Mass Recession Research Articles

Ablation mechanism of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composite during plasma ablation above 2000 °C

Air plasma ablation behavior of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composite was studied systematically with the surface temperature above 2000 °C at the ablation center. It presents a linear recession rate of 0.15 μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m2 (2000 °C) for 300 s. Associated with the temperature gradient of the ablation surface, the oxidation products at different locations mainly consist of (TiZrHfNbTa)Ox, (ZrxHf1–x)6(NbyTa1–y)2O17, Ti(NbxTa1–x)2O7, (HfxZr1–x)SiO4, and SiO2. Due to the synergistic effect of the multi-component oxides, oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases. It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring. It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.

Decoupling of body size, physiological state and subsequent performance in a developmentally manipulated songbird

Abstract It is generally assumed that larger juveniles are more physiologically mature, hence their overall condition and subsequent performance are higher. Some taxa face extreme workload transitions during development (e.g. nest departure in birds), which may select for non‐linear growth profiles that decouple relationships between body size and physiological state, making the links between metrics of development (e.g. body mass) and juvenile performance uncertain. We manipulated perceived mass in European starlings approaching fledging using 4.0 g weighted backpacks, measuring subsequent growth trajectories (mass, wing length) and physiological state (aerobic capacity, energy state, oxidative status) to test whether body size and physiology are coupled during a non‐linear developmental phase (pre‐fledging mass recession). Nanotag radio transmitters were then used to track post‐fledging performance (activity, activity‐slope, dispersal). Weighted nestlings had greater pre‐fledging mass recession and marginally reduced wing growth when compared to controls. Consequently, weighted birds had lower body mass at fledging, while also displaying markers of oxidative stress (increased reactive oxygen metabolites), yet aerobic capacity and energy state were equal between treatment groups. Previously weighted birds showed no correlation between fledgling state (body size, physiology) and subsequent performance. However, control fledglings that had decreased mass recession and greater wing growth prior to fledging dispersed earlier, while longer wings at fledging were associated with more rapid increases in post‐fledging activity (activity‐slope). In addition, control fledglings with lower haemoglobin also dispersed earlier, while increased reactive oxygen metabolites were associated with decreased activity levels. Body mass and energy state were unrelated to any metric of post‐fledging performance. Our data suggest mass‐independent development of some physiological traits in species with non‐linear growth profiles, potentially with a context‐dependent oxidative cost, and that physiology may predict some measures of post‐fledging performance not captured by body size. Read the free Plain Language Summary for this article on the Journal blog.

Efficient fabrication and properties of 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via slurry infiltration lamination combined with precursor infiltration and pyrolysis

In this work, an efficient processing route was developed to fabricate Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites via slurry infiltration lamination (SIL) combined with precursor infiltration and pyrolysis (PIP). The (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C powder was initially synthesized at 1900 °C. Then the 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites were obtained via SIL and PIP at temperatures no higher than 1100 °C. The as-fabricated composites show a density of 2.52 g/cm3 and an open porosity of 15.2 vol%, with a bending strength of 255 ± 15 MPa. The 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites also present excellent ablation resistance, with the linear and mass recession rates of 0.33 µm/s and 0.60 mg/s after ablation at 2000 °C/300 s. This work provides a route for the efficient fabrication of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites, and also inspires new strategies to develop high-entropy ceramic matrix composites with high performance.

Variation in oxidative status, but not structural and physiological development, associated with changing ontogenetic environments.

Despite the potential for temporally-dependent relationships between trait values and fitness (e.g., as juveniles approach life-stage transitions such as fledging), how developmental stage affects canalization (a measure of robustness to environmental variation) of morphological and physiological traits is rarely considered. To test the sensitivity of morphological and physiological traits to environmental variation in two developmental stages, we manipulated brood size at hatch in European starlings (Sturnus vulgaris) and cross-fostered chicks between enlarged and reduced broods approaching fledging. We measured body size (mass, tarsus, wing length) and physiological state (aerobic capacity, oxidative status) at asymptotic mass on day 15, then cross-fostered chicks between 'high' and 'low' quality environments and assessed the same traits again on day 20, after five days of pre-fledging mass recession. Chicks in reduced broods were heavier at asymptotic mass and had lower reactive oxygen metabolites than enlarged broods, while structural size, aerobic capacity, and antioxidant capacity were unaffected by experimental brood size. The observed canalization of structural and physiological traits during early development was maintained after cross-fostering, during late development. However, in contrast to early development, antioxidant capacity approaching fledging appeared sensitive to environmental conditions, as trajectories varied by cross-fostering treatment. Elevated reactive oxygen metabolites observed after early development in enlarged brood chicks were maintained after cross-fostering, suggesting canalized development in low-quality environments could produce oxidative costs that carry over between life-stages, even when conditions improve. These data reveal trait-specific relationships between environmental conditions and development and highlight how natal environment effects may vary by developmental stage.

Ablation behaviour of Csf/ZrB2-SiC composites fabricated by direct ink writing and reactive melt infiltration

Pitch-based short carbon fibres reinforced Csf/ZrB2-SiC composites were fabricated by direct ink writing of short carbon fibres, followed by slurry impregnation and reactive melt infiltration. Ablation behaviour of the Csf/ZrB2-SiC composite was studied by air plasma test. It is indicated that the skeleton of the oriented short carbon fibres provides heat diffusion channels. Consequently, temperatures at the ablation surface are as low as ∼1730 oC and ∼2000 oC respectively at 4 MW/m2 and 5 MW/m2. The composite presents outstanding ablation-resistant performance with a linear recession rate of ∼ − 0.04 µm/s and mass recession rate of ∼ − 3.40 mg/s at 4 MW/m2, ∼ − 0.17 µm/s and ∼ 3.58 mg/s at 5 MW/m2. It is revealed that the fibres area and matrix area of the composite present different ablation mechanisms. The fibres area is ablated severely, while the matrix area presents excellent ablation-resistance with continuous ZrO2-SiO2 protective layer.

Microstructure and properties of C/C–ZrC composites with matrix modification by slurry infiltration

C/C–ZrC composites are promising thermal structural materials for aerospace applications. However, until now, the reported C/C–ZrC composites exhibited a porous matrix and weaker mechanical properties. In this study, the matrices of C/C–ZrC composites were modified by slurry infiltration in order to improve density and properties. Different slurry powders such as SiC, ZrC, and ZrB2 were used to densify the C/C–ZrC composites. After slurry infiltration, the loose C–ZrC matrix was connected to a dense matrix, and some ceramic powders settled on the surface of the composites. The density of the composites increased from 1.94 to 2.42 ± 0.06 g cm-3, while the porosity decreased from 39.4 ± 4.4% to 10.3 ± 1.9% after infiltration with various slurries. The ablation and mechanical properties of the C/C–ZrC composites improved significantly by matrix modification. The flexural strength of the composites increased from 116 to 269 ± 21 MPa after slurry infiltration. Furthermore, the ablation properties of C/C–ZrC composites infiltrated with the ZrB2 slurry showed the lowest linear rate (24.7 μm s-1) and mass recession rate (7.5 mg s-1).

Ablation behavior and mechanisms of 3D-Cf/Ta0.8Hf0.2C-SiC composite at temperatures up to 2500 °C

In this work, ablation behavior and mechanisms of 3D-Cf/Ta0.8Hf0.2C-SiC composite were studied via air plasma test at temperatures up to 2500 °C. At temperatures below 2000 °C, a continuous oxides layer composed of o-Ta2O5(H) – t-Ta2O5 – Hf6Ta2O17(H) – SiO2 is formed on the ablation surface, which turns to o-Ta2O5(H) – SiO2 above 2200 °C. During ablation, o-Ta2O5(H) precipitates from the glassy SiO2 and grows up following Oswald ripening. Although the volatilization of SiO2 aggravates with ablation temperature increase and ablation time extension, o-Ta2O5(H) – SiO2 melt can still serve as effective self-healing similar to SiO2 glass. Accordingly, the multiphase oxides layer formed on the ablation surface provides a stable protective effect for the internal composite under all the tested ablation conditions. As a consequence, the 3D-Cf/Ta0.8Hf0.2C-SiC composite presents outstanding ablation-resistant performance even at 2500 °C for 300 s, with a linear recession rate of ∼ 5.7 µm/s and a mass recession rate of 2.91 mg/s.

Ablation behavior and mechanisms of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C–SiC high-entropy ceramic matrix composites

For the first time, air plasma ablation behavior of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C–SiC high-entropy ceramic matrix composites was studied systematically under a heat flux of 5 MW/m2, which provided a quasi-real hypersonic service environment at a temperature up to 2430 °C. The Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C–SiC composites present excellent ablation-resistant performance with a linear recession rate of ∼2.89 μm/s and mass recession rate of ∼2.60 mg/s, which can be attributed to the dense and stable oxides layer formed on the sample surface. (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C is oxidized to high-entropy oxide (TiZrHfNbTa)Ox at the ablation center and highly viscous SiO2 melt with uniformly dispersed (TiZrHfNbTa)Ox microspheres is formed. While at the edge of the ablation center, precipitation occurs during cooling and the oxides layer turns to a plate-like (Hf0.5Zr0.5O2)’ skeleton surrounded by (TiNbTaO7-y)’ nanocrystals and continuous SiO2 melt. In contrast, oxidation of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C to produce (Hf0.5Zr0.5O2)’ and (TiNbTaO7-y)’ is dominant at the ablation transition area and outer area with lower temperature. The multiphase oxides formed during ablation provide a stable and highly self-healing protective layer for the internal materials at ultra-high temperatures.

Long-term and cyclic ablation behavior of La2O3 modified Cf/ZrB2-SiC composites at 2500 ℃

In this work, long-term and cyclic ablation behavior of the La2O3 modified Cf/ZrB2-SiC composites were studied by air plasma torch at 2500 ℃. It is indicated that a micron-sized ZrO2-La2O3-SiO2 liquid phase layer forms on the ablation surface at 2500 ℃, which reduces the evaporation of SiO2 and decreases the mass recession rates of the composites. However, the ZrO2-La2O3-SiO2 liquid phase layer exhibits poor structure stability. In addition, the La2O3 weakens the pinning effect of bulk ZrO2. Consequently, the oxide layer with low viscosity tends to sputter out due to the mechanical scouring by plasma flame. Therefore, the linear recession rates of the composites are increased during cyclic ablation with the increase of the La2O3 content.

Flexible growth and body mass predict physiological condition at fledging in the synchronously breeding European starling, Sturnus vulgaris.

Recent studies have reported beneficial carryover effects of juvenile development that predict interspecific survival differences at independence. Yet, traits relating to body size (i.e. morphological traits) have proven to be unreliable predictors of juvenile survival within species. Exploring individual variation of growth trajectories and how they covary with physiology could reveal species-specific developmental modes which have implications for our assessments of juvenile quality. Here, we investigated morphological development of European starlings (Sturnus vulgaris) approaching fledging in relation to three components of physiological condition at independence: aerobic capacity, energy state and oxidative status. We found evidence of flexible mass and wing growth which independently covaried with fledgling energy state and aerobic capacity, respectively. By comparison, tarsus and wing length at fledging were unrelated to any physiological trait, while mass was positively associated with principal component scores that comprised aerobic capacity and energy state. Thus, flexible growth trajectories were consistent with ‘developmental plasticity’: adaptive pre-fledging mass recession and compensatory wing growth, which seemingly came at a physiological cost, while fledgling body mass positively reflected overall physiological condition. This highlights how patterns of growth and absolute size may differently reflect fledgling physiology, potentially leading to variable relationships between morphological traits and juvenile fitness.

Fabrication and properties of Cf/Ta4HfC5‐SiC composite via precursor infiltration and pyrolysis

AbstractIn this study, a Cf/Ta4HfC5‐SiC ultra‐high‐temperature ceramic matrix composite exhibiting a homogeneous phase distribution was successfully fabricated via precursor infiltration and pyrolysis processing. Initially, the pyrolysis and solid solution mechanisms exhibited by the Ta4HfC5 precursor were investigated and characterized through TG‐MS and XRD analysis. The as‐fabricated Cf/Ta4HfC5‐SiC composite exhibited a density and open porosity of 2.84 g/cm3 and 10.62 vol%, respectively. It also exhibited outstanding mechanical properties, with a flexural strength of 339 ± 20 MPa and fracture toughness of 11.56 ± 0.77 MPa·m1/2. The Cf/Ta4HfC5‐SiC composite demonstrated strong ablation resistance under a heat flux of 5 MW/m2 at ~2400℃, with corresponding linear and mass recession rates of 5.33 μm/s and 6.18 mg/s, respectively. The combination of strong mechanical properties and ablation resistance provides a solid basis for the use of the Cf/Ta4HfC5‐SiC composite in a new generation of ultra‐high‐temperature materials.

Fabrication and properties of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via precursor infiltration and pyrolysis

In this work, Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites were reported for the first time. Based on the systematic study of the pyrolysis and solid-solution mechanisms of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C precursor by Fourier transform infrared spectroscopy, TG-MS and XRD, Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC with uniform phase and element distribution were successfully fabricated by precursor infiltration and pyrolysis. The as-fabricated composites have a density and open porosity of 2.40 g/cm3 and 13.32 vol% respectively, with outstanding bending strength (322 MPa) and fracture toughness (8.24 MPa m1/2). The Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites also present excellent ablation resistant property at a heat flux density of 5 MW/m2, with linear and mass recession rates of 2.89 μm/s and 2.60 mg/s respectively. The excellent combinations of mechanical and ablation resistant properties make the Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites a new generation of reliable ultra-high temperature materials.

Improved ablation resistance of 3D-Cf/SiBCN composites with (PyC/SiC)3 multi-layers as interphase

Ablation behavior of 3D-Cf/SiBCN composites with (PyC/SiC)3 multi-layers as interphase was investigated in plasma ablation flame at a heat flux of 4.02 MW m−2. During ablation, amorphous SiBCN matrix is firstly oxidized and forms a borosilicate glass, in which B2O3 is volatilized as the ablation going on. At the ablation center with higher temperature, SiC and Si3N4 grains are precipitated from the amorphous SiBCN matrix. And then, these SiC and Si3N4 grains are oxidized, forming a certain viscous silica rich protective coating on the sample surface. Moreover, it is revealed that the SiC layers in (PyC/SiC)3 multi-layers interphase can protect the carbon fibers from ablation damage effectively. Compared with the Cf/(PyC)SiBCN composites, much improved ablation resistance is achieved for the Cf/(PyC/SiC)3SiBCN composites. The linear and mass recession rates of the Cf/(PyC/SiC)3SiBCN composites are as low as 1.7 ± 0.4 μm s−1 and 0.0427 ± 0.0053 mg mm−2s−1, which are ∼43 % and ∼21 % lower than those of Cf/(PyC)SiBCN.

A novel combination of precursor pyrolysis assisted sintering and rapid sintering for construction of multi-composition coatings to improve ablation resistance of SiOC ceramic modified carbon fiber needled felt preform composites

A double-layer coating composed of MoSi2–SiO2–SiC/ZrB2–MoSi2–SiC was designed and successfully constructed by a novel combination of precursor pyrolysis assisted sintering and rapid sintering to improve the ablation resistance of SiOC ceramic modified carbon fiber needled felt preform composites (CSs). The ZrB2–MoSi2–SiC inner layer coating was in relatively uniform distribution in the zone of 0–3 mm from the surface of CSs through the slurry/precursor infiltration in vacuum and SiOC precursor pyrolysis assisted sintering, which played a predominant role in improving oxidation and ablation resistance and maintaining the morphology of CSs. The MoSi2–SiO2–SiC outer layer coating was prepared by the spray and rapid sintering to further protect CSs from high-temperature oxidation. The ablation resistance of CSs coated with double-layer coating was evaluated by an oxygen-acetylene ablation test under the temperature of 1600–1800 °C with different ablation time of 1000 and 1500 s. The results revealed that the mass recession rates increased with the rise of ablation temperature and extension of ablation time, ranging from 0.47 g/(m2·s) to 0.98 g/(m2·s) at 1600–1800 °C for 1000 s and from 0.72 g/(m2·s) to 0.86 g/(m2·s) for 1000–1500 s at 1700 °C, while the linear recession rates showed negative values at 1700 °C due to the formation of oxides, such as SiO2 and ZrO2. The ablation mechanism of the double-layer coating was analyzed and found that a SiO2–ZrO2–Mo4.8Si3C0.6 oxidation protection barrier would be formed during the ablation process to prevent the oxygen diffusion into the interior CSs, and this study provided a novel and effective way to fabricate high-temperature oxidation protective and ablation resistant coating.

Ablation behavior and mechanism of Cf/SiBCN composites in plasma ablation flame

AbstractIn this work, Cf/SiBCN composites are fabricated by an improved precursor infiltration and pyrolysis (PIP) approach. Ablation behavior of the Cf/SiBCN composites is investigated in plasma ablation flame at a heat flux of 4.02 MW m−2, which provides a quasi‐real hypersonic service environment at a temperature up to 2200°C. After ablation, the ablated surface is covered with oxidation products in the form of oxide layer, fibrous residues, or bubbles, which effectively isolates the sample surface from the plasma flame and inhibits the scouring of high‐speed flame to the composites. As a result, the Cf/SiBCN composites present an excellent ablation‐resistant property, with linear and mass recession rates as low as 0.0030 mm s−1 and 0.0539 mg mm−2 s−1, respectively. It is also revealed that the material at ablation center undergoes crystallization and oxidation processes during ablation, while the ablation behavior at transition area and ablation fringe only contains oxidation process due to the local temperature difference. Si3N4 and SiC grains are precipitated from amorphous SiBCN matrix during the crystallization process, and the oxidation process mainly involves the oxidation of carbon fiber and SiBCN matrix, etc.

Ablation behavior of Cf/ZrC-SiC-based composites fabricated by an improved reactive melt infiltration

In this work, a highly dense Cf/ZrC-SiC-based composite is fabricated by an improved reactive melt infiltration (RMI). The ablation resistance of the composite is studied by air plasma test. The RMI-Cf/ZrC-SiC possesses a low porosity (3.49%) and high thermal conductivity. The dense microstructure can effectively retard oxygen from diffusing into the interior composite. Meanwhile, the high thermal conductivity makes the composite transfer heat timely during ablation, which reduces the heat accumulation on the ablation surface and weakens the thermal damage to the composite. Consequently, the as-fabricated composite exhibits an excellent ablation resistance. Compared to conventional PIP-Cf/ZrC-SiC composite, the linear and mass recession rates of the RMI-Cf/ZrC-SiC decline by 98.07% and 39.02% at a heat flux of 4.02 MW/m2. Also, a continuous SiO2-ZrO2 layer forms on the sample surface, which isolates the sample surface from the plasma flame and protect the composites from further oxidation and ablation.

Factors influencing pre-fledging mass recession by nestling Tree Swallows (Tachycineta bicolor)

ABSTRACT Nestlings of some aerial insectivores experience pre-fledging mass recession, possibly to achieve optimum wing loading at fledging. However, studies to date where mass recession was linked...

EXPERIMENTAL METHOD USING ARC WIND TUNNEL TO SIMULATE A NEW TECHNIQUE FOR COMMUNICATING WITH A REENTRY PROBE HAVING A THERMAL SHIELD MADE OF LATS MATERIALS

Entering a planetary atmosphere is one of the most claim missions as the space probe faces a loss of communication, acknowledged as communication blackout, due to the plasma sheath occurred, caused by temperatures of several thousand degrees in front of the space probe. This paper presents a study about a new method of communication called end of radio silence using the arc heating facilities of Japan. The purpose of the experiment was to test a heat shield equipped with transmitter placed behind it, in a plasma flow of high enthalpy. A receiver was installed in the shroud of the vacuum chamber, protected from the hot gas. Another purpose was to study the behavior of a new type of ablative materials called LATS (Light-weight Ablator Series for Transfer Vehicle Systems) for protecting the space probe against severe heating. The experiment was carried out by using LATS, placed in front of the transmitter for several megawatts per square meter of heat flux. The main measured data are the surface temperature, the thermal performances like mass recession rate, the temperature of transmitter and the electrical parameters as received signal strength indicator RSSI.

Energetic constraint of non‐monotonic mass change during offspring growth: a general hypothesis and application of a new tool

Post-natal growth is an important life-history trait and can be a sensitive indicator of ecological stress. For over 50 years, monotonic (never-decreasing) growth has been viewed as the predominant trajectory of post-natal mass change in most animal species, notably among birds. However, prevailing analytical approaches and energetic constraints may limit detection of non-monotonic (or multiphasic), determinate growth patterns, such as mass recession in birds (weight loss prior to fledging, preceded by overshooting adult mass), which is currently believed to be restricted to few taxa. Energetic surplus and shortfall are widespread conditions that can directly influence the degree of mass overshooting and recession. Thus, we hypothesize that in many species, prevailing energetic constraints force mass change away from a fundamental non-monotonic trajectory to instead follow a monotonic curve. We observed highly non-monotonic, mass change trajectories (overshooting adult mass by up to almost 20%) among common tern Sterna hirundo chicks, a well-studied species long-established as growing monotonically. We quantified the prevalence and magnitude of non-monotonic mass change prior to fledging for 313 common tern chicks that successfully fledged from two discrete populations in multiple years. We used a new approach for analysing non-monotonic curves to examine differences in mass change trajectories between populations under contrasting abiotic (freshwater vs. saltwater) and biotic stresses (low rates of food provisioning). Some degree of mass recession occurred in 73% of all study chicks. Overshooting adult mass followed by extensive mass recession was most prevalent at our freshwater colony, being detected among 34-38% of chicks annually. Non-monotonic trajectories were less marked in populations experiencing ecological stress and among lower quality individuals. Chicks that were provisioned at higher rates were more likely to both overshoot adult mass and experience subsequent mass recession. Our results in common terns provide strong support for the hypothesis that non-monotonic trajectories are the fundamental pattern of mass change but are constrained to be monotonic under energetic shortfall. This justifies future tests of the generality of this hypothesis across a broad range of taxa. We also demonstrate a recent analytical tool that prevents routine fitting of monotonic curves without prior investigation of non-monotonic trends.

The Triggers of Fledging in Rhinoceros AukletsCerorhinca monocerataChicks When They Experienced Mass Recession, Examined by a Supplementary Feeding Experiment

Abstract Older or heavier Rhinoceros Auklet Cerorhinca monocerata chicks are less likely to remain in their nest during pre-fledging mass recession. Older or heavier chicks have longer wings but the individual variation in wing length at fledging is small. To identify proximate triggers of fledging from a mix of candidates when chicks experienced mass recession, we selected 30 nest boxes each containing a chick and provided half of them with 30–60 g of supplementary foods in an attempt to expand their variation in growth rate. When chicks reached the minimum wing length required for fledging (130 mm), we stopped all provisioning (supplementary and parental) by closing a hatch on the nest box entrance thereby simulating mass recession and inducing fledging. With these treatments, we examined whether timing of fledging (=duration of mass recession) was only triggered by wing length to a threshold size or whether timing of fledging was delayed by younger age at peak mass or lighter peak body mass. Our result...