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Home , Bird migration, Ornithology

VOL. 130, NO. 1 March 2018 PAGES 1–352

The Wilson Journal of 130(1):1–12, 2018

Biology of landbird migrants: a stopover perspective

Frank R. Moore1

ABSTRACT—This perspective on the stopover of migratory landbirds is organized around the response of migrants to challenges that can arise during stopover and how events during stopover are interconnected with other phases of the annual cycle. Landbird migrants seldom move nonstop from origin to destination, rather they stopover periodically, sometimes for a few hours, sometimes days. How well migrants meet challenges that arise during passage in a timely manner influences the success of their migration; a successful migration is measured in terms of survival and reproductive performance over the annual cycle. What transpires during migration is not isolated from other phases of the migrant’s annual cycle. Events taking place in one phase carry over to affect an individual’s biology in other phases, including linkage between breeding and wintering phases and the intervening migratory phase. Received 28 November 2017. Accepted 4 December 2017.

Key words: annual cycle, carryover effects, migratory landbirds, stopover.

Biolog´ıa de aves terrestres migratorias: una perspectiva de sus sitios de abastecimiento y descanso

RESUMEN (Spanish)—Esta perspectiva sobre la biolog´ıa de las aves terrestres migratorias en sus sitios de abastecimiento y descanso esta organizada en torno a la respuesta de estas aves a los retos que se presentan durante sus paradas, y como´ los eventos que acontecen durante esos periodos de abastecimiento y descanso esta´n interconectados con otras fases del ciclo anual. Aunque en ocasiones las aves terrestres migratorias se desplazan sin parar de origen a destino, estas´ prefieren hacer paradas para periodicas´ a veces por algunas horas, a veces por d´ıas. El exito´ de su migracion´ es influenciado por que´ tan bien y que´ tan a tiempo enfrenten los retos que se presentan a su paso. Este exito´ se mide en terminos´ de sobrevivencia y desempeno˜ reproductivo a lo largo del ciclo anual. Lo que ocurre durante la migracion´ no esta´ aislado de otras fases del ciclo anual. Los eventos que tienen lugar en una fase de su ciclo anual afectan la biolog´ıa de los individuos y son acarreados a otras fases, incluyendo la conexion´ que existe entre las fases de reproduccion´ e invernada, adema´s de lo que pasa durante la migracion.´ Palabras clave: Aves terrestres migratorias, ciclo anual, efecto de acarreo, sitios de abastecimiento y descanso.

The benefits of intercontinental migration, re- and tropical areas comes with risks, and the gardless of whether they accrue through increased mortality associated with long-distance migration, survivorship by overwintering in the tropics, although difficult to estimate, may be substantial increased productivity by breeding in seasonally (Sillett and Holmes 2002, Paxton et al. 2017, Rockwell et al. 2017), is likely age-dependent rich temperate areas, or both, are balanced against (Greenberg 1980), and may limit populations the costs of migration. Traveling between temperate (Newton 2006). Although intercontinental migrato- ry move great, often awe-inspiring distances, 1 Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS, USA; e-mail: invariably over large inhospitable landscapes, they [email protected] seldom migrate nonstop from origin to destination, 1 2 The Wilson Journal of Ornithology  Vol. 130, No. 1, March 2018 but rather stopover periodically, sometimes for a terms of survival and reproductive performance few hours, sometimes days. Indeed, it is thought (Alerstam et al. 2003). that most of migration time is spent on stopover (Hedenstr¨om and Alerstam 1997) when energy Arrival and habitat use expended is high relative to migratory flight A migrant’s relationship to habitat during (Wikelski et al. 2003; see also Nudds and Bryant passage is best understood as a scale-dependent, 2000, Bowlin et al. 2005). hierarchically ordered process (Hutto 1985, Moore My research program has integrated field and et al. 1995, Simons et al. 2000, Buler et al. 2007). laboratory approaches to study the , For example, while traveling northward across the behavior, and ecophysiology of intercontinental Gulf of Mexico, prevailing wind patterns and not landbird (i.e., and near passerines with a habitat quality per se explain why a migrating terrestrial history) migrants when they stop- Red-eyed finds herself approaching the over during passage. This perspective on the southwest coast of Louisiana rather than barrier stopover biology of migratory landbirds is orga- islands off the coast of Mississippi, not likely nized around their response to challenges that can aware that landing in one place and not the other arise during stopover and the interconnection may have consequences (Simons et al. 2000). between events during stopover and other phases Although an interplay of intrinsic (e.g., fuel load) of the annual cycle. Why migrating stopover and extrinsic (e.g., weather) factors influence determines in large measure what they do during where landfall is made (Buler and Moore 2011), stopover: a migrant may be low on fuel stores, off hardwood forest cover is strongly linked to course and find it easier to correct and reorient migrant density (e.g., Buler and Dawson 2014, while on the ground, fatigued, and in need of rest Lafleur et al. 2016) and likely serves as an and sleep after flying long hours or against indicator of habitat quality (Cohen et al. 2014) and cue to select a landing site (Buler et al. 2007, unfavorable winds; experiencing or anticipating inclement weather; out of nighttime as a nocturnal Ktitorov et al. 2008, McCabe and Olsen 2015). migrant; or maybe the endogenous time–direction Nocturnally migrating songbirds generally end their flight before dawn (Kerlinger and Moore program (Gwinner 1996) simply dictates a pause 1989) when visual sensitivity may constrain a en route to destination. detailed evaluation of habitat features, so acoustic information may be used to recognize habitats Response to challenges when making landfall, including places already occupied by conspecifics (Herremans 1990, Mu- Visualize a Red-eyed Vireo (Vireo olivaceus) khin et al. 2008, Alessi et al. 2010). gleaning small geometrid larvae from the edge of Once on the ground, migrants often display a hackberry leaves in the middle of a long, narrow preference for certain habitats and select among cheniere near Johnson’s Bayou, Louisiana, fol- alternatives (Moore et al. 1990, Aborn and Moore lowing a mid-April flight across the Gulf of 1997, Chernetsov 2006, Slager et al. 2015), which Mexico. She finds herself in unfamiliar surround- is not surprising if selection of a habitat has ings at a time when energy demand may be high, consequences for time and condition (Cohen et al. and possibly faced with the need to acquire in 2012). The process of seeking preferred habitat a short period of time while balancing conflicting involves exploration (Aborn and Moore 1997; demands between predator avoidance and food Paxton et al. 2008; Cohen et al. 2012, 2014), acquisition, competition with other migrants and which may explain some landscape-scale move- resident birds if resources are limited, unfavorable ments observed at night (Mills et al. 2011) as well weather, exposure to parasites and pathogens, and as ‘morning flights’ of migratory songbirds shortly loss of sleep, not to mention the need to make after sunrise. Although some morning movements accurate and judicious decisions upon departure. may be ongoing migration (Bingman 1980, Moore How well she meets challenges in a timely manner 1986, Sandberg et al. 2002), and morning hours do determines the success of her migration (Alerstam provide favorable atmospheric flight conditions and Lindstr¨om 1990), measured as successful in (Kerlinger and Moore 1989), it is also likely that Moore  Stopover biology of landbird migrants 3 migrants engage in morning flight to seek suitable a combination of the 2 sources of information. For stopover habitat (Alerstam 1978, Lindstr¨om and example, focal sampling of free-ranging songbird Alerstam 1986, Chernetsov 2011, Van Doren et al. migrants following flight across the Gulf of 2015) or compensate for drift experienced during Mexico suggests that birds respond to a lack of nocturnal migration (Moore 1990, Van Doren et al. information by initially foraging in temporary 2015). Efforts notwithstanding, favorable stopover feeding assemblages and are more likely to do so if habitat, where a fat-depleted migrant, for example, fat-depleted (Nemeth´ and Moore 2007). Lean birds can rapidly meet nutritional needs, is probably are probably more willing to trade off the limited in an absolute sense (Simons et al. 2000), reliability of information gained on their own for or effectively so because migrants are probably quicker and safer access to albeit less reliable constrained to minimize exploration time during information gained by foraging in a flock (Nemeth´ stopover (Paxton et al. 2008, Cohen et al. 2014; and Moore 2014). sensu Hedenstr¨om and Alerstam 1997). Acquisition of nutrients Acquiring information in an unfamiliar place Arguably the most important constraint during After a migratory flight, a songbird almost migration is to acquire enough food to meet invariably finds herself in a place different from nutritional needs in a timely fashion. Birds in the one occupied the previous day, much less the migratory disposition are especially efficient previous year (Stanley et al. 2012), which begs the foragers (Moore and Simm 1985) and select a question: Why not stopover in a familiar place diet that achieves energy maximization relative to where resources and sources of stress are better birds not in migratory condition (Bairlein 2003). known? Certainly experienced adult songbird Moreover, observation of free-ranging migrants migrants have the navigational ability to return to during stopover reveals that energetic condition previously experienced places (Akesson˚ et al. influences microhabitat selection (Tietz and John- 2014), but the benefit of doing so for a small son 2007) and foraging behavior (Loria and Moore songbird en route is probably offset by 2 factors 1990, Wang and Moore 2005). Lean birds expand (Catry et al. 2004): (1) lost time to destination their foraging repertoire, broaden their use of correcting for wind drift and/or waiting for substrate, and forage at a faster pace than do birds favorable wind conditions at departure, and (2) with residual fat stores (Loria and Moore 1990). the general availability of terrestrial habitats where Consequently, they achieve a favorable energy a positive energy balance can at least be balance more quickly than they otherwise would maintained during passage (Wang and Moore (Wang and Moore 2005), thereby decreasing 1997). Moreover, changes in the abundance or length of stopover and presumably time spent on suitability of stopover sites (e.g., deforestation, migration. Younger migrants, however, are often fragmentation, urbanization) along the migratory less efficient foragers (Heise and Moore 2003), not route would likely select for increased departure to mention behaviorally subordinate to adults fuel load (greater margin of safety) and/or longer (Terrill 1987, Moore et al. 2003). Inefficiency flights rather than en route . and lack of experience would be especially Although the cues migratory birds use to make consequential if food becomes scarce or when decisions about resources and sources of stress migrants experience heightened energy demand in during stopover warrants more attention (Moore anticipation of a possible energetic ‘short fall’ and Aborn 2000, McGrath et al. 2009, Wolfe et al. (Moore and Simm 1986, Woodrey and Moore 2014), migrants that gather reliable information 1997). about unfamiliar places in a timely fashion (Cohen et al. 2014) increase the likelihood of a successful En route competition migration (Nemeth´ and Moore 2014). Individuals If migrants with similar nutritional requirements can estimate food availability or predator pressure and heightened energy find themselves locally using personal information gathered while sam- concentrated during stopover, competition could pling habitat or with social information obtained depress food resources and reduce the rate at while observing the behavior of other migrants, or which migrants restore essential fuel loads (Hans- 4 The Wilson Journal of Ornithology  Vol. 130, No. 1, March 2018 son and Petersson 1989, Moore and Wang 1991, predation risk is variable and unpredictable during Kelly et al. 2002). Further, social asymmetries migration; (2) migrants carry relatively large fuel often mediate competitive interactions, and subor- loads, which is known to affect escape perfor- dinate status is known to affect priority access to mance (Kullberg et al. 1996, Lind et al. 1999); (3) food during passage and handicap fuel deposition migrants often experience elevated foraging de- rates in landbird migrants (Lindstrom et al. 1990, mands; (4) there is pressure to travel quickly; and Carpenter et al. 1993, Wang et al. 1998, Moore et (5) information about predation risks and foraging al. 2003). Male Pied Flycatchers (Ficedula hypo- opportunities is lacking. Changes in risk of leuca), for example, have advantages over females predation during stopover alter both foraging competing for food resources, and females are location and intensity (Cimprich and Moore more likely to challenge dominants and success- 2006), which could affect fuel deposition rates fully access resources in a same-sex environment and stopover length. Fatter birds should be more than in an opposite-sex environment (Moore et al. cautious because they are more vulnerable, or lean 2003). Given the energetic demands of migration, birds may simply be more risk prone because of social asymmetries would be expected to be increased energetic demand (Moore 1994, Dier- condition dependent; lean migrants value food schke 2003, Cimprich and Moore 2006). While more than fat individuals and gain priority access predation risk clearly affects the behavior of to food despite pre-existing status (Moore et al. migrants during stopover, the proximate cues used 2003). to assess risk and how accurately they accomplish During passage, migrants encounter resident this task are poorly known. birds during stopover, including conspecifics that settled at a breeding destination earlier in spring. Microbes, pathogens, and parasites The influx of migrants may adversely affect the Migration is no time to be fighting an infection behavior and habitat use of residents (Bensusan et given time and energetic constraints, especially if al. 2011), whereas residents defending territorial birds in migratory disposition suppress immune space may constrain use of preferred stopover responsiveness (Owen and Moore 2006; Owen and habitat (E. Cohen, Smithsonian Conservation Moore 2008a, 2008b). Although migrating birds Biology Institute, 2007–2008, pers. obs.). may be expected to invest in immune function How often migrants actually compete for given exposure to parasites and pathogens during resources during stopover depends in part on their travels, immune function may be suppressed how often they are locally concentrated during in response to anticipated energetic demands or passage, which is tied to the number of birds aloft downregulated to avoid immunopathology during and the availability and configuration of stopover periods of stress. Whereas flight performance per habitat. The volume of birds aloft depends on the se may not be particularly stressful or immuno- occurrence of favorable synoptic weather events suppressive (Hasselquist et al. 2007), birds that (e.g., Richardson 1978, 1990; Gauthreaux 1991), arrive at a stopover site in poor condition display which creates ‘waves’ of migrants over a land- reduced immune responsiveness, although it scape that may consist of attractive habitat rebounds with improving condition during stop- fragments embedded within a less hospitable over (Owen and Moore 2008a). matrix (e.g., Tankersley and Orvis 2003). A variety of parasites and pathogenic microor- ganisms are associated with intercontinental song- Predation pressure bird migrants (Hubalek 2004). For example, it is Predation is a hazard during migration not uncommon to detect several blood parasites (Lindstr¨om 1989, Aborn 1994), and migrants (Haemoproteus, Plasmodium, Leucocytozoon, and assess risk of predation during stopover (Cimprich Trypanosoma) in migratory birds in spring, and et al. 2005). Moreover, a combination of factors fuel load is negatively associated with density of during stopover creates a complex, dynamic Haemoproteus spp. infection in several environment within which migrants trade-off (Garvin et al. 2006). When reduced energetic safety and foraging, which may be especially condition caused by blood parasites results in problematic for less experienced, young birds; (1) delayed arrival on the breeding grounds (DeGroote Moore  Stopover biology of landbird migrants 5 and Rodewald 2010, Hatch et al. 2010), infections mon. When observed, sleep events are short (e.g., may have important consequences for host fitness. Schwilch et al. 2002, Nemeth´ 2009, Covino and Migratory songbirds also serve as transport Cooney 2015), not unlike the daytime micro-naps carriers for immature , including exotic ticks recorded in captive Swainson’s Thrushes (Catha- carrying -borne pathogens from tropical win- rus ustulatus) when in migratory disposition tering areas to temperate breeding areas (e.g., (Fuchs et al. 2006, 2009). Mukherjee et al. 2014, Cohen et al. 2015), although it remains uncertain if migratory birds Weather are negatively affected by ticks during stopover Atmospheric conditions acting across widely (Morris et al. 2007) or whether they serve as different scales have a profound influence on the competent reservoir hosts for tick-borne pathogens biology of migratory birds (Richardson 1978, (Budachetri et al. 2017). Migratory birds are 1990; Gauthreaux et al. 2005; Shamoun-Baranes competent reservoir hosts and potential dispersal et al. 2017; LaSorte et al. 2014), including when vehicles for West (Owen et al. 2006). and where a migrant stops over (e.g., Gauthreaux Of course, not all microbes are harmful. 1971, 1972), the abundance and availability of Migrating birds are characterized by a diverse resources (Dobbs et al. 2009, Lain et al. 2017), gut microbiota (Lewis et al. 2016), the composi- likelihood of departure (e.g., Matthews and tion of which rapidly converges across individuals Rodewald 2010), and when during the day and that stopover in the same place (Lewis et al. 2017). in what direction to depart a stopover site The rapid change in composition is probably a (Danhardt and Lindstr¨om 2001, Smolinsky et al. response to local conditions, including available 2013, Sj¨oberg et al. 2015, Deppe et al. 2015). Yet, food resources, and similar reconstitution of gut surprisingly little is known about the effect of function after food withdrawal and prolonged precipitation (Smith and McWilliams 2014), flight. It remains to be seen if the composition of temperature, and wind condition on, for example, this microbiota has functional consequences for activity budgets during stopover, much less fuel migratory birds. deposition rates and departure fuel loads. For example, migrants might change their activity Sleepy migrants pattern during the day in anticipation of departure Most bird species are active during the day and when experiencing atmospheric conditions consis- much less so at night, except during migration tent with favorable conditions for migratory flight; when the migratory flights of most songbirds take that is, they increase foraging activity to reach place. Generally, a migratory bird begins a night’s appropriate departure fuel load or decrease activity flight after sunset before astronomical twilight and to reduce energy expenditure if carrying an flies for half or more of the night. By migrating at adequate fuel load for departure. night, a migrant experiences decreased predatory pressure, improved atmospheric conditions for Departure decisions flight, and more time to feed during the day Migration is about reaching destinations in a (Kerlinger and Moore 1989). Nevertheless, a night timely fashion and in good nutritional condition, migrant necessarily experiences loss of sleep, yet so stopover must come to an end. Some individ- surprisingly may not experience negative conse- uals stay but a few hours and depart as soon as quences (e.g., Rattenborg et al. 2004). If loss of possible, usually the night following arrival sleep has negative consequences, a migrating bird (‘transients/flyers’), while ‘non-transients/feeders’ should show compensatory adjustments (Fuchs et stay for a few to several days (Rappole and Warner al. 2006), including the possibility of semi- 1976). This dichotomy hints at the striking hemispheric sleep while aloft (Fuchs et al. 2009). variation in stopover duration within individuals Compensatory sleep during the day, however, is from site-to-site over a migration season, among not without costs; less time is available for individuals within species, age and sex cohorts as foraging, which could have consequences in units well as among species—variation that reflects the of time and condition, and may explain why complexity inherent in the stopover biology of observations of sleep during stopover are uncom- migratory birds and the capacity for individual 6 The Wilson Journal of Ornithology  Vol. 130, No. 1, March 2018 strategic variation in decision making (sensu depart within the window of time between sunset Winkler et al. 2014). and astronomical twilight regardless of age and A migrant’s decision to depart or remain at a move in a southerly direction out over the Gulf of stopover site is governed by the bird’s behavioral Mexico (Smolinsky et al. 2013). Doing so takes and physiological states as well as its temporal and advantage of the entire night in relation to a long- spatial position within a programmed migration distance, trans-Gulf flight, recognizing that trans- schedule (Jenni and Schaub 2003). This program Gulf migrants almost invariably arrive on the provides a framework within which other factors opposite coast the next day and often continue influence stopover decisions (Deppe et al. 2015), flight well beyond the coast (Gauthreaux 1971, including species-, age-, and sex-specific use of 1972; Lafleur et al. 2016). Birds departing later in habitat and day-to-day variation in the threat of the night invariably carried fuel loads insufficient predation, competitor density, and weather. Mi- for an entire night’s flight, much less a trans-Gulf grating birds gather information, integrate envi- flight, and moved in northerly directions away ronmental and internal state data, and make from the coast (Smolinsky et al. 2013), presum- departure decisions presumably in relation to ably in search of more extensive forested habitat current and anticipated conditions (Moore et al. (Buler and Moore 2011). In an ambitious follow 2017). How migrant’s gauge current, much less up study, Swainson’s Thrushes as well as Red- future, conditions is poorly known, but they do so eyed Vireos and Wood Thrushes (Hylocichla with success (Ward et al. forthcoming). mustelina) were radio-tracked before and after Just prior to the departure of free-ranging birds crossing the Gulf of Mexico in fall to assess (e.g., Cochran et al. 2004) and onset of migratory departure decisions in relation to trans-Gulf activity (zugunruhe) in captive birds (e.g., Rame- movement (Deppe et al. 2015, Bolus et al. 2017; nofsky et al. 2008), a period of inactivity, Ward et al. forthcoming 2018). These studies sometimes termed quiescence, is observed. This found that adequate fuel load is essential, seasonal poorly understood quiescent period may reflect a timing and synoptic weather matter, wind profit cessation of movement as light levels decline, but affects crossing time, species differ in their it also is probably the time when migrants gather willingness to cross the Gulf of Mexico, and age flight information and prepare for departure; that does not affect success. Migratory songbirds are is, they calibrate compasses, assess internal not intimidated by large stretches of inhospitable energetic state and meteorological conditions, terrain (e.g., Bulte et al. 2014, Gomez´ et al. 2017); switch metabolically from fuel deposition to a the key is risk management and a margin of safety mobilization phase, and maybe take a nap (Scho- field et al. forthcoming 2018). (see Moore and Kerlinger 1992). When during the day and in what direction to depart are important decisions also influenced by Carryover effects and seasonal transitions the interplay of intrinsic and extrinsic factors (Sandberg and Moore 1996a). Nocturnally migrat- The development and application of new ing landbirds generally depart on a migratory flight tracking technology is moving us closer to the shortly after sunset and before astronomical reconstruction of migratory routes and spatial twilight, a window of time linked to the onset of connectivity across the annual cycle while rein- favorable atmospheric conditions (Kerlinger and forcing the notion that what transpires during Moore 1989) and the opportunity to integrate migration is not isolated from other phases of the directional information known to be important in annual cycle (Marra et al. 2015). Events in one migratory orientation (Moore 1987, Pakhomov phase carry over to affect an individual’s biology and Chernetsov 2014). Not all nocturnal migrants in other phases (e.g., Sandberg and Moore 1996b), depart during this window of time, and that including linkage between breeding and wintering variation informs on the interplay of factors phases and the intervening migratory phase. For influencing this decision (Bolshakov et al. 2007, example, climatic variation in passage areas has Muller¨ et al. 2016). important carryover effects on breeding For example, Swainson’s Thrushes carrying and performance of intercontinental songbird sufficient fuel loads to cross the Gulf of Mexico migrants, presumably driven by en route effects Moore  Stopover biology of landbird migrants 7 on time and condition ( et al. 2014). More to however, do not carry larger fuel loads than later the point, climatic variability across tropical arriving birds that originate from poor-quality wintering areas affects the energetic condition of habitat, regardless of breeding destination, a Nearctic-Neotropical migratory songbirds during pattern consistent with males minimizing time at spring migration (Paxton et al. 2014). Species that the expense of energy. By contrast, female arrival over-wintered in experienced condition on stopover does not vary with timing of significantly drier environments during El Nino˜ migration or breeding destination, consistent with years than birds over-wintering in the Caribbean a strategy that minimizes energy expenditure and . During El Nino˜ years, birds during migration. Moreover, refueling rate and from South America arrive in poorer condition and duration of stopover is influenced by breeding are more likely to stopover immediately along the destination and timing of arrival at stopover site, northern coast of the Gulf of Mexico, whereas although the relationships are subtle and sex- Caribbean–Central American wintering birds dependent (Paxton and Moore 2017). showed no such differences between El Nino˜ and Imagine watching a Wilson’s Warbler (Cardel- La Nina˜ years (Paxton et al. 2014). If lean lina pusilla) forage in a cottonwood at a stopover migrants stay longer than usual to refuel and do site in southern along the Colorado not make up for lost time, arrival at the destination on her way to a distant breeding location. is delayed. Migrants that arrive late on the Knowing whether the bird is early or late in breeding grounds may jeopardize opportunities to relation to its programmed migration schedule, secure a territory or a mate (Smith and Moore how far she must travel to reach her breeding 2005a). If migrants depart a stopover site with low destination, and where she has been are essential departure fuel loads, they have a smaller ‘margin pieces of information when trying to draw of safety’ to buffer the effect of adverse conditions inferences about the individual’s stopover biology on the availability of food at the next stopover or and migration strategy (Paxton and Moore 2017).

the destination (Smith and Moore 2003, 2005b; Tracking the origin of a migratory songbird using Holzschuh and Deutschlander 2016). If a migrant noninvasive, intrinsic marking techniques is a expects to ‘catch-up’ with the overall time challenging endeavor, but methods are now schedule of migration and maintain a margin of available that combine information from high safety vis-a-vis anticipated energetic demands, she resolution genetic markers with stable isotopes must refuel faster than average during the next and habitat suitability models to spatially infer the stopover, and a domino effect may ensue. breeding origin of migrants captured anywhere Poorly known is how events during other phases along their migratory pathway (Ruegg et al. 2014, of the annual cycle affect migration strategy during 2017). Identifying migratory connections across stopover and vice versa (Moore et al. 2005). The the annual cycle is vitally important for studies of challenge is not simply to track the movement of a migrant ecology and conservation (Bayly et al. migrant through the annual cycle (difficult 2017, Cohen et al. 2017). enough), but rather to understand a migrant’s strategy (fuel deposition rate, departure fuel load, Acknowledgments stopover duration) based on conditions experi- Foremost, I thank my graduate students whose collective enced prior to stopover and the migrant’s destina- efforts and collaborative spirit defined my research program: tion. Intrinsic markers (e.g., carbon and hydrogen David Aborn, Alicia Mathis, Chris Szell, Emily Lain, David isotopic signatures) can be used to link stopover Cimprich, Colleen Dwyer, Amy Kuenzi, Jeff Mollenhauer biology to habitat quality and breeding Sarah Mabey, Jennifer Owen, Michael Sellers, Mike destination (Paxton and Moore 2015, 2017). Guilfoyle, Patricia Simm, Zoltan Nemeth, Sheri Glowinski Emily Cohen, Jennifer and Mike Buchanan, Jeff Clark, Among Black-and-White Warblers (Mniotilta var- Diane Loria, Kristina Paxton, Kristen Covino, Mark Wood- ia) migrating to the same breeding region, males rey, Robert Smith, Will Lewis, Stefan Woltmann, Jeff and females arriving early on stopover come from Farrington, Jeffrey Buler, Yong Wang, Jill Busby-High, higher quality wintering habitat; the benefits of Trecia Osachuk, Rachel Bolus, Megan Hughes, Sarah Wheeless, T.J. Zenzal, Jill Lafleur, Jaclyn Smolinsky, and occupying high-quality habitat during the winter Rodney Felix (co-advised with Robb Diehl). Many, many positively influence the timing of migration. Male assistants, literally too numerous to mention, ensured that warblers arriving early to the stopover site, our laboratory experiences and field seasons would be 8 The Wilson Journal of Ornithology  Vol. 130, No. 1, March 2018 productive and memorable. Our first long term study site Bensusan KJ, Shorrocks B, Hamer KC. 2011. Impacts of was established in the mid-1980s at Peveto Woods, part of a passage migrant songbirds on behavior and habitat use cheniere (coastal forest) in Cameron Parish, Louisiana, with of resident Sardinian Warblers Sylvia melanocephala in the help of my doctoral mentor, Sidney Gauthreaux, Jr, and . . 153:616–621. the Baton Rouge Society. ornithology later Bingman VP. 1980. Inland morning flight behavior of confirmed what birders suspected for years, namely that nocturnal migrants in eastern New York. southwest Louisiana consistently experiences some of the . 97:465–472. highest density of spring migration along the northern coast Bolshakov CV, Chernetsov N, Mukhin A, Bulyuk VN, of the Gulf of Mexico. It was in Peveto Woods that I Kosarev V, et al. 2007. Time of nocturnal departures in experienced my first ‘‘fallout’’ of trans-Gulf migrants. The European Robins, Erithacus rubecula, in relation to chenieres of coastal Louisiana provide a truly remarkable celestial cues, season, stopover duration and fat stores. setting to appreciate , not to mention to fall in Behaviour. 74:855–865. love with crawfish, blue crab, boudin, and cajun music. We Bolus R, Diehl R, Moore FR, Deppe J, Ward M, et al. 2017. established other study sites along the northern coast of the Swainson’s Thrushes do not show strong wind Gulf of Mexico, notably on Ft. Morgan Peninsula, Alabama, selectivity prior to crossing the Gulf of Mexico. and on the barrier islands off the coast of Mississippi, and Scientific Reports. 7:14280. over time studied stopover biology elsewhere in North Bowlin M, Wikelski M, Cochran W. 2005. Biotelemetry of America as well as in Europe. Our research over the years New World thrushes during migration: , gained support from the National Geographic Society, US energetics and orientation in the wild. Integrative and National Park Service, National Science Foundation, US Comparative Biology. 45:295–304. Fish & Wildlife Service, USDA Forest Service, National Budachetri B, Williams J, Mukherjee N, Sellers M, Moore Fish and Wildlife Foundation, US Department of the Navy, FR, Karim S. 2017. The microbiome of Neotropical NOAA/Sea Grant, US Department of Defense, Center for ticks parasitizing on passerine migratory birds. Ticks Disease Control/Mississippi Department of Health, Birming- and Tick-borne Diseases. 8:170–173. ham Audubon Society, and the Louisiana Ornithological Buler JJ, Dawson DK. 2014. Radar analysis of fall bird Society. migration stopover sites in the northeastern US. Condor: Ornithological Applications. 116:57–370. Literature cited Buler JJ, Moore FR, Woltmann S. 2007. A multi-scale examination of stopover habitat use by birds. Ecology.

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