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USGS2025

Relative abundance, seasonal occurrence, and distribution of marine birds in the northern Gulf of Mexico

Marine birds in the U.S. Gulf of Mexico have long been poorly studied. Given statutory obligations to protect migratory birds and endangered species, three broad-scale vessel and aerial programs initiated since 2010 have now surveyed the entire northern Gulf. Vessel coverage alone exceeds 700 d and 74,000 km of observer effort using 300-m strip transects. We supplemented these survey data with earlier, smaller-scale studies, eBird checklists, literature reviews, and other less accessible sources to create snapshot summaries of relative abundance, seasonal occurrence, and regional distribution for 117 taxa of marine and water birds reported from the northern Gulf (113 of which were substantiated with physical evidence). Using taxonomic and functional criteria, we identified 56 taxa characteristic of open shelf, slope, and pelagic waters (federal jurisdiction), 41 taxa with primarily coastal affinities (state and federal jurisdiction), and 20 taxa of sea and diving ducks. High species richness of marine birds in the northern Gulf is attributed to (1) a temperate-to-tropical gradient facilitating diverse marine environments year-round; (2) varied geographic origins of marine bird species using the Gulf; and (3) a mostly enclosed sea basin acting as a vagrant trap for wide-ranging species. Our taxonomic list and status updates seek to bridge information gaps for marine birds now subject to accelerated commercial uses of this region's continental shelf, including newly proposed offshore wind energy development. Other applications include guiding risk and vulnerability assessments of Gulf marine birds, providing core content for seabird observer training, and prioritizing environmental impact reviews and monitoring programs in offshore energy construction and operations plans.

Marine Ornithology: Journal of Seabird Research an↗

USGS1993

Population trends of Alaskan seabirds

Ornithology in Alaska formally began with the observations of Georg Wilhelm Steller during Vitus Bering's voyage of discovery in 1741. Steller's journal makes brief mention of various seabird species he encountered during his travels in the Gulf of Alaska and Aleutian Islands (Frost and Engel 1988). For more than 100 years following Steller, the Russian-American Company was active in commercial fur harvesting throughout southern coastal Alaska, but this period saw little contribution to a scientific understanding of the region's avifauna. With the purchase of Alaska by the United States in 1867, a period of American exploration began that included significant work by pioneering naturalists such as Dall (1873, 1874), Elliot (1881), Nelson (1883), and Turner (1885, 1886). While this activity established a comprehensive list and general knowledge of the distribution of seabird species occurring in Alaska, early observers provided no quantitative estimates of abundance for any colony or region. The observations of Heath (1915) and Willett (1912, 1915, 1917) at two locations in southeastern Alaska are notable for including the first numerical estimates of any seabird populations for comparison with recent data. Willett's (1912, 1915) estimates of 13 species are given in Table 1 with results from a 1976 Survey at Forrester Island (DeGange et al. 1977) and a 1981 survey at St. Lazaria Island (Nelson et al 1982). In the aggregate, seabird numbers appeared to increase dramatically at both sites, but the differences may be largely artificial. Because Willett (1915) did not employ rigorous sampling methods, DeGange et al. (1977) surmised that he grossly underestimated the populations of burrowing species such as storm-petrels, Cassin's Auklets. and Rhinoceros Aulkets. Nelson et al. (1982) offered a similar interpretation of total storm-petrel numbers at St. Lazaria, but felt that a shift in the species ratio of Leach's and Fork-tailed Storm-Petrels had likely occurred. It seems reasonably certain that real changes in some of the open-nesters like Common Murres (down at Forrester Island, up at St. Lazaria) and Glaucous-winged and Herring Gulls (absent or down at both sites) have occurred since Willet's time.

Alaska↗

USGS2014

Habitat and food preferences of the endangered Palila (Loxioides bailleui) on Mauna Kea, Hawai'i

Seeds and flowers of the leguminous māmane ( Sophora chrysophylla ) tree are the primary food resource of the federally endangered Palila ( Loxioides bailleui ; Fringillidae: Drepanidinae), which is now restricted to dry subalpine woodland on Mauna Kea Volcano on the island of Hawai'i because of centuries of habitat degradation by non-native ungulates. Palila are morphologically and behaviorally adapted to consume mÄmane seeds by grasping seed pods with their feet and opening pods with stout bills and demonstrate limited ability to exploit alternative food resources. This degree of single species dependency is rare among birds and illustrates unique adaptations that also occurred in other Hawaiian species that are now extinct. In mixed-woodland with co-dominant naio ( Myoporum sandwicense ), Palila spent 1.7-3.9 times longer in māmane than in naio during foraging observations where naio was 1.3-4.6 times as dense as māmane. Naio fruit was readily available, but it comprised proportionally <11% of food items taken by Palila. Although māmane flowers were more abundant than māmane pods throughout this study except at one lower-elevation mixed-woodland site, Palila spent more time foraging on pods than flowers in both māmane woodland and mixed-woodland, but consumed more flowers than pods in mixed-woodland. Insects, which have been reported as an important component of the diet of Palila, were apparently taken rarely in this study. Protecting and restoring māmane in woodlands adjacent to the current range of Palila will benefit their recovery, allowing them to exploit increased food availability in areas of their former range.

Hawai'i↗

USGS1993

Time-activity budget of Northern Pintails using nonhunted rice fields in southwest Louisiana (Presupuesto de actividades cotidianas por parte de individuos de anas acuta en campos de arroz no utilizados para cazar en el suroeste de Louisiana)

Monthly behavioral observations of Northern Pintails ( Anas acuta ) were conducted on five leased tracts of nonhunted private land, each including 60 ha of flooded rice fields, in southwest Louisiana during November-February 1988-1989. Pintails spent 52% of diurnal time resting, 21% feeding, 16% in comfort activities, 6% in locomotion, 4% courting and 1% in other behaviors. Activities differed among months and periods of the day. Pintails used nonhunted rice fields only during the day, departing after sunset. Pintail time budgets in Louisiana approximated those reported in California. Pintails using rice fields during the day, however, fed more than did those roosting on open water pools at Lacassine National Wildlife Refuge (NWR), Louisiana. Small (60 ha), nonhunted rice fields provided wintering Northern Pintails security plus food during the day. Desde noviembre a febrero de 1988-1989 hicimos observaciones mensuales de la conducta de individuos de Anas acuta en cinco localidades privadas y libres de cacería, del suroeste de Lousiana. Cada área incluyó un campo de arroz inundado de 60 hectáreas. Los patos emplearon el 52% del tiempo diurno para descansar, 21% para alimentarse, 16% para actividades de confort, 6% para locomoción, 4% para cortejo y 1% para otras actividades. Hubo diferencias en las actividades a través de los meses de estudio y períodos del día. Los patos utilizaron las áreas libres de cacería durante el período diurno y partieron de las mismas con la puesta del sol. El presupuesto de tiempo de las aves de Louisiana se aproximó a los informados en California para la especie. Sin embargo, los patos que utilizaron los campos de arroz se alimentaron más que los que descansaron en pozas del Refugio Nacional de Vida Silvestre de Lacassine. Los pequeños campos de arroz, libres de cacería, proveyeron a los patos invernales de lugares seguros y de alimentación durante el período diurno.

Louisiana↗

USGS2018

Population estimates of the Endangered Hawaiʻi ʻĀkepa (Loxops coccineus) in different habitats on windward Mauna Loa

Endangered Hawai‘i ʻĀkepas ( Loxops coccineus ) are endemic to Hawai‘i island, where they occur in five spatially distinct populations. Data concerning the status and population trends of these unique Hawaiian honeycreepers are crucial for assessing the effectiveness of recovery and management actions. In 2016, we used point‐transect distance sampling to estimate the abundance of Hawai‘i ʻĀkepas in portions of Hawai‘i Volcanoes National Park (HAVO) and the Kaʻū Forest Reserve (KFR) on Mauna Loa volcano. We then compiled the survey data from four other populations to provide a global population estimate. In our HAVO and KFR study area, we mapped habitat classes to determine the population densities in each habitat. Densities were highest (1.03 birds/ha) in open‐canopy montane ʻōhiʻa ( Metrosideros polymorpha ) woodland. In contrast, densities of the largest ʻĀkepa population on Mauna Kea volcano were highest in closed‐canopy ʻōhiʻa and koa ( Acacia koa ) forest where the species is dependent on nest cavities in tall (> 15 m), large (> 50‐cm diameter at breast height) trees. We surveyed potential nesting habitat in HAVO and KFR and found only one cavity in the short‐stature montane ʻōhiʻa woodland and five cavities in the tall‐stature forest. Differences in densities between the Mauna Kea and Mauna Loa populations suggest that Hawai‘i ʻĀkepas may exhibit different foraging and nesting behaviors in the two habitats. The estimated overall population density in the HAVO and KFR study area was 0.52 birds/ha, which equates to 3663 (95% CI 1725–6961) birds in their 11,377‐ha population range. We calculated a global population of 16,428 (95% CI 10,065–25,198) birds, which is similar to an estimate of 13,892 (95% CI 10,315–17,469) birds made in 1986. Our results suggest that populations are stable to increasing in the two largest populations, but the three other populations are smaller (range = 77–1443 birds) and trends for those populations are unknown.

Hawai'i↗

USGS2014

Selection of forest canopy gaps by male Cerulean Warblers in West Virginia

Forest openings, or canopy gaps, are an important resource for many forest songbirds, such as Cerulean Warblers ( Setophaga cerulea ). We examined canopy gap selection by this declining species to determine if male Cerulean Warblers selected particular sizes, vegetative heights, or types of gaps. We tested whether these parameters differed among territories, territory core areas, and randomly-placed sample plots. We used enhanced territory mapping techniques (burst sampling) to define habitat use within the territory. Canopy gap densities were higher within core areas of territories than within territories or random plots, indicating that Cerulean Warblers selected habitat within their territories with the highest gap densities. Selection of regenerating gaps with woody vegetation >12 m within the gap, and canopy heights >24 m surrounding the gap, occurred within territory core areas. These findings differed between two sites indicating that gap selection may vary based on forest structure. Differences were also found regarding the placement of territories with respect to gaps. Larger gaps, such as wildlife food plots, were located on the periphery of territories more often than other types and sizes of gaps, while smaller gaps, such as treefalls, were located within territory boundaries more often than expected. The creations of smaller canopy gaps, <100 m 2 , within dense stands are likely compatible with forest management for this species.

Wilson Journal of Ornithology↗

USGS2015

The nest-concealment hypothesis: New insights from a comparative analysis

Selection of a breeding site is critical for many animals, especially for birds whose offspring are stationary during development. Thus, birds are often assumed to prefer concealed nest sites. However, 74% of studies ( n = 106) that have evaluated this relationship for open-cup nesting songbirds in North America failed to support the nest-concealment hypothesis. We conducted a comparative analysis to identify factors that contribute to variation in the ability of researchers to find support for the nest-concealment hypothesis. We found that some of the discrepancy among studies can be explained by interspecific differences in morphological and extrinsic factors that affect nest predation. Moreover, methods that investigators used to estimate concealment affected whether studies found support for the nest-concealment hypothesis; 33% of the studies that used quantitative estimates found support for the nest-concealment hypothesis whereas only 10% of the studies that used qualitative estimates found support. The timing of measurements also explained some of the ambiguity; studies that provided little information regarding the timing of their foliage density estimates were less likely to support the nest-concealment hypothesis. Species with more conspicuous male plumage were less likely to support the nest-concealment hypothesis when we analyzed studies that used visual estimates. Whereas species with more conspicuous female plumage were more likely to support the nest-concealment hypothesis when we analyzed studies that used quantitative measures. Our results demonstrate that support for the nest-concealment hypothesis has been equivocal, but that some of the ambiguity can be explained by morphological traits and methods used to measure concealment.

Wilson Journal of Ornithology↗

USGS2014

Age-Ratios and Condition of En Route Migrant Blackpoll Warblers in the British Virgin Islands

The en route migration ecology of Blackpoll Warblers ( Setophaga striata ) is poorly understood, yet intriguing. Blackpoll Warblers undertake the longest open water migration of any wood warbler species, traveling from northeastern North America to South America, with the first potential landfall being the West Indies. This migration requires substantial energy reserves and subjects Blackpoll Warblers to unpredictable weather events, which may influence survival. Few studies have examined age ratios or condition of Blackpoll Warblers while the warblers are en route through the Caribbean region. I captured and banded Blackpoll Warblers in the British Virgin Islands over 10 consecutive autumn migrations. Ratios of hatch-year to adult Blackpoll Warblers were variable but averaged lower than the ratios reported at continental departure locations. Average mass of Blackpoll Warblers was less than that reported at continental departure locations, with 26% of adults and 40% of hatch-year birds below the estimated fat free mass; hatch-year birds were consistently in poorer condition than adults. Blackpoll Warblers captured in the British Virgin Islands were also in poorer condition than those reported from the Dominican Republic and Barbados; this may be because of the British Virgin Islands being the first landfall after the transatlantic crossing, whereas Blackpoll Warblers arriving at the other Caribbean study locations may have had opportunities for stopover prior to arrival or have departed from farther south on the continent. However, this suggests that the British Virgin Islands likely provide important stopover habitat as a first landfall location for Blackpoll Warblers arriving from the transatlantic migration route.

Guana Island↗

USGS2022

Demography and site fidelity of a grassland bird, the Henslow’s Sparrow, in powerline right-of-way habitat

Grassland birds are among the fastest declining avian species in North America, primarily due to habitat loss. In the southeastern U.S., much grassland and open savanna habitat has been converted to timber production or agriculture, neither of which typically provides habitat for breeding or wintering grassland birds. Powerline right-of-ways could provide suitable habitat for many grassland species as these areas are maintained to be treeless. We studied the population dynamics of Henslow’s Sparrows ( Centronyx henslowii ) wintering in powerline right-of-ways in southeastern Georgia through an 11-year mark-recapture study. We used a robust design Cormack-Jolly-Seber model to estimate probability of detection and apparent survival. Abundance varied substantially among years at each site, with density varying from 1.7 to 8.5 birds/ha. Within-year detection probability was moderately high at 28% (24-33%, 95% credible interval [CI]), but apparent survival was very low at 13% (9-17%, 95% CI). This low apparent survival was likely due to low return rates (and not necessarily low survival). However, birds that did return to the study sites had extremely high site fidelity, with 82% of across-year recaptures < 200 m apart. This apparent incongruity between low apparent survival rates (likely due to emigration from the study sites) and high site fidelity for returning individuals could be explained by the dependability of the right-of-way habitat, which differs from typically patchy and temporally variable grassland and savanna wintering habitats. Dependable habitat may allow for higher site fidelity than this species would otherwise have, potentially resulting in the high densities we observed. Thousands of miles of right-of-ways in Georgia, and other southeastern states, could be managed to maximize potential habitat for declining grassland bird species.

Georgia↗