Abstract Great blue herons ( Ardea herodias ) represent important ecological indicators within aquatic ecosystems and local population trends may provide insight into ecosystem health. We surveyed heron colonies throughout the tidal reach of the Chesapeake Bay in 2013 to determine status and distribution and to make comparisons to previous (1975–1976, 1985, 1993, 2003) benchmark surveys. We located 423 colonies supporting 15,094 pairs distributed throughout the estuary. Compared to the 1975–1976 benchmark (37 colonies, 3,680 pairs), the number of colonies and estimated population have increased, with an average doubling time of 10.8 and 18.8 years, respectively. The majority of colonies were in supercanopy trees within continuous forests, along forest edges, or on isolated islands or marsh hammocks that provide for crown access. The size of colonies declined over the nearly 40‐year period (β = −0.032 ± 0.004, P < 0.001) with an annual rate of −3.2%. By 2013, <4% of all colonies had >100 pairs compared to 34% in 1985. The fragmentation or abandonment of large colonies and establishment of small colonies appears to be a response to the recovery of bald eagles ( Haliaeetus leucocephalus ). In 2013, most (60%) colonies accounted for <0.1% of the Bay‐wide population. The size distribution of colonies suggests that the equitable threshold between the burden borne by landowners (number of colonies protected) and the benefit to herons (proportion of population protected) lies somewhere between 25 and 50 pairs.

Summary The global population and status of Snowy Owls Bubo scandiacus are particularly challenging to assess because individuals are irruptive and nomadic, and the breeding range is restricted to the remote circumpolar Arctic tundra. The International Union for Conservation of Nature (IUCN) uplisted the Snowy Owl to “Vulnerable” in 2017 because the suggested population estimates appeared considerably lower than historical estimates, and it recommended actions to clarify the population size, structure, and trends. Here we present a broad review and status assessment, an effort led by the International Snowy Owl Working Group (ISOWG) and researchers from around the world, to estimate population trends and the current global status of the Snowy Owl. We use long-term breeding data, genetic studies, satellite-GPS tracking, and survival estimates to assess current population trends at several monitoring sites in the Arctic and we review the ecology and threats throughout the Snowy Owl range. An assessment of the available data suggests that current estimates of a worldwide population of 14,000–28,000 breeding adults are plausible. Our assessment of population trends at five long-term monitoring sites suggests that breeding populations of Snowy Owls in the Arctic have decreased by more than 30% over the past three generations and the species should continue to be categorised as Vulnerable under the IUCN Red List Criterion A2. We offer research recommendations to improve our understanding of Snowy Owl biology and future population assessments in a changing world.

During migration, birds make a variety of decisions that may impact their overall survival and fitness. These decisions include but are not limited to their overall migration route as well as their departure timing considering variable weather conditions. Understanding how birds make these decisions can provide insight into not only their general migration strategy, but also the constraints they face during migration. Unfortunately, the migratory ecology of many members of the Rallidae family remains poorly documented. From 2017 to 2022, we fitted 202 Porzana carolina (Sora) with transmitters at Jug Bay, a critical stopover site along the Patuxent River, Maryland, USA, and tracked their migratory movements and decisions using the Motus Wildlife Tracking System. Tracking data revealed a tendency to follow the Atlantic coast in the fall. Spring migrants took variable paths, with routes primarily to the Great Lakes region, and had shorter stopovers. We also determined the timing and atmospheric conditions under which P. carolina initiated migration. Rising atmospheric pressure 24 hr before departure increased departure likelihood, as did wind profit (favorable tailwinds), while increased cloud cover slightly reduced departure probability, possibly due to disrupted nighttime navigation. Porzana carolina may select these conditions to maximize their travel speed and limit likelihood of disorientation while aloft. This time-minimization strategy is offset by their extended stopovers on the ground, which extend the duration of their migration. Porzana carolina needs to spend more time fueling to ensure they have enough energy to survive any obstacles they face while en route. By looking at the migration strategies of this understudied species, we can better understand the constraints birds face on migration. center dot Motus Wildlife Tracking System was used to track migratory pathways and departure decisions of Porzana carolina (Sora).center dot Migrating P. carolina in the fall tended to follow coastal pathways en route to their wintering grounds while birds captured in the spring were most often tracked to sites in the Great Lakes, generally following inland routes.center dot P. carolina took extended stopovers at the study site, particularly in the fall. However, there was no evidence of a difference in stopover duration across age and sex classes.center dot Most P. carolina departed within 2 hr of civil dusk when the sun was between 6 and 25 degrees C below the horizon. Porzana carolina migrating in the fall favored departing on nights characterized by rising air pressure trends in the fall and tailwinds in both spring and fall. Birds also favored conditions with lower cloud cover, though to a lesser extent. Durante la migraci & oacute;n, las aves toman una variedad de decisiones que pueden afectar su supervivencia y aptitud biol & oacute;gica. Estas decisiones incluyen, entre otras, su ruta migratoria general, as & iacute; como su momento de partida considerando las condiciones clim & aacute;ticas variables. Comprender c & oacute;mo toman estas decisiones puede aportar informaci & oacute;n sobre su estrategia migratoria y tambi & eacute;n sobre las limitaciones que enfrentan durante la migraci & oacute;n. Lamentablemente, la ecolog & iacute;a migratoria de muchos miembros de la familia Rallidae sigue siendo poco conocida. Entre 2017 y 2022, colocamos transmisores a 202 individuos de Porzana carolina en la Bah & iacute;a Jug, un sitio cr & iacute;tico de parada a lo largo del R & iacute;o Patuxent, en Maryland, EUA, y rastreamos sus movimientos migratorios utilizando el sistema de seguimiento de fauna silvestre Motus. Los datos de rastreo revelaron una tendencia a seguir la costa atl & aacute;ntica durante el oto & ntilde;o. Los migrantes de primavera siguieron rutas variables, principalmente hacia la regi & oacute;n de los Grandes Lagos, y realizaron paradas m & aacute;s cortas. Tambi & eacute;n identificamos el momento y las condiciones atmosf & eacute;ricas bajo las cuales P. carolina iniciaba la migraci & oacute;n. El aumento de la presi & oacute;n atmosf & eacute;rica 24 horas antes de la partida incrementaba la probabilidad de salida, al igual que el beneficio del viento (vientos de cola favorables); en cambio, el incremento de nubosidad reduc & iacute;a ligeramente la probabilidad de partida, posiblemente debido a interferencias en la navegaci & oacute;n nocturna. P. carolina podr & iacute;a seleccionar estas condiciones para maximizar su velocidad de vuelo y reducir el riesgo de desorientaci & oacute;n en el aire. Esta estrategia de minimizar el tiempo en vuelo se compensa con paradas prolongadas en tierra, lo que extiende la duraci & oacute;n total de la migraci & oacute;n. P. carolina necesita pasar m & aacute;s tiempo aliment & aacute;ndose para garantizar suficiente energ & iacute;a para superar los obst & aacute;culos durante la ruta. Al examinar las estrategias migratorias de esta especie poco estudiada, podemos comprender mejor las limitaciones que enfrentan las aves durante la migraci & oacute;n.

Ongoing climate change can affect migration phenology in a variety of species. We assessed autumn migration phenology of Northern Saw-whet Owls (Aegolius acadicus) using 25 years of banding data from 7 sites throughout eastern North America. Using a linear mixed model, we found a significant trend toward a later passage for the median passage date. Phenological changes in migration could be a way to cope with changing environmental conditions.

Human-dominated environments often include ecological traps for wildlife, such as airports that may be perceived as suitable habitat by grassland birds but reduce fitness because of collisions with aircraft. Birds of prey are often attracted to airports where collisions with aircraft (i.e., bird strikes) are usually fatal for the birds and are a significant threat to flight safety. The snowy owl (Bubo scandiacus) is known for its nomadism, exhibiting unpredictable and highly variable movements during the nonbreeding season, including being a common visitor to airports, which often have high small-mammal populations and mimic flat, open habitats used naturally by owls. Since 2009, the Federal Aviation Administration reported an average of 22 snowy owl deaths annually due to aircraft collisions throughout 55 North American airports. To aid in active management of owls at airports, we assessed relocation data of 42 telemetry-tracked snowy owls from 2000-2020 in the United States and Canada. Owls that returned to the airport after relocation (33%) frequently crisscrossed and perched near runways where they were at risk of strikes. Adult females and immature males were more likely to return than the other sex and age classes, and returns were less likely to occur as the distance between the release site and the airport increased. Owls relocated in open habitats with a greater proportion of wetland and cropland (including grasslands and pasture) land cover classes were also less likely to return. We conclude that inclusion of multiple factors to limit return rates of relocated snowy owls from airport facilities can unspring the ecological trap presented by airports to these owls.

Marking birds with transmitters allows for the collection of data that are critical for fully understanding avian life history, but researchers must also be confident that performing such studies is as safe as possible for transmittered individuals. While much could be learned from tracking juveniles across dependency periods and first migration, doing so would require a harness-based attachment method which has not been evaluated on any species of juvenile tern. Therefore, we monitored the reproductive success and behavior of adult Common Terns (Sterna hirundo) and the growth and behavior of juvenile Common Terns after attaching transmitters to adults and juveniles with leg-loop harnesses made of elastic cord. We found that transmittered adults had similar reproductive success to untransmittered controls (hatching success for nests of transmittered adults = 0.553; nests of control adults = 0.665). Transmittered adults also expressed minimal behavioral differences from untransmittered controls when the groups were compared via paired treatment-control nest observations along with observations away from the nest. Transmittered juveniles had similar fledging success and growth rates to untransmittered control juveniles (fledging success for transmittered juveniles = 0.766; control juveniles = 0.817). Transmittered juveniles exhibited slight differences in behavior from controls, with increased rates of preening, although these differences did not appear to be detrimental. Finally, monitoring efforts during the breeding season following transmitter deployment found no difference in the return rate, nesting attempt rate, or hatching success rate based on treatment (P > 0.05). However, despite evidence of an individual retaining its transmitter into fall migration, no individuals retained their transmitters when resighted the following breeding season. While our results show that leg-loop harnesses made of elastic cord present a potential option for transmitter attachment to both adult and juvenile Common Terns, additional testing could provide further insight into potential long-term impacts.

Population estimates derived from monitoring efforts can be sensitive to the survey method selected, potentially leading to biased estimates and low precision relative to true population size. While small unmanned aerial systems (UAS) present a unique opportunity to survey avian populations while limiting disturbance, relatively little is known about how this method compares with more traditional approaches. In this study we compared population estimates of Snowy (Egretta thula) and Cattle Egrets (Bubulcus ibis) in a mixed-species colony in the Chesapeake Bay (Maryland, USA) derived from UAS photo counts, flush counts, flight-line surveys, and in-colony nest counts along with the time required to derive an estimate via each approach. We found that UAS counts and flush counts produced lower pair estimates than nest counts and flight-line surveys (P < 0.05), and required dramatically less time (x- = 6, 8, 84 and 90 min, respectively). These results suggest that while UAS have the potential to collect valuable survey data from breeding colonies that are hard to reach or are especially sensitive to the disturbance inherent in other methods, inherent biases should be considered and caution should be used when comparing results between survey types. Received 26 Mar 2021, accepted 21 Sept 2022.

Divergent life histories by sex are common within species of birds; thus, the ability to accurately determine sex is essential in many studies of avian ecology and can possibly lead to more effective conservation strategies. However, sex determination can be difficult in species not displaying dimorphic plumage, including most raptors, and size dimorphism has limited use during observations but is promising for determining sex of raptors in hand. The Broad-winged Hawk (Buteo platypterus), known for its longdistance migrations between North and South America, has yet to be examined for morphometric variation across its wide range. We analyzed body mass, wing chord, and tail length data for 119 adult Broad-winged Hawks captured in eastern North America during the breeding seasons from 1974 to 2020. We found that adult female Broad-winged Hawks were larger than adult males overall. Hawks from Wisconsin were larger than hawks from Pennsylvania and Maryland, and hawks from Ontario were larger than those from other populations, suggesting geographic variation in size. Using linear discriminant analysis, we showed that it was possible to determine sex of adults with 99% accuracy in Wisconsin populations using only body mass as a predictor, and 100% accuracy in Pennsylvania and Maryland populations using body mass, wing chord, and tail length as predictors. Morphometric measurements combined with discriminant function analysis proved useful in discerning sex of breeding-season Broad-winged Hawks, and results of this study can guide researchers working in similar regions. We encourage researchers to collect body measurements for this species and other monomorphic raptors to further inform sex determination.

Migrating animals occur along a continuum from species that spend the nonbreeding season at a fixed location to species that are nomadic during the nonbreeding season, essentially continuously moving. Such variation is likely driven by the economics of territoriality or heterogeneity in the environment. The Snowy Owl (Bubo scandiacus) is known for its complex seasonal movements, and thus an excellent model to test these ideas, as many individuals travel unpredictably along irregular routes during both the breeding and nonbreeding seasons. Two possible explanations for this large variation in the propensity to move are (1) dominance hierarchies in which dominant individuals (adult females in this case) monopolize some key, consistent resources, and move less than subdominants; and (2) habitat heterogeneity in which individuals foraging in rich and less heterogenic environments are less mobile. We analyzed fine-scale telemetry data (global positioning system [GPS]/global system for mobile communication [GSM]) from 50 Snowy Owls tagged in eastern and central North America from 2013 to 2019, comparing space use during the winter period according to sex and age, and to land cover attributes. We used variograms to classify individuals as nomadic (58%) or range-resident (42%), and found that nomadic owls had ten times larger wintering areas than range-resident owls. The frequency of nomadism was similar in socially-dominant adult females, immatures, and males. However, nomadism increased from west to east, and north to south, and was positively associated with the use of water and negatively associated with croplands. We conclude that many individual Snowy Owls in Eastern North America are nomadic during the nonbreeding season and that movement patterns during this time are driven primarily by extrinsic factors, specifically heterogeneity in habitat and prey availability, as opposed to intrinsic factors associated with spacing behavior, such as age and sex.

Whereas most migratory animals, such as many birds of prey, return to the same breeding area each summer, nomadic breeders search over large distances to locate breeding areas that vary greatly in location from year to year. Nomadic breeders are assumed to extensively sample patch quality before selecting a summer settlement site (e.g. breeding site) with a high abundance of prey. In addition, patch selection during migration might vary, with immature birds sampling the summer environment for the first time. Here, we examined the migratory movements of a nomadic breeder, the Snowy Owl, to determine whether there are differences in phenology among age and sex classes, and where stopovers occur along their migratory journey. Each owl (n = 24) was equipped with a GPS‐GSM transmitter during the overwintering period in the USA and Canada from 2014 to 2018. Movement patterns followed a two‐process Poisson distribution, allowing us to separate stopovers from directional flights (i.e. migration). Adults completed migration earlier than immatures, with no difference in number of stopovers or time spent at each stopover. Snowy Owls had a higher probability of having a stopover at the beginning of their migration than at the end. Moreover, stopovers occurred primarily on frozen waterbodies more suitable for foraging or roosting outside of the summer range. We conclude that Snowy Owls use stopovers primarily to build up reserves or to rest during migration and they can potentially select appropriate summer settlement sites via short overflights without extensive sampling of patches during lengthy stopovers.

Eastern Black Rails (Laterallus jamaicensis jamaicensis) were surveyed during 1990, 2007, 2014 within the Chesapeake Bay region in Maryland and Virginia, USA. A network of point count locations (n = 182) was established and surveyed within tidal salt marshes. Occupancy declined during the study period from 0.84 +/- 0.13 (. +/- SE) in 1990 to 0.06 +/- 0.02 in 2014. The annualized rate of decline was estimated to be 6.5%. Extinction and colonization rates between 1990 and 2014 were 0.81 +/- 0.09 and 0.04 +/- 0.02 respectively. Abundance declined from 1.98 +/- 0.05 Black Rails/point in 1990 to 0.26 +/- 0.02 in 2014 with a 3.2% annualized rate of decline. Recruitment was 1.32 +/- 1.35 between 1990 and 2007 and 0.003 +/- 0.05 between 2007 and 2014. Species detection was negatively influenced by advancing season and waxing moon phase while individual detection was most strongly influenced by survey year and advancing season. Anecdotal observations of range-wide strongholds within the Chesapeake Bay suggest that sites have experienced significant declines with birds being extirpated by 2016. Declines throughout the core breeding area and within individual strongholds in the Chesapeake Bay are consistent with Black Rail declines in tidal habitats throughout the broader Northeast region.

Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption years. This could occur if subordinate individuals (mainly immatures) are forced into suboptimal habitats due to density-dependent effects in irruption years. To test whether irruptive individuals had lower survival than non-irruptive ones, we combined necropsy results (N = 365) with telemetry (N = 185) from more than 20 years to record timing and causes of mortality in snowy owls (Bubo scandiacus), which irrupt into eastern North America during winter following high breeding output caused by lemming peaks in the Arctic. Mortality was more than four times higher in irruption years than non-irruption years, but only for immatures, and occurred disproportionately in early winter for immatures, but not adults. Mortality was also higher in eastern North America, where owl abundance fluctuates considerably between years, compared to core winter regions of the Arctic and Prairies where populations are more stable. Most mortality was not due to starvation, but rather associated with human activity, especially vehicle collisions. We conclude that immature snowy owls that irrupt into eastern North America are limited by density-dependent factors, such as increased competition forcing individuals to occupy risky human-altered habitats. For highly mobile, irruptive animals, resource pulses may have a limited impact on population dynamics due to low subsequent survival of breeding output during the nonbreeding season.

Background While nest attentiveness plays a critical role in the reproductive success of avian species, nest attentiveness data with high temporal resolution is not available for many species. However, improvements in both video monitoring and temperature logging devices present an opportunity to increase our understanding of this aspect of avian behavior. Methods To investigate nest attentiveness behaviors and evaluate these technologies, we monitored 13 nests across two Common Tern ( Sterna hirundo ) breeding colonies with a paired video camera - temperature logger approach, while monitoring 63 additional nests with temperature loggers alone. Observations occurred from May to August of 2017 on Poplar (Chesapeake Bay, Maryland, USA) and Skimmer Islands (Isle of Wight Bay, Maryland, USA). We examined data respective to four times of day: Morning (civil dawn‒11:59), Peak (12:00‒16:00), Cooling (16:01‒civil dusk), and Night (civil dusk‒civil dawn). Results While successful nests had mostly short duration off-bouts and maintained consistent nest attentiveness throughout the day, failed nests had dramatic reductions in nest attentiveness during the Cooling and Night periods ( p < 0.05) with one colony experiencing repeated nocturnal abandonment due to predation pressure from a Great Horned Owl ( Bubo virginianus ). Incubation appeared to ameliorate ambient temperatures during Night, as nests were significantly warmer during Night when birds were on versus off the nest ( p < 0.05). Meanwhile, off-bouts during the Peak period occurred during higher ambient temperatures, perhaps due to adults leaving the nest during the hottest periods to perform belly soaking. Unfortunately, temperature logger data alone had limited ability to predict nest attentiveness status during shorter bouts, with results highly dependent on time of day and bout duration. While our methods did not affect hatching success ( p > 0.05), video-monitored nests did have significantly lower clutch sizes ( p < 0.05). Conclusions The paired use of iButtons and video cameras enabled a detailed description of the incubation behavior of COTE. However, while promising for future research, the logistical and potential biological complications involved in the use of these methods suggest that careful planning is needed before these devices are utilized to ensure data is collected in a safe and successful manner.

Migratory species display a range of migration patterns between irruptive (facultative) to regular (obligate), as a response to different predictability of resources. In the Arctic, snow directly influences resource availability. The causes and consequences of different migration patterns of migratory species as a response to the snow conditions remains however unexplored. Birds migrating to the Arctic are expected to follow the spring snowmelt to optimise their arrival time and select for snow-free areas to maximise prey encounter en-route. Based on large-scale movement data, we compared the migration patterns of three top predator species of the tundra in relation to the spatio-temporal dynamics of snow cover. The snowy owl, an irruptive migrant, the rough-legged buzzard, with an intermediary migration pattern, and the peregrine falcon as a regular migrant, all followed, as expected, the spring snowmelt during their migrations. However, the owl stayed ahead, the buzzard stayed on, and the falcon stayed behind the spatio-temporal peak in snowmelt. Although none of the species avoided snow-covered areas, they presumably used snow presence as a cue to time their arrival at their breeding grounds. We show the importance of environmental cues for species with different migration patterns.

Due to the low detectability of Northern Saw-whet Owls (Aegolius acadicus; hereafter, NSWO) throughout their annual cycle, standardized monitoring during migration allows for population assessments over time. We assessed age-class population trends in NSWO throughout eastern North America using banding data from 7 sites over a 25 year period. Using a mixed linear model, we did not detect any significant trends over time for the total owl count, adult owl count, and juvenile owl count from 1992 to 2017. During the period when all 7 sites were active from 2001 to 2017, trend estimates remained nonsignificant despite showing negative slopes. We confirmed this nonsignificant, negative trend through a similar mixed linear model of NSWO data from Christmas Bird Counts. Our results suggest that NSWO populations across eastern North America have been relatively stable since 1992 throughout their migration and winter ranges and demonstrate the value of standardized banding data for monitoring the regional population status of NSWO.

Despite extensive accounts in the literature describing Barred Owls (Strix varia) as obligate forest-interior species, Barred Owls have increasingly been observed in urbanized landscapes. To determine if certain habitat characteristics, such as mature urban trees, facilitate the occurrence of Barred Owls in developed regions, we deployed GPS transmitters on 20 breeding Barred Owls in northwestern South Carolina. We selected territories containing a gradient of development density and habitat types to examine predictors of home range size and habitat selection along an urban-rural gradient. We related nocturnal locations to habitat features using resource selection functions (RSFs). We explored differential use along a development gradient by modeling interactions between habitat parameters and measures of development in the home range. Home range size varied from 0.38 km(2)to 3.38 km(2); size increased with the percentage of treeless area in the territory such as agricultural fields and power lines. Distance to nest, tree height, and distance to canopy edge were the most important predictors of owl use. Barred Owl selection for roadsides and aquatic features increased with degree of fragmentation in the home range. This is the first resource selection study using GPS data to examine habitat use of Barred Owls in the context of development. Our results highlight the behavioral plasticity of a species previously described as sensitive to anthropogenic impacts. The presence of this large avian predator in urban forests suggests that retaining key habitat features can promote multi-trophic communities even when other aspects of the habitat are highly altered.

Scientific study of raptors often requires the use of a lure to capture individuals for marking or collecting various data and samples. Live lure owls in the genus Bubo are commonly used with mist nets or dho-gazas to trap nesting raptors, but the use of these live lures presents ethical, logistical, and financial challenges. Although owls mounted by taxidermists and mechanical owls have been used in place of a live bird, the success of these types of lures varies widely. We created a more realistic mechanical owl with a greater range of motion than previous models, and then tested the owl on six raptor species in a variety of habitats. For all but one species, capture rates using our mechanical owl were similar to or slightly higher than those reported in studies using live lure owls or previously designed mechanical owls. Time to rapture of Northern Goshawks (Accipiter gentilis) was, on average, 8 min faster when using our mechanical owl compared to a live owl. Cost analysis revealed that both the initial expense and long-term maintenance of a mechanical owl were less than that of a live lure owl. Mechanical owls can be a useful tool for capturing raptors. Although there are some drawbacks to using a mechanical owl, our results suggest that mechanical birds are comparable to live lure owls and we believe the benefits of using a mechanical owl often outweigh the costs.

Patterns of winter irruptions in several owl species apparently follow the ‘lack of food’ hypothesis, which predicts that individuals leave their breeding grounds in search of food when prey populations do not allow breeding and are too small to ensure survival. Recent analyses, however, suggest an alternative mechanism dubbed the ‘breeding success’ hypothesis, which predicts that winter irruptions might instead be the result of a very successful breeding season, with a large pool of young birds subsequently migrating south from the breeding grounds. Here we assessed age‐class (juvenile vs. non‐juvenile) composition of winter irruptive Snowy Owls Bubo scandiacus over a 25‐year period (winter 1991–1992 to 2015–2016) between regular (North American Prairies and Great Plains) and irregular wintering areas (northeastern North America) using live‐trapped individuals and high‐resolution images of individual owls. Our results show that the proportion of juveniles (birds less than 1 year of age) varies considerably annually but is positively correlated with irruption intensity in both regions. In irregular wintering areas, it can constitute the majority (up to more than 90%) of winter irruptive Snowy Owls over a large geographical area. These results are consistent with the idea that large winter irruptions at temperate latitudes are not the result of adults massively leaving the Arctic in search of food after a breeding failure but are more likely to be a consequence of good reproductive conditions in the Arctic that create a large pool of winter migrants.

Many waterbird populations have faced declines over the last century, including the common tern (Sterna hirundo), a waterbird species with a widespread breeding distribution, that has been recently listed as endangered in some habitats of its range. Waterbird monitoring programs exist to track populations through time; however, some of the more intensive approaches require entering colonies and can be disruptive to nesting populations. This paper describes a protocol that utilizes a minimally invasive surveillance system to continuously monitor common tern nesting behavior in typical ground-nesting colonies. The video monitoring system utilizes wireless cameras focused on individual nests as well as over the colony as a whole, and allows for observation without entering the colony. The video system is powered with several 12 V car batteries that are continuously recharged using solar panels. Footage is recorded using a digital video recorder (DVR) connected to a hard drive, which can be replaced when full. The DVR may be placed outside of the colony to reduce disturbance. In this study, 3,624 h of footage recorded over 63 days in weather conditions ranging from 12.8 °C to 35.0 °C produced 3,006 h (83%) of usable behavioral data. The types of data retrieved from the recorded video can vary; we used it to detect external disturbances and measure nesting behavior during incubation. Although the protocol detailed here was designed for ground-nesting waterbirds, the principal system could easily be modified to accommodate alternative scenarios, such as colonial arboreal nesting species, making it widely applicable to a variety of research needs.

Winter irruptions, defined as irregular massive movement of individuals over large distances, have been linked to food supply. Two hypotheses have been put forward: the “lack-of-food” suggests that a shortage of food forces individuals to leave their regular winter range and the “breeding output” suggests that unusually large food supplies during the preceding breeding season allows production of a large number of offspring dispersing in winter. According to the breeding output hypothesis, irruptive Snowy Owls (Bubo scandiacus (Linnaeus, 1758)) in eastern North America should not exhibit a lower body condition than individuals in regular wintering regions and individuals on the breeding grounds. Additionally, body condition of irruptive individuals should be unrelated to irruption intensity. Although body condition of juveniles was generally lower than that of adults and improved during the winter, we measured a fair body condition in both juvenile and adult irruptive Snowy Owls across North America. The results showed that Snowy Owls are not in a starving state during winter and that body condition of all age classes was not related to winter irruption intensity. Those results support the breeding output hypothesis suggesting that winter irruptions seem to be primarily the result of a large number of offspring produced when food availability on the breeding grounds is high.