Connecting the dots: Stopover strategies of an intercontinental migratory songbird in the context of the annual cycle

The phases of the annual cycle for migratory species are inextricably linked. Yet, less than five percent of ecological studies examine seasonal interactions. In this study, we utilized stable hydrogen isotopes to geographically link individual black‐and‐white warblers (Mniotilta varia) captured during spring migration with breeding destinations to understand a migrant's stopover strategy in the context of other phases of the annual cycle. We found that stopover strategy is not only a function of a bird's current energetic state, but also the distance remaining to breeding destination and a bird's time‐schedule, which has previously been linked to habitat conditions experienced in the preceding phase of the annual cycle. Birds in close proximity to their breeding destination accumulate additional energy reserves prior to arrival on the breeding grounds, as reflected by higher migratory condition upon arrival, higher refueling rates measured via blood plasma metabolites, and longer stopover durations compared to birds migrating to breeding destinations farther from the stopover site. However, late birds near their breeding destination were more likely to depart on the day of arrival (i.e., transients), and among birds that stopped over at the site, the average duration of stopover was almost half the time of early conspecifics, suggesting late birds are trying to catch‐up with the overall time‐schedule of migration for optimal arrival time on the breeding grounds. In contrast, birds with long distances remaining to breeding destinations were more likely to depart on the day of arrival and primarily used stopover to rest before quickly resuming migration, adopting similar strategies regardless of a bird's time‐schedule. Our study demonstrates that migrants adjust their en route strategies in relation to their time‐schedule and distance remaining to their breeding destination, highlighting that strategies of migration should be examined in the context of other phases of the annual cycle.     

Molecular systematics and taxonomic overview of the bird's nest fungi (Nidulariaceae)

Fungi in the Nidulariaceae, otherwise known as ‘bird's nest fungi’, are among the least studied groups of Agaricomycetes (Basidiomycota). Bird's nest fungi are globally distributed and typically grow on woody debris or animal dung as saprotrophs. This group of fungi is morphologically diverse with ca. 200 described species. Phylogenetic relationships of bird's nest fungi were investigated with four commonly used loci (ITS, LSU, tef, and rpb2). The family was resolved as a monophyletic group with Squamanitaceae as a potential sister taxon. Cyathus and Crucibulum each formed its own independent and well-supported clade. Nidula and Nidularia formed a clade together, but each genus is polyphyletic. Two Mycocalia species included in our analyses were on their own separate branches, indicating that this genus is also polyphyletic. Misidentifications were detected in most genera, suggesting that species concepts need to be revisited and refined throughout Nidulariaceae. Several bird's nest fungi species have global geographical distributions whereas others may have more limited ranges. Basic morphological characters of bird's nest fungi have likely been lost or gained multiple times. The phylogenetic placement of Crucibulum is unclear and the sister lineage of bird's nest fungi is not conclusive. Further studies with data from rare species and additional informative genes are needed to fully resolve the topology of Nidulariaceae and identify its sister group with more certainty.     

Effects of satellite transmitters fitted to breeding Cory's shearwaters

We studied the effects of a new technique to fix satellite transmitters on the feeding behavior and chick body growth of the Cory's shearwater (Calonectris diomedea). Transmitters did not significantly affect the breeding bird's body mass or diving performance. However, on average, pairs with ≥1 adult equipped with a transmitter brought a lighter meal (54.8 ± 18.9 g) to nestlings than did control birds or the same pair with the transmitter removed (77.4 ± 8.3 g) leading to a decreased chick body growth. However at fledging, chicks in control and treatment groups had similar body mass whether parents were equipped with a PTT or not. Our method of transmitter attachment could therefore be an appropriate alternative for studying the ecology of procellariiforms weighing <1 kg given that birds are fitted with transmitters for <2 weeks and restricted to 1 parent only. © 2011 The Wildlife Society.     

Oil palm expansion into rain forest greatly reduces ant biodiversity in canopy,epiphytes and leaf-litter

Oil palm cultivation is expanding rapidly into many of the world's most biodiverse tropical regions. One of the most functionally important and ecologically dominant animal groups in these environments is the ants. Here, we quantify the overall impacts of clear-felling lowland dipterocarp rainforest and conversion into oil palm plantation on ant diversity. At study sites in Sabah, Malaysia we collected ants from three microhabitats: 1 – the canopy, 2 – bird's nest ferns (Asplenium nidus complex, a common epiphyte in forest and oil palm), and 3 – leaf litter. We also measured temperature, humidity and light at collection sites to assess their impacts on ant community composition. Total ant species richness decreased from 309 to 110 (?64%) between forest and oil palm plantation. However, this impact was not the same across all microhabitats, with bird's nest ferns maintaining almost the same number of ant species in oil palm compared to forest (forest-oil palm, ferns: 36–35 (3% loss), canopy: 120–58 (52% loss), leaf litter: 216–56 (74% loss)). Relative abundance distributions remained the same for fern-dwelling ants, but became less even for oil palm ants in both the canopy and the leaf litter. These differences may be due in part to the ability of bird's nest ferns to provide a stable microclimate in hot, dry plantations. We also found that non-native ant species were more abundant in oil palm than in forest, and few forest ant species survived in plantations in any of the microhabitats. Only 59 of the 309 forest species persisted in oil palm plantations, corresponding to an 81% loss of forest species resulting from habitat conversion. Although oil palm supports many more ant species than has been previously reported, converting forest into plantation still leads to a dramatic reduction in species richness. The maintenance of forested areas is therefore vital for the conservation of ant biodiversity.     

Assessing the short‐term effects of capture,handling and tagging of sandgrouse

Capturing and marking free‐living birds permits the study of important aspects of their biology but may have undesirable effects. Bird welfare should be a primary concern, so it is necessary to evaluate and minimize any adverse effects of procedures used. We assess short‐term effects associated with the capture, handling and tagging with backpack‐mounted transmitters of Pin‐tailed Pterocles alchata and Black‐bellied Pterocles orientalis Sandgrouse, steppe birds of conservation concern. There was a significantly higher mortality (15%) during the first week after capture than during the following weeks (< 2.5%) in Pin‐tailed Sandgrouse, but no significant temporal mortality pattern in Black‐bellied Sandgrouse. In Pin‐tailed Sandgrouse, mortality rate during the first week increased with increasing relative transmitter and harness weight regardless of season, and with increasing handling time during the breeding season. There were no significant differences in mortality rate between study areas, type of tag, sex or age or an effect of restraint time. These results suggest the use of lighter transmitters (< 3% of the bird's weight) and a reduction of handling time (< 20 min), particularly during the breeding season, as essential improvements in procedure to reduce the mortality risk associated with the capture, handling and tagging of these vulnerable species.     

Quantitative assessment of song-selectivity in the zebra finch “high vocal center”

1. Auditory responses in the zebra finch (Taenopygia guttata) song-system nucleus HVc were assessed at 54 recording sites by 3 different methods: discriminated action potentials; excitatory summed responses; and excitatory minus inhibitory summed responses. Four standard stimuli were presented at each site: the bird's own song; this song reversed; a conspecific song; and a noise burst. Responses were quantified by calculating a relative response index that partitioned the response, to provide a response profile, across the stimuli.
2. Regardless of analysis method, the strongest response was most often to the bird's own song (78–82%, depending on method). The predominant rank order of response strength across the remaining three stimuli was conspecific song > reversed song > noise.
3. The distribution of relative response magnitude was sensitive to analysis method. Discriminated spikes captured the heterogeneity of HVc neurons, whereas the excitatory summed responses reflected the overall trends more consistently. When inhibition was subtracted from excitation in the summed responses, the variance of the relative responses increased, but this method presented some problems for statistical analysis.
4. A small sample of neurons in other forebrain auditory areas was used for comparative analyses. At these recording sites, the bird's own song did not consistently elicit the best response and there were generally smaller differences in the relative responses to the four stimuli. The smaller degree of stimulus selectivity among these cells resulted in less sensitivity to differences in the assessment methods.

     

Modified method for external attachment of transmitters to birds using two subcutaneous anchors

ABSTRACT Of the transmitter attachment techniques for birds, the subcutaneous anchor provides a secure attachment that yields relatively few secondary effects. However, the use of subcutaneous anchors has been limited by transmitter size and retention time. Using a modified method of attachment that utilized two subcutaneous anchors, we deployed 69 GPS transmitters, plus 13 VHF transmitters that were similar in size and weight to GPS models, on Pacific Black Brant (Branta bernicla nigricans). Prior to our study, only harnesses were used for attaching GPS transmitters on birds, mainly because GPS transmitters are too large for other external attachment techniques and implantation in the body cavity attenuates the GPS signal. Thus, to increase the size capacity of anchor attachment and to avoid the well‐documented negative effects of harnesses on behavior and survival, we added a second anchor at the transmitter's posterior end. The double‐anchor attachment technique was quickly and easily accomplished in the field, requiring bird handling times of <10 min. Incidental recoveries of tagged Brant indicate a high degree of transmitter retention. Five recaptured birds (4–6 weeks after deployment) and eight killed by hunters (3–6 mo after deployment) retained their GPS transmitters. For studies involving the use of relatively large transmitters, the double‐anchor method appears to provide a viable alternative for external attachment.     

Finding your mate in a seabird colony: contrasting strategies of the Guillemot Uria aalge and King Penguin Aptenodytes patagonicus

Capsule King Penguins recognize their mates by voice, but Guillemots do not need acoustic cues even though their calls show individual variation.

Aims To determine whether the structure of Guillemot calls could allow individual recognition, as with King Penguin, and whether acoustic cues are used to locate mates among a dense mass of conspecifics at a colony.

Methods Observations were made on breeding Guillemots and King Penguins. Calls made by birds returning to their mates were recorded, the signals digitized and the calls analysed. Calls were later played back to the mates of the birds concerned and the effects noted on both them and their neighbours.

Results Both Guillemots and King Penguins emitted calls on return to the breeding site which contained individual signatures and were therefore potentially usable for mate recognition. In King Penguins, auditory recognition was essential for finding a mate, whereas in Guillemots most of the arriving birds located their mate in a dense crowd of conspecifics without the help of acoustic signals. Guillemots could differentiate neighbours from strangers without auditory cues.

Conclusion Calls are essential for the successful identification of mates by King Penguins but not by Guillemots.     

Can wind help explain seasonal differences in avian migration speed?

A bird's ground speed is influenced by the wind conditions it encounters. Wind conditions, although variable, are not entirely random. Instead, wind exhibits persistent spatial and temporal dynamics described by the general circulation of the atmosphere. As such, in certain geographical areas wind's assistance (or hindrance) on migratory flight is also persistent, being dependent upon the bird's migratory direction in relation to prevailing wind conditions. We propose that, considering the western migration route of nocturnal migrants through Europe, winds should be more supportive in spring than in autumn. Thus, we expect higher ground speeds, contributing to higher overall migration speeds, in spring. To test whether winds were more supportive in spring than autumn, we quantified monthly wind conditions within western Europe relative to the seasonal direction of migration using 30 years (1978–2008) of wind data from the NCEP/NCAR Reanalysis dataset. We found that supporting winds were significantly more frequent for spring migration compared to autumn and up to twice as frequent at higher altitudes. We then analyzed three years (2006–2008) of nocturnal migratory ground speeds measured with radar in the Netherlands which confirmed higher ground speeds in spring than autumn. This seasonal difference in ground speed suggests a 16.9% increase in migration speed from autumn to spring. These results stress the importance of considering the specific wind conditions experienced by birds when interpreting migration speed. We provide a simple methodological approach enabling researchers to quantify regional wind conditions for any geographic area and time period of interest.     

Predation by Ravens Corvus corax on Brunnich's Guillemot Uria lomvia eggs and chicks and its possible impact on breeding site selection

We studied the behaviour of Ravens Corvus corax taking the eggs or chicks of Brunnich's Guillemots Uria lomvia at East Digges Island, Northwest Territories, Canada. We classified the characteristics of the breeding sites attacked by Ravens according to their location on the cliffs, the width of the breeding ledge, the number of adjacent rock faces and the density of nearby breeding guillemots. Ravens selectively attacked peripheral sites near the top of the occupied area, those on narrow ledges and those with few close neighbours. The risk of predation at the most vulnerable sites was more than seven times the average. For the most part, breeding success at 419 sites near the cliff top conformed to predictions based on the observations of Raven predation. However, losses observed over 3 years suggested that more eggs fall accidentally than are taken by avian predators. We concluded that the risks of predation and of accidental dislodgement both contribute to choice of nest sites by Brunnich's Guillemots. The effect of multiple close neighbours in deterring predation by Ravens may be important in determining the density of guillemot breeding sites within the colony.     

Probable loss of tolerance and simulation of autoimmunization in induced chimeras in doves

Chimeras were induced in doves (Streptopelia) by making parabionts of embryonating eggs that carried genes for erythrocyte antigens, which were readily identified. The parabiotic pairs were chosen so that new antigenic specificities would appear if somatic cell mating took place. However, no evidence of somatic cell mating was noted. Erythrocytic chimerism was no longer. detectable in some birds after varying periods of time. In a few others tolerance was presumably lost, since their plasma contained antibodies against cellular antigens that either were present, or had been present, in the bird's circulation.     

Adaptive management assists reintroduction as higher tides threaten an endangered salt marsh plant

In theory, extirpated plant species can be reintroduced and managed to restore sustainable populations. However, few reintroduced plants are known to persist for more than a few years. Our adaptive‐management case study illustrates how we restored the endangered hemiparasitic annual plant, Chloropyron maritimum subsp. maritimum (salt marsh bird's beak), to Sweetwater Marsh, San Diego Bay National Wildlife Refuge, California, United States, and used monitoring and experimentation to identify the factors limiting the reintroduced population. After extirpation in 1988, reintroduction starting that year led to a resilient, genetically diverse population in 2016 (a “boom” of approximately 14,000) that rebounded from a “bust” (62 in 2014). Multiple regressions attributed 82% of the variation in population counts to tidal amplitude, rainfall, and temperature. Populations of salt marsh bird's beak crashed when the diurnal tide range peaked during the 18.6‐year lunar nodal cycle (a rarely considered factor that periodically added approximately 12 cm to tidal ranges). We explain booms as follows: During smaller tidal amplitudes, above‐average rainfall could desalinize upper intertidal soils and stimulate salt marsh bird's beak germination. Then, moderate temperature in May favors growth to reproduction in June. In addition, salt marsh bird's beak needs a short and open canopy of native perennial plants, with roots to parasitize (not non‐native annual grass pseudohosts) and nearby upland soil for a preferred pollinator, ground‐burrowing bees. Although our reintroduced salt marsh bird's beak population is an exceptional case of persistence, this rare species‐specific environmental and biological requirement makes it vulnerable to rising sea levels and global warming.     

Trade‐offs between reproduction and self‐maintenance (immune function and body mass) in a small seabird,the little auk

Breeding season is the most energetically and physiologically demanding phase in the avian annual cycle, challenging adults' physiology and survival. However, the timing and extent that self‐maintenance of breeding adults is compromised during the breeding season is poorly understood. We investigated the trade‐off between reproduction and self‐maintenance in relation to breeding phase (prelaying, incubation, chick rearing) and sex in a small Arctic seabird, the little auk Alle alle. To measure a bird's allocation of time for self‐maintenance, we examined size‐adjusted body mass and immunocompetence expressed by bacteria (Escherichia coli) killing capacity (BKC) of blood plasma, heterophils/lymphocyte ratio (H/L) and their numbers of particular leucocytes per 10 000 red blood cells (RBC). We found that size‐adjusted body mass decreased as the breeding season progressed. BKC, number of heterophils and H/L values were all was significantly higher at prelaying when compared to all other phases. Interestingly, we found that heavier individuals had higher BKC and number heterophils at the prelaying and chick rearing phases than light individuals. There were no differences by sex in any studied variables. Our results indicate that immunocompetence and body mass of breeding adults decreases over the course of breeding season. The efficiency of the immune system appears to be dependent on the bird's body reserves. Our results suggest that little auks allocation of resources into reproduction negatively affects their self‐maintenance.     

Interspecific song imitation by a Prairie Warbler

Song development in oscine songbirds relies on imitation of adult singers and thus leaves developing birds vulnerable to potentially costly errors caused by imitation of inappropriate models, such as the songs of other species. In May and June 2012, we recorded the songs of a bird that made such an error: a male Prairie Warbler (Setophaga discolor) in western Massachusetts that sang songs seemingly acquired by imitating the songs of a Field Sparrow (Spizella pusilla). Another song type in the bird's repertoire was a near‐normal Group A Prairie Warbler song, but the bird used this song in contexts normally reserved for Group B songs. Despite its abnormal singing behavior, the aberrant bird successfully defended a territory and attracted a mate that laid two clutches of eggs. Results of playbacks of the focal bird's heterospecific song suggested that neighboring conspecific males learned to associate the Field Sparrow‐like song with the focal male, and responded to the song as if it were a Prairie Warbler song. Our evidence suggests that the focal bird's aberrant singing evoked normal responses from potential mates and rivals. If such responses are widespread among songbirds, the general failure of heterospecific songs, once acquired, to spread through populations by cultural transmission is probably not attributable to a lack of recognition by conspecifics of the songs of heterospecific singers.     

Survival of adult Common Guillemots Uria aalge at three Scottish colonies

We present the results of a mark–recapture analysis of survival rates of Common Guillemots with at least one year's breeding experience for birds from three Scottish colonies. Estimates of overall survival of adults from the Isle of May (North Sea), Canna and Colonsay (both off northwest Scotland) from an analysis combining data from the three colonies were 94.8% (se = ±0.6), 92.4% (se = ±0.9) and 96.7% (se = ±0.6) respectively. The rates from Canna (but not Colonsay) differed significantly from those of guillemots on the Isle of May. The Canna and Colonsay figures are the first survival estimates for guillemots in northwest Scotland, an area of high conservation concern for this species. Low input, long-term studies of seabirds can produce important data on adult survival.     

Prior Residence Influences Contest Outcome in Flocks of Non-Breeding Birds

We sought to determine whether early arrival was a determinant of contest outcome in loosely organized, non‐breeding flocks of birds. In White‐throated Sparrows (Zonotrichia albicollis) arrival date during autumn migration, i.e. within‐year prior residence, was a significant determinant of contest outcome for those birds that were not present on the study site in previous years. To determine whether the advantage of early arrival was due to prior residence per se, as opposed to some correlate of arrival date (e.g. condition), we experimentally delayed the arrival of 60 migrants. We found a significant effect of the delay: the outcome of contests between naturally arriving (control) birds and experimentally delayed birds was significantly related to the difference between the control bird's natural arrival date and the experimental bird's delayed arrival date. Thus, prior residence per se, and not some correlate of arrival date, had a significant effect on a naïve individual's ability to win contests. Interestingly, arrival date had no effect on contest outcome among birds that had wintered on the site in previous years. Because a prior residence advantage accumulates in a time‐dependent manner, our results suggest that fighting ability or perceived resource value increases with site familiarity. Thus, there may be selection on arrival date and site‐faithfulness as behavioral strategies to increase access to resources.     

Habitat Quality Affects Early Physiology and Subsequent Neuromotor Development of Juvenile Black-Capped Chickadees

In songbirds, the ability to learn and render the species-specific song is influenced by the development of both the song nuclei in the brain and the syrinx (bird''s vocal apparatus) early in the bird''s life. In black-capped chickadees (Poecille atricapillus), habitat quality is known to affect song structure, with birds in high-quality habitat (mature forest) having a higher song consistency than birds in low-quality habitat (young forest). Although this difference is suspected to stem from differences in development, the developmental status of juvenile birds in either habitat remains unexplored. In this study, we used ptilochronology and feather corticosterone to compare the conditional state of juvenile chickadees in young and mature forest during two distinct periods of song learning - the sensory phase, which occurs prior to settlement, and the sensorimotor phase, which occurs post-settlement. A sample of juvenile males was captured and euthanized several weeks prior to their first breeding season to compare the development of song center nuclei and syrinx in both habitats. The corticosterone levels of natally-grown feathers were greater among birds that settled in mature than young forests - as these feathers were grown pre-settlement, they reflect differences in physiology during the sensory phase. This difference in conditional state is reflected by differences in syrinx and song center nuclei development later during the sensorimotor phase - birds in young forest have smaller syrinx, and moderately-larger RA, than birds in mature forest. Those differences could be responsible for the difference in consistency in song structure observed across habitats. The difference in physiological state across habitats, combined with potential compounding effect of differences in winter resources between habitats, could influence the difference in syrinx and neural development seen in juvenile males during the early spring, and influence the male''s ability to learn and render their species-specific song.     

The effects of food abundance on breeding performance and adult time budgets of Guillemots Uria aalge

The breeding performance, food fed to chicks and adult time budgets of Guillemots Uria aalge were examined in a year of high and a year of low food availabiIity. There was no difference between the 2 years in reproductive success, although the rate of chick feeding, chick weight and fledging success were greater in the year of high food availability. On average, chick prey items were larger in the poor food year, but this was insufficient to compensate for the lower feeding frequency. Chick feeding frequency did not differ between days in the good year but did increase later in the season in the poor food year. Compared with the high food availability year, adult Guillemots in the year of low food availability spent much less time resting at the breeding colony. and their foraging trips were twice as long. Foraging birds tended to make several successive trips before resuming brooding duties from their mates when food supplies were good, but in the low food availability year single trips were the norm. These results demonstrate that predators experiencing reduced food supply may mitigate the effects on their reproductive output by shifting their time allocation such that more time is available for foraging.     

Bird's nest ferns promote resource sharing by centipedes

Bird's nest ferns (Asplenium spp.) support large numbers of invertebrates, including centipedes. As top invertebrate predators, centipedes drive ecosystem function, for example, by regulating decomposer populations, but we know little of their ecology in forest canopies. We provide the first detailed observations of the diversity and structure of the centipede communities of bird's nest ferns, revealing the importance of these epiphytes as nurseries for centipedes. We collected 305 centipedes equating to ˜11,300 mg of centipede biomass from 44 bird's nest ferns (22 of which were from the high canopy and 22 from the low canopy) in primary tropical rainforest in Sabah, Malaysian Borneo. Most abundant were the Scolopendromorpha (n = 227 individuals), followed by the Geophilomorpha (n = 59), Lithobiomorpha (n = 14), and Scutigeromorpha (n = 5). Although we observed very little overlap in species between the forest strata, scolopendromorph centipedes dominated throughout the canopy. Null model analysis revealed no significant competitive interactions; on the contrary, we observed centipedes sharing nest sites within the ferns on three of the ten occasions that we found nests. All nests belonged to centipedes of the family Scolopendridae, which are typically aggressive, and usually show negative spatial association. This study reveals a diverse community of canopy centipedes, providing further evidence of the importance of bird's nest ferns to a wide range of animals, many of which use the ferns at critical life stages. Future conservation strategies should regard these ubiquitous epiphytes as umbrella species and protect them accordingly in landscape management decisions.