Over an 18-year period (1987–2004), we examined variation in body mass of female Prothonotary Warblers (Protonotaria citrea) captured throughout their nesting cycle. As is typical for many small passerine birds, body mass was greatest during egg laying and decreased throughout incubation and feeding of young. Mass decreased significantly between the onset of incubation and fledging of both first and second broods. Mass loss was gradual during incubation, noteworthy during the first 2 days of feeding nestlings, but did not continue to decrease throughout the feeding period. Mass lost while raising the first brood was regained before initiating the second brood. Mass of female warblers, adjusted for effects of nest attempt, year, clutch size, and day and stage of nesting, increased slightly with age. Body mass of nesting female warblers varied significantly with day of the nest cycle during incubation but not during egg laying or feeding of young. Mass was associated with clutch size during incubation in both first and second broods, but was not associated significantly with brood size when females were feeding nestlings. Frequency of food delivery to nestlings was associated negatively with female body mass. Females typically made more feeding trips per day than males. Feeding rates were correlated among pairs; that is, females with higher rates of delivery were mated to males that made a higher number of trips.

In July 2001, a Louisiana State University Museum of Natural Science expedition rediscovered the White-masked Antbird (Pithys castaneus) at a site along the Río Morona in northwestern Departmento Loreto, Peru. Prior to this rediscovery, the species was known only from the type specimen, taken in 1937, and nothing was recorded concerning its natural history. The lack of additional specimens led to speculation that P. castaneus was a hybrid. Here, we present data demonstrating that the White-masked Antbird is a valid species, and we report the first observations of its behavior, habitat, morphology, and voice.

Despite the fact that the Lesser Prairie-Chicken (Tympanuchus pallidicinctus) is a species of conservation concern, little is known about its nesting ecology, particularly in sand sagebrush (Artemisia filifolia) habitats. To find and monitor nests, we captured and equipped 227 female Lesser Prairie-Chickens with transmitters (87 yearlings, 117 adults, and 23 of unknown age) from 1997 to 2002 in southwestern Kansas. Apparent nest success was similar for yearlings (31%, n = 74) and adults (27%, n = 97) but differed marginally (P = 0.090) between first nests (29%) and renests (14%). An estimated 31% of females that were unsuccessful in their first nesting attempt initiated a second nest. The probability that a female would initiate a second nest after failure of the initial attempt was negatively influenced by the day of incubation on which the initial attempt failed. Over 95% of all nests were initiated and completed between 5 May and 2 July. The primary cause of nest failure was predation by coyotes (Canis latrans) and gopher snakes (Pituophis melanoleucus). Mean clutch size, egg fertility, hatching success, nesting and renesting frequency, and incidence of interspecific parasitism were all similar across years and between yearlings and adults. Distances between nest sites were used as an index to nest-site fidelity between first nests and renests and for across-year nesting attempts. Mean distances between first nests and renests were similar for yearlings (1,071 m) and adults (1,182 m). Mean distance between nests constructed by the same female in subsequent years (918 m) did not differ between age classes or success of the first year's nest. Most females (80%) nested closer to a lek other than the lek where they were captured.

We compared male strut behavior of the genetically distinct Lyon, Nevada/Mono, California Greater Sage-Grouse (Centrocercus urophasianus) population with that of two proximal populations: Nye, Nevada, and Lassen, California. We measured strut rates and nine acoustic components of the strut display in all three populations. Male strut rates did not differ among populations. Acoustic components of the Lyon/Mono and Lassen populations were similar, whereas the Nye population was distinct. The genetically distinct Lyon/ Mono population was more similar behaviorally to the Nye population than the genetically similar Nye and Lassen populations were to each other. Overall, the Lyon/Mono population did not exhibit detectable differences in male strut behavior. Reproductive isolation through sexual selection does not appear to have occurred in the Lyon/Mono population.

We report a specimen that appears to be a hybrid between Swainson's Hawk (Buteo swainsoni) and Rough-legged Hawk (B. lagopus), which, to our knowledge, is the first hybrid specimen for the genus. There are few reports of hybridization between Buteo species, most of which have been observations of interspecific nesting pairs. The specimen described herein was collected in Louisiana and initially identified as a Rough-legged Hawk because of its feathered tarsi and the dark bellyband and carpals. A DNA sequence from the maternally inherited mitochondrial ND6 gene was identical to a published sequence for Swainson's Hawk. Nuclear DNA sequences from two introns contained only five variable sites among a panel of five potential parental taxa, but the hybrid sequence was most consistent with parentage by Rough-legged and Swainson's hawks. The feathered tarsi of the hybrid strongly suggested that the father was either a Rough-legged or Ferruginous hawk (B. regalis), the only North American raptors other than Golden Eagle (Aquila chrysaetos) that have feathered tarsi. Plumage and size characters were inconsistent with those of Ferruginous Hawk, and, other than the darkly pigmented leg feathers, were intermediate between the light morphs of Swainson's and Rough-legged hawks. The breeding range of Swainson's Hawk in Alaska and northern Canada is poorly known, but it overlaps that of the Rough-legged Hawk in at least a few locations, albeit at low densities, which may be a factor in hybridization. The occurrence of this hybrid is evidence of the potential for interbreeding between North American members of the genus Buteo, most of which are genetically closely related. Such hybridization could have implications for genetic diversity, adaptation, or the evolution of reproductive barriers. In any case, such hybrids present field and museum identification problems.

We report on nocturnal hunting by Peregrine Falcons (Falco peregrinus) at the Empire State Building in Manhattan, New York City. From 4 August through 13 November 2004, we saw Peregrine Falcons on 41 of 77 nights of observation. During this period, they hunted migrating birds on 25 evenings, with the first hunting attempt occurring an average of 119 min after sunset. Peregrine Falcons made 111 hunting attempts and captured 37 birds (33% success). Hunting success was highest in September, but was most often observed in October. Peregrines hunted migratory birds at night more frequently in autumn than in spring. Peregrines were significantly more likely to be present on autumn nights when >50 migrants were passing by the Empire State Building. Although the lights associated with skyscrapers are believed to disorient migrating birds and result in many bird-to-skyscraper collisions each year, Peregrine Falcons are able to take advantage of the situation. Skyscrapers provide hunting perches at altitudes often flown by nocturnal migrants, and disorientation caused by the lights sometimes results in birds circling skyscrapers and possibly becoming more vulnerable to predation by falcons.

I conducted 18 eggshell removal trials at six Mountain Plover (Charadrius montanus) nests in the Pawnee National Grassland, Weld County, Colorado, during June 1994. Eggshell fragments were placed at various distances (10 cm to 10 m) from active nests. Attending adult plovers removed eggshells throughout the incubation period. When eggshells were placed within 2 m of the nest, plovers usually removed them immediately upon their return to the nest. Shells placed farther away—up to 10 m—were removed after longer time intervals. Plovers removed shells by picking them up with their bills and running or flying away with them before dropping them 6 to 100 m from the nest. When returning to their nests, plovers approached by ground. Of the five hypotheses proposed in the literature to explain the function of eggshell removal behavior in birds, only one (reducing cues predators might use for finding nests) predicts removal of shells already outside the nest and disposal of shells far from the nest. Thus, my results support an anti-predator function for eggshell removal in Mountain Plovers.

I studied seed-size selection among Mourning Doves (Zenaida macroura) and Eurasian Collared-Doves (Streptopelia decaocto), two newly sympatric species for which mechanisms of seed selection are not well understood. I measured and compared mean length, breadth, and thickness of seeds available to, and consumed by, these species in feeding trials of penned birds. Both species selected corn (Zea mays) seeds that were shorter and narrower than average, but Eurasian Collared-Doves selected corn that was thicker than average and sunflower (Helianthus annuus) seeds that were broader and thicker than average. Mourning Doves consumed corn of average thickness, and wheat (Triticum aestivum) and sunflower seeds of average size with respect to all dimensions. Corn consumption by both species seems limited by seed length and breadth, but Mourning Dove consumption of smaller seed types (wheat and milo [Sorghum vulgare]) appears largely unaffected by seed size. Among larger seed types (corn and sunflower), Eurasian Collared-Doves may select thicker- and/or broader-than-average seeds to maximize foraging efficiency. Sunflower and corn seeds consumed did not vary between species with respect to any dimension, but Eurasian Collared-Doves seemed willing to select, and able to eat, broader and thicker seeds than Mourning Doves, which may limit foraging competition between these species.

Southeastern Illinois is dominated by cropland, and the remaining pastures or grasslands are marginally suitable for breeding Loggerhead Shrikes (Lanius ludovicianus), owing, in part, to limited nest sites. From 1998 through 2000, we recorded poor nest success (26%) among shrikes, although results of earlier studies (1967–1972) in this region indicated that nest success was 72 to 80%. Clutch size (5.7 eggs) and fledglings/ successful nest (4.4 young/successful nest) were similar to those reported in previous studies. During our study, generalist mammalian predators were abundant, and most nest failures (88%) were caused by predation. We suggest that the loss of grassland habitat and agricultural intensification has resulted in reduced nest success, and this may be true in other areas of the species' range as well.

Using video cameras, we documented at least two fledgling Loggerhead Shrikes (Lanius ludovicianus) visiting their parent's second active nest. We recorded 70 visits during a 10-day period, with visits averaging 7 min. We observed the fledglings sitting on the nest contents on 21 occasions. We concluded that these visits were not indicative of cooperative breeding behavior, because the fledglings were destructive to the nest structure and contents, and the adult female exhibited aggressive behavior toward the fledglings. An early reduction in post-fledging parental care by their father (who was of captive-bred origin) and slow development of the fledglings' hunting skills might have caused them to seek food resources from their mother. However, this is the first time that we have observed these behaviors in this intensively managed population.

We document the first breeding record of Mountain Plovers (Charadrius montanus) in the state of Nuevo Leon, Mexico. On 9 July 2004, we located a nest with two eggs and one chick in a colony of Mexican prairie dogs (Cynomys mexicanus). Mean height of vegetation near the nest was 7.1 cm, and bare ground cover was 41.2% (30 m² sampled). Although this record represents the second nesting for this species in Mexico, it is the first to document successful breeding.

The Double-collared Seedeater (Sporophila caerulescens) is the most common seedeater in southern South America. Because information on its breeding biology is mostly limited to descriptions of nests and eggs, I studied the reproductive biology of the Double-collared Seedeater in southeastern Brazil. I found 41 active nests during seven breeding seasons (1997–2003). Nesting occurred from December to May. All nests found during incubation contained two eggs, eggs were laid on consecutive days, and incubation started the morning the female laid the last egg. Incubation and nestling periods were 12 and 12–15 days, respectively. Only females incubated the eggs. Mean time spent incubating/hr was 52.3 min, and incubation recesses averaged 6.6 min. Nestlings were fed 7.6 times/hr, and although both males and females fed the young, the participation of females was significantly greater than that of males. Predation was the major cause of nest failure. Daily survival rates during the incubation (0.990) and nestling (0.935) stages differed. Overall nesting success was 36%. Although studies conducted in disturbed areas can reveal greater rates of nest predation than those found in undisturbed areas, some Sporophila species seem to benefit from habitat disturbance. The conversion of native habitats to agricultural lands in Brazil, as well as the spread of exotic grasses, has resulted in the expansion of the Double-collared Seedeater to previously forested areas.

We analyzed diet and prey selection of the relatively unknown albicaudatus subspecies of the White-tailed Hawk (Buteo albicaudatus). Our study was based on an analysis of 259 pellets collected from September 2000 to September 2001 in the municipality of Juiz de Fora in southeastern Brazil. We also assessed the abundance of small mammals with pitfall traps (2,160 trap-nights). Small mammals composed 52.5% of the estimated biomass consumed by the hawks, and selection appeared to be mediated by abundance. The Bonferroni confidence intervals procedure revealed that when abundance of small mammals was higher, the hawks were selective, preying on Calomys tener more than would be expected by chance (P < 0.05); other rodents were consumed less than expected. Oligoryzomys nigripes, Oxymycterus sp., and Gracilinanus spp. were taken in the same proportion as they were found in the field. During reduced prey abundance (October–March), White-tailed Hawks preyed opportunistically on small mammals. Differences in habits and vulnerability of small mammals may explain prey selectivity in the White-tailed Hawk.

Although post-fledging care by adult males seems unlikely in bird species that are obligate, interspecific brood parasites, there have been numerous reports of adult male Chrysococcyx cuckoos apparently feeding conspecific young. Most researchers currently view these observations with skepticism, in large part because Chrysococcyx and other cuckoo species engage in courtship feeding, and it is possible that field observers could mistake adult females receiving food from courting males for fledglings, especially given the similar appearances of females and juveniles. Here, we report an observation of an extended provisioning bout by an adult male Klaas's Cuckoo (C. klaas) feeding a conspecific individual with juvenile plumage and behavior, and we summarize our observations of similar occurrences in the Diederik Cuckoo (C. caprius) in Kenya. We suggest that the available evidence indicates that male provisioning, and hence potential parental care, is present in these brood-parasitic cuckoos at a higher frequency than currently recognized. The mechanism that causes males to associate with fledglings is unknown, but warrants further study.

I studied the diet and foraging behavior of fledgling Black-crowned Night-Herons (Nycticorax nycticorax) in a mixed-species nesting colony of Black-crowned Night-Herons and Snowy Egrets (Egretta thula) in New Orleans, Louisiana. In 1 of 5 years, cannibalism of nestlings that had fallen or climbed out of nests was common, accounting for 66 of 94 (70.2%) prey items taken by fledglings. Juveniles took younger conspecifics by both predation and scavenging. Isolated incidents of cannibalism among Black-crowned Night-Herons have been reported previously, but not on a colony-wide scale.

Black Terns (Chlidonias niger surinamensis) breed locally in freshwater wetlands across the northern United States and central Canada, often building their nests over shallow water on a floating substrate of matted marsh vegetation. Here, we report the first nesting record of this species on a coastal barrier island. The nest, which consisted of two eggs laid in a slight scrape of sand, was located on 6 July 2004 in a large breeding colony of Common Terns (Sterna hirundo) on Kelly's Island at Kouchibouguac National Park, New Brunswick, Canada. The observation also represents the current northeastern breeding limit for this species in North America. Both eggs hatched, but neither chick survived beyond 4 days.

On 21 May 2003, we discovered a completed Blue Grosbeak (Passerina caerulea) nest in an Eastern Bluebird (Sialia sialis) nest box. On 28 May, the nest contained four whitish-tan eggs with light-brown, streaky and spotty markings, an unusual color pattern for Blue Grosbeak eggs. Species' identification was confirmed by capturing the breeding female in the nest box, and confirmed again later with identification of the chicks as Blue Grosbeaks. To our knowledge, this is the first published account of cavity nesting, artificial or otherwise, for this species.

The ecology of the White-winged Nightjar (Eleothreptus candicans) is poorly known. Only three breeding populations (one from Brazil and two from Paraguay) are known, and populations are decreasing due to continuing destruction of cerrado habitat. On 14 September 2003, we took several photos of an unidentified nightjar in Beni Biosphere Reserve, Departmento Beni, Bolivia. The bird was later determined to be an adult male White-winged Nightjar. Interestingly, the only previous record for Bolivia was a male collected in 1987 at the same locality and time of year. Because the White-winged Nightjar is nonmigratory and secretive, we hypothesize that there may be a sustainable population of White-winged Nightjars in Bolivia, and the paucity of sightings may be due to the species' low detectability.

Great Blue Herons (Ardea herodias) typically prey upon fish and other aquatic organisms, and they occasionally take small mammals and birds. We observed a Great Blue Heron attack, kill, and attempt to consume an Eared Grebe (Podiceps nigricollis). The heron was unable to swallow the grebe, and it abandoned the carcass after approximately 30 min. An examination of the carcass showed that the grebe lacked obvious physical deformities. Our observation, coupled with a similar one nearby, indicates that Great Blue Herons attack and kill birds larger than reported previously.

A long-term (>5 years) study of Northern Bobwhite (Colinus virginianus) provided the first record of runt eggs and two observations of prolonged incubation. During 2004, we located two clutches (n = 11 and 9 eggs)—laid by the same hen— consisting entirely of runt eggs. Mean length, width, and mass were 18.8 mm, 15.4 mm, and 2.0 g, respectively, 26% of the volume and 24% of the mass of typical bobwhite eggs. Based on our long-term data set for bobwhites (n = 3,566 eggs), runt eggs occur at a frequency of 0.56%, within the range (0.02–4.32%) reported for other avian species. The two records of prolonged incubation behavior represented 75 days (326%) and 47 days (204%) beyond the normal incubation period (23 days) of bobwhites. This prolonged incubation behavior is in excess of the time frame reported for most birds exhibiting prolonged incubation (50–100% beyond normal incubation).