Nest & Partner Selection
Chinstrap Penguins show high fidelity to their natal colonies. In studies on the S. Shetlands, emigration was less than 1% per year even between monitored colonies less than 3 km apart (Hinke et al. 2007. Oecologia 153, p.845-855). Fidelity to nest sites is also high, especially in experienced breeders. Partner fidelity in the Chinstrap fluctuates strongly between seasons as in other penguins, but appears to lie at around 80%, thus being higher than that of the Adelie and lower than that of the Gentoo. Partner changes are often due to death or late arrival of the previous partner. As explained below, bill size and nest size are two factors playing a role in partner selection. General size and health state are probably also critical.
Most colonies are in elevated areas near to the sea and consist of a number of subcolonies containing from as few to 5 up to as many as thousands of individual nests. These subcolonies are separated by nest-free areas. Colonies are generally on elevated ground up to about 100 m above sea level on rocky headlands and foreshores free of vegetation.
Whilst Chinstrap Penguins may share rookeries with Adelie and Gentoo penguins, the actual nesting sites within the rookeries are still largely segregated by species, in part reflecting different nest area preferences. In mixed colonies, Chinstraps were observed to have a greater tendency to occupy sloping nesting sites near to the sea than the other Pygoscelids. Interestingly, Chinstrap and Adelie Penguins also tend to use larger but fewer stones for nest-building than Gentoos (Volkman and Trivelpiece 1981. Wilson Bull. 93(2), p.243-248).
At Deception Island, it was shown that breeding success is higher in the larger subcolonies (Barbosa et al., 1997. Polar Biol. 18, p.410-414). This was attributed to differences in chick mortality during the guard phase. Mortality (loss of eggs or chicks) was 50% higher in the small subcolonies and was probably caused by increased predation by Skuas. This may however not always be the case, since nests in the smaller subcolonies were found to be larger and may thus confer advantages when weather conditions are poor. The study revealed no significant difference in breeding success between central and peripheral nests within the individual subcolonies. Generally, it is however considered that central nesting positions are favourable. In fact, central nests are generally occupied by more aggressive males with larger beaks which were shown to be preferred by females (Barbosa et al., 1997. J. Morphol. 232(3), p.232). Nests occupied by these penguins also tended to be larger. Nest size may play a role in partner selection although beak size may be a more crucial direct selection criterium, since females were also found to have larger beaks in the center of the colony, in spite of the fact that the male is responsible for nest size until a pair has been established (Minguez et al., 2001. Waterbirds 24(1), p.34-38).
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Hannah Point (Antarctic Peninsula ) Chinstrap Colonies
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Chinstrap Colony at Hannah Point
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Bailly Head Chinstrap Colonies - Deception Island
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Chinstrap Colony on Cliff-Top - Deception Island
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Nests are usually spaced about 50 cm apart in Chinstrap penguins, compared to only about 37 cm in Adelies (Trivelpiece and Volkman 1979. Auk 96, p.675-681). Gentoo nests are the most widely spaced amongst the Pygoscelid penguins. The nests are usually constructed from a pile of stones placed over a small scrape in the ground. Nest size is one important determinant of breeding success. Nest size and maintenance thereof by stone-collection has been studied in some detail. It has been suggested by various authors that stone gathering behaviour during incubation and chick-rearing may play a role in pair-bonding or in maintaining nest size above a critical level needed to protect nest contents. During this period, birds may spend several hours gathering stones after they have been relieved at the nest by their partners. Stones are obtained by collection around the nest-site, but largely by theft from nearby nests. Male birds are both more adept at defending their nests and at stealing from their neighbours (Moreno et al., 1995. Polar Biol. 15(8), p.533-540). In small subcolonies, more stones are available both within and around the colony. This accounts for the larger nests and reduced level of stone theft compared to in larger colonies. In large colonies, stones may often only be obtainable by theft and larger stones are focused on (Carrascal et al., 1995. Polar Biol. 15(8), p.541-545). Theft is however only resorted to if necessary, since when stones were artificially made available to birds in the larger colonies these were eagerly collected and levels of theft dropped.
Studies at Deception Island investigated the response of nesting birds to nest manipulation (Fargallo et al., 2001. Behav. Ecol. Sociobiol. 50, p.141-150). Pre-manipulation nest weights ranged from 3-16 kg with an average of about 8 kg. Nests were artificially reduced in size by removing stones, or were reduced in size and surrounded by snow to simulate poor weather conditions. In both cases, stone-gathering behaviour intensified, yet the effect was much more significant for those nests around which snow had been placed. These nests were rapidly built up to above pre-manipulation levels, suggesting that the birds were responding to a perceived risk of flooding by melt-water by increasing the sizes of their nests. Certainly, it was evident that stone-gathering was adapted to nest condition and environmental conditions, rather then being a mere display performed at constant levels during the breeding period to maintain the pair bond. The study also showed that birds that invested most time in stone-gathering had lower haematocrit levels, suggesting poorer condition as energy was consumed in the process and less time was available for foraging.
The importance of nest size to reduce the risk of egg / chick loss has been directly observed in a previous study (Moreno et al., 1995. Polar Biol. 15(8), p.533-540). Here, 14% of eggs/hatchlings were lost due to flooding following a snow-storm, and the smaller nests were much more severely affected. Once chicks are thermoemancipated, flooding appears to present little risk to them and stone-gathering behaviour of parents rapidly declines at this stage from a peak around chick hatching time.
Penguins at the nest always defecate outwards in apparently relatively random directions. This serves to keep the nest clean. Studies on Chinstrap and Adelie Penguins suggest that the faeces in propelled away with pressures of up to about 60 kPa (450mm Hg) with the highest pressure being achieved at the beginning of the process (Meyer-Rochow and Gal 2003. Polar Biol. 27, p.56-58). This is about 5-fold higher than in humans.
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Collecting Rocks for Nest
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Moving Old Feather Shaft on Nest
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Placing Rock into Nest Bowl
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Seeking Gift (Stone) For Mate
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Chinstrap Penguins have been observed ejecting nesting Adelie Penguins from their nests in mixed colonies. This behaviour has been investigated at Deception Island. In some parts of the colony, over 50% of nests occupied by Adelies were taken over by Chinstrap Penguins (Trivelpiece and Volkman 1979. Auk 96, p.675-681). When the Chinstraps returned to their colonies to breed (about 25 days later than the Adelies), male Adelie penguins were generally on the nest incubating recently laid eggs. The Chinstraps pecked at the heads of the resident Adelies and beat them with their flippers until they left the nest. Several attempts to regain the nest were observed but these were generally unsuccessful. The eggs were usually lost as a result, although one example of an Adelie chick raised by Chinstrap parents was reported.
A subsequent study found that in most cases, the ejected birds were inexperienced Adelie penguins that had nested at sites occupied the previous year by Chinstrap Penguins. These inexperienced Adelies had also lost weight as they had been fasting for several weeks and were thus nearly a kg lighter than the arriving Chinstraps that wanted to reoccupy their nests (Trivelpiece et al., 1984. Auk 101(4), p.882-884). The lower experience and weight probably account for the inability of the Adelies to defend their nests.
Timing of Breeding
Chinstrap penguins only make a single breeding attempt each year, taking advantage of the short antarctic summer. Chinstrap penguins return to their breeding sites in November, with exact dates varying between location and year. Males usually return about 5 days earlier than females in order to (re)claim and maintain a nest. Once the females arrive, a short period of courtship is followed by establishment of a pair bond and shortly afterwards copulation. Eggs start to be laid over an about 2 week period in December with peaks around the 7th on Laurie Island (S. Orkneys) in 1997 or on the 22nd on Deception (S. Shetlands) in 1995 (De Leon et al., 2001. Polar Biol. 24, p.338-342; Belliure et al., 1999. Polar Biol. 21, p.80-83). Generally, it appears that within a given population individual birds lay at a similar date within the range from year to year, i.e. early breeders consistently breed early (Vinuela et al., 1996. J. Zool. 240, p.51-58).
Laying and Incubation
Chinstrap Penguins generally lay two eggs of relatively similar size. These eggs can be genetically identified as belonging to the nesting parents, showing that the penguins are both socially and sexually monogamous (Moreno et al., 2000. J. Avian Biol. 31(4), p.580-583).
Taking studies at Laurie Island as an example, these eggs are generally laid over a period of about 3.3 days (from 2-5). Brood patch temperature is already high, averaging 37'C when the first egg is laid and reaching over 38'C by the middle of the incubation period, although the patch is small at the onset of incubation (De Leon et al., 2001. Polar Biol. 24, p.338-342). Egg temperature is slightly lower. Eggs have an approx. volume of 90 cubic cm and are about 6.7 cm long. In about 95% of cases, the first laid egg hatched first. Laying intervals and the degree of hatching asymmetry could not be correlated, but size asymmetry of the eggs within a clutch could be correlated to hatching asymmetry, suggesting that egg size is a significant determinant of incubation period length, possibly in part due to greater temperature fluctuation in small eggs during incubation. Female condition could not be correlated to laying intervals, although it appeared to correlate to clutch asymmetry.
Incubation periods may be from as short as 31 up to 40 days. The second egg must hatch within 4 days of the first, since thereafter incubation of the remaining egg becomes physically impossible due to the size of the first chick (Fargallo et al., 2006. Behav. Ecol. 17(5), p.772-778).
Evidence for a brood reduction mechanism like in Eudyptid penguins such as the Macaroni Penguin could not be found, although when food is scarce, it was found that it was more likely that the later-hatching starves if the eggs hatch several days apart. This did however not seem to significantly enhance the survival chances of the remaining chick (Moreno et al., 1994. Polar Biol. 14(1), p.21-30).
An extremely detailed study on mortality of chicks depending on hatching order and brood sex compositions was performed at Deception Island (Fargallo et al., 2006. Behav. Ecol. 17(5), p.772-778). Again it was shown that hatching asymmetry could be correlated to size asymmetry of the eggs. Further, it was found that the hatching asymmetry increased when the second egg contained a female embryo. This can be partly accounted for by the fact that the hatching period (time between pipping of the egg by the embryo and emergence of the chick from the egg) averages 1.3 days for males and 1.5 for females. Male chicks are thought to be more muscular due to the effect of yolk testosterone which aids development of the hatching muscle allowing the male embryo to break out of the egg faster. Chicks from larger eggs also hatch faster. The second-hatched chicks were generally subject to higher mortality. Also, male chicks were more likely to survive in mixed sex broods, whilst females were more likely to survive than males when pure female broods were compared to pure male broods. This is probably due to the fact that it is more difficult to provision two male chicks due to their larger size and higher food demands, plus the higher competitive ability of male chicks.
Interestingly, male chicks are generally more frequently found on larger nests (Fargallo et al., 2004. Polar Biol. 27, p.339-343). Large nest size correlates to healthy parents. It is hypothesized that only strong parents can raise healthy male chicks (which require more food than females) able to later effectively compete with other males in a population with a surplus of males due to higher female mortality.
When both chicks survive the first days after hatching, egg size asymmetries could no longer be correlated to respective chick sizes by about 15 days. Interclutch differences were however significant, with those chicks hatching early in the breeding season due to relatively early breeding by the parents growing faster than later-hatching chicks (Belliure et al., 1999. Polar Biol. 21, p.80-83).
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Incubating Chinstrap Penguin
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Standing over Unhatched Egg
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Egg Visible under Brood Patch
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Preening on Nest - Note: Egg not under Brood Patch
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Incubation Duties / Nest Relief
Chinstrap Penguins alternate in taking care of the clutch with the length of shifts changing at different stages. Behaviour of Chinstrap Penguins at the nest has been observed in detail at Bouvetoya Island (Haftorn 1986. Polar Res. 4 n.s., p.33-45). During incubation, average shifts were 35 hours, with a reduction to about 12 hours during the brood period when chicks require regular meals. As can be seen from the section on foraging, birds may be absent for only a few hours or more than a whole day, depending on food availability. During the incubation period, 92% of time was spent prone on the nest. The rest of the time was taken up standing at the nest or performing various behaviours such as preening. During the early brood, about equal proportions of time were spent prone or standing, with the male spending more time upright than the female. Upon return of the relieving partner, mutual displays were observed and the incubating partner was often relieved within a minute or two. However, on average, nest relief only took place after about 15 min during the early brood. The relieved bird often stayed in attendance of the nest for minutes to hours following relief.
The nest relief ritual, involving the Loud Mutual Display (LMD) and Quiet Mutual Display (QMD) in Chinstrap and Adelie Penguins has been described in detail (Müller-Schwarze and M.-S. 1980. Auk 1997, p.825-831). In the LMD, the birds stand and swing their heads back and forth whilst uttering a cackling noise from their open bills. On the other hand, the QMD also involves similar head swinging but the bills are kept shut and the display is accompanied by a humming sound. Further, the arriving bird may circle the nest nodding its head gently. The resident bird may also leave the nest and circle or circles after relief. Relief was observed on average 3.6 min after arrival, slower than in the other Pygoscelid penguins. The LMD was infrequent (mean 1.38 per nest relief ceremony), whereas the QMD was more frequent (mean 4.88). The LMD was usually the first display and could be instigated by either bird, whilst the QMD was more often instigated by the bird on the nest. The speed of nest relief could however only be correlated to the circling behaviour.
When nest relief is delayed, such as in 1998 at the S. Orkneys when extensive sea-ice restricted access to the sea and inhibited foraging, high levels of nest desertion (52% in the study) during incubation and brood are observed (Rombola et al., 2003. Polar Biol. 26, p.41-48). Nest desertion is the most significant cause of egg / brood mortality in most years since it invariably leads to loss of eggs and chicks due to predation or starvation. In fact, Chinstrap Penguins appear to be poorly adapted to fasting, since they reach the final phase of fasting, when waste products of protein catabolism (e.g. urea) rapidly increase in plasma, more rapidly than other penguins such as the Gentoo (Alonso-Alvarez 2003. Polar Biol. 26, p.14-19). It is thought that a certain level of urea, produced by breakdown of muscular tissue once lipid reserves are exhausted, may be a trigger for abandonment of parental duties.
Chinstraps vigorously defend their nests. Interestingly, once one egg has been removed, the intensity of nest defence is reduced slightly, since the brood has a reduced total reproductive value (Amat et al., 1996. J. Avian Biol. 27(2), p.177-179).
Brood / Guard Phase
Chicks hatch with a protoptyl down which allows efficient heat transfer from parent to the initially poikilothermic chick. This starts to be replaced within days by the mesoptile down which progressively increases in thickness. The increasing thickness, together with metabolic changes, leads to thermoemancipation of the chick by the end of the brood period. Chinstrap chicks have higher metabolic rates than Gentoo chicks, probably due to adaptation to their on average colder environment. By about 10 days the chicks can generate sufficient heat, but only after over 15 days are the completely homeothermic, i.e. the insulating capacity of their down is sufficient to prevent excessive heat dissipation under dry conditions (Taylor 1985. Envir. Physiol. 155(5), p.615-628). The insulation of the chicks down is reduced when wet, although it does remain watertight. After about 15 days, the parents no longer need to brood the chicks but still guard then against predation. This guard phase lasts till chicks reach an age of about 30 days. Chicks are guarded vigorously during the brood / guard phase and nest defence is stronger in comparison to birds defending eggs (Vinuela 1995. Ethol. 99(4), p.323-331), presumably as chicks are considered more valuable.
Chicks have a mass of under 100 g at hatching and, after an initial period of slow absolute growth, rapidly gain weight in a more or less linear fashion, with the rate determined largely by food availability. For example, at Deception Island in 1993/94, chicks reached about 1 kg by 15 days and 3 kg by 32 days (just after the end of the guard phase), after which mass increase stopped. Similar patterns can be observed for flipper and bill growth, the latter however continuing strongly from 32 to 47 days, when the last measurement in the study was taken (Moreno et al., 1998. J. Field Ornithol. 69(2), p.269-275). The study at Deception also addressed the effect of experimental brood reduction on growth of the resulting single chicks compared to two-chick nests. Experimental brood reduction was performed to exclude effects of parental quality, which may be lower in broods that have already lost a chick. Little difference was observed in the size of chicks approaching fledging from reduced broods compared to those from complete broods, although a slight but not statistically significant advantage in terms of mass reached and structural size could be seen. However, near the end of the guard phase (between days 15 and 21), when growth is potentially fastest, single chicks grew significantly faster. Thus at this stage food availability may be limiting.
Parental provisioning behaviour is different when the brood only contains a single chick (Meyer et al., 1997. Polar Biol. 17, p.228-234). At Seal Island (Antarctic Peninsula), parents with 2 chicks were found to spend 15% more time at sea. The duration of foraging trips did not change, but the parents made a larger number of trips and appeared to land with more than 10% higher food loads (reaching 360 g in 1993 and over 600 g in 1994). In the study, chick growth rate in 1 and 2 chick broods was found to be similar in 2 years and higher in 1 chick broods in the other 2 years studied.
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Stretching Chinstrap with 2 Chicks
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Parent Inspecting Nest While Chick Underneath
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Chick Adopting Preferred "Head-First" Brooding Position
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Parent and Chick Changing Position
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2 Chicks Resting by Guarding Parent
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Creche Phase
After anything from about 20-40 (usually 30) days, Chinstrap chicks are left unattended as both parents start to forage to meet their own nutritional needs and those of the chicks. The unattended chicks gather in groups (creches) of between a few to several hundred birds. Chicks are usually in the range of 2.5-3 kg when they creche.
The timing of the end of the guard phase is probably determined by the condition of the parents rather than that of the chicks, since chicks that creche late tend to reach larger final sizes (Vinuela et al., 1996. J. Zool. 240(1), p.51-58). It has been shown that high Urea build-up in parental birds can be correlated to a younger creching age for chicks (Penteriani et al., 2003. Polar Biol. 26, p.538-544). Logically, if parental condition is poor (e.g. if food is in short supply), the parents need to both spend more time foraging and have to leave the chicks unguarded earlier to do so. Creching also tends to occur earlier in late-hatching birds, probably because the parents have to reduce the length of the creche period in order to allow themselves sufficient time to forage in preparation for moult (Fledging age is also younger in these birds). However, interestingly, also early-hatching birds were found to creche earlier. These were however found to suffer significant mortality due to aggression from brooding adults. Chicks being raised alone creche significantly older than chicks with a sibling. Raising a single chick has less impact on a parents condition (De Leon 2000. Waterbirds 23(1), p.117-120). The reason that parents leave chicks unattended earlier when their own condition is poor can be explained by the fact that the adult may breed in subsequent seasons and thus has a higher reproductive value than a young chick with an uncertain future. Hence, from a population point of view in a long-lived species like the penguin, it makes more sense for an adult to survive at the expense of a chick than the other way round.
One interesting study suggests that hatching date per se may be the determining factor for creching date rather than parental quality, which has frequently been suggested to correlate to the exact timing of breeding (Moreno et al., 1997. Auk 114(1), p.47-54). One day old chicks were exchanged with 6 day old chicks on other nests and it was still found that the later-hatching chicks creched earlier. Hence, parental quality could not explain differences in creching date according to this study. It should however be noted that parental quality and parental condition are not the same thing, since a parent of essentially good quality will also have a poorer condition as the breeding season progresses and in this study would have to spend additional time raising two sets of chicks from the 1-6 day stage. Further, monitoring immune status, which is one indicator of parental quality, revealed that late breeder and failed breeders had poorer immune status compared to early breeders (Moreno et al., 1998. Oecologia 115, p.312-319). Further, early breeders suffered a decline in health status as the chick-raising period progressed.
The reason for creching remains a subject for debate. Breeding adults regularly attack chicks (apart from their own). In some cases this occurs to avoid interference from unrelated chicks during feeding. However, the majority of aggressive interactions are not related to feeding. It has been suggested that adult aggression towards chicks is a trigger for creching behaviour and may serve to shepherd chicks. A study on about 45 day old chicks at Deception found that aggression did not lead to movement of chicks in any particular direction. Further, passing adults from other subcolonies were involved in aggressive behaviour. These facts were taken to suggest that no shepherding is taking place (De Leon 2002. Polar Biol. 25, p.355-359). However, another study at the same site reached a different conclusion (Penteriani et al., 2003. Polar Biol. 26, p.538-544). Lone chicks were found to move around (about 1.25 m/min), yet chicks in creches were largely static. The movement of the lone chicks was largely induced by adult aggression, which was more frequently directed at lone chicks or those in small groups. Chicks thus aggregated into larger groups when more neighbouring adults were present. Shepherding may thus be an inappropriate term for the adults aggressive behaviour since displacement may not be directional, but aggression may nevertheless ultimately result in creche formation due to increased random movement of chicks until these are in creches.
The aggregation of chicks into larger groups when more adults are present nearby may also be partially explained by a defensive role of the adults (Martin et al., 2006. Behav. Ecol. Sociobiol. 60, p.778-784). In response to a simulated predator attack, a higher density of adults resulted in less rapid and shorter distances of retreat of chicks. Interestingly, younger checks responded less intensely to predator approach, as did healthier chicks. This suggests that younger chicks may not yet be as aware of the risk of predation, and that chicks in poor health condition may sense their greater vulnerability. This higher sensitivity may however simply be due to foregoing increased social harassment by adults or siblings, possibly partly explaining the poor condition.
One of the main reasons generally proposed for creching is the safety-in-numbers hypothesis which suggests that chicks in creches should be less vulnerable to predation. This is based on observations of chicks fleeing into denser aggregations when approached by e.g. Skuas. However, the density of chicks alone did not modify escape responses in the Penteriani et al. study. Since Skuas may examine their potential prey before focusing their attack on a particular chick, the creche may provide little direct protection for a weak chick. However, its chance of being targeted is reduced if it groups together with chicks in even poorer condition. On the other hand, the presence of more adults in the vicinity may be protective. On the S. Shetlands, adult birds have been observed driving giant petrels away from creched chicks (Jansen et al., 2002. Oecologia 131, p.306-318).
Whilst the amount of food provided to chicks gradually increases during the brood phase, chick meals at the end of the guard phase and during the creche phase are relatively constant when krill is abundant. It is considered that at the end of the guard phase parents (of which only one can forage at a time) struggle to meet the chicks needs, and again at the end of the creche phase when both parents can hardly provide enough food for the demanding chicks.
It was long assumed that if both parents can forage during creche, the chicks may be provisioned with twice as much food. This could however not be confirmed in studies on other penguin species. Studies on Chinstraps at Seal Island (South Shetlands) revealed that the adults focused more on more productive diurnal foraging after the end of the guard phase, at the expense of overnight foraging (Jansen et al., 2002. Oecologia 131, p.306-318). The proportion of time at sea increased from guard to post-guard (creche) phase by 17% in parents with one and 21% in parents with 2 chicks. Two-chick parents were generally at sea longer by 7% during guard and 12% during post-guard, this being achieved by increased time at sea overnight and during the day, respectively. Further, parents of two chicks were found to be landing about 10% greater food loads than those of single chicks. The amount of food delivered to single chicks increased linearly, but was higher and constant when two chicks were present. In addition, parents of two chicks performed 11 trips for every 10 of those with a single chick during guard phase, and 12 for every 10 thereafter, as food demands continue to rise.
At Deception Island, during the creche phase, the amount of food brought to land could be correlated to flipper length which was used as a measure of general body size (De Leon et al., 1998. Polar Biol. 19, p.358-360). Mean feed mass of 630 g was determined by stomach lavage of returning adults, with a range of from 300-1000 g. Larger birds tended to land more food, suggesting that where possible adult birds only return to land when their stomachs are full. Interestingly, the smaller females as a whole landed as much food as the males and there was no difference in food landed at a given time between early and late breeders. It should however be noted (see section on feeding) that this mean feed mass is higher than in most other studies, suggesting that Chinstraps are rarely actually limited by stomach size. Feeding is addressed in far more detail in the dedicated section.
Feeding chases can often be observed when parents return to land to feed creche phase chicks. These chases illustrate the relatively high speed with which some penguins can run on land. Several different hypotheses that may account for this form of behaviour have been proposed and assessed (Bustamante et al., 1992. Anim. Behav. 44, p.753-759). These include roles in chick recognition, locomotory training, separation of chicks from unrelated chicks in the creche, separation of siblings to favour feeding of the hungrier or the stronger chick, and avoidance of intense begging which may unsettle the adult or reduce the efficiency of transfer of food. On average, 17 separate feedings were observed per adult visit. When only one chick was present, chases were less frequent and shorter and more chicks were fed within the creche. This is incidentally also observed when one chick is experimentally removed (Moreno et al., 1996. Bird Behav. 11(1), p.31-34). Unrelated chicks are repelled aggressively by parent or own chick and even if the unrelated chicks participated in food chases, they are almost never observed obtaining food. Chasing was observed more frequently after first feedings in about 90% of adults observed. Hence, all these observations make a recognition role seem unlikely. When both chicks were present and participated in a chase, in nearly half of these cases both chicks were still present when feeding began. Hence, separation may also not be the main function.
The data in fact favours a role in the assessment of relative nutritional needs of the chicks. If both chicks are in similar condition, the hungrier chick may be more motivated to chase and thus receives more food. The chick chasing longest was generally observed to obtain more feedings. Further, where one chick is in poor condition, the chase may serve to select against the chick that is unlikely to have a good survival chance, thus increasing the chances of the stronger sibling. This could even be considered as a form of brood reduction mechanism. The separation of chicks observed in many cases may be an additional benefit, since food transfer is more efficient when only one chick is begging and food dropped on the ground as a result of competition is not recovered. Indeed, another study attributed primary importance to the avoidance of harassment of the adult by both chicks during feeding, since it was observed that competition between the chicks slowed the transfer of food. (Moreno et al., 1998. Emu 98(3), p.192-196).
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Chinstrap Parent with 2 Chicks
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Parent Taking Chick under its "Wing"
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Chinstrap Adult with 2 Chicks
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Chinstrap Adult with 2 Chicks
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Adult Provisioning Chick
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Note: Pinkish Krill Visible in Top of Parents Bill
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Adult Provisioning Chick
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Adult Provisioning Chick
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Fat Chinstrap Chick After Feeding
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Adult Provisioning Chick
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Chick Begging - Fat (Fed) Chick Does Not Compete
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Begging Was Successful
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Chinstrap Penguin Chicks in Various Poses
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Acoustic Parent-Chick Recognition
During the creche phase, the chicks no longer remain at the nest and tend to gather into groups (creches). Adult-chick recognition now relies at least partially on acoustic signals, especially as the chicks venture further from their nests as the creche phase progresses. Acoustic recognition has been studied in the other two Pygoscelid penguin species, but no detailed studies have been performed on the Chinstrap. It is however likely that the calls are similar to those in the Gentoo or Adelie penguin. Interestingly, in a study performed for an entirely different purpose, one and six day old chicks were exchanged between nests. These chicks were readily fed by the foster parents, suggesting that acoustic recognition is not determined genetically or acquired acoustically through the egg-shell or in the first days after hatching (Moreno et al., 1997. Auk 114(1), p.47-54).
When arriving at the nesting site, Pygoscelid adults call their chicks. The calls are made up of a single series of sound components known as syllables which are relatively evenly spaced in the Gentoo (Jouventin and Aubin 2002. Animal Behav. 64, p.747-757). In this species, recognition is solely based on the harmonic content of the call. The Adelie Penguin call is fundamentally similar. In contrast, Eudyptid penguins (e.g. Macaroni and Rockhopper) have a double vocal signature, where a distinctive pattern of the syllables additionally contributes to recognition. This is in turn less complex than the double vocal signature of the Aptenodytes penguins (i.e. Emperor, King), in which two simultaneous series of harmonically related bands are combined to create distinctive beats due to band interaction. The higher complexity of the call in non-nesting penguin species is accounted for by the fact that the acoustic signal does not only have to distinguish between birds at a particular location (i.e. nest and immediate surroundings) within a colony, but has to be able to discriminate essentially all birds in a colony without a supplementing positional signal.
Fledging
Once the chicks have developed a waterproof juvenile plumage they are able to enter the sea. The parents continue to feed the chicks for a while before they are left to their own devices. Shortly before Chinstraps fledge, chicks move from the nesting areas towards the sea, often congregating on the beach. Fledging tends to occur in Chinstrap Penguins between about 50 and 65 days of age. This is relatively early compared to other penguins, and is possibly the result of the late start of the Chinstrap breeding season. The chicks are forced to fledge particularly early when conditions are poor or they have hatched late in the season. This is detrimental to their survival. In productive years, chicks tend to fledge weighing 3-4 kg.
Post-fledging mortality is considered to be an important determinant of Pygoscelid population levels. At Deception Island, large numbers of dead chicks are regularly swept onto the beaches shortly after the fledging period (Moreno et al., 1999. J. Evol. Biol. 12(3), p.507-513). These birds were found to have relatively short flippers and were presumably relatively light when they fledged, meaning that their reserves were evidently not sufficient to allow them to survive whilst they started to learn to forage.
Post-Breeding Moult
Little is known in detail about the moult period in Chinstrap Penguins. It is thought that breeding adults spend between 2 and 3 weeks at sea after chicks fledge before returning to moult. The moult occurs in late February / March and is thought to be relatively short (maybe as little as 13 days). It serves to replace the worn plumage with a new one before the penguins head to sea for the long winter foraging season. The moult is energetically highly demanding and severely underweight penguins are unlikely to survive it. At Seal Island (S. Shetlands) in 1990, Chinstraps weighed about 4.1 kg after breeding, 5.1 kg immediately before moult and 2.8 kg post-moult (Croll et al., 2006. J. Zool. 269, p.506-513).
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