Seasonal variations in trace metal levels,speciation and physicochemical determinants of metal availability in dumpsite soils within Akwa Ibom State,Nigeria

Physicochemical properties, total metals and metal species were investigated in surface soil samples from six urban dumpsites within Akwa Ibom State, Nigeria. Results obtained indicated that Pb, Cd and Cr levels were higher in the dry season than in wet season, whereas Ni levels were higher during the wet season. Soil pH, organic matter and cation-exchange capacity (CEC) showed higher values in wet season than in dry season, whereas sand and clay levels were higher in the dry season. Speciation analysis showed the principal fraction of the metals to be Pb (reducible), Cd (acid extractable) and Ni (residual), whereas Cr existed in the residual fraction during the dry season and in the acid-extractable fraction during the wet season. Soil pH was positively correlated at p<0.1 with all metals in both seasons, sand was negatively correlated with the metals in both seasons, and CEC was negatively correlated with all metals in both seasons, except Pb in the wet season. Organic matter showed variable relationships with metals in both seasons. Seasonal variations affected metal availability and physicochemical properties of the soil. Total metal concentrations followed the order Pb>Ni>Cd>Cr, whereas their bioavailability followed the trend Cd>Pb>Cr>Ni.     

贵阳市西郊水厂所供管网末梢水重金属污染物季节性特征及潜在健康风险评价

以贵阳市西郊水厂2014年3月和7月所供管网末梢水中10种重金属污染物检测数据为基础,进行了季节性特征分析,并采用美国环保局(USEPA)推荐的健康风险评价模型进行了潜在健康风险评价。结果表明,贵阳市西郊水厂所供管网末梢水中10种重金属的浓度均符合国家饮用水卫生标准;重金属污染物的浓度随季节呈现出不同的特征,汞、锌、硒、钼和钡5种重金属的平均浓度呈现枯水期高于丰水期的特征,而铅、铜、锰和镍4种重金属正好相反,砷浓度的季节性特征不显著;成年人的年平均致癌风险显著大于儿童,但两者年平均非致癌风险接近;儿童和成年人2类人群经口暴露途径的健康风险值均大于皮肤暴露,其中致癌风险分别在2.49×10-6~9.16×10-6和3.26×10-8~9.59×10-8之间,非致癌风险在2.29×10-8~3.20×10-8和1.85×10-10~4.14×10-10之间,且致癌风险均大于非致癌风险。贵阳市西郊水厂所供管网末梢水中10种重金属污染物致癌风险和非致癌风险均未超过最大可接受水平,未对该供水区居民的健康造成威胁。     

九洲江流域水环境重金属污染特征及来源解析

九洲江流域环境综合治理已被列为国家跨地区生态补充试点,开展流域重金属污染调查与研究,能为流域生态补偿和综合治理提供科学依据.为了研究九洲江流域水环境重金属浓度分布特征,在流域干流和支流选取了33个采样点,于2018年枯水期、丰水期和平水期分3次进行采样监测,测定13种重金属(Cu、Zn、Pb、Cd、Cr、Ni、Fe、M...     

Heavy Metal Concentrations in Sea Urchin Tissues From Egypt,Ireland and United Kingdom

Abstract

Sea urchins (Paracentrotus lividus) were collected from the Mediterranean coast off Alexandria, Egypt and the Atlantic coast of Ireland to the west of Galway. Samples of another urchin species, Psammechinus miliaris, were collected from the entrance to Southampton Water, U.K. Both the Alexandria coast and Southampton Water receive domestic and industrial waste water inputs whilst the western Irish coast is relatively unpolluted.

Sampled animals were dissected to separate coelomic fluids, Aristotle's lantern, gonads and tissue (digestive tract plus connective tissue). the concentrations of heavy metals (cadmium, copper, lead, nickel and zinc) in the different parts were measured using flame atomic absorption spectroscopy.

Many levels of heavy metals in the different parts were similar in specimens taken across the wide range of sites and the two species. A notable exception was the high level of copper (33 μg g^?1 dry wt.) and zinc 328 μg g^?1? dry wt.) in urchin tissue from Southampton Water.

The metal concentrations in the gonads of Paracentrotus lividus are of particular interest because of human consumption of this species. the highest levels of copper (3.3–5.2 g^?1? dry wt.) and zinc (74–181 μ g^?1? dry wt.) dry wt.) in gonads were found in the samples from Egypt. Data from this study are compared with other results reported from the Mediterranean.

A simple, short term, elevated water column copper uptake experiment was undertaken with Paracentrotus lividus which showed an increase in gonad concentrations of this element.     

Investigation of correlativity between heavy metals concentration in indigenous plants and combined pollution soils

The accumulation of heavy metals (HMs) in soils is potentially hazardous to human, livestock and plant species. HMs in the combined pollution soils and indigenous plants were investigated in a non-ferrous metal-smelting area. The purpose of this study was to determine the HMs in the contaminated soil and different plant species found growing on it, as well as calculation of bioaccumulation coefficients (BACs). Representative sampling sites were identified according to the land-use types. A total of 12 surface soil samples and 32 plant samples were collected. HMs were analysed by inductively coupled plasma mass spectrometry. The levels of soil pollution were assessed using Nemerow’s synthetical contamination index method. The synthetical index was in the range of 16.81–198.11. This result indicated a heavy burden on local environment. HM concentrations in plants were directly related with soil concentrations. The average BACs of five metals were found in the order of Cd (0.309)?>?Zn (0.178)?≈?Pb (0.160)?>?Cu (0.105)?>?Sb (0.0672). Spontaneous weeds including Chenopodium album Linn, Kochia scoparia and trees of Leuce, Ulmus pumila were deemed HM accumulators. The results provided a practical basis for phytoremediation of HM-contaminated soils using accumulator species.     

The potential of Berkheya coddii for phytoextraction of nickel,platinum, and palladium contaminated sites

The study involved assessing the potential of the native plant species (Berkheya coddii) for the phytoextraction of nickel, palladium, and platinum contaminated sites. Plant and soil samples were randomly collected from Barberton area, near Agnes mine, Mpumalanga Province, South Africa. Samples were analysed for total nickel, palladium, and platinum concentrations together with other elements found in the soil and in the plants' roots, and leaves. Soil versus leaves and soil versus roots uptake of these metals by the plant were compared. The mean concentration of nickel in the leaves/canopy was found to be 13,980?±?10,780?mg?kg^?1?dry mass, in the roots it was 2046?±?789?mg?kg^?1 dry mass, and in the soil it was 1040?±?686?mg?kg^?1?dry mass. This resulted in a mean concentration ratio in the leaves to soil of 13.44. The platinum mean concentration in the leaves was 0.22?±?0.15?mg?kg^?1?dry mass, in the roots it was 0.14?±?0.04?mg?kg^?1?dry mass, and in the soil it was 0.04?±?0.03?mg?kg^?1?dry mass. This resulted in a mean concentration ratio in the leaves to soil of 5.5. Palladium was found to have a mean soil concentration of 0.07?±?0.045?mg?kg^?1?dry mass. The mean concentrations in the roots and in the leaves were 0.18?±?0.07 dry mass and 0.71?±?0.52?mg?kg^?1?dry mass, respectively. This gave a mean concentration ratio in the leaves to soil of 10.1 for palladium. Other elements that were found to have a mean concentration ratio in the leaves to soil of around 2.5 or above are sodium, potassium, magnesium, calcium, and sulfur. Berkheya coddii was found to be most efficient in accumulating nickel, palladium, and platinum from the soil. The results for the first time revealed that the plant may have the potential to uptake platinum and palladium; both metals are in the same group of the periodic table as nickel.     

Occurrence and health risk assessment of trace heavy metals via groundwater in Shizhuyuan Polymetallic Mine in Chenzhou City,China

The Shizhuyuan Polymetallic Mine in Chen-zhou City is an important multi-metal deposit in China. After a dam accident in 1985, there are still a number of mining plants, smelters and tailing ponds in this area. These had the potential to pollute the surrounding groundwater. In this study, groundwater samples were collected from 20 residents’ wells in this area during both dry and wet seasons. In particular, this study focused on the exposure and the health risk assessment of trace heavy metal in groundwater. Multiple statistical analysis and fuzzy comprehensive method were employed to reveal the distribution characteristics of heavy metal and to assess the groundwater quality. Results indicated that Cr, Fe, Ni, Cu, Zn, As, Cd, Ba, Hg and Pb were widespread with low exposure levels. There were 19 wells with low level exposure and one well with a moderate level exposure in the dry season. All of the wells were in low level exposure during the wet season. As and Mn exhibited potential non-carcinogenic concern, because their maximum hazard quotient (HQ) was higher than 1.0. This may cause adverse health effect on adults in dry season or on children in both seasons. Only As, showed that the maximum carcinogenic risk was more than 10⁻⁴, suggesting a high cancer risk for children in both dry and wet seasons. Therefore, analysis and reduction the concentrations of As and Mn in groundwater are needed in order to protect the health of residents and especially children in the area.     

Heavy metal concentration in soil and woody plants in a quarry

This study determined the concentration of three heavy metals zinc (Zn), lead (Pb), and cadmium (Cd) in soil and in a woody plant species, Milicia excelsa, at Ishiagu quarry, Nigeria. The highest soil concentrations of Zn, Pb, and Cd in soil were obtained at 1?m from the quarry site. In M. excelsa, the highest concentrations of Zn, Pb, and Cd were 3.12–9.1, 3.9–6.01, and 0.51–1.12?mg?kg^?1, respectively. There were significant positive correlations between Cd and Zn (r?=?0.963) and Cd and Pb (r?=?0.974) in plants as well as between Cd and Pb (r?=?9.84) in soil. The level of Cd in soil reflected significant pollution compared to average global concentrations in soils.     

Assessment of methane from agricultural field during the entire paddy cropping seasons – a case study

A systematic effort was made to assess the emission of methane from paddy fields using closed chamber technique. Methane emission measurements were performed over a year during the Kharif (wet season), Rabi (dry season), and fallow periods. Various soil parameters like redox potential, organic carbon and ferrous ion were determined to evaluate their control on methane emissions. Diurnal measurement of the flux showed a minimum (0.44?mg?m^?2?h^?1) in the morning (8?a.m.), which increased gradually to a value of 1.16?mg?m^?2?h^?1 till the evening due to the rise in soil temperature. The seasonally integrated flux (E _SIF) for CH₄ was calculated. The E _SIF for methane during Kharif and Rabi crops were found to be 5.97?g?m^?2 and 2.59?g?m^?2, respectively. It was observed that the methane flux was maximum during flowering and fertilizer application stages for both paddy cropping seasons. The redox potential was low and the ferrous ion was higher during flowering and tiller stages. The methane emission was higher at E _AIF) was calculated for methane to make a budget estimate of methane emission from rice cultivated under rain fed drought prone water regime.     

Effect of monsoonal climate on sulfate reduction in coastal sediments of the central Great Barrier Reef lagoon

Rates of sulfate reduction were measured during the spring dry and summer wet seasons of 1992 in shallow coastal sediments of the central Great Barrier Reef lagoon. In the dry season, sulfate reduction rates, integrated to 18–20 cm depth, ranged from 23.8 to 30.8 mmol S m^-2 d^-1. In the wet season, heavy monsoonal rains and wind-induced waves caused severe disturbance of sediments leading to less anoxic conditions, and to a 2- to 3-fold decline in rates of sulfate reduction (10.2 to 12.8 mmol S m^-2 d^-1). The percentage of reduced ³⁵S recovered as acid-volatile sulfide (% AVS_red) ranged from 15.8 to 44.9% in spring, and was significantly reduced at each station in summer (range 14.5 to 31.4%). An analysis of variance indicated that seasonality accounted for 31.5% of the total variance in total rates of sulfate reduction, with only 7.5% of the variance accounted for by depth into the sediment; there were no station differences. In both seasons, there were no clear patterns in the proportion of radiolabel incorporated into the AVS and chromium-reducible sulfur (CRS) pools with depth into the sediment. These results are contrary to the seasonal patterns and pathways of sulfate reduction in temperate coastal sediments.     

Ecological and human health risk assessment of heavy metal contamination in soil of a municipal solid waste dump in Uyo,Nigeria

The study assessed the levels of some heavy metals in soils in the vicinity of a municipal solid waste dumpsite with a view to providing information on the extent of contamination, ecological risk of metals in the soils and human health risk to the residents in Uyo. Soil samples were collected in rainy and dry seasons and analyzed for metals (Pb, Cd, Zn, Mn, Cr, Ni and Fe) using atomic absorption spectrometry. The concentrations of heavy metals (mg/kg) at the dumpsite in rainy season were Pb (9.90), Zn (137), Ni (12.56), Cr (3.60), Cd (9.05) and Mn (94.00), while in dry season, the concentrations were Pb (11.80), Zn (146), Ni (11.82), Cr (4.05), Cd (12.20) and Mn (91.20). The concentrations of metals in the studied sites were higher than that of the control site (P < 0.05). Pollution indices studies revealed that soil samples from dumpsite and distances from 10 and 20 m east of the dumpsite were highly polluted with cadmium. Ecological risk assessment carried out showed that cadmium contributed 98–99 % of the total potentially ecological risk. No probable health risk was observed as the total hazard index of all the metals was less than one. However, children were found to be more susceptible to heavy metal contamination than adult.     

The prevalence of heavy metals in Cladophora glomerata L. from Farahabad Region of Caspian Sea – Iran

The presence of toxic heavy metals in the environment is considered as a risk factor for adverse human and environmental health effects. Farahabad Region is a tourist center in the southern coast of Caspian Sea in Mazandaran Province of Iran. Environmental monitoring of this site is important for public health for individuals visiting and residing in this region. Although numerous biomonitoring data are available globally, very few if any apparent investigations have been conducted in this region. In this study, concentration of three heavy metals chromium (Cr), lead (Pb), and cadmium (Cd) was determined for one year in Cladophora glomerata, the predominant macroalga species present in this region. Detection of heavy metals was performed with atomic absorption spectrophotometer using standard methods. Results showed that the range of Cr metal in various algal samples was 29–55 ppm/g dry weight. The levels of Pb in algal samples (Cladophora) ranged from 2 to 8 ppm/g dry weight. The Cd concentrations in C. glomerata biomass ranged from 1.5 to 8.2 ppm/g dry biomass. In view of potential threats of such high metal concentrations in coastal waters and in algal tissues, it is necessary to adopt conservation measures to ensure public health safety.     

Scalp hair metal analysis in the assessment of the occupational exposure of arc welders

Eleven metals (Ca, Mg, Fe, Zn, Cu, Mn, Cd, Co, Cr, Ni and Pb) were estimated in hair samples of metal arc welders and a control group with the same socioeconomic background. Nitric acid–perchloric acid wet digestion procedure was adopted for the estimation of endogenous metal contents by ICP-AE technique. The study exhibited the following increasing order of the metal concentrations: Cd??1, dry weight, respectively. On average, the levels of Mn, Ni, Pb and Fe were found to be 1.5–2.4 times higher in the hair of welders compared with controls. Besides age and exposure which were strongly correlated, Cu–Mg, Mn–Mg, Ca–Co and Cd–Zn also showed significantly positive correlations. The identification of metal sources, done by cluster and principal component analyses, revealed four factors: age and exposure; Cu, Mg, Mn and Fe; Ca and Co; Cd, Zn, Ni and Pb. High levels of Fe were found to have a depleting impact on Co levels. The arc welders were feared to accumulate heavy metals in their bodies due to long-term endogenous exposure.     

Metal partitioning in sediment pore water from the Ondo coastal region,Nigeria

Distribution and equilibrium partitioning of metals (Cd, Cu, Cr, Fe, Ni, Pb, Mn, and Zn) between pore water and surface sediments at the Ilaje coast of Ondo State, Nigeria, were studied. The Ilaje River can be one of the interesting research locations because of its economic nature and history of oil pollution. Seasonal variations were observed to investigate possible variations in the availability of metals for organisms throughout the year. The concentrations in both sediments and pore water during the dry and wet seasons were as follows: Cu?>?Fe???Mn?>?Pb?>?Ni?>?Cr?>?Cd?>?Zn. The pore water–sediment partition coefficient (K _p) showed that Zn and Cd were highly mobile while Fe and Cu have restricted mobility. Dissolved organic carbon (DOC) in pore water had a strong influence on mobility and bioavailability of all the metals (p?K _oc), increased levels of Fe and Cu were linked to lithological origin. Concentrations of Pb and Ni were associated with petroleum-related sources. The significance of the field-based techniques for ecotoxicological purposes is discussed.     

Assessment of metals in soil extracts and their uptake and movement within Tamarix nilotica at Lake Nasser banks,Egypt

This study aims to determine heavy-metal levels in soil from the banks of Lake Nasser, the ability of Tamarix nilotica to accumulate such metals from soil and hence its potential for phytoextraction. Soil and Tamarix samples were collected from the banks of four bights around Lake Nasser and analysed for Fe, Mn, Ca, Mg, Cr, Cu, Ni, Zn, Cd and Pb by atomic absorption spectrometry, whereas Na and K were measured by atomic emission spectrophotometry. Three different methods of extraction were used for the soil samples. Lead, copper and zinc were equally distributed between the exchangeable phase and Fe/Mn oxide-bound form, while other measured metals were mainly present in the Fe/Mn oxide fraction. With the exception of iron, all metals studied showed total concentrations within the geochemical background values. T. nilotica exhibited elevated concentrations of Na (36.2–48.5?mg?g^?1) and K (2.74–4.33?mg?g^?1) in stems, and relatively high concentrations of Pb, Cd and Co (0.39–1.03?µg?g^?1, 0.24–1.3?µg?g^?1 and 1.94–5.3?µg?g^?1, respectively) are found in plant leaves. Bioaccumulation factors of Na and K (9.3 and 12.63, respectively) were high in T. nilotica stems. While the bioaccumulation of Pb, Cd, Co and Ni (2870.1, 2035.4, 10.5 and 5313.2, respectively) was high in plant leaves, Fe, Mn, Ca and Mg were accumulated relatively equally in plant stems and leaves. T. nilotica was found to secrete high amounts of Na, Ca and K, in addition to small amounts of all accumulated metals except Cd and Cu. These secreted metals appeared as salt crystals (67.5% Na; 25.8% Ca; 5% Mg; 1.5% K and 0.16% trace and minor elements) on the plant surface. The concentrations of all the metals studied in T. nilotica were higher than in the salt crystals. Statistical analysis of the database suggests bioaccumulation of these metals from soil to T. nilotica. This reflects the importance of using T. nilotica as a model in the phytoremediation process as an established environmental clean-up technology.     

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).     

Mercury concentrations in the surface sediments of the intertidal area along the west coast of Peninsular Malaysia

Total mercury (Hg) levels in the intertidal surface sediments along the west coast of Peninsular Malaysia were analysed by using heat vaporization method. Total Hg levels in these sediments ranged from 3.00 to 201?µg?kg^?1 dry weight with a mean concentration of 60.0?µg?kg^?1 dry weight. More than 90% of the samples studied have the total Hg concentrations less than 150?µg?kg^?1 dry weight. Compare with the regional data and sediment quality guidelines, the Hg contamination in the intertidal area along the west coast of Peninsular Malaysia was not serious, except for a few sites that might have received anthropogenic Hg in the samples collected between 1999 and 2000. It is suggested that a similar study of heavy metals in the sediments of the west coast of Peninsular Malaysia be conducted regularly.     

A new comprehensive ecological risk index for risk assessment on Luanhe River,China

With the enhancement of human activities which influence the physical and chemical integrity of ecosystem, it was bound to increase ecological risk to the ecosystem, and the risk assessment of small scale, single pollutant, or only on water quality have been not satisfied the demand of sustainable development of basin water environment. Based on the response relationship between environmental flow requirements guarantee ratio (GEF) and river ecological risk index (ERI), the Sediment Quality Guideline Quotient index (SQG-Q), and the Biotic Index (BI), we construct a new comprehensive ecological risk index (CERI) to evaluate the ecological risk of Luanhe River, China. According to the response relationship between GEF and ERI, upper and lower reaches of Luanhe River (Goutaizi to Hanjiaying) were at moderate risk level (0.41 < ERI < 0.56) in dry season, and all sites were at low risk level (ERI < 0.40) in wet season; considering the contribution of heavy metals contamination in the SQG-Q, the Luanhe River was the most influenced by higher levels of heavy metals in dry season and wet season; when this index was applied to the PAHs levels, only 30 and 20% of the sampling sites appeared to be moderately impacted (0.1 < SQG-Q PAHs < 0.5) by the PAHs in dry season and wet season, respectively. The results of BI showed that half of the sites appeared to be at moderately polluted level (50% of the sites, 0.25 < BI < 0.32) and heavily polluted level (Zhangbaiwan, BI = 0.36) in dry season, and 40% of the sites appeared to be at moderately polluted level (0.26 < BI < 0.29) in wet season. The CERI showed that 70 and 30% of the sites were at moderate risk level in dry season (0.25 < CERI < 0.36) and wet season (0.26 < CERI < 0.29), respectively. The results could give insight into risk assessment of water environment and decision-making for water source security.

     

Major shifts in Amazon wildlife populations from recent intensification of floods and drought

In the western Amazon Basin, recent intensification of river‐level cycles has increased flooding during the wet seasons and decreased precipitation during the dry season. Greater than normal floods occurred in 2009 and in all years from 2011 to 2015 during high‐water seasons, and a drought occurred during the 2010 low‐water season. During these years, we surveyed populations of terrestrial, arboreal, and aquatic wildlife in a seasonally flooded Amazonian forest in the Loreto region of Peru (99,780 km²) to study the effects of intensification of natural climatic fluctuations on wildlife populations and in turn effects on resource use by local people. Shifts in fish and terrestrial mammal populations occurred during consecutive years of high floods and the drought of 2010. As floods intensified, terrestrial mammal populations decreased by 95%. Fish, waterfowl, and otter (Pteronura brasiliensis) abundances increased during years of intensive floods, whereas river dolphin and caiman populations had stable abundances. Arboreal species, including, macaws, game birds, primates, felids, and other arboreal mammals had stable populations and were not affected directly by high floods. The drought of 2010 had the opposite effect: fish, waterfowl, and dolphin populations decreased, and populations of terrestrial and arboreal species remained stable. Ungulates and large rodents are important sources of food and income for local people, and large declines in these animals has shifted resource use of people living in the flooded forests away from hunting to a greater reliance on fish.     

Territory defence in tropical birds: are females as aggressive as males?

Much of our knowledge concerning the functions of territorial behaviour and how territories are defended by individuals comes from research on birds. The vast majority of this work has focused on temperate zone breeding territoriality in which territories are defended most obviously by males. Our understanding of the female role in territory defence is limited because they are less conspicuous and much harder to observe. We studied sex roles in territory maintenance and defence in a duetting, resident neotropical passerine, the white-bellied antbird (Myrmeciza longipes). This species maintains territories and pair bonds year round and both sexes sing and actively participate in territory defence. We performed a series of playback experiments throughout the dry (non-breeding) and wet (breeding) seasons. We exposed territorial pairs to three types of stimuli including: (1) single sex, male only songs, (2) single sex, female only songs, and (3) both sex songs/duets. Contrary to findings for most other tropical species, individuals defended their territories with equal levels of aggression regardless of stimuli. Furthermore, sex roles were very different, with males responding more aggressively than females to all stimuli throughout both seasons. Both males and females consistently responded more aggressively to territorial intrusions during the dry season than during the wet season, likely because food abundance is low in the dry season and territory value is high. Our analysis of duetting behaviour suggests that duets do not serve a significant role in mate guarding, or territory defence.