Plasticity by Migrant Yellow-Rumped Warblers: Foraging Indoors During Unseasonable Cold Weather

GENERAL NOTES

NORTHWESTERN NATURALIST 97:139–143 AUTUMN 2016

PLASTICITY BY MIGRANT YELLOW-RUMPED WARBLERS: FORAGING INDOORS DURING UNSEASONABLE COLD WEATHER

KRISTIN JBONDO AND RMARK BRIGHAM

ABSTRACT—From 11 to 15 October 2009, we ob- siding, and several unscreened vents near the served Yellow-rumped Warblers (Setophaga coronata roof. Other observations were made in an older coranata) foraging inside an unheated barn on 4 d, and wooden barn 450 m from the milking parlor. The inside a heated modern milking parlor on 2 d at a dairy older barn had wooden slat floors and large farm in southeastern Saskatchewan, Canada. Warblers doors which were usually left open for ventila- fed on dormant flies that were huddled on the walls tion during the day, and was dimly lit inside inside of the barn and sallied for flies in mid-air and gleaned them from the window screens inside of the unless the barn doors were wide open. The milking parlor. These observations were preceded by 2 inside of the milking parlor was only lit during d of unseasonable cold weather on 9 and 10 October, milking, which usually occurred between 6:00 to when maximum temperatures were below 08C. Yel- 10:30 (CST) and 16:30 to 20:00. Although the low-rumped Warblers fed indoors until 15 October daily temperature of the barn and the milking after which the days became warmer, and we observed parlor is unknown, the barn was considerably them only outside. Yellow-rumped Warblers most colder than the milking parlor, and it was likely entered buildings to feed because unseasonable common in the barn for drinking water, kept in weather conditions increased their energetic demands 4.7-L pails for the calves, to freeze on a daily and provided incentive for them to exploit shelter and basis during winter months; whereas the parlor food in novel places. was kept near room temperature to make it Key words: behavior, Canada, foraging, indoors, comfortable for humans while milking (KJB, migratory birds, Myrtle Warbler, plasticity, Setophaga pers. obs.). From September 2008 to May 2010, coronata coronata, unseasonable weather, Yellow- KJB worked in the milking parlor up to 5 d a rumped Warbler week from 16:00 to 20:00. Between May 2009– 2010, KJB also did other duties in the barn or Yellow-rumped Warblers (formerly Myrtle milking parlor from 8:00 to 11:00 and 15:00 to Warbler; Setophaga coronata coronata) breed from 16:00. Vegetation within 30 m of the outside of northcentral Alberta east to Newfoundland, the barn and milking parlor was sparse, so north to Labrador and northern Quebec, and casual outdoor observations of birds were made south in the Appalachians to West Virginia when entering or exiting the buildings by (Hunt and Flaspohler 1998). Although migration visually scanning the trees and bushes within peaks in mid-October, they are one of the last 17 m of the barn and milking parlor. warblers to leave in the fall, remaining in the During late morning 11 October 2009, 2 northernmost part of the breeding range well Yellow-rumped Warblers were observed feeding into October (Hunt and Flaspohler 1998). Thus, on dormant flies huddled together on the walls many individuals are likely exposed to low inside the barn. At 08:30 on 12 October 2009, 3 temperatures on a regular basis. Here, we report warblers foraged in the same manner through- a novel case of several individual migrants in out the barn. Three other warblers seen inside southeastern Saskatchewan, Canada, coming the milking parlor hawked flies in mid-air and inside buildings and feeding on flies during also plucked them from window screens from unseasonable cold weather in October. 16:00 to 19:30. When not actively pursuing prey, Observations were made in October 2009 the birds perched on the beams of the ceiling and while KJB lived and worked on Darian Farms, near the vents. They continued to forage inside a 300-cow dairy farm near Zehner in rural the parlor until 19:30 when the lights were southeastern Saskatchewan (UTM: Zone 13, turned off for the night. It is unknown whether 538669 E, 5609952 N, NAD83). Some observa- they spent the night in the building after we left tions were made in the milking parlor, a modern and closed the doors. According to the sunrise- building with heated concrete floors, aluminum sunset calculator from National Research Coun-

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TABLE 1. Maximum temperature, minimum temperature, mean temperature, mean wind direction, snow on the ground, and wind chill obtained from Environment Canada showing the unseasonable weather conditions from 1 to 19 October 2009, during which warblers were observed feeding indoors. Date Max. Min. Mean Mean wind speed Mean wind Snow Wind (2009) temp. (8C) temp. (8C) temp. (8C) (km/h) direction (8)1 (cm) chill (8C) Oct. 1 6.8 3.8 5.3 39.5 344 0 0 Oct. 2 7.4 2.5 5 21.0 328 0 0 Oct. 3 8.4 2.5 5.5 9.6 106 0 0 Oct. 4 8.6 3.1 5.9 8.04 98 0 0 Oct. 5 5.5 1.3 3.4 8.8 102 0 0 Oct. 6 9.4 –1.3 4.1 17.2 221 0 –3.7 Oct. 7 3.9 1.5 2.7 40.3 321 0 0.0 Oct. 8 3.6 –4.5 –0.5 22.5 294 0 –7.4 Oct. 9 –3.4 –8.7 –6.1 33.5 312 1 –14.0 Oct. 10 –2.6 –6.3 –4.5 30.5 309 1 –12.0 Oct. 11 –2.1 –5.4 –3.8 10.6 302 2 –8.1 Oct. 12 –1.0 6.6 –3.8 5.8 205 2 –6.9 Oct. 13 1.5 –5.7 –2.1 22.8 119 2 –8.6 Oct. 14 0.0 –1.4 –0.7 24.5 111 0 –6.8 Oct. 15 1.3 –2.0 –0.4 10.9 139 1 –5.7 Oct. 16 2.0 –1.5 0.3 12.4 269 0 –4.6 Oct. 17 19.2 –1.8 8.7 16.3 178 0 –6.4 Oct. 18 17.5 –0.1 8.7 24.5 236 0 0.0 Oct. 19 6.5 –3.2 1.7 7.5 215 0 –3.4 1 Mean wind direction is geographic (not magnetic) direction that the wind blows (0 ¼ calm wind; 90 ¼ 908 true or east wind; 360 ¼ 3608 true or north wind)

cil Canada (http://www.nrc-cnrc.gc.ca/eng/ ature during this time period were downloaded services/sunrise), sunrise and sunset occurred from Environment Canada from 1990 to 2011 at 7:17 and 18:12, respectively, on this date in and plotted using Microsoft Excel (Microsoft Regina, approximately 27 km away. Office 2007). All data except snowfall were On 13 October 2009, 3 Yellow-rumped War- collected at a weather station at the Regina blers were observed feeding on dormant flies in International Airport, 29.4 km away. Snowfall the barn from 09:00 to 11:00. On 15 October 2009, data were collected at Saskatchewan Polytechnic 1 warbler was observed feeding on active flies in in Regina, 27.6 km away. We also accessed data the milking parlor around 10:30. After 15 on wind direction (8) from Environment Canada, October, warblers were not observed inside because migrants often depart when cold fronts either the barn or the milking parlor. While no clear the area, producing tailwinds for south- warblers were observed inside either building ward-flying birds (Akesson˚ and Hedenstrom¨ during the same period in 2008, flies congregat- 2000). ed inside the barn beginning in August and Yellow-rumped Warblers were observed on 4 overwintered in clusters inside it in both 2008 d in the milking parlor following 2 d (9 and 10 and 2009. The warblers entered the wooden barn October 2009) of unseasonable cold weather through the large doors and through an opening when mean daily temperatures were 6.18C in the wall made for a feed dispenser. The and 4.58C, respectively, and daily maximum warblers most likely gained access to the milking temperatures reached only 3.48C and 2.68C, parlor through the vents. It was customary to respectively (Table 1). On 9 and 10 October 2009, have a radio playing at a loud volume during 1 cm of snowfall was reported, and the wind milking, but the birds did not appear to be chill for these 2 d was 148Cand128C, disturbed by the noise. respectively (Table 1). On 17 October 2009, when To determine whether the period from 1 to 15 mean daily temperature was 8.78C and maxi- October 2009 was unseasonably cold relative to mum temperature reached 19.28C, warblers other years, mean daily temperature, maximum were only observed in the tree outside the daily temperature, and minimum daily temper- milking parlor. No warblers were observed

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when warblers entered the buildings during sub-zero maximum temperatures, because although flies in the milking parlor were active, flies in the unheated barn were dormant (KJB, pers. obs.). Lack of prey outdoors during cold temperatures could have had significant energetic implications for migrants. After 3 d of restricted feeding by captive migrant Yellow- rumped Warblers that were not discernibly starving, the birds had lost 16% of their body mass, or 5.3% per day (Lee and others 2002). Other studies found that smaller migratory birds can undergo a 30% reduction in body mass if starved for a matter of hours (McCue 2010). FIGURE 1. Mean maximum daily temperature (top dashed line), mean daily temperature (middle solid Wind was likely another important factor in line), and minimum daily temperature (bottom dashed prompting birds to seek shelter and warmth line) for 1 to 15 October 1990–2011, showing that the inside buildings, because the most extreme daily year 2009 had unseasonably cold mean and maximum mean wind chills were recorded on 9 and 10 temperatures relative to other years. October 2009, which were 1 to 2 d prior to when birds were observed indoors. Although migratory passerine birds have been found to depart during days with strong tail-winds and to depart indoors or observed in the trees within 30 m of during times correlated with wind direction the milking parlor or barn after 17 October. (Akesson˚ and Hedenstrom¨ 2000), the Yellow- Mean daily temperature and maximum temper- rumped Warblers we observed may have been ature from 1 to 15 October 2009 were unseason- reluctant to depart despite considerable tail- ably cold relative to the same time period in winds because of poor visibility, including light other years (Fig. 1). blowing snow that began on 9 October. Yellow-rumped Warblers may have entered Individuals of a variety of bird species have buildings to feed because unseasonal weather been reported to benefit from human-created conditions increased their energetic demands environments by modifying behavior during and provided incentive to seek shelter indoors. times of energetic stress such as cold periods or Mortality of migrants may occur during unsea- migration. Warblers and other small birds have sonable cold weather soon after they arrive at or been reported to enter buildings on misty nights depart from a breeding area (Newton 2007). during migration (Pearson and Backhurst 1976), Whitmore and others (1977) analyzed climatic whereas swifts and swallows, which were likely data to determine whether there were any yearly short of food in cold weather and potentially weather differences that might explain mortality suffering from hypothermia, sought shelter of 569 individuals of 32 species of passerine inside buildings (Brown and Brown 2000). A spring migrants, which occurred during cold variety of bird species including passerine and stormy weather in Utah. Although they migrants have been observed feeding around found that the years in which mortality occurred lights at night (Lebbin and others 2007), and a had a significantly harsher climate than the Siberian Accentor (Prunella montanella) from Asia preceding 5 y, mean maximum temperature was subsisted over the winter in Alaska on freeze- found to be the most important variable ex- dried insects killed the previous summer by a plaining weather differences between time peri- ‘‘bug zapper’’ (Obmascik 2004). ods in the year mass mortality was observed Although it is not uncommon for birds to compared to the years it was not observed. forage in anthropogenic habitats, to our knowl- Maximum temperature is likely important dur- edge this is the 1st report of warblers entering a ing migration because cold can greatly reduce building and feeding on insects indoors. It is food supplies for insectivorous migrants by possible that the warblers entered the vents and stimulating dormancy in insects (Newton barn for shelter or out of curiosity due to 2007). Insects were likely dormant outdoors energetic demands and then continued to enter

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and exit after learning of the availability of the anonymous reviewers for helpful comments on the food inside. Not only has the Yellow-rumped manuscript. Warbler been described as a generalist species (Greenberg 1979) with plastic foraging behavior LITERATURE CITED (Parrish 2000), but it also has been found to be A˚ KESSON S, HEDENSTRO¨ M A. 2000. Wind selectivity of one of the most ecologically generalized of all migratory flight departures in birds. Behavioral warbler species with regard to diet, foraging Ecology and Sociobiology 47:140–144. technique, and habitat use (Hunt and Flaspohler BROCKIE RE, O’BRIEN B. 2004. House Sparrows (Passer 1998), and to have the highest ecological domesticus) opening autodoors. Notornis 51:52. BROWN CR, BROWN MB. 2000. Weather-mediated plasticity score of the genus (Simon and others natural selection on arrival time in Cliff Swallows 2003). High phenotypic plasticity and behavioral (Petrochelidon pyrrhonota). Behavioral Ecology and flexibility in adapting to new environments are Sociobiology 47:339–345. associated with both generalist and invasive GREENBERG R. 1979. Body size, breeding habitat, and species (Lodge 1993). Being the most flexible winter exploitation systems in Dendroica.Auk forager of the spruce-forest warblers may allow 96:756–766. Yellow-rumped Warblers to withstand adverse HUNT PD, FLASPOHLER DJ. 1998. Yellow-rumped Warbler conditions better than other warbler species (Setophaga coronata). In: Poole A, editor. The birds of when foraging options are reduced (Morse North America, No. 376. Ithaca, NY: Cornell Lab of Ornithology. 1989). For example, Yellow-rumped Warblers LEBBIN DJ, HARVEY MG, LENZ TC, ANDERSON MJ, ELLIS can be found in almost any habitat during the JM. 2007. Nocturnal migrants foraging at night by non-breeding season (Hunt and Flaspohler artificial light. Wilson Journal of Ornithology 1998), and will eat fruit during inclement 119:506–508. weather (Wilz and Giampa 1978) or when LEE KA, KARASOV WH, CAVIEDES-VIDAL E. 2002. Diges- insects are scarce. Woolfenden (1962) also noted tive response to restricted feeding in migratory behavioral changes in Yellow-Rumped Warblers, Yellow-rumped Warblers. Physiological and Bio- which he argued may have been related to chemical Zoology 75:314–323. LODGE DM. 1993. Biological invasions: Lessons for weather induced food shortages. ecology. Trends in Ecology and Evolution 8:133–137 Some species of birds may learn to come MCCUE MD. 2010. Starvation physiology: Reviewing indoors opportunistically, regardless of energetic the different strategies animals use to survive a stress. For example, a Prothonotary Warbler common challenge. Comparative Biochemistry and (Protonotaria citrea) has been reported entering Physiology 156:1–18. and exiting through an open window to nest MORSE DH. 1989. American Warblers: An ecological inside a building (Perkins 1926), and House and behavioral perspective. Cambridge, MA: Har- Sparrows (Passer domesticus) in New Zealand vard University Press. 406 p. NEWTON I. 2007. Weather-related mass mortality events cities learned how to open automatic doors to in migrants. Ibis 149:453–467. gain access to food inside a cafeteria (Brockie OBMASCIK M. 2004. The big year: A tale of man, nature, and O’Brien 2004). Many theories have been and fowl obsession. New York, NY: Free Press. 268 proposed to explain variation in behavioral p. tendencies that may occur both among and PARRISH JD. 2000. Behavioral, energetic, and conserva- within species (see Sih and others 2011). More tion implications of foraging plasticity during research is needed to understand whether or migration. Studies in Avian Biology 20:53–70. how the evolutionary history of a bird species PEARSON DJ, BACKHURST GC. 1976. The southward migration of Palaearctic birds over Ngulia, Kenya. influences its ability to adapt to novel anthro- Ibis 118:78–105. pogenic situations (for example, feeding at lights PERKINS SE III. 1926. An unusual nesting site of the at night, coming indoors to feed or nest), during Prothonotary Warbler. Wilson Bulletin 38:233. times of increased energetic demands such as SIH A, FERRARI MCO, HARRIS DJ. 2011. Evolution and unseasonable weather, breeding, and migration. behavioural responses to human-induced rapid environmental change. Evolutionary Applications. Acknowledgements.—We thank Darian Farms for the 4:367–387. employment opportunity for KJB and for taking an SIMON NPP, DIAMOND AW, SCHWAB FE. 2003. Do interest in these observations. We also thank JB northern forest bird communities show more Dunning, B Pranty, AW Diamond, J Hagar, and 2 ecological plasticity than southern forest bird

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communities in eastern Canada? Ecoscience Department of Biology, University of Regina, 10:289–296. Regina, SK S4S 0A2 Canada; Present address: WHITMORE RC, MOSHER JA, HH FROST. 1977. Spring Department of Pathobiology, University of Guelph, migrant mortality during unseasonable weather. Ontario Veterinary College, Guelph, ON N1G 2W1 Auk 94:778–781. Canada; [email protected] (KJB); Department of WILZ KJ, GIAMPA V. 1978. Habitat use by Yellow- rumped Warblers at the northern extremities of Biology, University of Regina, Regina, SK S4S 0A2 their winter range. Wilson Bulletin 90:566–574. Canada; [email protected] (RMB). Submit- WOOLFENDEN GE. 1962. Aggressive behavior by a ted 22 April 2015, accepted 27 October 2015.Corre- wintering Myrtle Warbler. Auk 79:713–714. sponding Editor: Joan Hagar.

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