Rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata breeding in a seasonal environment

We removed first eggs from early‐laying females to measure rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata at Triangle Island, British Columbia, Canada. Based on egg size and composition, the investment that Cassin's auklets made in first eggs was very close to that predicted from adult body mass, whereas rhinoceros auklets invested more. In both species, a high percentage of females relaid (90% of Cassin's and 87% of rhinoceros auklets). Breeding success declined weakly with later laying among control Cassin's auklet pairs, but pairs that we induced to relay bred more successfully than naturally late pairs, and similar to values predicted from laying dates of their first eggs. Their chicks also fledged heavier and younger than late control chicks, and similar to values in early control chicks, but followed the population‐wide seasonal decline in wing length at fledging. Nestling diets were dominated by Neocalanus copepods until late in the season, a sign that feeding conditions remained favourable until late. In contrast, rhinoceros auklet pairs induced to relay followed the population‐wide seasonal decline in breeding success, which was driven by a decline in hatching success. Pacific sandlance Ammodytes hexapterus, thought to be a preferred prey species, virtually disappeared from nestling diets in mid‐to‐late season, yet there was no seasonal decline in fledging mass. However, chicks from replacement eggs followed the declines among control chicks in both age and wing length at fledging. Despite the female having produced a replacement egg, and despite delayed breeding, there appeared to be little immediate consequence associated with relaying for Cassin's auklets, except for a tendency for their chicks to fledge with short wings. Consequences were more marked in rhinoceros auklets (greatly reduced hatching success, and having their chicks fledge with short wings), and this may have been due to the large investment made in eggs, and/or to delayed breeding. Results of this study show that attributes of Cassin's and rhinoceros auklets that lay at different times in the season can be important in driving seasonal declines in breeding performance, as found in studies on other Alcidae. They also show how decisions taken during the egg stage can have variable yet potentially important implications for fitness, even in relatively long‐lived species that lay single‐egg clutches.     

Predicting population consequences of ocean climate change for an ecosystem sentinel,the seabird Cassin's auklet

Forecasting the ecological effects of climate change on marine species is critical for informing greenhouse gas mitigation targets and developing marine conservation strategies that remain effective and increase species' resilience under changing climate conditions. Highly productive coastal upwelling systems are predicted to experience substantial effects from climate change, making them priorities for ecological forecasting. We used a population modeling approach to examine the consequences of ocean climate change in the California Current upwelling ecosystem on the population growth rate of the planktivorous seabird Cassin's auklet (Ptychoramphus aleuticus), a demographically sensitive indicator of marine climate change. We use future climate projections for sea surface temperature and upwelling intensity from a regional climate model to forecast changes in the population growth rate of the auklet population at the important Farallon Island colony in central California. Our study projected that the auklet population growth rate will experience an absolute decline of 11–45% by the end of the century, placing this population on a trajectory toward extinction. In addition, future changes in upwelling intensity and timing of peak upwelling are likely to vary across auklet foraging regions in the California Current Ecosystem (CCE), producing a mosaic of climate conditions and ecological impacts across the auklet range. Overall, the Farallon Island Cassin's auklet population has been declining during recent decades, and ocean climate change in this century under a mid‐level emissions scenario is projected to accelerate this decline, leading toward population extinction. Because our study species has proven to be a sensitive indicator of oceanographic conditions in the CCE and a powerful predictor of the abundance of other important predators (i.e. salmon), the significant impacts we predicted for the Cassin's auklet provide insights into the consequences that ocean climate change may have for other plankton predators in this system.     

Is the citrus-like plumage odorant of crested auklets (Aethia cristatella) a defense against lice?

Plumage odors may function as chemical defenses against ectoparasites in birds. We tested this hypothesis for crested auklets (Aethia cristatella), a species of colonial seabird that emits a very strong citrus-like odor from its plumage. This odorant contains known chemical repellents. We evaluated evidence for chemical defense in this species using two approaches. First, we exposed pigeon lice to the volatiles emitted by freshly plucked plumage and by whole specimens. Louse survivorship was compared between these treatments and two controls. Second, we compared louse abundance on crested auklets versus a closely related congener that nests in close association. Louse survivorship did not differ between crested auklet treatments and controls. Comparison of ectoparasite loads showed that crested auklets had significantly higher louse abundance than least auklets (A. pusilla), even after controlling for body size. Our results failed to support two expectations for chemical defense. Presence of the crested auklet plumage odorant in our experiments did not reduce louse life span. Presence of the aldehyde odorant in nature did not reduce louse abundance on crested auklets. Hence we conclude that the aldehyde odorant is not immediately lethal to lice at natural concentrations in plumage.     

Disentangling effects of growth and nutritional status on seabird stable isotope ratios

A growing number of studies suggest that an individual’s physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather δ¹⁵N and δ¹³C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing δ¹⁵N and δ¹³C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in δ¹⁵N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC δ¹⁵N, with chicks exhibiting lower δ¹⁵N when they were growing the fastest. As growth slowed, δ¹⁵N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted δ¹⁵N in chick RBCs by 0.92‰. We propose that increased nitrogen-use efficiency is responsible for ¹⁵N depletion in both growing and food-restricted chicks. δ¹⁵N values in RBCs of free-ranging auklets fell within a range of only 1.03‰, while feather δ¹⁵N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue.     

Habitat constraints and spatial bias in seabird colony distributions

What governs the size and location of seabird colonies has long intrigued population ecologists. Previous analysis of the distribution of colonies of four European seabirds revealed a spatial bias - large colonies occurred farther apart than expected by chance alone - suggesting that intraspecific competition for food supplies during breeding may regulate colony size. Here we use computer intensive statistics to show that a similar spatial bias exists in three burrow-nesting seabirds - Cassin's auklet Ptychoramphus aleuticus , rhinoceros auklet Cerorhinca monoccrata , and ancient murrelet Synthliboramphus antiquns - nesting off the Pacific coast of Canada. Local habitat constraints explain much of the existing spatial bias: large colonies cannot fit on small islands, and large islands suitable for colonies tended to occur far apart. However, a residual spatial bias still remained for ancient murrelets and Cassin's auklets (but not rhinoceros auklets) after habitat constraints are built into the analysis, for which intraspecific food competition remains a plausible explanation.     

Field experiments on the effect of ticks on breeding success and chick health of cattle egrets

Abstract Two experiments compared broods that were naturally tick-infested with an equal number that were rendered tick-free by application of an acaricide to their nests and of barriers against further infestation. In the first experiment conducted in 1991–92 nestlings in tick-infested broods had up to 159 larval ticks at once and a mean infestation of 23.6 larval ticks per chick per day. The chick's mean tick load was inversely correlated with its longevity. Chicks that survived to at least 18 days post-hatching had significantly lower larval tick loads than those that died by 18 days, excluding the third-hatched chick in each brood whose survival rate was low irrespective of tick-infestation. At 7 days post-hatching, tick-infested chicks had a lower haematocrit and higher polychromasia than tick-free chicks. I infer that blood loss anaemia caused the deaths of tick-infested chicks in their first week. None died in their second week and the demise of those in their third week may have been due to the paralysis manifested prior to their death. I conclude that heavy tick infestation of their chicks reduced the breeding success of the parent egrets below that of the egrets whose chicks were kept free of ticks. In the second experiment in the 1992–93 season the mean level of tick infestation was much lower (5.1 per chick) and these chicks survived equally with tick-free chicks through fledging.     

Seasonal changes of the at-sea distribution and food provisioning in rhinoceros auklets

Central-place foraging seabirds increase food-loads and decrease meal frequency when they forage in areas that are distant from the breeding colony. In 2001–2002, we studied the seasonal changes in at-sea distribution, food-load mass, meal frequency, and fledging mass in rhinoceros auklets (Cerorhinca monocerata), which forage in coastal waters during the day and feed their chicks at night. In both years, greater numbers of auklets were observed flying in northern waters that are more distant from the colony in June (65 km) and July (65–66 km) than in May (38–47 km). In July of both years, many auklets flew northward across the transect set 65–120 km north of the colony at sunrise; the birds returned south again at sunset, indicating that they foraged in waters outside the study area. This seasonal northward movement of the foraging area may reflect the migration of their main prey item, the Japanese anchovy (Engraulis japonicus), which move with the Tsushima Warm Current flowing from the southern Sea of Japan. Food-load mass did not increase seasonally. In both years, the estimated daily meal frequency was lower in July than in May or June, partly because of the increased foraging distance in July. Late-hatched chicks also displayed lighter fledging masses than early chicks in both years. We suggest that late breeders are required to forage at great distances for longer periods, which may result in decreased meal frequency and lighter fledging mass of their chicks.     

Yolk carotenoids and stable isotopes reveal links among environment, foraging behavior and seabird breeding success

Nutrients that are limited in availability, such as carotenoids, are potentially involved in trade-offs between homeostasis and reproduction. Despite their importance, factors that affect the capacity of female birds to meet their carotenoid requirements are poorly understood. We used δ¹⁵N stable isotope analysis to relate foraging behavior to yolk carotenoid deposition in two seabirds, Cassin’s auklet (Ptychoramphus aleuticus) and rhinoceros auklet (Cerorhinca monocerata), during each of five years. As expected from their narrower trophic range, Cassin’s auklets produced yolks with fewer carotenoid types than did rhinoceros auklets (one vs. three). Cassin’s auklets also fed on a lower trophic level diet richer in carotenoids, yet had lower total yolk carotenoid levels, which suggests a role for species-specific adaptations for carotenoid uptake and utilization. Within both species, lower trophic-level feeding was linked to higher yolk carotenoid levels, but through different mechanisms. In Cassin’s auklets, it was due to a population-wide response to environmental variation: in warm-water years, all females fed at a low trophic level and produced carotenoid-rich yolks. In rhinoceros auklets, it was due to individual differences similarly expressed in all years: females fed across a wide trophic range, and those that fed at a low trophic level produced carotenoid-rich yolks. Rhinoceros auklets bred more successfully in years when their yolks were rich in carotenoids, probably due to a correlated response to stronger marine primary production. Our results are novel because they link avian yolk carotenoid deposition to behavioral and environmental variations.     

Assessment of 17 new whiskered auklet (Aethia pygmaea) microsatellite loci in 42 seabirds identifies 5–15 polymorphic markers for each of nine Alcinae species

We isolated 17 microsatellite loci in the whiskered auklet (Aethia pygmaea) and tested them for amplification in 48 species from 13 seabird families (including 42 seabirds). Fifteen of these loci were also tested for polymorphism in 38 of the species, which included nine species of Alcinae (four auklets, Atlantic puffin, dovekie, razorbill and two murre species). On the average, nine loci were polymorphic per Alcinae species.     

Activity periods and questing behavior of the seabird tick Ixodes uriae (Acari: Ixodidae) on Gull Island, Newfoundland: the role of puffin chicks

Questing behavior of Ixodes uriae and their associated seasonal, host-feeding patterns are crucial to our understanding of tick life history strategies and the ecology of diseases that they transmit. Consequently, we quantified questing behavior of nymphs and adult female I. uriae ticks at Gull Island, a seabird colony in Newfoundland, Canada, to examine seasonal variation of off-host and on-host tick activity. We sampled a total of 133 adult Atlantic puffins (Fratercula arctica), 152 puffin chicks, and 145 herring gull (Larus argentatus) chicks for ticks during the breeding seasons of 2004 and 2005. Questing ticks were sampled by dragging a white flannel cloth across the grassy breeding areas during the mo of May, June, July, and August. Nymph questing activity reached a peak during mid-July (79 and 110 individuals/hr in 2004 and 2005, respectively). The prevalence of nymphs and adult female ticks on different seabird hosts varied between years and during the seasons. Puffin chicks had the highest prevalence (above 70% in July) of nymphs in both years and this was correlated with questing activity. Female ticks rarely fed on puffin chicks, but were prevalent on adult puffins and gulls, although prevalence and questing of ticks were not correlated in these hosts. These patterns of off-host and on-host tick activity suggests that I. uriae ticks likely use a combination of questing and passive waiting, e.g., in puffin burrows, to detect hosts, depending on the tick stage and the host species.     

Detrimental effects of two widespread invasive ant species on weight and survival of colonial nesting seabirds in the Hawaiian Islands

Invasive ants are a significant conservation concern and can have far-reaching effects in ecosystems they invade. We used the experimental control of ant numbers on two pairs of small (<5 ha) offshore islets dominated by either the big-headed ant, Pheidole megacephala or the tropical fire ant, Solenopsis geminata to investigate the influence of these species on seabird hatching success, fledging success and weight. Limited unpublished observations of both ant species attacking nesting seabirds exist, but the frequency of attacks or how they affect seabird growth and survival are unknown. Island-wide treatments with hydramethylnon resulted in the eradication of P. megacephala and the temporary reduction of S. geminata densities. No difference in hatching success, growth, or fledging success of Wedge-tailed Shearwaters (Puffinus pacificus), a common colonial nesting seabird in the Hawaiian Islands was observed on the pair of islets dominated by P. megacephala. On islets dominated by S. geminata, ant control resulted in a temporary increase in fledging success. Injury frequency increased dramatically on the untreated islet (8.3–100%) while remaining the same on the treated islet (27–38%). Severely injured chicks (i.e., chicks that lost >20% of tissue on their feet) weighed significantly less than uninjured chicks and did not fledge. It is unclear if the chicks were being preyed upon or stung in defense of nearby ant colonies. Radical changes in invasive ant populations have been noted, and booming ant populations could cause short-term, but widespread damage to seabird colonies. The negative effects of invasive ants on seabirds may be difficult to detect, and therefore unknown or underestimated throughout the world where the two groups overlap.     

Molting and Seasonal Bill-Plate Shedding in the Whiskered Auklet (Aethia pygmaea)

Feather molting and bill-late shedding were studied because of the unique features of the whiskered auklet biology; i.e., they continue to visit the colony after departure of their young. Like other auklets, the whiskered auklets begin to molt during breeding and do not lose their capacity for flight. The molt pattern of different wing feathers is adaptive and allows new feathers to be protected (when they are soft and could be easily injured) by old or full-grown new feathers during flight or feeding (diving) due to the different timing of the molt of primary feathers and their coverts. The possibility of combining breeding with molt appears to be related to the feeding features of the species. The species that feed on abundant and highly aggregated plankton are able to molt during breeding. The pattern of bill-plate shedding in the whiskered auklet is similar to that in the crested auklet.     

Phylogenetic relationships within the Alcidae (Charadriiformes: Aves) inferred from total molecular evidence

The Alcidae is a unique assemblage of Northern Hemisphere seabirds that forage by "flying" underwater. Despite obvious affinities among the species, their evolutionary relationships are unclear. We analyzed nucleotide sequences of 1,045 base pairs of the mitochondrial cytochrome b gene and allelic profiles for 37 allozyme loci in all 22 extant species. Trees were constructed on independent and combined data sets using maximum parsimony and distance methods that correct for superimposed changes. Alternative methods of analysis produced only minor differences in relationships that were supported strongly by bootstrapping or standard error tests. Combining sequence and allozyme data into a single analysis provided the greatest number of relationships receiving strong support. Addition of published morphological and ecological data did not improve support for any additional relationship. All analyses grouped species into six distinct lineages: (1) the dovekie (Alle alle) and auks, (2) guillemots, (3) brachyramphine murrelets, (4) synthliboramphine murrelets, (5) true auklets, and (6) the rhinoceros auklet (Cerorhinca monocerata) and puffins. The two murres (genus Uria) were sister taxa, and the black guillemot (Cepphus grylle) was basal to the other guillemots. The Asian subspecies of the marbled murrelet (Brachyramphus marmoratus perdix) was the most divergent brachyramphine murrelet, and two distinct lineages occurred within the synthliboramphine murrelets. Cassin's auklet (Ptychoramphus aleuticus) and the rhinoceros auklet were basal to the other auklets and puffins, respectively, and the Atlantic (Fratercula arctica) and horned (Fratercula corniculata) puffins were sister taxa. Several relationships among tribes, among the dovekie and auks, and among the auklets could not be resolved but resembled "star" phylogenies indicative of adaptive radiations at different depths within the trees.      

Accelerated growth rates in late‐hatched Rhinoceros Auklet Cerorhinca monocerata chicks depend on food conditions and growth stage: an experimental approach

In some bird species, the survival of chicks hatching later in the season is lower than those hatched earlier due to increased risk of predation and a seasonal decline in feeding conditions. To reduce these risks, it might be advantageous for late‐hatched chicks to grow faster and hence fledge at younger age. In this experimental study, the growth rates of early‐ and late‐hatched Rhinoceros Auklet Cerorhinca monocerata chicks were compared under average and poor food supplies in captivity. Controlling for potentially confounding effects of chick mass at 10 days old, chick age and nest‐chamber temperature, late‐hatched chicks had higher wing growth rate than early‐hatched chicks before attaining the minimum wing length required for fledgling under both average and poor food supplies. After attaining the minimum wing length, however, late‐hatched chicks had a lower fledging mass, indicating a potential cost that could diminish the early advantage of fast wing growth.     

Dispersal and distribution of the tick Ixodes uriae within and among seabird host populations: the need for a population genetic approach

The aim of this study was to characterize the spatial distribution of the tick Ixodes uriae within and among populations of its seabird hosts and to consider the potential insight that could be gained by a population genetic approach to the issue of dispersal of this tick. Analyses of data collected around the Avalon Peninsula, Newfoundland, indicated that both the prevalence and mean abundance of ticks varied significantly among sample locations. Whereas ticks were found on all 4 host species examined (Rissa tridactyla, Uria aalge, Alca torda, Fratercula arctica), infestation prevalence and mean abundance differed among the species. On R. tridactyla, ticks were significantly aggregated at the among-nest scale and nestling infestation was spatially autocorrelated. Conversely, ticks were not aggregated among chicks within nests. These results enabled us to make a priori predictions regarding tick dispersal and host specificity and suggest there may be spatial structure of Ixodes uriae populations at both macro- and microgeographic scales. Investigating the population genetic structure of ticks within and among populations of hosts with different breeding biologies should provide direct insight into the metapopulation dynamics of such a spatially structured system.     

Inter- and intra-season stability of vocal individual signatures in a social seabird, the crested auklet

Vocal plasticity due to changes of social context is well documented in passerine birds. In other bird species, the impact of social environment changes on the whole vocal structure and on individual specific signatures remains largely unexplored. Here, we assessed inter- and intra-season stability of specific features of individual signatures in advertising calls of crested auklet (Aethia cristatella) males and tested the effects of pair mate and territory changes on the stability of the calls. The crested auklet is a highly social seabird of the North Pacific that breeds in dense colonies, and its individuals switch pair mates and territories with probability of 25–54%. During summer 2008–2010, we recorded 464 trumpet calls from 21 individually marked males and determined their pair mates and positions of their displaying places on a breeding colony of Talan Island, Sea of Okhotsk. We found that strong individual specific features of crested auklet trumpet calls stay stable not only during one season but also from year to year. However, we failed to find any effects of pair mate or territory changes on individual signatures of crested auklet trumpet calls. Our results suggest that crested auklets can potentially use their individually specific trumpet calls to form long-term social bonds both between pair mates and between neighbors; however, future experimental studies should test whether this is indeed the case.     

Ticks on snakes: The ecological correlates of ectoparasite infection in free‐ranging snakes in tropical Australia

Parasites profoundly influence the lives of their hosts, yet the dynamics of host–parasite interactions are poorly understood – especially in reptiles. We examined the ecological correlates of parasitism by ixodid ticks in an assemblage of 10 snake species in tropical Australia. In total, we recorded 3803 ticks on 1841 individual snakes of six species (no ticks were found on the other species). Molecular analyses confirmed the tropical reptile tick (Amblyomma fimbriatum: Ixodidae) to be the most common snake tick at our study site, with inter‐ and intraspecific variation in tick prevalence and intensity. Tick attachment sites were random on most snake species, but both male and female ticks congregated on the heads of the colubrid snake Boiga irregularis and the python Simalia amethistina. In these same species, tick loads were higher on snakes captured in woodland than in rainforest. Females of two python species (Aspidites melanocephalus and S. amethistina) had higher tick loads than did males. In B. irregularis, individuals captured in the dry season had higher tick loads than those captured in the wet season. In most parasitized snake species, larger individuals had greater tick loads. Data from snake recaptures confirmed individual tick burdens frequently varied, with little correlation between tick loads on the same snake at successive captures (except for B. irregularis). Finally, tick intensity was not correlated with (and thus, presumably did not influence) the body condition of any snake species in our study. Use of specific types of refuge sites may strongly influence tick loads on snakes in this system.     

Tick prevalence and species diversity on Aldabran giant tortoises (Dipsochelys dussumieri) in relation to host range and host size in a restored ecosystem, Kenya

Tick species density and diversity on Aldabran tortoises was investigated in relation to the habitat range and size of each tortoise. Identification of tick infestation patterns forms an important aspect of effective tick control. Ten Aldabran tortoises were de‐ticked and monitored over the course of 2 months. Tick species found were Amblyomma sparsum, Amblyomma nuttalli, Amblyomma hebraeum and Boophilus decoloratus, with the most prevalent species found being A. sparsum. Tick loads varied considerably from 20 to 214 ticks per tortoise, with most ticks collected from the head/neck region. Tortoises ranging outside Haller Park had higher tick loads (70–214) compared with tortoises ranging within Haller Park (20–99). Tick load was not correlated with tortoise size. Results indicate that tick loads are related to the habitat range of the tortoises and may indirectly also be related to food preference and host food availability. Implications of the findings and appropriate tick control measures are discussed.     

Vocal and Optical Indicators of Individual Quality in a Social Seabird,the Crested Auklet (Aethia cristatella)

Indicators of individual quality in ornamentation or in vocalizations have been reported for different animal species. However, no studies have jointly investigated ornamentation and vocalizations in one species. The crested auklet (Aethia cristatella, Alcidae) is a small colonial seabird of the North Pacific and is unusual for a bird in using optical, vocal, and olfactory signals. We estimated the potential for coding individual quality in vocalizations and plumage ornamentation and the relationship between vocal and optical traits in crested auklets. During the summer seasons of 2008–2009, we recorded 359 trumpet calls from 28 individually marked males and measured indices of body size, condition, and plumage patterns of 58 male and 48 female crested auklets from a breeding colony on Talan Island, Sea of Okhotsk. We found strong interindividual differences in trumpet call characteristics. Furthermore, we found that the maximum fundamental frequency of the loudest notes of the trumpet call is negatively correlated with body condition, and head crest length is positively correlated with body size. However, we found no relationship between vocal and ornamental traits. The results suggest that advertising calls of crested auklets signal caller individuality and quality, but future experimental studies should test whether or not this is indeed case.     

Mating and remating of least auklets (Aethia pusilla) relative to ornamental traits

We investigated mating patterns of the least auklet, a smallmonogamous seabird, at St. Paul Island, Alaska, during threebreeding seasons. Least auklets mated assortatively with respectto both plumage color, a trait important in status signaling,and tarsus length, an index of body size. Least auklets mateddisassortatively with respect to the extent of facial plumes,but neither assortatively nor disassortatively for any otherornamental trait (bill color, bill ornament size). Mate fidelitywas lower in least auklets than in some long-lived seabird species;when both members survived to a following year, only about two-thirdsof pairs reunited. Nearly half of the auklets paired in 1 yearobtained a new mate in the following year, either because ofmate disappearance or divorce. Interyear fidelity to mates wasrelated only to male ornamentation; males with larger facialplumes were more likely to reunite with their mates the nextyear than males with smaller plumes. There were no significantdifferences in the ornaments of females in reunited and divorcedpairs. Pairs that reunited also had significantly lighter plumagethan pairs that divorced, and the plumage of males reunitingwith their mates was significantly paler than that of divorcedmales. We conclude that the probability of both divorce andremating in this species is influenced by ornamental traits.Our finding that remating was related to male plumage colorand ornaments is consistent with the idea that remating is influencedby female choice. Pairs that reunited also bred earlier in theseason and had higher reproductive success than pairs with experiencedindividuals breeding together for the first time. We also foundevidence that failure to breed in a given year increased theprobability of subsequent divorce.