (Table 1), and were typically found in as- Aquatic insects represented 12.4–35% of sociation with other food items suggesting they the diet of male and female Wilson’s Snipe. were picked up incidentally. Coleoptera (i.e., Hydrophilidae larvae and unidentified adult parts), Diptera larvae (i.e., DISCUSSION Ceratopogonidae, Chironomidae, Culicidae, The proportion of Wilson’s Snipe contain- and Tipulidae), and Hemiptera were the most ing ingesta in their UDT was greatest during frequently eaten aquatic insects by male and fall and spring. These periods coincide with female snipe (Table 1). There were seasonal molting, and protein demand may be greater differences in the amount of aquatic insects for snipe during these periods (Ankney 1979, consumed (H ϭ 10.96, df ϭ 2, P ϭ 0.004), Murphy and King 1982). Spring migration oc- with both males and females increasing their curred between 16 March and 10 April (Mc- consumption during spring. The combined dry Closkey 1999), and aggregate percent dry mass of Coleoptera, Diptera, and Ephemer- mass of animal foods was greatest during this optera in spring represented 33% of the diet time suggesting snipe were storing lipid re- for females and 35% for males, which ap- serves for migration. Much of the southern proximated the dry mass of Oligochaetes in portion of the snipe’s winter range in the Unit- the diet during this period (Table 1). Male and ed States is characterized by wet, but relative- female snipe consumed dipteran larvae most ly warm weather, which results in continuous often during spring (P ϭ 0.056). periods of invertebrate reproduction and Crustaceans were ingested almost exclu- growth (Merritt and Cummins 1996). If food sively by female snipe with males consuming is readily available and energy requirements only trace amounts (i.e., Ͻ1%) of isopods dur- for thermoregulation are relatively low in win- ing winter and spring (Table 1). Females con- ter, snipe may alter their foraging strategy to sumed amphipods and isopods only during specific times of the day or night. This may winter and spring (Table 1). We found no partially explain the lower proportion of our crustaceans in the UDT of any individuals sample that contained ingesta in their UDT during fall, and females ate decopods only during winter. during spring (Table 1). Female snipe consumed a wider variety of The remaining animal foods consisted of invertebrates than males during winter with Arachnoidea (i.e., Hydracarina), mollusks crustaceans, mollusks, and arachnids compris- SHORT COMMUNICATIONS 437 he Male F (16) W (11) S (17) Percent occurrence Female F (16) W (19) S (26) Male F(16) W (11) S (17) Aggregate % dry mass spring period. ϭ Female W (19) S (26) winter period, S ϭ b (16) 3.80.21.2 13.95.6 0.20 5.70 4.7 5.11 1.9 1.7 0.2 0 1.6 0 7.4 0 2.9 0.5 3.8 0 4.4 0.7 0.04 6.1 0 10 0 0 2.8 0 0.05 0 0 0 37.5 12.5 4.3 12.5 0.3 31.6 0.02 10.5 0 25 10.5 11.5 7.7 0 7.7 0 5.3 37.5 6.25 31.25 5.3 3.8 12.5 0 27.3 0 9.1 0 23.5 9.1 3.8 12.5 11.8 0 5.9 0 0 0 0 0 0 0 0 5.9 5.9 0 a F fall period, W ϭ Food item Sample size. Seasonal categories: F TABLE 1. Aggregate percent dry-mass and percent occurrence of foods consumed by male and female Wilson’s Snipe during fall, winter, and spring along t OligochaetaColeopteraDipteraHemiptera 55.7OdonataEphemeroptera 38.3 12.9Gastropoda 33.1Pelecypoda 0 0 0 2.8 0Isopoda 13.1Decapoda 5.3 6.9 67.3 0Amphipoda 6.3 0.1 0 18.4 0 63.4Hydracarina 0.6 13 1.1 5.3 0 0Invertebrate 0 39 0 6.4Vertebrate 3.3 0 1 6.2 1.3 0 3.2 0 6.4Cyperus 0 62.5 0.2 21.1 2.1 0 0.2Juncus 9.1 2.9 0.02 3.8Eleocharis 0 0 8.1Polygonum 42.1 2.3 0.01 12.3Achillia 2.1 0 0 0Sisymbrium 37.5 0 38.5Echinochloa 1.6 0.1 0 0 0 0 15.8 0 5.9 5.9 0 0 75 0 0.4 26.9 0 0 0 0 0 10.5 63.6 0 6.25 0.4 6.25 5.3 25 30.8 0 3.2 0 0 7.8 47.1 0 5.3 5.3 0 0 0 9.1 0 0 3.8 11.5 0 3.8 0 23.5 0 0 6.25 12.5 0 5.3 0 9.1 0 6.25 10.5 6.25 5.3 0 19.2 9.1 17.6 0 0 15.8 3.8 0 3.8 0 0 0 11.5 3.8 0 9.1 5.9 5.9 5.9 0 0 0 0 0 9.1 0 0 0 0 5.9 0 9.1 0 0 0 6.25 0 0 0 a b central Gulf Coast of Texas. Insecta Mollusca Crustacea Arachnoidea Unidentified Total animalSeeds 81.4 73.2Unidentified seeds 90.3Plant partsTotal plant 6.5 84.8 0 0.3 84 18.6 0 0.2 26.8 86.2 0.8 9.7 93.8 0.3 15.2 0.1 89.5 0 96.2 16 1.2 0 13.8 0.6 87.5 90.9 18.75 56.25 25 88.2 0 47.4 10.5 42.3 0 19.2 62.5 18.75 12.5 54.5 27.3 0 41.2 17.6 0 Annelida 438 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 ing 9.6, 5.9, and 2.1% of their diet, respec- during cold spells, and migration in spring. tively. These food items were essentially ab- Snipe use a variety of habitats on wintering sent from the diet of males during winter. areas that are both permanent and ephemeral These apparent differences in invertebrate use in nature (Arnold 1994), which can affect the between male and female Wilson’s Snipe dur- distribution and abundance of invertebrates ing winter may be related to differential par- throughout the non-breeding period. Thus, titioning of winter habitats (McCloskey and snipe need a diversity of habitat types in win- Thompson 2000). tering areas. These habitats should contain Fall rains flood marshes and probably ben- moist soils and provide a diversity of plant efit earthworms initially, which may explain and animal foods. The ability to identify and why earthworms were more common in the maintain potential snipe habitat will become diet of snipe during fall. However, continued increasingly important with continuing wet- flooding and subsequent drying of soils can land loss along the Gulf Coast of Texas increase salinity levels, which can limit earth- (Moulton et al. 1997). worm populations (Curry 1998). While earthworms were the predominant food of snipe ACKNOWLEDGMENTS during fall and winter, aquatic insects became The 1997 Webless Migratory Game Bird Research equally important in their diet during spring. Program (USDI, Fish and Wildlife Service and Geo- Emergence of aquatic insects is synchronized logical Survey—Biological Resources Division) and primarily by water availability, temperature, the Caesar Kleberg Wildlife Research Institute provid- and oxygen levels (Merritt and Cummins ed funding for this project. We thank Jeff Stephens for help in collecting and processing birds. We also thank 1996), and may explain their increased inges- Keith Treybig for access to El Rancho de los Patos tion during spring. Increased availability of and Rick Spears, Rick Antonette, and Ron Bisbee for aquatic insects may allow snipe to obtain nu- access to Brazoria National Wildlife Refuge. We also trient stores required for spring migration thank Todd Merendino, Justin Hurst, Ernest Love, and without expending as much energy. Brent Ortego for access to Texas Wildlife Management Previous studies on the diet of wintering Wil- Areas. We thank personnel at Attwater’s Prairie Chick- en National Wildlife Refuge for providing housing and son’s Snipe reported high frequency of occur- hospitality. This is publication Number 99-116 from rence of seeds, but most discounted their im- the Caesar Kleberg Wildlife Research Institute. portance suggesting seeds were ingested incidentally while probing for invertebrates (Erick- LITERATURE CITED son 1941, Whitehead 1965, White and Harris ANKNEY, C. D. 1979. Does the wing molt cause nutri- 1966, Owens 1967, Booth 1968, Jirovec 1971, tional stress in Lesser Snow Geese? Auk 96:68– Tuck 1972). Fritzell et al. (1979) also discounted 72. the importance of seeds, suggesting they were ARNOLD, K. A. 1994. Common Snipe. Pages 116–125 ingested incidentally, remained relatively un- in Migratory shore and upland game bird man- changed during digestion, or would eventually agement in North America (T. C. Tacha and C. E. Braun, Editors). International Association of Fish be regurgitated. However, we found UDT con- and Wildlife Agencies, Washington, D.C., USA. tents of nine snipe to be comprised solely of BOOTH JR., T. W. 1968. The availability and utilization seeds. Booth (1968) found over 45,000 seeds of of the foods of the Common Snipe (Capella gal- 48 plant species in gizzards of 260 wintering linago delicata) in the rice growing region of snipe collected in Louisiana. Although animal southwestern Louisiana. Thesis. Louisiana State foods clearly dominate the diet of wintering University, Baton Rouge, USA. CURRY, J. P. 1998. Factors affecting earthworm abun- snipe, seeds may be an important source of car- dance in soils. Pages 37–64 in Earthworm ecology bohydrates and may be more than just inciden- (C. A. Edwards, Editor). St. Lucie Press, Boca tally consumed. Raton, Florida, USA. Wintering Wilson’s Snipe consume a vari- ERICKSON, A. V. 1941. A study of the Wilson’s Snipe. ety of plant and animal foods during the non- Wilson Bulletin 53:62. breeding period. Snipe spend ϳ8 months of FRITZELL,E.K.,G.A.SWANSON, AND M. I. MEYER. the year in wintering areas and the diversity 1979. Fall foods of migrant Common Snipe in North Dakota. Journal of Wildlife Management of food types in these areas provide them with 43:253–257. energy required for basal metabolic require- JIROVEC, D. J. 1971. Food habits and migratory movements, daily activity, molt, thermoregulation ments of the Common Snipe (Capella gallinago SHORT COMMUNICATIONS 439

delicata) in the central Brazos Valley of Texas. REINECKE,K.J.AND R. B. OWEN JR. 1980. Food use Thesis. Texas A&M University, College Station, and nutrition of Black Ducks nesting in Maine. USA. Journal of Wildlife Management 44:549–558. MCCLOSKEY, J. T. 1999. Sex and age determination and RUNDLE, W. D. 1982. A case for esophageal analysis nutritional ecology of wintering Common Snipe. in shorebird food studies. Journal of Field Orni- Thesis. Texas A&M University–Kingsville, thology 53:249–257. Kingsville, USA. SAS INSTITUTE INC. 1999. SAS/STAT user’s guide. MCCLOSKEY,J.T.AND J. E. THOMPSON. 2000. Sex- Version 8. SAS Institute Inc., Cary, North Caro- related differences in migration chronology and lina, USA. winter habitat use of Common Snipe. Wilson Bul- SWANSON,G.A.AND J. C. BARTONEK. 1970. Bias as- letin 112:143–148. sociated with food analysis in gizzards of Blue- MERRITT,R.W.AND K. W. CUMMINS. 1996. An intro- winged Teal. Journal of Wildlife Management 34: duction to the aquatic insects of North America. 739–746. Kendall/Hunt Publishing Co., Dubuque, Iowa, TUCK, L. M. 1972. The snipes: a study of the genus USA. Capella. Monograph Series 5. Canadian Wildlife MOULTON, D. W., T. E. DAHL, AND D. M. DALL. 1997. Service, Ottawa, Ontario, Canada. Texas coastal wetlands; status and trends, mid- WHITE,M.AND S. HARRIS. 1966. Winter occurrence, 1950s to early 1990s. USDI, Fish and Wildlife foods, and habitat use of snipe in northwest Cal- Service, Albuquerque, New Mexico, USA. ifornia. Journal of Wildlife Management 30:23– MURPHY,M.E.AND J. R. KING. 1982. Amino acid 34. composition of the plumage of the White-crowned WHITEHEAD, C. J. 1965. Foods and feeding habits of Sparrow. Condor 84:435–438. the Common Snipe (Capella gallinago delicata) OWENS, J. 1967. Food habits of the Common Snipe in Cameron Parish, Louisiana, with ecological (Capella gallinago delicata) in the pastures of notes and a discussion of methods of sexing and south central Louisiana. Thesis. Northeast Loui- aging. Thesis. Louisiana State University, Baton siana State College, Monroe, USA. Rouge, USA.

The Wilson Journal of Ornithology 121(2):439–441, 2009

An Overlooked Cost for the Velvety Plumage of Owls: Entanglement in Adhesive Vegetation

Airam Rodrı´guez,1,5 Felipe Siverio,2 Rube´n Barone,3 Beneharo Rodrı´guez,4 and Juan J. Negro1

ABSTRACT.—We used data collected during 1995– died. A higher incidence of entanglement occurred 2007 at the only Wildlife Rehabilitation Center on during summer, coinciding with seed-head ripening Tenerife Island (Canary Islands) to quantify entangle- and dispersing recently-fledged owls. Velvety plumage ment mortality of owls. At least 66 of 1,206 Long- may be an important cost for owls, and responsible for eared (Asio otus) and 5 of 231 Barn (Tyto alba)owls owls acting as seed dispersers. Received 28 June 2008. admitted to the Wildlife Rehabilitation Center were en- Accepted 14 December 2008. tangled in burr bristlegrass (Setaria adhaerens). Twelve (18.2%) of the 66 Long-eared Owls died as a result of entanglement while one of five Barn Owls Owls have evolved adaptations to hunt in 1 Estacioń Biolo´gica de Donãna (CSIC), Avenido poor light conditions, including frontally lo- Ame´rico Vespucio s/n, 41092 Sevilla, Spain. cated and disproportionately large eyes or, in 2 Los Barros 21, 38410 Los Realejos, Tenerife, Ca- some species, an asymmetrical placement of nary Islands, Spain. the ear openings for improved hearing (del 3 Њ C/ Eduardo Zamacois 13-3 A, 38005 Santa Cruz Hoyo et al. 1999). Owls also have feathers de, Tenerife, Canary Islands, Spain. with traits which have been considered as ad- 4 C/ La Malecita s/n, 38480 Buenavista del Norte, Tenerife, Canary Islands, Spain. aptations for silent flight. The main structural 5 Corresponding author; e-mail: feather adaptations of owls are: (1) elongated [email protected] barbs on the leading edge at the outer prima- 440 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 ries, (2) a trailing edge on the flight feathers, owls do not appear capable of freeing them- and (3) modified distal barbules on the dorsal selves from the plant. The highest incidence surface of feathers (del Hoyo et al. 1999). The of entanglements occurred during summer last trait makes velvety plumage easily per- with the largest number of reports in July and ceived by the unaided human eye (Mikkola August. 1983). This plumage is also exhibited by other nocturnal or crepuscular birds, including DISCUSSION nightjars (Order Caprimulgiformes), Bat Hawk (Macheiramphus alcinus) (J. J. Negro, The interaction between owls and a plant pers. obs.), and Elanus kites (Negro et al. adapted to exozoocore dispersal can be a con- 2006). Silent flight permits owls to go unde- siderable cause of mortality in the Canary Is- tected by their prey, and improves their ability lands. This factor has been overlooked, de- to detect noises (Taylor 1994, del Hoyo et al. spite several published records, and has not 1999). been quantified in the literature. Entanglement Development of velvety plumage may have of owls in vegetation appears to be the result associated costs, including increased risk of of anthropogenic perturbations in the Canary entanglement in dense vegetation during hunt- Islands, even though S. adhaerens is possibly ing (Glayre 1959, Mendelsohn 1983, Nozer- a native plant (Izquierdo et al. 2004). Burr and 1994, Molnar 1996). We describe mortal- bristlegrass is mainly associated with human- ity, caused by a grass species, of the resident affected landscapes and is almost absent in owl community in the Canary Islands. Only natural areas. The highest densities of S. ad- two species of owls regularly breed in the Ca- haerens are in human-transformed areas, nary Islands: Long-eared Owl (Asio otus) and which is where owls tend to become entan- Barn Owl (Tyto alba). gled. The temporal pattern with maximum Burr bristlegrass (Setaria adhaerens, Fam- values during the summer, may be related to ily Poaceae) is an annual species, possibly na- ripening of seed-heads, as well as to dispersal tive in the Canary Islands (Izquierdo et al. of fledgling owls (age of affected owls is not 2004). It grows in orchards, abandoned farm- available). lands, road ditches, and field margins. It flow- Entanglement of birds with velvety plum- ers and dries during spring and early summer, ages has been reported involving Long-eared and retains ripe seed-heads in the dry plant Owls, Barn Owls, and Black-winged Kites (R. Mesa, pers. comm.). Ripe seed-heads are (Elanus caeruleus) (Glayre 1959, Mendelsohn adhesive and adapted to exozoocore dispersal. 1983, Nozerand 1994, Molnar 1996). Entan- OBSERVATIONS glement as a cause of mortality is not exclu- sive to birds with velvety plumages. At least Owls admitted during 1995–2007 were two instances involving Common Kestrels identified by the staff of the Wildlife Reha- bilitation Center ‘‘La Tahonilla’’ (WRC), (Falco tinnunculus) entangled in S. adhaerens which annotated recovery circumstances. The in the Canary Islands are known (WRC, un- center is in Tenerife, the largest island (2,034 publ. data; J. Curbelo, pers. comm.). The km2 and 3,718 m of altitude) of the Canarian Common Kestrel is the most abundant raptor Ͼ archipelago (27Њ 37Ј–29Њ 24Ј N, 13Њ 20Ј–18Њ in the Canary Islands, and 1,200 have been 8Ј W), and our data correspond to owls found admitted to the WRC in the study period. only on this island. Whether Common Kestrels become entangled At least 66 (5.5%) of 1,206 Long-eared and less often than owls due to different plumage 5 (2.2%) of 231 Barn owls admitted were en- characteristics or due to different micro-habi- tangled in S. adhaerens plants. Entanglement tat use remains unknown. in burr bristlegrass likely occurred when owls It is possible that some owls escape un- were hunting. Twelve of 66 Long-eared Owls scathed from contact with S. adhaerens, but (18.2%) and one of five Barn Owls died as a seeds of this species may become affixed to result of becoming entangled in the plants. their plumage and transported elsewhere. This Most entangled birds that were recovered interaction implies a new ecological role for alive would have died if not found because owls as exozoocore seed dispersers. SHORT COMMUNICATIONS 441

ACKNOWLEDGMENTS Canarias (Hongos, Plantas y Animales Terrestres). Consejerıá de Medio Ambiente y Ordenacioń Ter- We are grateful to those who helped rescuing owls ritorial, Gobierno de Canarias, Santa Cruz de Ten- and the staff of Wildlife Rehabilitation Center ‘‘La Ta- erife, Spain. honilla’’ (Cabildo Insular de Tenerife). Ricardo Mesa, MENDELSOHN, J. M. 1983. Causes of mortality in Juani Curbelo, and Rubeń Garcıá provided valuable Black-shouldered Kites. Bokmakierie 35:11–13. information about the genus Setaria and entanglement MIKKOLA, H. 1983. Owls of Europe. T. & A.D. Poyser, observations. G. R. Bortolotti, J. S. Marks, an anony- London, United Kingdom. mous reviewer, and C. E. Braun provided useful com- MOLNAR, G. 1996. Ragados muhar (Setaria verticilla- ments on an early draft of the manuscript. ta) mint bagolycsapda. Tuzok 1:185. NEGRO, J. J., C. PERTOLDI,E.RANDI,J.J.FERRERO,J. LITERATURE CITED M. LO´ PEZ-CABALLERO,D.RIVERA, AND E. KORPI- ¨ DEL HOYO, J., A. ELLIOTT, AND J. SARGATAL (Editors). MAKI. 2006. Convergent evolution of Elanus kite 1999. Handbook of the birds of the world. Volume and the owls. Journal of Raptor Research 40:222– 5. Barn-owls to hummingbirds. Lynx Editions, 225. Barcelona, Spain. NOZERAND, R. 1994. Hiboux Moyens-Ducs Asio otus GLAYRE, D. 1959. Une Choutte effraie captureé pas des emprisonne´s dans des gramineés. Alauda 62:116. gramineés. Nos Oiseaux 266:122. TAYLOR, I. 1994. Barn Owls. Predator-prey relation- IZQUIERDO, I., J. L. MARTIŃ,N.ZURITA, AND M. ARE- ships and conservation. Cambridge University CHAVALETA. 2004. Lista de Especies Silvestres de Press, Cambridge, United Kingdom.

The Wilson Journal of Ornithology 121(2):441–444, 2009

Aggressive Response of Adult Bobolinks to Neck Ligatures on Nestlings

Lynn P. Little,1,2 Allan M. Strong,3,5 and Noah G. Perlut4

ABSTRACT.—We monitored provisioning behavior Quantitative assessments of avian diets may at 18 Bobolink (Dolichonyx oryzivorus) nests during be critical for evaluating habitat quality. How- 240.5 min of videotape data from June to July 2006, ever, methods used to quantify avian diets and observed 64 nest visits by adults while nestlings were fitted with neck ligatures. Adults pecked or have associated biases and/or shortcomings as pulled at the ligatures, often aggressively, at 72% of most studies require techniques tailored to nests (n ϭ 18) and 52% of visits (n ϭ 64). These specific studies and hypotheses (Rosenberg behavioral responses by adults indicate the neck liga- and Cooper 1990). Neck ligatures have been ture technique is more invasive than previously be- used to quantify diets of nestling birds as this lieved. We documented no mortality as a result of lig- technique allows collection of prey items prior ature placement, but researchers should minimize the time that ligatures are in place to reduce stress to both to onset of digestion. Modifications have been parents and nestlings. Received 8 September 2008. Ac- suggested to improve ligature function and cepted 30 January 2009. minimize negative effects on nestlings. For example, Johnson et al. (1980) described ab- normal behavior of nestlings after leaving ligatures in place for 1 hr and suggested that col- 1 Department of Animal Science, University of Ver- mont, Burlington, VT 05405, USA. lection of prey immediately after each parental 2 Current address: 5060 Bentley Lane, Columbus, visit would minimize biases. Further, Mellott OH 43220, USA. and Woods (1993) found that cable ties sim- 3 Rubenstein School of Environment and Natural plified ligature placement compared to coated Resources, 81 Carrigan Drive, University of Vermont, wire, especially when used by untrained per- Burlington, VT 05405, USA. sonnel. 4 Vermont Cooperative Fish and Wildlife Research Neck ligatures are considered an invasive Unit, The Rubenstein School of Environment and Nat- ural Resources, University of Vermont, Burlington, VT technique (Rosenberg and Cooper 1990, Poul- 05405, USA. sen and Aebischer 1995), but most studies ad- 5 Corresponding author; e-mail: [email protected] dressing their effects have focused on the be- 442 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009 havioral responses of nestlings. We used video items among nestlings by adults (Johnson et cameras and neck ligatures simultaneously in al. 1980). a study of nestling Bobolink (Dolichonyx oryzivorus) diets. We report on the response of RESULTS adult Bobolinks to placement of neck ligatures We monitored 18 Bobolink nests during on nestlings. 240.5 min of videotape data. We applied neck ligatures to 50 nestlings, and successfully col- METHODS lected 99 prey items from 28 of those nest- Study Site.—Our study was conducted dur- lings. No nestling mortality occurred while ing June–July 2006 in three hayfields in nests were videotaped. Leaf hoppers (27.3% Hinesburg, Shelburne, and Charlotte, Chitten- based on numerical abundance), holometabo- den County, Vermont, USA. Bobolinks breed lous larvae (24.2%), grasshoppers (16.2%), in hayfields and pastures throughout this ag- mayflies (8.1%), spiders (7.1%), and moths ricultural region (Shustack 2004, Perlut et al. (5.1%) were the most common prey types fed 2006) and their ground nests are relatively to nestlings. Mean Ϯ SD prey length was 14.5 easy to locate. Ϯ 10.2 mm with 17% of prey items delivered Video and Ligature Data Collection.—Nest Ͼ25 mm. Sixteen of the 18 nests were suc- observations, video monitoring, and ligature cessful with 56 nestlings fledged. sampling occurred between 0400 and 1300 hrs We observed 64 nest visits by adults while EST during precipitation-free periods. A nestlings were fitted with ligatures. Seventy- small, wide-angle ‘‘lipstick’’ lens (www. two percent of visits were by females and helmetcamera.com) was mounted 10 cm from 28% by males. On average, females and males the nest when nestlings reached 6 days of age. visited nests 2.6 and 1.0 times, respectively The lens was attached by cable to an 8-mm while ligatures were in place (ϳ45 min). camcorder (Sony DCR-TRV460 Digital8 Adults pecked at ligatures of nestlings in 13 Handycam) placed 2 m from the nest and con- of 18 nests (72%) and in 33 of 64 (52%) vis- cealed by vegetation. Recording sessions its. They directed pecks at more than one nest- commenced with an initial 45-min acclimation ling in 70% of the visits during which adults period during which nestlings were left undis- pecked at the ligatures. Females had a greater turbed. Recording was paused while neck lig- propensity to peck at ligatures with 59% of all atures were placed on nestlings following female visits eliciting pecks to ligatures com- Johnson et al. (1980) and subsequent modifi- pared to 33% of all male visits. The first adult cations (Mellott and Woods 1993). We placed to return to the nest pecked at the ligatures in ligatures on a maximum of three nestlings per 12 of 13 nests in which adults pecked at lig- nest using plastic cable ties (10 cm length be- atures. There was no indication that probabil- fore cutting off excess, 2.5 mm width), tem- ity of pecking changed across the time period porarily removing any additional nestlings for ligatures were in place (logisitic regression, ␹2 the remainder of the videotaping period (gen- ϭ 1.68, df ϭ 1, P ϭ 0.20). erally 45 min). Removal of some of the nest- Adults generally pecked at the thin band of lings reduced the number of nestlings that the cable tie. In these cases, the adults ap- were not fed by parents during a feeding ses- peared to be assessing whether or not the lig- sion (adults were not observed feeding all ature could be easily removed from the nestlings in a single feeding trip when a nest chicks. Adults also grasped and pulled at the contained five or six nestlings; N. G. Perlut, bulkier locking mechanism of the cable tie unpubl. data) and reduced the number of nest- with the appearance that removal was the lings that would be exposed to any potential goal. Parents were notably aggressive in about stress during the ligature process. We attempt- half of the nests in their attempts to remove ed to remove ligatures and collect diet sam- the ligatures, grasping the ligature and forc- ples from the nestlings as soon as we ob- ibly pulling the nestlings’ heads upwards or served the adults return to the nest with food. sideways. In one instance, a female inspected, Prolonged use of ligatures can induce abnor- grasped, and pulled at a nestling’s ligature for mal swallowing and gaping behavior in nest- 30 sec. No aggressive actions toward nestlings lings, which leads to the redistribution of prey were noted when ligatures were not present SHORT COMMUNICATIONS 443 on nestlings based on video data prior to lig- relatively safe, inexpensive, and informative ature placement and a few tapes which we left method, but do present welfare concerns. In- running after the ligature sessions. One female vestigation into the efficacy of less-invasive visually inspected her nestling’s throats upon alternatives such as videography should be her first visit to the nest ϳ20 min after re- conducted, especially when working with rare moval of the ligatures. and declining species. We documented no mortality as a result of ligature placement, but DISCUSSION researchers should minimize the time that lig- Use of neck ligatures has been shown to atures are in place to reduce stress to both provide quality dietary data for nestling birds parents and nestlings. (Orians 1966, Martin et al. 2000, Clotfelter et al. 2007). Our data support these results as we ACKNOWLEDGMENTS were able to collect a relatively large sample This research was conducted under University of of prey items over a short period of time. Prey Vermont Institutional Animal Care and Use Committee length data suggest that adults did not adjust protocol 05-039. The project was supported by the Na- tional Research Initiative of the USDA Cooperative the size of prey items brought to nestlings State Research, Education and Extension Service with ligatures. However, we do not have ad- (grant number 03-35101-13817) and the Natural Re- equate control data (nestlings without liga- source Conservation Service’s Wildlife Habitat Man- tures) for a quantitative comparison. agement Institute. Supplies and summer support to Our data show that undesirable behavioral LPL were provided by the University of Vermont’s responses to ligatures are not restricted to Hughes Endeavor for Life Science Excellence nestlings. The strong and consistent response (HELiX) program. Additional funding was provided by University of Vermont’s College of Agriculture and of adults to ligatures suggests this technique Life Science. We thank Shelburne Farms and Sam elicits stress that was not previously docu- Dixon, and the Ross and Thibault families for allowing mented. Attempts by female Red-winged us to conduct research on their property. Field assis- Blackbirds (Agelaius phoeniceus) to remove tance was provided by Thomas Lawrence, Stacey pipe cleaner ligatures have been documented, Thompson, Roger Masse, Christopher Lang, and Za- but no behavioral data were provided (Rob- chary Rowe. T. B. McFadden, R. C. Hovey, F.-Q. Zhao, and the Strong Graduate Laboratory provided ertson 1966). Our results indicate that Bobo- support and comments on earlier versions of the man- links are strongly attuned to the appearance of uscript. their nestlings and, in most cases, neck ligatures trigger a response upon the first visit to LITERATURE CITED the nest. Females in our sample were more CLOTFELTER, E. D., C. R. CHANDLER,V.NOLAN JR., likely to attempt to remove ligatures than AND E. D. KETTERSON. 2007. The influence of ex- males (but also made more nest visits). Ap- ogenous testosterone on the dynamics of nestling proximately half of the attempts to remove the provisioning in Dark-eyed Juncos. Ethology 113: ligatures were aggressive with parents lifting 18–25. GAUNT,A.S.AND L. W. ORING. 1999. Guidelines to and/or dragging nestlings by the ligature. the use of wild birds in research. Second Edition. These responses indicate the neck ligature The Ornithological Council, Washington, D.C., technique is more invasive than previously be- USA. lieved. Comparable data from other species JOHNSON, E. J., L. B. BEST, AND P. A . H EAGY. 1980. would be useful to better address the gener- Food sampling biases associated with the ‘‘liga- ality of our findings. ture method’’. Condor 82:186–192. MARTIN, P. A., D. L. JOHNSON,D.J.FORSYTH, AND B. Gaunt and Oring (1999) noted the potential D. HILL. 2000. Effects of two grasshopper control for changes in blood circulation, tracheal insecticides on food resources and reproductive function, and food delivery rates with use of success of two grassland songbirds. Environmen- neck ligatures. Our data suggest there may be tal Toxicology and Chemistry 19:2987–2996. additional stress to nestlings beyond physical MELLOTT,R.S.AND P. E. WOODS. 1993. An improved placement of the ligatures. The majority of ligature technique for dietary sampling in nestling nest visits by adults included pecking or pull- birds. Journal of Field Ornithology 64:205–210. ORIANS, G. H. 1966. Food of nestling Yellow-headed ing at neck ligatures and there was no indi- Blackbirds, Cariboo Parklands, British Columbia. cation that adults became habituated to the Condor 68:321–337. presence of ligatures. Neck ligatures remain a PERLUT,N.G.,A.M.STRONG,T.M.DONOVAN, AND 444 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 121, No. 2, June 2009

N. J. BUCKLEY. 2006. Grassland songbirds in a Red-winged Blackbird. III. Growth rate and food dynamic management landscape: behavioral re- of nestlings in marsh and upland habitat. Wilson sponses and management strategies. Ecological Bulletin 85:209–222. Applications 16:2235–2247. ROSENBERG,K.V.AND R. J. COOPER. 1990. Approaches POULSEN,J.G.AND N. J. AEBISCHER. 1995. Quantita- to avian diet analysis. Studies in Avian Biology tive comparison of two methods of assessing diet 13:80–90. of nestling Skylarks (Alauda arvensis). Auk 112: SHUSTACK, D. P. 2004. Bobolink and Savannah Spar- 1070–1073. row habitat selection in the Champlain Valley. ROBERTSON, R. J. 1973. Optimal niche space of the Thesis. University of Vermont, Burlington, USA.