bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Governing the Distribution of Swainson's Warbler Along a Hydrological Gradient in Great Dismal Swamp
Authors: Graves Gary R.
Published: September 2019

Due to extensive clearing of bottomland forest in the southeastern United States, Swainson's Warbler (Limnothlypis swainsonii) is restricted in many drainages to seasonally inundated buffer zones bordering rivers and swamps. This migratory species is especially vulnerable to flooding because of its ground foraging ecology, but little is known about patterns of habitat occupancy at wetland ecotones. I investigated the physiognomic and floristic correlates of habitat use along a subtle hydrological gradient in the Great Dismal Swamp, southeastern Virginia. Hydrology is the driving force influencing vegetation and the distribution of Swainson's Warbler in that habitat. Foraging and singing stations of territorial males were significantly drier and more floristically diverse than unoccupied habitat. There was scant evidence that the distribution and abundance of particular plant species, including giant cane (Arundinaria gigantea), influenced habitat selection. Instead, Swainson's Warbler seems to evaluate potential territories on the basis of multiscale physiognomic, hydrological, and edaphic characteristics. Territories were characterized by extensive understory thickets (median = 36,220 small woody stems and cane culms per hectare; range, 14,000–81,400/ha), frequent greenbriar tangles, deep shade at ground level, and an abundance of leaf litter overlying moist organic soils. Those sites occurred most frequently in relatively well-drained tracts of broad-leaf forest that had suffered extensive canopy damage and windthrow. Data suggest a preference for early successional forest in the current landscape or disturbance gaps in primeval forest. Because territories in otherwise optimal habitat are abandoned when flooding extends into the breeding season, it is recommended that the water table be maintained at subsurface levels from late March through September in natural areas managed primarily for this species. Direct and indirect environmental factors that influence the breeding biology of the warbler are summarized in an envirogram.
Activity Patterns and Effect of Ticks on Growth and Survival of Tropical Roseate Tern Nestlings
Authors: Ramos Jaime A. , Bowler John , Davis Laura , Venis Sarah , Quinn John , Middleton Carole
Published: September 2019

Patterns of abundance of the seabird tick Amblyomma loculosum and their effects on Roseate Tern (Sterna dougallii) nestling growth, fledging age, and survival are described on Aride Island, Seychelles, in 1997–1999. Female ticks attached to nestlings from 4 to 14 days (to engorge) whereas male ticks attached for 1–3 days. The linear growth rate of birds carrying female ticks (0.24 g/day) was significantly different from that of nonparasitized nestlings of the same age and similar (or even lower) hatching weight (4.07 g/day). Parasitized nestlings that fledged did so 5.2 days later than nonparasitized nestlings of similar age. Only 37.5% of the nestlings infested with female ticks fledged compared with 83.3% of the noninfested nestlings. During the successful 1998 breeding season, around 100 nestlings died from tick infestation (24.3% of the nestling deaths). Ticks appeared to accelerate nestling mortality during periods of food shortage. Despite an annual difference of two weeks in the timing of breeding of the Roseate Terns between 1997 and 1998, adult ticks parasitized nestlings in July, with an infestation peak occurring between 8–12 July in both years. However, in 1997, nestlings were parasitized at a younger age, suggesting that ticks (nymph stage) must attach to Roseate Tern adults as soon as they make a nest scrape (usually in May). Ironically, the frequent breeding failures of the Roseate Terns will result in lower infestation levels in subsequent years, which will benefit the birds.
Phylogenetic Utility of Avian Ovomucoid Intron G: A Comparison of Nuclear and Mitochondrial Phylogenies in Galliformes
Authors: Armstrong Margaret H. , Braun Edward L. , Kimball Rebecca T.
Published: September 2019

A novel nuclear marker, the avian ovomucoid intron G (OVOG) was sequenced from 19 galliform taxa. Results of the phylogenetic analyses using OVOG were compared to those obtained using the mitochondrial cytochrome b (cytb) gene to determine the phylogenetic utility of OVOG. OVOG appeared to have strong phylogenetic signal for reconstructing relationships among genera and families, and the only difference between OVOG and cytb was in the placement of the New World quail (Odontophoridae). Genetic distances estimated using OVOG are approximately half of those estimated using cytb, although that relationship was not linear. OVOG exhibited patterns of nucleotide substitution very different from cytb, with OVOG having little base compositional bias, a relatively low transition–transversion ratio, and little among-site rate heterogeneity.
Stable-Isotope Analysis of Canvasback Winter Diet in Upper Chesapeake Bay
Authors: Haramis G. Michael , Jorde Dennis G. , Macko Stephen A. , Walker Jane L. , Karasov W. H.
Published: September 2019

A major decline in submerged aquatic vegetation (SAV) in Chesapeake Bay has altered the diet of wintering Canvasbacks (Aythya valisineria) from historically plant to a combination of benthic animal foods, especially the ubiquitous Baltic clam (Macoma balthica), supplemented with anthropogenic corn (Zea mays). Because the isotopic signature of corn is readily discriminated from bay benthos, but not SAV, we used stable-isotope methodology to investigate the corn–SAV component of the winter diet of Canvasbacks. Feeding trials with penned Canvasbacks were conducted to establish turnover rates and fractionation end-point loci of δ13C and δ15N signatures of whole blood for individual ducks fed ad libitum diets of (1) Baltic clams, (2) Baltic clams and corn, and (3) tubers of wild celery (Vallisneria americana). Turnover time constants averaged 4.5 weeks, indicating that signatures of wild ducks would be representative of bay diets by late February. Isotopic signatures of wild Canvasbacks sampled in February fell on a continuum between end-point loci for the Baltic clam and the combination Baltic clam and corn diet. Although that finding verifies a clear dependence on corn–SAV for wintering Canvasbacks, it also reveals that not enough corn–SAV is available to establish ad libitum consumption for the 15,000+ Canvasbacks wintering in the upper bay. On the basis of mean δ13C signature of bay Canvasbacks (n = 59) and ingestion rates from feeding trials, we estimated that 258 kg corn per day would account for the observed δ13C enrichment and supply 18% of daily energetic needs for 15,000 Canvasbacks. That level of corn availability is so realistic that we conclude that SAV is likely of little dietary importance to Canvasbacks in that portion of the bay.
Avian Nesting Success in Forested Landscapes: Influence of Landscape Composition, Stand and Nest-Patch Microhabitat, and Biotic Interactions
Authors: Rodewald Amanda D. , Yahner Richard H. , Brawn J.
Published: September 2019

Although area and isolation effects on avian communities in highly fragmented landscapes are well known, importance of landscape composition in more forested landscapes remains poorly understood. We determined if the type (agriculture and silviculture) and extent (percentage within 1 km radius) of disturbance within forested landscapes influenced avian nesting success, and then examined if differences in stand-level habitat structure, nest-patch microhabitat, distance of nests to habitat edges, brood parasitism rates, and nest-predator abundance were potential underlying mechanisms of observed associations between landscape composition and nesting success. We monitored active songbird nests (n = 341), surveyed Brown-headed Cowbirds (Molothrus ater) and nest predators, and measured stand-level and nest-patch microhabitat from May–July 1998 and 1999. Each of 10 study sites was located within contiguous mature forest in central Pennsylvania and contained either agricultural or silvicultural disturbances (n = 5 each). Sites of the two landscape types had similar ranges of disturbance within 1 km (21–55% for agriculture, 18–51% for silviculture). Daily nest survival for all species combined (94.0 ± 0.55 in agriculture and 96.9 ± 0.87 in silviculture) and midstory-canopy nesters (93.8 ± 0.97 in agriculture and 97.4 ± 0.75 in silviculture) were greater within forested landscapes disturbed by silviculture than by agriculture, but rates did not significantly differ between landscapes for ground nesters (92.2 ± 1.32 in agriculture and 94.6 ± 1.63 in silviculture) or understory nesters (95.4 ± 1.60 in agriculture and 95.0 ± 1.47 in silviculture). Nest survival was not significantly associated with disturbance extent. Rates of brood parasitism were low, with only 11% of nests containing cowbird eggs or young. Neither nest fate nor differences in daily nest survival between the two landscape types were explained by variation in brood parasitism rates, stand-level or nest-patch habitat characteristics, or distance of nests to edges. Instead, the lower nest success within forested landscapes disturbed by agriculture was best explained by greater abundances of some avian and small mammalian predators (American Crow [Corvus brachyrhynchos] and squirrels) in those landscapes in one or both years. Results suggest that landscape composition within forested landscapes significantly influences avian nesting success by altering interactions between nest predators and nesting birds.
Nest Defense as Parental Care in the Northern Hobby (Falco subbuteo)
Authors: Sergio Fabrizio , Bogliani Giuseppe , Bildstein K.
Published: September 2019

Intensity of nest defense against a human intruder was recorded for 42 male and 43 female Northern Hobbies (Falco subbuteo) from 1992 to 1994. Defense did not vary between repeatedly and rarely visited nests. Except during incubation, intensity of nest defense by females was higher than that by males. For both sexes, defense intensity increased from incubation to fledging, within the nestling stage, and from fledging to the first 10 days of the postfledging period. Intensity of nest defense was positively correlated with brood size in females, but not in males. Experiments with dummy nests showed that defense was effective in deterring nest predation, and that its effect was positively related to its intensity. Hobby nest defense was an individually varying “plastic” trait, probably tuned to the reproductive value of the offspring. Parents apparently trade off the costs and risks of the behavior against the increasing likelihood of offspring survival.
Experimental Support for a New Drift Block Design to Assess Seabird Mortality from Oil Pollution
Authors: Wiese Francis K. , Jones Ian L. , Nettleship D.
Published: September 2019

Seabird mortality from large oil spills and chronic oil pollution is often significant. Total mortality estimates are derived from counts of dead birds that wash ashore and are corrected for numbers lost at sea. Past attempts to estimate proportion of birds that die at sea and wash ashore have included several experiments using carcasses and different types of wooden drift blocks. Results varied greatly depending on environmental conditions and distance from shore where blocks or carcasses were released. Wind seemed to be the predominant factor determining movement over large distances, whereas tidal currents influenced deposition on specific beaches. Determining timing and location of arrival of dead birds on beaches are crucial for accurate mortality estimates. Drift experiments using beached birds that have already drifted at sea for an undetermined length of time are inaccurate due to natural buoyancy loss and decomposition. To determine accuracy of drift block designs used in the past, we compared drift characteristics and patterns between four drift block designs and fresh murre (Uria spp.) carcasses. Our experiments showed that drift blocks used in the past have none of the drift characteristics of dead seabirds, because they have much larger areas exposed to wind and hence drift much faster and farther than murre carcasses. Past mortality estimates using those blocks are therefore doubtful. The drift block design that most accurately mimicked murre carcass drift during our experiments was a 9 × 9 × 14.5 cm wooden block with a 450 gram steel weight that adjusts buoyancy and area exposed to the wind. We propose that in areas where murres are predominant victims of oil spills, that block design be used for all future estimates of oiled seabird mortality.
Fitness-related Consequences of Relaying in an Arctic Seabird: Survival of Offspring to Recruitment Age
Authors: Hipfner J. Mark , Nettleship D.
Published: September 2019

Seasonal declines in rates of renesting following clutch loss are common features of avian breeding, and are generally thought to reflect underlying seasonal declines in food availability that lower survival prospects for late-season offspring. However, in Thick-billed Murres (Uria lomvia), long-lived Arctic seabirds that lays a single-egg clutch, previous research has shown that early laying females will continue to relay until late in the laying period. Moreover, hatching success is similar between first and replacement attempts, as are nestling growth and survival, when parental quality is controlled. I compared survival between departure from the breeding site and recruitment age (4–5 years) for Thick-billed Murres that hatched from first and replacement eggs, but that were raised by parents that laid their first eggs early in the season. Replacement-egg offspring hatched and departed the colony about three weeks later than did first-egg offspring, but despite that, they were no less likely to survive to recruitment age. That result indicates that the potential fitness payoff from a replacement egg is similar to that from a first egg for the more capable members of the population. I suggest that an adequate and predictable late-season food supply ultimately underlies the considerable relaying capacity exhibited by Thick-billed Murres.
Protein Requirements of a Specialized Frugivore, Pesquet's Parrot (Psittrichas fulgidus)
Authors: Pryor Gregory S. , Levey Douglas J. , Dierenfeld Ellen S. , Bosque C.
Published: September 2019

For those few bird species that are exclusively frugivorous, the low protein content of fruits is likely a major nutritional constraint. Physiological mechanisms that allow strict frugivory remain enigmatic, but reduced protein requirements may suffice. We investigated protein requirements of Pesquet's Parrot (Psittrichas fulgidus), a highly specialized, obligate frugivore. Three isocaloric, fruit-based diets of varying protein content (6.1, 3.3, and 2.6% dry mass crude protein) were used in feeding trials lasting three to five days per diet. A minimum dietary protein requirement of 3.2% dry mass was estimated from balance trials. Endogenous nitrogen losses were 0.05 gN kg−0.75 day−1 and nitrogen equilibrium occurred at 0.32 gN kg−0.75 day−1. Those values are extremely low compared to those of granivorous and omnivorous bird species, but higher than those of nectarivorous species. In terms of nitrogen losses and requirements, Pesquet's Parrot most closely parallels the highly frugivorous Cedar Waxwing (Bombycilla cedrorum). Thus, reduced protein requirements appear to play an important physiological role in ability of highly frugivorous birds to subsist on fruit diets.
Bounce and Double Trill Songs of Male and Female Western Screech-Owls: Characterization and Usefulness for Classification of Sex
Authors: Herting Brian L. , Belthoff James R. , Kroodsma D.
Published: September 2019

Both sexes of adult Western Screech-Owls (Otus kennicottii) sing in response to playback of conspecific song within their territories. Two primary songs are the bounce and double trill. Using sonographic analysis of tape-recorded vocalizations, our study quantified characteristics of bounce and double trill songs uttered by individuals within a population of Western Screech-Owls inhabiting riparian woodlands in southwestern Idaho. We asked if songs of males and females differed and, if so, how accurately could songs be classified by sex. On average, male bounce songs were ∼30% lower in frequency than bounce songs of females, but song duration, note duration, number of notes per bout, and internote duration did not differ. Similarly, double trill songs of males were significantly lower in frequency than those of females, and double trill songs uttered by females had significantly greater internote distances in the leading portion. A discriminant model based on frequency at maximum amplitude of bounce songs correctly classified all males and females in our sample. Presence of sex-specific patterns of vocalizations in that species would allow owls to assess the sex of potential intruders and respond appropriately. Moreover, sonographic analysis of Western Screech-Owl songs provides a means for noninvasive classification of sex.
Is Diet-shifting Facilitated by Modulation of Pancreatic Enzymes? Test of an Adaptational Hypothesis in Yellow-rumped Warblers
Authors: Ciminari M. Eugenia , Afik Daniel , Karasov William H. , Caviedes-Vidal Enrique , Blem C.
Published: September 2019

Many birds exhibit seasonal switches in diet and thus alter nutrients predominating their food intake. We tested for dietary modulation of pancreatic enzymes in Yellow-rumped Warblers (Dendroica coronata), a species for which such dietary changes are documented. Birds were fed three diets formulated from either fruit, insect, or seed. We predicted that pancreatic carbohydrase amylase, and the proteases trypsin and chymotrypsin, would be modulated in direct correlation with relative levels of dietary carbohydrate and protein, respectively. In contrast to the prediction, there was no significant dietary effect on activities of amylase and chymotrypsin, and a significant change in trypsin activity (highest on seed diet) occurred in the wrong direction with regard to the prediction. Considering the statistical power of our tests, we conclude that Yellow-rumped Warblers represent a case of only modest ability, at best, to modulate pancreatic enzymes. For some diets, especially high-starch diets that they digest relatively poorly and on which they tend to lose body mass, they may lack sufficient enzyme and hence are constrained in their dietary niche.
True Winter Range of the Veery (Catharus Fuscescens): Lessons for Determining Winter Ranges of Species That Winter in The Tropics
Authors: Remsen Jr. J. V. , Moore F.
Published: September 2019

Most recent references describe the winter range of the Veery (Catharus fuscescens) as including an extensive area from northern Colombia, Venezuela, and Guyana south to south-central Brazil. Analysis of seasonal distribution of specimen records in South America, however, shows that 91 of 105 specimens were taken during spring and fall, not winter; the remaining 14, taken from 2 December to 20 February, are all from three small areas at the periphery or south of the Amazon basin. Thus, the true winter range is almost completely south and east of the area generally described. The seasonal distribution of specimen records is consistent with observational data from South America and banding data from the Neotropics. Although those data must be treated cautiously, it appears that the true winter range of the Veery is in south-central and southeastern Brazil, an area where habitat destruction threatens many natural habitats, rather than in the relatively undisturbed areas of western Amazonia. Widespread erroneous portrayal of the winter range of the Veery seems to have been caused largely by the assumption that the species winters in South America wherever it has been recorded and by overlooking a previously published analysis of its winter distribution.
Phylogeny and Systematics of Ground Rollers (Brachypteraciidae) of Madagascar
Authors: Kirchman Jeremy J. , Hackett Shannon J. , Goodman Steven M. , Bates John M. , Prum R.
Published: September 2019

We studied relationships of five extant members of the endemic Malagasy family Brachypteraciidae, the ground rollers, using several mitochondrial genes (cytochrome-b, NADH dehydrogenase 2, 12S ribosomal RNA, and cytochrome oxidase I). As outgroups, we used other coraciiforms including the Cuckoo Roller (Family Leptosomatidae, Leptosomus discolor), several true rollers (Corcaciidae) and a tody (Todidae). Partial sequences of the Long-tailed Ground Roller (Uratelornis chimaera) were obtained from toe pad samples taken off museum specimens. For a combined data set of all genes, Kimura two-parameter distances between sequences of the five ground roller species were high, averaging 11% divergence. For several species, samples were available from widely separated geographic regions and intraspecific sequence divergence was low (≤0.8%). Unweighted and weighted parsimony and maximum-likelihood analyses consistently recovered monophyly of the family, a sister relationship between Brachypteraciidae and Coraciidae, and monophyly of one of three currently recognized ground roller genera (Atelornis). At the base of the Brachypteraciidae clade, we could not fully resolve relationships between Uratelornis and two species currently placed in Brachypteracias. Because of the uncertainty of basal nodes in our phylogenetic reconstructions, we recommend returning B. squamigera to the monotypic genus Geobiastes. High levels of divergence among ground rollers are similar to levels found in other avian groups endemic to Madagascar. However, we suggest that molecular divergences appear far too low to be consistent with mid-Eocene fossils attributed to the family.
A Molecular Phylogeny of the Dove Genera Streptopelia and Columba
Authors: Johnson Kevin P. , de Kort Selvino , Dinwoodey Karen , Mateman A. C. , ten Cate Carel , Lessells C. M. , Clayton Dale H. , Sheldon F.
Published: September 2019

Evolutionary history of the dove genus Streptopelia has not been examined with rigorous phylogenetic methods. We present a study of phylogenetic relationships of Streptopelia based on over 3,600 base pairs of nuclear and mitochondrial gene sequences. To test for monophyly of Streptopelia, we used several other columbiform taxa, including Columba (Old and New World), Macropygia, Reinwardtoena, and the enigmatic Pink Pigeon (Nesoenas mayeri). On the basis of our analyses, Streptopelia (as currently defined) is not monophyletic; Nesoenas mayeri is the sister species to S. picturata, resulting in paraphyly of Streptopelia. Three main clades of Streptopelia are identified: (1) S. chinensis plus S. senegalensis, (2) S. picturata plus Nesoenas mayeri, and (3) all other species of Streptopelia. It is unclear whether those clades form a monophyletic group to the exclusion of Old World Columba, but several analyses produce that result. Species of Old World Columba are closely related to Streptopelia, with species of New World Columba clustering outside that group. Taxonomic changes suggested by our results include merging Nesoenas with Streptopelia and changing the generic name for New World Columba species to Patagioenas. Vocal similarities between S. picturata and N. mayeri are striking, given the general diversity of vocalizations in other species.
Site Fidelity, Philopatry, and Survival of Promiscuous Saltmarsh Sharp-Tailed Sparrows in Rhode Island
Authors: DiQuinzio Deborah A. , Paton Peter W. C. , Eddleman William R. , Brawn J.
Published: September 2019

We investigated site fidelity and apparent survival in a promiscuous population of Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) in southern Rhode Island. Based on capture–recapture histories of 446 color-banded sparrows studied from 1993 to 1998 at our primary study site, Galilee, we observed significant variation in apparent survival rates among years, but not between sexes. Return rates of adult males (37.6%) and females (35.6%) were not significantly different during any year. Juveniles exhibited high return rates, ranging from 0 to 44%, with males (61% of returns) more likely to return than females (35%). In addition, we monitored movements of 404 color-banded sparrows at nine satellite marshes in 1997 and 1998, which supported our findings at Galilee and documented intermarsh movements by 10% of all banded birds. Lack of gender-bias in adult dispersal and strong natal philopatry of sparrows in Rhode Island occurs regularly among passerines possessing a variety of mating systems. Despite emancipation from parental and resource defense duties, adult male Saltmarsh Sharp-tailed Sparrows exhibited apparent survival rates similar to adult females. Availability of high-quality breeding habitat, which is patchy and saturated, may be the most important factor limiting dispersal for Saltmarsh Sharp-tailed Sparrows in Rhode Island.
Energetics of Toucans, A Barbet, and A Hornbill: Implications for Avian Frugivory
Authors: McNab Brian K. , Bosque C.
Published: September 2019

Rate of oxygen consumption was measured in eight species of toucans, one barbet, and one hornbill to examine factors that influence their energy expenditures. Basal rate of metabolism in those species, supplemented with measurements from three woodpeckers and three mousebirds, is correlated with body mass and either food habits or climate: temperate acorn- and insect-eating species have basal rates that are ∼70% greater than tropical fruit-eating species. The temperate, insect- or acorn-eating species are woodpeckers, so level of basal rate is also correlated with familial affiliation. The toucans, barbet, and hornbill have basal rates similar to those of frugivorous pigeons and bats, which collectively are low by avian standards. The effects of climate, food habits, and family affiliation on basal rates in endotherms are difficult to separate, given the restricted data set available. Earlier conclusions that the basal rates of birds greatly exceed those of mammals are confounded by character interactions that influence dependence of basal rate on body mass. The largest toucan showed a remarkable ability to reduce energy expenditure at low ambient temperatures without reducing core body temperature, possibly as a result of peripheral vasoconstriction.
Does Kleptoparasitism by Glaucous-Winged Gulls Limit the Reproductive Success of Tufted Puffins?
Authors: St. Clair Colleen Cassady , St. Clair Robert C. , Williams Tony D. , Danchin E.
Published: September 2019

Interspecific kleptoparasitism (food stealing) occurs in many seabird species and can sometimes significantly affect host individuals and populations. We investigated effects of kleptoparasitism by Glaucous-winged Gulls (Larus glaucescens) on a population of Tufted Puffins (Fratercula cirrhata) in which almost all chicks die before fledging in some years. Rates of kleptoparasitism were estimated during two seasons and compared with several spatial and temporal factors that have been predicted to influence kleptoparasitism rates both within and among seasons. Kleptoparasitism rates increased from 2% in the first year to 19% in the second, whereas puffin fledging success declined precipitously from 81% in the first year to 11% in the second. Within years, kleptoparasitism rates increased with number of puffins returning with fish, decreased during fair weather, and were unaffected by tidal height. Spatially, those rates increased with puffin burrow density and declined with angle of the nesting slope. Gull kleptoparasitism success increased during foul weather and at higher puffin nesting elevations. Despite those associations, survival of puffin chicks was not influenced by kleptoparasitism activity near their nests although it increased with a combination of low elevation and high slope at the nesting burrow. Neither kleptoparasitism nor predation by gulls were exceptional relative to other seabird colonies and they were unlikely to cause reproductive failures that characterize puffins at that site. Other factors, particularly food shortages at sea, merit further attention in explaining those failures.
Prefledging Energy Requirements in Shorebirds: Energetic Implications of Self-Feeding Precocial Development
Authors: Schekkerman Hans , Visser G. Henk , Blem C.
Published: September 2019

Understanding ecological consequences of avian developmental modes requires knowledge of energy requirements of chicks of different positions in the precocial–altricial spectrum, but those have rarely been measured in birds with self-feeding precocial young. We studied prefledging energy budgets in chicks of Black-tailed Godwit (Limosa limosa) and Northern Lapwing (Vanellus vanellus) in the field and in the laboratory. Lapwings show slower growth than godwits, reaching a 29% lower fledging mass (142 vs. 201 g) in a 32% longer period (33 vs. 25 days). Daily energy expenditure (DEE), measured by the doubly labelled water (DLW) technique, and daily metabolized energy (DEE plus energy deposited into tissue) increased proportionally to body mass at similar levels in both species. Total metabolized energy (TME) over the fledging period was 8,331 kJ in godwits and 6,982 kJ in lapwings, 39 and 29% higher than an allometric prediction (Weathers 1992). That suggests that self-feeding precocial chicks have high energy requirements compared with parent-fed species, due to costs of activity and thermoregulation associated with foraging. Those components made up 50–53% of TME in the shorebirds, more than twice as much as in seven parent-fed species for which DLW-based energy budgets are available. In captive lapwings and godwits growing up under favorable thermal conditions with food readily accessible, thermoregulation and activity costs were 53–58% lower and TME was 26–31% lower than in free-living chicks. The proportion of TME allocated to tissue formation (13–15% deposited as tissue plus 10–12% synthesis costs) was low in the shorebirds, and reductions in food intake may therefore sooner lead to stagnation of growth than in parent-fed chicks. Furthermore, the need to forage limits potential for saving energy by reducing activity in periods of food scarcity, because that will further decrease food intake. Self-feeding precocial chicks thus seem to operate within fairly narrow energetic margins. At the same time, self-feeding may allow birds to use food types that could not be profitably harvested if they had to be transported to the young.
Geographical Variation in the Contact Calls of Orange-Fronted Parakeets
Authors: Bradbury Jack W. , Cortopassi Kathryn A. , Clemmons Janine R. , Kroodsma D.
Published: September 2019

We examined patterns of geographic variation in contact calls of Orange-fronted Parakeets (Aratinga canicularis) during the nonbreeding season. Calls were recorded throughout the range of that species in Costa Rica. Recordings of wild-caught birds held for one to two weeks indicated that each individual favors one dominant call type and different birds use different favored calls. We used that fact to cull replicate calls from the same individual in field recordings of flocks observed at various locations throughout the sample area. Remaining recordings from a given year were submitted to spectrographic cross-correlation and principal coordinates analysis as described by Cortopassi and Bradbury (2000). Principal coordinates were then correlated with site location using MANOVA. Call durations were also examined for geographical patterns. Like sympatric Yellow-naped Parrots (Amazona auropalliata) studied over the same region by Wright (1996), Orange-fronted Parakeets exhibited significant geographic variation but, unlike the larger species, showed no discrete dialect patterns. Call duration varied clinally but with different patterns for the Nicoya Peninsula and the Guanacaste mainland. Two principal coordinates also showed clinal variation even after removing any correlated duration effects. Scale over which local calls were statistically homogeneous was 7–10 km. We compared that figure to home ranges of 18 birds radio-tracked concurrently with call sampling. Both range areas and range lengths were asymptotic after a week of tracking. Asymptotic range lengths were 2–9 km. Scale of movements of birds, at least during that period, was thus similar to distance within which calls tended to be statistically homogeneous. This study and that by Wright show that several well-known patterns of geographical variation seen with passerine song are replicated quite closely in contact calls of parrots, despite the fact that the functions of vocal signals are quite different in the two taxa.
How Many Baskets? Clutch Sizes That Maximize Annual Fecundity of Multiple-Brooded Birds
Authors: Farnsworth George L. , Simons Theodore R. , Brawn J.
Published: September 2019

We developed deterministic models on the basis of nest survival rates and renesting behavior capable of predicting annual fecundity in birds. The models calculate probabilities of fledging from one to four nests within a discrete breeding season. We used those models to address theoretical issues related to clutch size. In general, birds require at least one day to lay an egg, and many species delay incubation until their entire clutch is laid. Because it takes longer to complete a larger clutch, and fewer such clutches can fit into a limited breeding season, there exists a clutch size for which annual fecundity is maximized. We asked, for a given amount of reproductive effort (i.e. a set number of eggs), does the age-old maxim “don't put all your eggs in one basket” apply? If so, in how many “baskets” should a nesting bird place its eggs? The answer depends on both likelihood of nest predation and length of the breeding season. Those results are consistent with the observed increase in clutch size with latitude (shorter breeding season length) and larger clutch sizes characteristic of cavity-nesting species (with higher nest survival rates). The models also predict that the size of replacement clutches should decrease as the breeding season progresses, and that intraseasonal decline in clutch size should be more pronounced when the breeding season is short.
Growth and Development of Homeothermy in Nestling European Shags (Phalacrocorax Aristotelis)
Authors: Østnes Jan Eivind , Jenssen BjØrn Munro , Bech Claus , Nettleship D.
Published: September 2019

European Shag (Phalacrocorax aristotelis) nestlings were studied on a small island off the coast of central Norway. Increase in body mass (BM) with age (t, days) was described by the logistic equation: BM = 1,622 g/[1 + e−0.172(t−19.9)]. All growth parameters measured (body mass, and length of tarsus, wing and head) showed highest relative growth rate when the nestlings were 5–10 days old, that is, before the nestlings had achieved homeothermy. An incipient endothermic response was noted when nestlings were 9 days old, and they became homeothermic at ages of 15–18 days. Respective mass-specific resting metabolic rates for nestlings 0, 15, and 45 days old were 47, 261, and 147% of the predicted value for adult nonpasserine birds of similar body masses. Mass-specific minimal thermal conductance decreased from 366% of predicted adult value at hatching, to 220% of that predicted when nestlings were 21 days old. For nestlings 15 days old, the factorial metabolic scope (resting metabolic rate/peak metabolic rate) was only 1.5, but that increased rapidly thereafter. Rapid increase in the mass-specific RMR and decrease in minimal thermal conductance is suggested to contribute importantly to improve homeothermic ability during the first two weeks of the developmental period. At hatching, leg and pectoral muscles constituted 5.3 and 2.2%, respectively, of total wet body mass. Relative leg-muscle mass increased rapidly and had almost reached adult proportions when the nestlings were 25–30 days old. In contrast, pectoral-muscle mass increased in an almost direct proportion to the body mass during the first 30 days of the growth period, and increased rapidly thereafter. At hatching, the water fraction (water content/lipid-free wet mass) was significantly lower in the leg than in the pectoral muscles (0.920 vs. 0.931). The water fraction of leg muscles also remained lower during the entire growth period. Judging from the proportionately greater mass and higher degree of maturity of the leg compared to pectoral muscles, the former would seem to be the main site of cold-induced heat production during early development of homeothermy in European Shag nestlings.
Age at First Breeding and Natal Dispersal in a Declining Population of Cassin's Auklet
Authors: Pyle Peter , Nettleship D.
Published: September 2019

Age of first breeding (AFB) and natal dispersal distance (NDD) were investigated relative to proximate and ultimate factors in 276 known-age Cassin's Auklets (Ptychoramphus aleuticus) breeding during 1981–1999 on Southeast Farallon Island, California. Breeding density in 446 study boxes declined significantly during the period 1987–1999, confirming other information indicating a long-term decline (since at least the 1970s) in the population. Mean AFB was 3.34 years when sexes were combined, ranging from 2–10 (mean 3.36) years in females and 2–9 (mean 3.36) years in males. AFB showed a significant linear increase with decreasing colony density, suggesting that increased stress on the entire population, such as that caused by decreasing food availability, may have prevented younger birds from attaining breeding condition at an early age. Median NDD was 8.84 m, ranging from 0–448.7 m; two individuals of each sex recruited into their natal boxes. NDD showed a significant linear increase with decreasing breeding density but no significant linear or curvilinear correlations with mate fidelity, annual reproductive success, or lifetime reproductive output. A significant proportion (66.9%) of movements after recruitment (breeding dispersal) resulted in closer proximity to the natal site. Thus, although natal philopatry was strongly developed in the Cassin's Auklet, it did not seem to be adaptive. Those paradoxical results suggest that selective equilibrium may be acting on natal philopatry in response to the population decline: a low-philopatry, low-cost (later breeding and increased survival) strategy has become increasingly adaptive in Cassin's Auklets, explaining increases in AFB and NDD with the declining breeding densities. The lack of sex-specific effects on AFB and NDD suggests that an even sex-ratio and roughly equal roles in reproduction among Cassin's Auklets exists on Southeast Farallon Island, and that inbreeding avoidance may be counter-balanced by relatively low mate fidelity in this species.
Wood Thrush Movements and Habitat Use: Effects of Forest Management for Red-Cockaded Woodpeckers
Authors: Lang Jason D. , Powell Larkin A. , Krementz David G. , Conroy Michael J.
Published: September 2019

We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes (Hylocichla mustelina) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers (Picoides borealis), thinning and burning >30 year old loblolly pine (Pinus taeda) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (Ψ) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site (x̄ = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood–pine mixed habitat (P < 0.05) with moderate overstory cover (P < 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management.
Maternal Condition and Nestling Sex Ratio in House Wrens
Authors: Whittingham Linda A. , Valkenaar Stacy M. , Poirier Nicole E. , Dunn Peter O.
Published: September 2019

Parents are expected to vary the sex ratio of their offspring in relation to the sex-specific fitness benefits. However, benefits of producing sex-biased broods may be dependent on condition of the female. For example, mothers in good condition could achieve greater fitness if they produced high-quality sons, whereas, mothers in poor condition would gain more by producing daughters rather than poor-quality sons. As a consequence, we would expect to see a relationship between female condition and sex ratio of offspring. We examined effect of maternal condition on nestling condition and sex ratio in the House Wren (Troglodytes aedon). Overall sex ratio of nestlings in the population was not biased, but females in better condition produced relatively more sons. Overall positive relationship between female condition and proportion of male offspring was due to second broods, which were significantly male-biased and more likely to be produced by females in good condition. Females in better condition also tended to provision young more often and produced both male and female nestlings in better condition. Polygyny and extrapair mating are common in House Wrens. If males in good condition are more likely to be successful breeders as adults, then it may benefit mothers in good condition to produce more sons.
Manakins (Pipridae) in Second-Growth and Old-Growth Forests: Patterns of Habitat Use, Movement, and Survival
Authors: Blake John G. , Loiselle Bette A.
Published: September 2019

We used capture and recapture data (1985 to 1994) to examine seasonal variation in habitat use, movements within and among habitats, and survival rates of manakins (Manacus candei, Corapipo altera, Pipra mentalis, P. pipra) in northeastern Costa Rica. Manakins were captured in young and old second-growth woodlands in the lowlands and in old-growth forest at approximately 50, 500, and 1,000 m. Manakin species differed in their use of habitats, with old-growth forest species showing large and predictable seasonal variation in capture rates. Corapipo capture rates in lowland (nonbreeding) habitats were greater during the wet season than during the dry season and were greater in old-growth forest than in second growth. Capture rates at 500 m were higher in the dry season. Pipra mentalis capture rates were high in second growth and old growth. Capture rates were higher in the wet season and were correlated with capture rates of Corapipo, indicating that at least some individual P. mentalis migrate along the elevational gradient. P. pipra capture rates were highest at 1,000 m; few individuals descended to lowlands in the wet season. Manacus capture rates were highest in young second growth and did not vary between wet and dry seasons. Use of second-growth habitats by species typically associated with old-growth forests illustrates the value of maintaining a mosaic of habitats to accommodate seasonal changes in use of habitats. Contrary to expectations based on lek mating systems, there was little evidence that movements within habitats (i.e. recapture distances) varied between sexes. Yet, recapture percentages were higher in all species for adult females than males. Adult survival rates were ∼0.75 for Manacus in young second growth, 0.62 for Corapipo in old-growth forest at 50 m and 0.66 at 500 m, and 0.70 for Pipra mentalis in lowland old-growth forest. Results support the suggestion that geographic variation in survival rates may be common in the tropics and illustrate the need for examining survival rates separately by age and sex.
Importance of Seed Ingestion to an Avian Frugivore: An Experimental Approach to Fruit Choice Based on Seed Load
Authors: Stanley Margaret C. , Lill Alan
Published: September 2019

Frugivorous birds may be able to reduce the cost of processing seeds by discarding seeds, selecting fruits that have a high pulp-to-seed ratio, or by choosing fruit in which seeds are packaged in a way that the frugivore's gut can void them more rapidly. A preference for fruit based on pulp-to-seed ratio or seed composition within a fruit is likely to have important implications for plants and evolution of seed size. We tested whether captive Silvereyes (Zosterops lateralis) discriminate among artificial fruit on the basis of seed presence by presenting birds with artificial fruit with or without a seed. In the first experiment, fruit were translucent so that birds could see which fruit contained a seed. In the second experiment, the visual cue was removed. When Silvereyes were presented with a choice between translucent, artificial fruit with or without a seed, they showed a strong preference for fruit that did not contain a seed. However, when the visual cue to seed presence was removed, preference for seedless fruit was still significant, but markedly reduced. We also tested seed-size preference of Silvereyes in the field in Victoria, Australia. Seeds from a fruit commonly consumed by Silvereyes, fragrant saltbush (Rhagodia parabolica), were recovered from Silvereye faecal samples and their volumes measured. Comparisons were made between seed volumes of fruit consumed by Silvereyes and those within fruit available on the plant. Silvereyes consumed significantly smaller seeds than the mean size available on saltbush plants. When Silvereyes were presented with a cereal-based diet containing artificial seeds (designed to mimic large fruit containing many small seeds), they avoided seed ingestion and were able to consume proportionally more cereal than seeds, even when on a high seed-load diet (30%). Seed dispersal by Silvereyes may be inefficient for plant species with large fruit containing many small seeds, because Silvereyes in this experiment were able to avoid ingesting seeds.
Orientation of Nocturnally Migrating Swainson's Thrush at Dawn and Dusk: Importance of Energetic Condition and Geomagnetic Cues
Authors: Sandberg Roland , Moore Frank R. , Bäckman Johan , Lõhmus Mare
Published: September 2019

We studied the early morning cage orientation of nocturnally migrating Swainson's Thrushes (Catharus ustulatus) during three fall migration seasons. The results were compared with earlier free-flight release tests under starry skies and were found to be consistent with continuation of migratory flights in the expected seasonally appropriate direction. Energetic condition proved decisive: fat birds chose directions in accordance with migration across the Gulf of Mexico, whereas lean birds oriented away from the coast, possibly in search of habitats suitable for refuelling. Whereas the orientation of fat Swainson's Thrushes was affected by experimental shifts of the magnetic field, the response during morning tests was larger than expected. A parallel series of orientation cage experiments performed during evening twilight showed a response to deflected magnetic fields that was close to the expected shift, which suggests a difference in integration of directional information between early morning and evening twilight activity. However, within-individual response to deflected magnetic fields was of the same magnitude during both morning and evening tests.