Small Passerine Birds Research Articles

Integration of a Tick-Borne Encephalitis Virus andBorrelia burgdorferisensu lato into Mountain Ecosystems, Following a Shift in the Altitudinal Limit of Distribution of Their Vector,Ixodes ricinus(Krkonoše Mountains, Czech Republic)

The altitudinal shift in the limit of Ixodes ricinus occurrence above the previously established altitude of 750 m above sea level has been monitored over the long-term (2002-2008) in the Krkonose Mts. (Giant Mts.), the highest in the Czech Republic, along two vertical transects in their eastern and central parts (600-1020 and 600-1270 m). Ticks were collected by flagging three times annually, and examined individually by PCR or RT-PCR for the presence of Borrelia burgdorferi sensu lato or tick-borne encephalitis virus (TBEV). A total of 5999 I. ricinus ticks were tested. TBEV RNA was detected in 26 ticks at up to 1140 m. Demonstration of TBEV in two larvae of I. ricinus indicates transovarial transmission. Similar infection rates in larvae and nymphs show vertical transmission in TBEV circulation to be very important under these mountain conditions. B. burgdorferi sensu stricto was found at up to 1040-1065 m, Borrelia garinii and Borrelia afzelii up to 1080-1140 m, and Borrelia valaisiana up to 1270 m. The total infection rates of nymphs and larvae were 7.3% and 2%, respectively. B. garinii was the most prevalent (37%), followed by B. afzelii (29%), B. burgdorferi s.s. (11%), and B. valaisiana (9%). Double to quadruple coinfections were detected in 32% of the infected ticks, most frequently B. garinii/B. afzelii. Predominance of B. garinii and B. valaisiana over B. afzelii suggests that small passerine birds moving on the ground are responsible for permanent local populations of I. ricinus in mountain localities with low numbers of small terrestrial mammals. The detection of B. burgdorferi sensu lato and TBEV in host-seeking larvae indicates an autochthonic infection. Upon analysis of the local climate we consider climate warming to be responsible for the spreading of ticks and tick-transmitted pathogens to higher altitudes.

Breeding biology of Montagu’s Harrier Circus pygargus in north-central Kazakhstan

The ecology and conservation status of Central Asian populations of Montagu’s Harriers Circus pygargus are poorly known. We studied the breeding biology of this species during 3 years in the Naurzum region, north-central Kazakhstan. Most Montagu’s Harriers in the study area nested in the forest-steppe transition area, in bushy areas dominated by dogrose Rosa canina, which was apparently the nesting vegetation type providing highest and densest nest cover in the study area. Laying occurred from 26 April to 7 June (average 13 May, n = 49) and, although it varied significantly between years, was earlier than in western European populations of similar latitude. Mean (±SD) clutch size was 4.44 ± 0.86 (range 2–6; n = 50), in the higher range observed for the species. There was no significant interannual variation in clutch size, despite large variations in the abundance of small mammals in the area. Diet was mainly composed of lizards (54.2%, n = 533 identified prey in all 3 years), with small mammals (17.1%), passerine birds (14.3%) and insects (13.6%) also being consumed. Mean brood size at the last visit was 2.55 ± 2.10 (range 0–6; n = 51). Failure rate was relatively high; the main identified cause of nest failure was predation. We compare the data obtained in this population breeding in natural steppes with breeding parameters from the well-studied western European populations, and discuss the implications for the conservation of this species.

Species trends, turnover and composition of a woodland bird community in southern Sweden during a period of fifty-seven years

The number of small passerine bird territories was determined annually during 57 years (1953–2009) in a 13 ha broadleaf deciduous wood with several grazed glades, surrounded by crop farmland in southernmost Sweden. Only marginal habitat changes occurred. Both number of species and number of territories increased. Resident species and short-distance migrants tended to increase whereas tropical migrants declined. Many of the changes were similar to trends recorded by the national Breeding Bird Survey, suggesting that they were due to regional population trends. Notable changes were: former dominant Willow Warbler now rare but closely related newcomer Chiffchaff now well established, Garden Warblers replaced by Blackcaps, Tree Pipit strong recent decline, increase of cavity-nesting Great and Blue Tits, locally extinct Yellowhammer recovered. Species turnover between adjacent pair of years was without trend but turnover increased with increasing distance between pair of years predicting complete turnover by about 2190. A comparison with a larger oldgrowth wood nearby indicated no obvious effects of the small size and narrow configuration of the study site on its community.

Metal exposure and effects in voles and small birds near a mining haul road in Cape Krusenstern National Monument, Alaska

Voles and small passerine birds were live-captured near the Delong Mountain Regional Transportation System (DMTS) haul road in Cape Krusenstern National Monument in northwest Alaska to assess metals exposure and sub-lethal biological effects. Similar numbers of animals were captured from a reference site in southern Cape Krusenstern National Monument for comparison. Histopathological examination of selected organs, and analysis of cadmium, lead, and zinc concentrations in liver and blood samples were performed. Voles and small birds captured from near the haul road had about 20 times greater blood and liver lead concentrations and about three times greater cadmium concentrations when compared to those from the reference site, but there were no differences in zinc tissue concentrations. One vole had moderate metastatic mineralization of kidney tissue, otherwise we observed no abnormalities in internal organs or DNA damage in the blood of any of the animals. The affected vole also had the greatest liver and blood Cd concentration, indicating that the lesion might have been caused by Cd exposure. Blood and liver lead concentrations in animals captured near the haul road were below concentrations that have been associated with adverse biological effects in other studies; however, subtle effects resulting from lead exposure, such as the suppression of the activity of certain enzymes, cannot be ruled out for some individual animals. Results from our 2006 reconnaissance-level study indicate that overall, voles and small birds obtained from near the DMTS road in Cape Krusenstern National Monument were not adversely affected by metals exposure; however, because of the small sample size and other uncertainties, continued monitoring of lead and cadmium in terrestrial habitats near the DMTS road is advised.

Environmental effects at two nested spatial scales on habitat choice and breeding performance of barn swallow

Parental effects comprise a wide range of mechanisms that individuals may adopt to enhance viability and adjust the phenotype of their offspring according to the conditions that the offspring will experience after birth. For example, individual choice of breeding habitat may mediate such parental effects via an effect of prenatal breeding conditions independently or in combination with offspring post-natal environment. However, ecological factors relevant to adaptive breeding habitat choice may vary at different spatial scales, which have been rarely investigated simultaneously. In the first part of the present study we use hierarchical linear models to disentangle micro- and macro-environmental variation in abundance and breeding performance of a small passerine bird, the barn swallow Hirundo rustica. We show that environmental conditions at the scale of nesting microhabitat are more influential than macro-environmental conditions at the scale of foraging range. We then experimentally investigate the effect of variation in micro-environmental conditions on growth and immunity of chicks by partially cross-fostering nestlings immediately after hatching between different nesting micro-habitats. Our results disclosed significant effects of environmental conditions where eggs were laid and incubated but not of those where nestlings grew-up on some components of nestling phenotype important for fitness. These results suggest that adults may enhance offspring quality by adjusting prenatal parental effects mediated by e.g., egg quality according to micro-habitat conditions where parents are breeding.

Development of stress response in nestling pied flycatchers

Birds respond to unpredictable events by secreting corticosterone, which induces various responses to cope with stressful situations. However, the evidence is still elusive whether altricial nestlings perceive and respond to external stressors. We investigated the development of adrenocortical stress response to handling-related stressor in nestlings of a small passerine bird, the pied flycatcher (Ficedula hypoleuca). Nestlings were held in isolation from their parents during the experiment to ensure that they indeed respond to handling, not to parental alarm calls. We found that both 9- and 13-day-old nestlings were able to elicit hormonal stress response. Although baseline as well as stress-induced corticosterone levels rose slightly with age, the magnitude of difference between the control and stress-induced levels remained similar in both age groups. However, comparison with adults showed that the stress response of nestlings prior to fledging was still incomplete and significantly lower than in adults. Overall, our results indicate that altricial nestlings do respond to acute stressors, but on the contrary to previous predictions the development of corticosterone stress response during growth period is not gradual and varies remarkably between different passerine species.

Habitat and fig characteristics influence the bird assemblage and network properties of fig trees from Xishuangbanna, South-West China

Abstract:To understand how fruit tree characteristics and microhabitats shape the assemblage of birds on fig trees and the pattern of fig–bird interactions, we observed and recorded, over 96 d and 816 h, the frugivorous birds visiting 32 individual trees belonging to 14 species ofFicusthat were distributed across four different sites. A total of 30 bird species were recorded as eating figs, comprising 66.7% of the total number of frugivorous bird species recorded at the four sites. Small passerine birds such as bulbuls were the dominant frugivores for fig species. The number of bird species visiting different fig trees was significantly influenced by the crop size and canopy volume. Fruit colour and fruit size did not significantly influence the number of bird species, whereas habitats appeared to influence the composition of visiting birds. The fig–frugivorous bird interaction was asymmetrically structured, and the degree of nestedness appeared to be influenced by the forest type and degree of disturbance: the degree of nestedness in non-limestone forest tended to be higher than limestone forest; forest with less disturbance tend to be more nested compared with the open forest with high disturbance.

Local survival of pied flycatcher males and females in a pollution gradient of a Cu smelter

Survival is one of the most central population measures when the effects of the pollution are studied in natural bird populations. However, only few studies have actually measured rigorous survival estimates on adult birds. In recent years there has been a methodological advance in survival analyses by mark-recapture models. We modelled local survival (including mortality and emigration) with the program MARK in a population of a small insectivorous passerine bird, the pied flycatcher ( Ficedula hypoleuca), around a point source of heavy metals. The local survival of females in the polluted area was about 50% lower than in the other areas. Males, however, survived relatively well in the heavily polluted area, but showed somewhat lower survival in the moderately polluted area. Different pollution effects between two sexes might be due to pollution-related differences in reproductive effort in females and males, and/or more intensive uptake of heavy metals by laying females.

Cadmium, lead, and mercury levels in feathers of small passerine birds: Noninvasive sampling strategy

Bird feathers have been widely used as a nondestructive biological material for monitoring heavy metals. Sources of metals taken up by feathers include diet (metals are incorporated during feather formation), preening, and direct contact with metals in water, air, dust, and plants. In the literature, data regarding the origin of trace elements in feathers are not univocal. Only in the vast literature concerning mercury (as methyl mercury) has endogenous origin been determined. In the present study, we investigate cadmium, lead, and mercury levels in feathers of prey of Falco eleonorae in relation to the ecological characteristics (molt, habitat, and contamination by soil) of the different species. Cluster analysis identified two main groups of species. Differences and correlations within and between groups identified by cluster analysis were then checked by nonparametric statistical analysis. The results showed that mercury levels had a pattern significantly different from those of cadmium and lead, which in turn showed a significant positive correlation, suggesting different origins. Nests of F. eleonorae proved to be a good source for feathers of small trans-Saharan passerines collected by a noninvasive method. They provided abundant feathers of the various species in a relatively small area--in this case, the falcon colony on the Isle of San Pietro, Sardinia, Italy.

Estimating lipid and lean body mass in small passerine birds using TOBEC, external morphology and subcutaneous fat‐scoring

To assess regression models for lipid and lean body mass in small birds, we recorded live body mass ±0.1 g, total body electrical conductivity (TOBEC; from “third generation” TOBEC machine EM‐SCAN® SA‐3000) or E‐Value, visual fat score (VisFat), and seven body measurements for 52 migratory passerine birds of 13 species (5–40 g). We determined lipid and lean mass of each bird after petroleum‐ether extraction of lipids. We obtained “net”E‐Value (NEV) for each scanned bird by subtracting the E‐Value of the empty bird‐restraining tube, because these showed an inverse temperature dependence (P<0.005). Leave‐one‐out cross validation was used to assess model selection and construct 95% confidence intervals. Although precision of TOBEC increased with bird size (CV of NEV vs. live mass: r=−0.276, P=0.002) and it explained an increasing proportion of variation in lean mass moving from small‐ to medium‐ to large‐bird classes of our data, it did no better than head length in single‐variable prediction of lean or lipid mass and was included in five of the 14 multivariate models we developed. The best multiple regression to predict lean mass included live weight, VisFat, bill length, tarsus and lnNEV (adjusted R2=99.0%); however, the same model lacking only lnNEV yielded aR2=98.9%. A parallel to the above pair of models, but predicting lipid mass, yielded aR2=90.3% and 90.0%, respectively. Subdividing the data by three size classes and three taxa (American redstart Setophaga ruticilla, ovenbird Seiurus aurocapilla, warblers), best‐subset multiple‐regression models predicted lean mass with aR2 from 94.7 to 99.6% and lipid mass with aR2 from 85.4 to 98.3%. Best models for the size‐ and species‐groups included VisFat and zero to five body measurements, and most included live weight. lnNEV was included only in the models for ovenbird (lipid), warblers (lipid), all birds (both), and large birds (both). Actual lipid mass of all birds was more highly correlated with multiple‐regression‐predicted lipid mass (r=0.955) than with visual subcutaneous fat‐scoring (r=0.683). These multiple‐regression models predicting lipid content using live‐bird measurements and visual fat score as independent variables represent more accurate and precise estimates of actual lipid content in small passerines than any previously published. They are particularly accurate for placing birds into percentage body‐fat classes.

Seventy new microsatellites for the pied flycatcher, Ficedula hypoleuca and amplification in other passerine birds

The pied flycatcher (Ficedula hypoleuca) is a small migratory passerine bird commonly distributed across Europe which has been the focus of considerable ecological and evolutionary research. Here, we present details of 70 microsatellite markers for the species adding to the six which are currently available. Sixty-six markers were also polymorphic in the closely related collared flycatcher (Ficedula albicollis), while 54 were polymorphic in another related passerine, the bluethroat (Luscinia svecica), and 12 were polymorphic in the more distantly related Siberian jay (Perisoreus infaustus).

Natural and experimental Salmonella Typhimurium infections in foxes ( Vulpes vulpes)

The red fox ( Vulpes vulpes) can be considered as a relevant indicator species for Salmonella in the local environment and Salmonella faecal carriage was investigated in 215 red foxes in Norway shot during the winters 2002/2003 and 2003/2004. Fourteen (6.5%) of the foxes carried Salmonella. Four isolates were determined as serovars Kottbus ( n = 2) and Hessarek ( n = 2) of Salmonella enterica subspecies enterica, and one as S. enterica subspecies IIIb:61:k:1,5,(7). The remaining nine isolates were S. enterica subspecies enterica serovar Typhimurium 4,12:i:1,2 and all displayed the same pulsed-field gel electrophoresis (PFGE) profile designated A2. This serovar regularly causes disease outbreaks amongst small passerine birds during winter and most of these outbreaks are associated with the PFGE profile A2. The results strongly indicated that the Salmonella Typhimurium infections in red foxes were primarily acquired through ingestion of infected small passerines. To investigate the capability of the A2 strain to establish a true intestinal infection in the fox an inoculation experiment with an A2 isolate from small passerines was carried out in farmed silver foxes ( V. vulpes). The experiment also included one strain with an uncommonly occurring profile (X201) from small passerines. To highlight possible differences in capability of the two inoculation strains to pass the acid gastric juice in the fox, in vitro studies of their acid tolerance was carried out. Also their catalase activity and biofilm production were studied. All three foxes inoculated with the A2 strain developed sub-clinical intestinal infection of 2 weeks duration, whereas none of the three foxes inoculated with the X201 strain shed this bacterium. The X201 strain displayed a much lower capability, than the A2 strain, to survive at pH 3 in vitro. The low acid tolerance probably made it difficult for the X201 strain to pass the stomach and establish an intestinal infection in the experimental foxes. Reduced catalase activity and biofilm production were found for the X201 strain, indicating that the low acid tolerance was caused by a defect in the stationary-phase stress response system.

Offspring sex ratio in the sequentially polygamous Penduline Tit Remiz pendulinus

Despite the growing literature on facultative sex-ratio adjustment in chromosomal sex-determining vertebrate taxa (birds, mammals), the consistency of results is often low between studies and species. Here, we investigate the primary and secondary offspring sex ratio of a small passerine bird, the Eurasian Penduline Tit (Remiz pendulinus) in three consecutive years. This species has a uniquely diverse breeding system, in which the male (and/or the female) abandons the nest during egg-laying, and starts a new breeding attempt. This allowed us to test (1) whether patterns of parental care, i.e., male-only care, female-only care or biparental desertion, influence offspring sex ratio, and (2) whether the offspring sex ratio is repeatable between successive clutches of males and females. Using molecular markers to sex 497 offspring in 176 broods, we show that (1) offspring sex ratio does not depend on which parent provides care, and (2) the offspring sex ratio is not repeatable between clutches of a given individual. The overall primary and secondary offspring sex ratio at a population level is not different from parity (54 ± 6% males, and 50 ± 3% (mean ± SE), respectively). We suggest that ecological and phenotypic factors, rather than individual traits of parents, may influence offspring’s sex, and conclude that there is currently no evidence for a facultative adjustment of offspring sex ratio in the Penduline Tit.

The Influence of Habitat Structure on Sexual Conflict Over Care in Penduline TitsRemiz pendulinus Woodpecker

Spatial and temporal distributions of resources and habitats often influence breeding systems. These influences are particularly relevant in those species that exhibit variable breeding systems. We studied such a species, the Penduline Tit Remiz pendulinus. This small passerine bird has sequential polygamy by both sexes, and evidence suggests intense sexual conflict between males and females over care. We estimated habitat structure by scoring the vegetation important for nest building and foraging in the immediate surroundings of the nest. Using four principal components we show that sites with more abundant vegetation are occupied earlier than sites with sparse vegetation. However, habitat structure does not predict mating success or reproductive success, and it neither predicts which parent (the male, the female or both) deserts the clutch. We therefore suggest that habitat structure does not have a direct effect on reproductive success or on the resolution of sexual conflict in Penduline Tits. Specific aspects of habitats, such as food and nest material availability, remain to be tested.

AGE-RELATED CHANGES IN THE ACTIVITY OF BONE ALKALINE PHOSPHATASE AND ITS APPLICATION AS A MARKER OF PREFLEDGING MATURITY OF NESTLINGS IN WILD PASSERINES

Abstract Recent studies have suggested that bone alkaline phosphatase (ALP) may be a valuable indicator of skeletal development in wild birds. However, the information about age-related dynamics of ALP isoforms in passerines is very scanty. We examined age-related changes in the activity of bone ALP and liver ALP and tested the applicability of these isoenzymes as indicators of chick maturity in randomly selected nestlings of a small passerine bird, the Great Tit (Parus major). Bone ALP activity was elevated in the middle of the nestling period (day 8), when skeletal growth is assumed to be most rapid, and declined significantly during the prefledging stage (day 15 posthatch). Bone ALP activity at this age was positively and highly significantly related to the overall duration of nestling period and negatively and less significantly related to wing length and body mass. All three morphological traits of the 15-day-old nestlings were nearly significantly negatively correlated with the duration of the nestl...

Sexual conflict and consistency of offspring desertion in Eurasian penduline tit Remiz pendulinus

BackgroundThe trade-off between current and future parental investment is often different between males and females. This difference may lead to sexual conflict between parents over care provisioning in animals that breed with multiple mates. One of the most obvious manifestations of sexual conflict over care is offspring desertion whereby one parent deserts the young to increase its reproductive success at the expense of its mate. Offspring desertion is a wide-spread behavior, and its frequency often varies within populations. We studied the consistency of offspring desertion in a small passerine bird, the Eurasian penduline tit Remiz pendulinus, that has an extremely variable breeding system. Both males and females are sequentially polygamous, and a single parent (either the male or the female) incubates the eggs and rears the young. About 28–40% of offspring are abandoned by both parents, and these offspring perish. Here we investigate whether the variation in offspring desertion in a population emerges either by each individual behaving consistently between different broods, or it is driven by the environment.ResultsUsing a three-year dataset from Southern Hungary we show that offspring desertion by females is consistent between nests. Male desertion, however, depends on ambient environment, because all males desert their nests early in the season and some of them care late in the season. Therefore, within-population variation in parental care emerges by sexually different mechanisms; between-individual variation was responsible for the observed pattern of offspring desertion in females, whereas within-individual variation was responsible for the observed pattern in males.ConclusionTo our knowledge, our study is the first that investigates repeatability of offspring desertion behavior in nature. The contrasting strategies of the sexes imply complex evolutionary trajectories in breeding behavior of penduline tits. Our results raise an intriguing question whether the sexual difference in caring/deserting decisions explain the extreme intensity of sexual conflict in penduline tits that produces a high frequency of biparentally deserted (and thus wasted) offspring.

The Rate of Bone Mineralization in Birds Is Directly Related to Alkaline Phosphatase Activity

Recent studies have suggested that a biochemical marker, plasma alkaline phosphatase (ALP), can be used as a general indicator of skeletal development in vertebrate animals. In birds, age-related variation in ALP activity, presumably due to bone formation processes, has been demonstrated, but to date, a direct connection between bone mineralization and enzyme activity has been elusive. In this study, we show that the activity of a bone isoform of ALP (bone ALP) is closely related to the overall rate of skeletal mineralization in nestlings of a small passerine bird, the great tit (Parus major L). Moreover, bone ALP activity predicted the rate of mineralization of leg and wing bones but not that of the skull. Liver isoform of ALP was only marginally related to the overall rate of skeletal mineralization, while no association with the mineralization of long bones was found. We conclude that bone ALP activity in the blood plasma is a reliable biomarker for skeletal mineralization in birds. This marker enables detection of subtle developmental differences between chicks of similar structural size, potentially facilitating the prediction of offspring mid- and long-term survival.

Using cross-classified multivariate mixed response models with application to life history traits in great tits (Parus major)

Longitudinal observations on known individuals are an important source of data with which to test evolutionary theory within natural populations, in particular, the evolution and maintenance of life-history traits. In this paper, we concentrate on the reproductive behaviour and survival of a small passerine bird, the great tit ( Parus major). The dataset we consider is taken from the long-term study of great tits in Wytham Woods in Oxfordshire. The models we consider are designed to relate variation in several phenotypic response variables that are linked to evolutionary fitness, alongside the correlations between them, to both general environmental and individual-specific factors. We fit multivariate cross-classified random effects models using a Markov chain Monte Carlo (MCMC) estimation algorithm described in the paper. Our results show for which traits variability is influenced by environmental factors and for which traits individual bird factors are more important. The partitioning of correlations is particularly illuminating, producing some pairs of ‘antagonistic’ correlations which are biologically meaningful.

Reintroduction of rifleman Acanthisitta chloris to Ulva Island, New Zealand: evaluation of techniques and population persistence

AbstractRifleman, or titipounamu Acanthisitta chloris, is New Zealand’s smallest endemic passerine. The species has a fragmented distribution and is threatened in the Rakiura region in the south of the South Island. The only known population of South Island rifleman A. c. chloris in the Rakiura region persisted on Codfish Island/Whenua Hou. To create a second population of rifleman in Rakiura, 30 caught from Codfish Island were reintroduced onto nearby Ulva Island in February 2003, the first translocation of rifleman. Survival and dispersal were monitored for 1 month post-release, and subsequently during the first and second breeding seasons. Mortality was greatest during holding and transfer, with low to moderate post-release mortality. All founding pairs bred in the first breeding season, and both founders and offspring bred in the second season. Dispersal across the island was greater for offspring. A simple deterministic matrix model indicated positive annual population growth (λ = 1.33), and low risk of short-term extinction. Holding/transfer techniques should be improved for future reintroductions, and longer-term monitoring should be undertaken for a more accurate assessment of vital rates. Based on the survival of founding birds, reproduction by the release generation and their offspring, and high probability of population persistence, the rifleman reintroduction was considered to be successful and a good model for future reintroductions of small passerine birds.

Sexual conflict over parental care in Penduline Tits Remiz pendulinus: the process of clutch desertion

Do the two parents at a nest make simultaneous decisions whether to care for their offspring or to desert? If a single parent is sufficient for rearing young, one parent (typically, the male) may desert and reproduce with a new mate within the same breeding season, leaving the other parent with the brunt of care. As each parent is expected to maximize its own reproductive success, the interests of the two parents do not necessarily coincide, and a sexual conflict over care may emerge. Here we investigate the process of clutch desertion in a small passerine bird, the Penduline Tit Remiz pendulinus. Among birds, this species has a remarkably variable breeding system, because a single parent (either the male or the female) may provide the full care of the young, whereas about 30% of clutches are abandoned by both parents. First, we show that biparental desertion occurs within a single day in 73.7% of the clutches (n = 14), whereas desertion decisions are sequential in 26.3% of the clutches (n = 5) (male first: 10.5% (n = 2); female first: 15.8% (n = 3); n = 19 clutches in total). Secondly, we observed the behaviour of both parents before desertion, and investigated whether desertion can be predicted from their behaviour. However, neither singing nor nest‐building behaviour predicted whether the male or the female would desert. We therefore suggest that biparental desertion may be simultaneous by male and female in our population of Penduline Tits. Furthermore, the parents do not appear to signal their intention to desert their mate. We argue that the parents’ interest may be actually to disguise their intention to desert.