Variation in the extra-pair mating systems of Acadian Flycatchers and Wood Thrushes in forest fragments in southern Ontario

ABSTRACT.   The application of molecular tools to studies of avian mating systems has revealed that most songbird species engage in extra-pair matings. However, little is known about the possible effects of habitat fragmentation on extra-pair mating systems. During the breeding seasons of 2002 and 2003, we quantified the frequency of extra-pair matings in Acadian Flycatchers ( Empidonax virescens ) and Wood Thrushes ( Hylocichla mustelina ) nesting in forest fragments in southern Ontario. Acadian Flycatchers are at the limit of their northern range in southern Ontario and occurred at low densities (0.005–0.015 males/ha). Across forest fragments, 14% of young Acadian Flycatchers were the result of extra-pair fertilizations. In contrast, Wood Thrushes were common in forest fragments, with breeding densities ranging from 0.37 to 1 males/ha. Extra-pair mating was common among Wood Thrushes, with 40% of young the result of extra-pair matings. Compared to populations studied in less fragmented habitats in Pennsylvania, rates of extra-pair paternity in Ontario were lower for Acadian Flycatchers and higher for Wood Thrushes. Our results demonstrate that rates of extra-pair mating can vary across landscapes. However, the extra-pair mating systems of Acadian Flycatchers and Wood Thrushes appear to respond differently to fragmentation. We suggest that low breeding densities on fragments may be mediating the low rates of extra-pair mating observed in Acadian Flycatchers in southern Ontario, whereas changes to the behavioral tactics of male and female Wood Thrushes in southern Ontario may explain the high levels of extra-pair mating.     

Effect of radio transmitters on return rates of Swainson's Warblers

ABSTRACT.   Although radio telemetry can provide useful information, the possible negative effects of transmitters, including biased results and detrimental effects on the birds, must also be considered. Several investigators have examined the effects of transmitters on larger birds, but few have examined their possible long-term effects, as assessed by return rates, on small passerines. We examined the possible negative effects of transmitters on a small (15.5 g) passerine. We used glue to attach radio transmitters to 40 male Swainson's Warblers ( Limnothlypis swainsonii ) at two study sites in Arkansas in 2005 and 2006. To assess possible effects of transmitters on survival, we compared the following-year return rates of radio-tagged birds to birds that were captured and color banded, but did not receive transmitters. Least squared mean return rates for all birds ranged between 0.46 and 0.57. We found no significant difference in the following-year return rate of radio-tagged and nonradio-tagged birds. In addition, we found no significant differences in return rates between study sites or years, and no significant interactions between any combination of radio transmitter (radio tagged or not), site, and year. Our results indicate that attachment of transmitters did not affect return rates of male Swainson's Warblers and that the glue-on technique is a good option for short-term studies of small passerines.     

Floating mist nets: a technique for capturing birds in flooded habitat

ABSTRACT.   Banding birds is essential for detailed demographic studies of avian populations. Mist nets are a widely used, effective method of capturing birds for banding, but are difficult to use under certain conditions. While conducting a demographic study of Southwestern Willow Flycatchers ( Empidonax traillii extimus ), rising reservoir levels flooded large tracts of flycatcher breeding habitat and made traditional mist-netting techniques impossible to use. In response, we devised a technique for capturing birds over deep water using mist nets suspended between poles kept afloat on compact buoys. In 2005, we used this technique to safely capture 17 Willow Flycatchers that could not have been captured by any other means, and over 40 additional passerines were incidentally captured with no injuries occurring. This versatile apparatus was simple to build and employ, and capture success was similar to that over dry land.     

Reproductive ecology of the river lamprey

The reproductive ecology of river lamprey Lampetra fluviatilis was investigated during the spawning period 2003 in the River Derwent, north‐east England. Over this period 1199 ± 104 individuals day⁻¹(mean ±  s . d .) were counted on one spawning site (area c . 450 m²), but mark‐recapture estimates suggested that >5000 river lamprey used this site over the same period and egg deposition was estimated as 168 000 eggs m⁻². The operational sex ratio of river lamprey in spawning clusters changed between spawning phases, from domination by females during the nest‐building phase (male : female ratio, 1 : 3·46), to a preponderance of males during the spawning phase (male : female, 1 : 0·37), followed by a return to a majority of females after spawning (male : female, 1 : 3·74). Recapture data showed that >97% of recaptured, tagged males were recorded at two or more nests, whereas almost 50% of recaptured, tagged females were recorded at the same nest, suggesting a promiscuous mating system, with a tendency towards polygyny within the population. Within the lower 80 km of the River Derwent and its tributaries, evidence of river lamprey spawning was found at only six sites, and most spawning (>80% of the observed spawning population) was at one site.     

Predicting the macroinvertebrate faunas of rivers by multiple regression of biological and environmental differences

1.   The prediction of macroinvertebrate community composition in flowing waters from environmental data has enabled pollution assessments that take account of natural variability. Polluted sites are identified by discrepancies between the observed fauna and the fauna expected at an unpolluted site on the same type of river.
2.   The usual method of prediction involves a sequence of (a) classification of unpolluted reference sites by cluster analysis of macroinvertebrate community data (b) multiple discriminant analysis to relate site clusters to environmental variables, and (c) use of site clusters, discriminant functions and environmental data to estimate the probability of collection of each macroinvertebrate taxon at sites that are to be assessed (test sites).
3.   This paper describes an alternative method that does not require classification and predicts abundance rather than probability of occurrence. The main steps are (a) multiple regression of biological differences between pairs of reference sites on differences in physical variables (b) use of the multiple regression relationship to predict the biological similarity of a test site to each reference site, and (c) estimation of the expected fauna at the test site as a weighted mean of the faunas at the reference sites. The predicted similarities of the test site to each reference site are used to derive the weightings.
4.   The method is illustrated using macroinvertebrate and environmental data collected in the upper Murrumbidgee River catchment as part of Australia's Monitoring River Health Initiative. In comparison with a classification-based analysis of these data, macroinvertebrate indices generated by the new method showed a greater distinction between human-disturbed and undisturbed test sites, and a similar or higher degree of correlation with physical and chemical indicators of human disturbance.     

Wood warblers copy settlement decisions of poor quality conspecifics: support for the tradeoff between the benefit of social information use and competition avoidance

Social information use in songbird habitat selection commonly involves a conspecific attraction strategy. Individuals copy the breeding‐site choices of conspecifics, that is, bias their own settlement decisions towards sites (tracts of spatially limited habitat with similar structure) already occupied by others. In order to be adaptive, social information use has to be discriminative. Especially the decisions of good quality individuals, i.e. measuring high at observable fitness correlates, should be copied more frequently than those of poor quality individuals. It is unknown, however, whether songbirds discriminatively use conspecific presence by evaluating the quality of information providers in habitat selection. We experimentally tested whether wood warblers Phylloscopus sibilatrix selectively copied settlement decisions of conspecifics in relation to the quality of observed individuals. We also tested whether the use of social cues was influenced by the population density at a particular site in the preceding year. We found that wood warblers selectively used intraspecific social information, but in a pattern opposite to that expected based on existing hypotheses. Wood warblers copied breeding‐site choices of poor quality conspecifics and despite temporary attraction to sites where the presence of good quality individuals was simulated, they did not ultimately settle near these individuals. Population density in the preceding year did not influence settlement patterns. We argue that when making settlement decisions, wood warblers assessed the expected level of local intraspecific competition and selectively copied breeding‐site choices of conspecifics or refused to settle, depending on competitive abilities of observed individuals. This adds a novel aspect to the patterns and processes of social information use proposed thus far, and provides support for the predicted negative effect of intraspecific competition on benefit of information. Moreover, it seems that habitat selection in wood warblers is a complex decision‐making process, in which initial decisions are adjusted after acquiring more accurate information. Synthesis Social information use in songbird habitat selection commonly involves copying the breeding‐site choices of conspecifics (so‐called conspecific attraction). To be adaptive, this strategy has to be discriminative, but almost no empirical studies have tested this assertion. Our study shows that birds may selectively use social information by copying settlement decisions of poor quality conspecifics, but avoid settling near good quality individuals, likely because of their high competitive abilities. This decision‐making pattern supports the predicted, yet not experimentally tested, tradeoff between information value and cost of competition in social information use. Our study highlights also that the use of social cues in settlement decisions may be both positively and negatively biased.     

北京小龙门林场黄眉姬鹟的巢与巢址特征

2003—2006年,在北京小龙门林场共发现黄眉姬鹟(Ficedula narcissina elisae)巢43个。其中34巢筑于天然巢址:开放巢占29.4%,位于树枝间(10巢);洞巢占70.6%,位于树桩顶端凹坑中(10巢)和树洞中(14巢)。开放巢距地高度高于洞巢。黄眉姬鹟的主要营巢树种是棘皮桦(Betula dahurica)。在研究区内共悬挂了100个大洞口巢箱和130个小洞口巢箱,结果发现黄眉姬只利用大洞口巢箱(9巢),不利用小洞口巢箱。以巢为中心,取半径6m的样方测量巢址的植被特征。对海拔、坡向、林冠郁闭度、乔木数量、乔木高、乔木胸径、枯树数量、树桩数量和林下郁闭度等变量进行主成分分析。结果表明,黄眉姬鹟的巢址具有乔木高大、林冠郁闭度高、多枯树和树桩等特征。黄眉姬鹟的繁殖成功率为51.2%,天敌破坏是造成繁殖失败的主要原因。     

Flight songs of Dusky Flycatchers: a response to bird‐hunting raptors?

ABSTRACT.   Flight-song displays usually include distinctive vocalizations and behaviors that are probably energetically expensive and also likely to attract the attention of aerial predators. We observed flight songs performed by Dusky Flycatchers ( Empidonax oberholseri ) in two breeding populations. During 15 yr at Tioga Pass, California, we observed the display twice and, during 9 yr at Steamboat Mountain, British Columbia, we observed 21 flight-song displays. These displays were generally observed later in the breeding season, suggesting that they were not used for courtship, mate attraction, or territory defense. However, for 83% of these displays, a raptor was observed to be present, usually either an American Kestrel ( Falco sparverius ) or a Sharp-shinned Hawk ( Accipiter striatus ). We hypothesize that these displays, like stotting or other pursuit-deterrent signals, may be directed at small raptors that represent a greater threat to Dusky Flycatchers and might deter attack by signaling awareness. However, because only males were observed performing flight-song displays, it is also possible that these displays serve to alert mates and offspring about the presence of an aerial predator and reduce their vulnerability to attack.     

Wintering Shorebird Assemblages and Behavior in Restored Tidal Wetlands in Southern California

Habitat restoration can partially compensate for the extensive loss of coastal wetlands, but creation of functional habitat and assessment of restoration success remain challenging tasks. To evaluate wintering shorebird use of restored coastal wetlands, we quantified shorebird assemblages and behavior of selected focal species at five restored sites and paired reference sites in Mugu Lagoon, southern California, United States. The Shannon–Wiener index of species diversity (for all birds in order Charadriiformes) was higher in the restored than in the reference portion of three of the five sites, higher in the reference portion of a fourth site, and similar between reference and restored areas of the fifth site. Species diversity was lower in sites closer to man‐made structures. The four most abundant species groups across the five sites were selected for detailed analysis of site use and behavior: Willets (Catoptrophorus semipalmatus), Marbled Godwits (Limosa fedoa), Dowitchers (Limnodromus spp.), and Sandpipers (Calidris spp.) (Western, Least, and Dunlin). Each focal species group exhibited distinct site preferences, and densities in restored sites were often as high or higher than in reference sites. Willets and Dowitchers preferred habitats with more extensive tidal flats, a characteristic of restored sites. Godwits and Sandpipers preferred heterogeneous habitats with a mix of water and tidal flats. Most birds were engaged in feeding activities during the ebb tides surveyed, and there were no apparent differences in behavior between reference and restored sites. Though not all restored sites were used equally by all species, the creation of multiple restored sites with varied habitat characteristics attracted a diverse assemblage of shorebirds and may have contributed to the integrity of the regional wetland landscape.     

Fall migration of Empidonax flycatchers in northwestern Colombia

ABSTRACT South of Mexico, little is known about the fall migration patterns of most Neotropical migrants. I studied the migration of Empidonax flycatchers using mist‐net surveys in northwestern Colombia from late September to mid‐October in 4 yr (2003–2005, 2008). Empidonax species were identified using linear measurements and color patterns. About 62% of captured individuals were reliably identified to species, with 86% identified as Willow Flycatchers (Empidonax traillii) and 14% as Alder Flycatchers (E. alnorum). No Acadian Flycatchers (E. virescens) were identified. Most birds captured were adults (84.9%) and, due to overlap in measurements, I was only able to determine the sex of 16.3% of the birds. Most Empidonax flycatchers migrated through northwestern Colombia during September and October, with individuals migrating through my study area over a period of at least 1 mo. Willow Flycatchers tended to migrate earlier than Alder Flycatchers, a pattern consistent with the fall movements of these two species at other locations. No captured flycatchers were molting either remiges or rectrices, and most (89%) had either no or slight traces of subcutaneous fat. No Empidonax flycatchers were recaptured, suggesting that stopover duration at my study site was brief. My results show that many Empidonax flycatchers can be identified as Willow and Alder flycatchers during the nonbreeding period, and such identification will enhance our knowledge of their geographical distribution and improve our understanding of possible patterns of segregation on their wintering grounds.     

Effects of landmarks on territorial establishment

The period of territorial settlement is critical for territorial species, and the initial disputes to fix the boundaries can be energetically expensive. Territorial residents may be able to reduce defensive costs during settlement by selecting territories with landmarks at the sites of potential boundaries. We examined the effects of landmarks on defensive costs in a laboratory study of a cichlid fish, the blockhead, Steatocranus casuarius. In the landmark treatment, we placed a row of flat rocks across the centre of the aquaria; trials in the control treatment were identical but lacked landmarks. When landmarks were present, blockheads spent significantly less time in territorial defence, as they had fewer and shorter aggressive interactions with their neighbours. In addition, fights in landmark trials tended to be of lower intensity than fights in control trials: most fights in landmark trials included only low-level displays but most fights in control trials included physical contact. Both of these measures thus indicated that defensive costs were lowered by landmarks. In addition, in landmark trials typically both pairs of fish successfully established territories; in contrast, in control trials generally only one pair was able to establish a territory, with the other pair being evicted. The presence of landmarks appeared to make possible the division of the area available for settlement, with pairs establishing smaller territories than when there were no landmarks. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

The ionization of clusters. II. Pairwise isotropic interactions and individual site binding data

Evaluation of the parameters describing the binding of protons to clusters of interacting sites requires some reasonable assumptions and procedures because it is impossible to observe an unperturbed site in its interacting environment. When the unperturbed sites are not identical, individual site binding data allow for the evaluation of the differences (or ratios) between the unperturbed (or intrinsic) binding constants but not their actual values (or the interaction energies). In this paper we extend our previous treatment of the ionization of clusters in order to generalize pairwise isotropic interactions and take into account the present availability of individual site binding data.     

The distribution and species characteristics of the Culicoides biting midge fauna of South Africa

Abstract.  1. Monthly light trap collections over 2 years at 39 sites across South Africa captured over 3 000 000 Culicoides of 86 species, some of them known vectors of African horse sickness and bluetongue viruses.
2. To aid disease control and risk evaluation, cluster analysis and association measurements were carried out on species present at each site. Six species occurred at almost all sites. From the remaining 80 species, eight clusters were identified at > 48% similarity.
3.  Culicoides citroneus and C. krameri were characteristic of cluster 8, C. loxodontis of cluster 4, and two numbered, but un-named, species, C. #119 and C. #89 , of cluster 5.
4. Multiple anova and multiple discriminant analysis on the climatic and geographic parameters of sites in each cluster gave two significant discriminant functions that explained 91.5% of the variance between clusters. Function 1 contrasted sites with high cold cloud duration and high vegetation index with sites with high wind speeds. Function 2 contrasted upland clusters that also had high cold cloud duration with hotter, lower altitude sites.
5. Species associations were explained in terms of biotic provinces, based on ecogeographic factors that have previously been useful to describe communities of birds.
6. None of the clusters was ideal for siting an African horse sickness-vector free quarantine station as C. imicola and C. bolitinos , the main vectors, were found in all clusters but in very low abundance in cluster 5. The analysis provides a firm basis for studying the changing patterns of species distribution under varying climatic influences.     

Brain extract causes acetylcholine receptor redistribution which mimics some early events at developing neuromuscular junctions

We studied the effect of rat brain extract on rat muscle cells in vitro by light and electron microscope (EM) autoradiography after labeling acetylcholine receptors (AChR's) with 125I-alpha-bungarotoxin. We found that: (a) In the absence of brain extract, peak site densities within AChR clusters usually do not exceed 4,000 sites/micrometer2. (b) Within hours after exposure to brain extract, AChR's redistribute to form clusters in which the peak site densities are greater than 10,000 sites/micrometer2. Receptor concentration within extract-induced clusters is thus within a factor of 2 of that at the neuromuscular junction (nmj). (c) In the absence of extract, the AChR's and AChR clusters are predominantly on the bottom surface of the myotubes (facing the tissue culture dish). After extract treatment, they are predominantly at the top surface. (d) Plasma membrane in regions of high-density AChR clusters is enriched in membrane with enhanced electron density and surface basal lamina whether or not cells are treated with extract. Extract causes an increase in both these specializations on the top surface of the myotubes. (e) Brain extract does not produce an overall increase in AChR site density or a marked change in degradation rate of receptors in either clustered or nonclustered regions. By producing AChR clusters with junctional site densities and enhanced surface specialization, and by causing an overall shift in AChR's distribution, brain extract mimics early events reported at developing neuromuscular junctions.     

Alongshore dispersal and site fidelity of juvenile plaice from tagging and transplants

Juvenile plaice Pleuronectes platessa ( n  = 1281) were tagged and released at two locations 300 m apart on a 1 km long sandy beach. Most (>90%) of the fish were recaptured within 100 m of the release site (shown by the colour of the tag), with very few caught >200 m distance after 6 weeks. The changing spatial distribution of marked fish was adequately reproduced by a simple dispersal model with a single parameter: a 78% probability of remaining in a 100 m wide zone from one day to the next, with a 22% chance that fish move into an adjacent zone. In a subsequent similar study at the same beach, fish were either released at the point of capture ( n  = 881) or transplanted to the alternate site ( n  = 910) 100 m distant. After 6 weeks, transplanted fish moved along the shore towards their sites of original capture. Fish replaced at the point of capture showed no such movement along the shore. Further modification of the dispersal model to allow for a distinction between dispersal from home sites and from sites away from the original point of collection, was sufficient to reproduce the behaviour of the populations of both transplanted and control treatment groups. The likelihood of dispersal from home sites was much less than that seen at sites away from home. Juvenile plaice thus have a degree of long‐shore site fidelity not expected of a fish with strong depth‐related migration behaviour in a relatively homogenous habitat.     

Nest‐site selection by Interior Least Terns and Piping Plovers at managed,off‐channel sites along the Central Platte River in Nebraska,USA

Given the high productivity of Interior Least Terns (Sternula antillarum athalassos) and Piping Plovers (Charadrius melodus) on constructed off‐channel nesting sites along the central Platte River in Nebraska, USA, and the possibility of creating similar habitats at other locations in their breeding range, understanding how these species use off‐channel nesting habitats is important. We used data collected along the central Platte River in Nebraska, USA, over a 15‐year period (2001–2015), and a discrete‐choice modeling framework to assess the effects of physical site attributes and inter‐ and intraspecific associations on off‐channel nest‐site selection by Interior Least Terns and Piping Plovers. We found that Piping Plovers avoided nesting near each other, whereas colonial Interior Least Terns selected nest sites near those of conspecifics. In addition, the relative probability of use for both species was maximized when distance to the nearest predator perch was ≥ 150 m and elevation above the waterline was ≥ 3 m. Probability of use for nesting by Interior Least Terns increased as distance to water increased, whereas the probability of use by Piping Plovers was maximized when distance to water was ~50 m. Our results suggest that important features of constructed, off‐channel nesting sites for both species should include no potential predator perches within 150 m of nesting habitat and nesting areas at least 3 m above the waterline. Efficient site designs for Interior Least Terns would be circular, maximizing the area of nesting habitat away from the shoreline, whereas an effective site design for Piping Plovers would be more linear, maximizing the area of nesting habitat near the waterline. An efficient site design for both species would be lobate, incorporating centralized nesting habitat for Interior Least Terns and increased access to foraging areas for nesting and brood‐rearing Piping Plovers.     

Elephant herbivory of knob-thorn (Senegalia nigrescens) and ivory palm (Hyphaene petersiana) in Bwabwata National Park,Caprivi, Namibia: The role of ivory palm as a biotic refuge

African elephants have major impacts on vegetation, particularly at high densities. Knob-thorns (Senegalia nigrescens) are typically ring-barked by elephant, and high levels of mortality are common at high elephant densities. Our study aimed to test whether ivory palm clusters (Hyphaene petersiana) form a biotic refuge for knob-thorn against elephant herbivory. We measured the density, damage and mortality of knob-thorns in sites differing according to ivory palm presence and elephant density, and thus, the probability of knob-thorn encounter by elephants. The site with palms and low elephant density, had a high density of knob-thorns, but lower proportions of damaged and dead trees, than sites without palms but with similar or higher elephant density. In the former, knob-thorns were associated with palm clusters, particularly saplings and young adults. In this site, low proportions of damaged and dead knob-thorns were recorded in palm clusters, compared with outside clusters, and to those in the other sites. Our study also showed that juvenile palms which protected knob-thorns, suffered low mortality in contrast to subadult palms. We have no evidence but implicate elephants and suggest that in palm clusters, subadult palms are more accessible to elephants than knob-thorns because of the different methods of utilisation.     

Climate‐driven uncertainties in modeling terrestrial gross primary production: a site level to global‐scale analysis

We used a land surface model to quantify the causes and extents of biases in terrestrial gross primary production (GPP) due to the use of meteorological reanalysis datasets. We first calibrated the model using meteorology and eddy covariance data from 25 flux tower sites ranging from the tropics to the northern high latitudes and subsequently repeated the site simulations using two reanalysis datasets: NCEP/NCAR and CRUNCEP. The results show that at most sites, the reanalysis‐driven GPP bias was significantly positive with respect to the observed meteorology‐driven simulations. Notably, the absolute GPP bias was highest at the tropical evergreen tree sites, averaging up to ca. 0.45 kg C m^?2 yr^?1 across sites (ca. 15% of site level GPP). At the northern mid‐/high‐latitude broadleaf deciduous and the needleleaf evergreen tree sites, the corresponding annual GPP biases were up to 20%. For the nontree sites, average annual biases of up to ca. 20–30% were simulated within savanna, grassland, and shrubland vegetation types. At the tree sites, the biases in short‐wave radiation and humidity strongly influenced the GPP biases, while the nontree sites were more affected by biases in factors controlling water stress (precipitation, humidity, and air temperature). In this study, we also discuss the influence of seasonal patterns of meteorological biases on GPP. Finally, using model simulations for the global land surface, we discuss the potential impacts of site‐level reanalysis‐driven biases on the global estimates of GPP. In a broader context, our results can have important consequences on other terrestrial ecosystem fluxes (e.g., net primary production, net ecosystem production, energy/water fluxes) and reservoirs (e.g., soil carbon stocks). In a complementary study (Barman et al., 2013 ), we extend the present analysis for latent and sensible heat fluxes, thus consistently integrating the analysis of climate‐driven uncertainties in carbon, energy, and water fluxes using a single modeling framework.     

Philopatry, Site Fidelity and Local Kin Associations within Grey Seal Breeding Colonies

Abstract Colonially breeding animals such as grey seals typically have a discrete number of breeding sites. The extent to which offspring are philopatric (return to breed at their natal site) and the prevalence of philopatry by sex of pup has fundamental consequences for the social and genetic structure within and between each colony.
Grey seals born and marked by tagging and cohort brands at colonies on North Rona, Outer Hebrides since 1960 and at the Isle of May, Firth of Forth since 1981 have shown philopatry. Overall re-sight rates of 1620 pups tagged at North Rona and 1667 pups at the Isle of May ranged from 0 to 17%. Although most evidence of philopatry relates to females, males at each colony displayed philopatry. In addition, females born at N. Rona pupped closer to their natal sites than would be expected by chance (p = 0.005), providing evidence of fine scale natal site fidelity. Females born at the Isle of May did not show the same degree of fine scale natal site fidelity, but there was considerable individual variation. The spatial scale of philopatry shown by seals differed according to the local area within each island. Fidelity of known adult females to pupping sites at both colonies was high. In addition, we found an instance of mother and daughter pupping together away from the daughter's natal site.
These data: (i) provide evidence of philopatry in both sexes at each site; (ii) describe occurrences of fine scale philopatry at both sites; (iii) show that mothers and offspring occupied the same areas on the colony, suggesting the possibility of highly related groups within colonies, which would provide conditions for kin-specific altruistic behaviours; (iv) suggest the possibility of individual or kin recognition, even though contact between mothers and offspring has been thought to cease after the 18 d lactation period.