Mike Ko Personal Portfolio

 

Home-School Education
2001-2012
Hong Kong

University of Durham
Bachelor of Science
2014-2017
United Kingdom

University of Sussex

Master of Arts
2017-2018
United Kingdom




Academic Works
                                Year 2
: Behaviour

The Influence of Pup Age and Anthropogenic Disturbances on Mother Attentiveness in Grey Seals (Halichoerus grypu)

Introduction

            Juveniles of mammalian species such as the pinniped pups are often dependent on parental care for survival prior to reaching adulthood. Seal pups are notably reliant on their mothers’ fat-rich milk to accumulate the blubber needed for post-weaning thermoregulation, energy reserves and physical protection. (Noren et al., 2008). Furthermore, pups also face various dangers that can cause premature deaths. These include other adult seals, who can either intentionally or accidently inflict physical injuries, as well as aspects of the physical environment that can kill or trap the pups (Coulson and Hickling, 1964). Accordingly, mother seals exhibit a variety of behaviours that functions to nurture and protect their pups. Examples include presentation of the nipples to encourage suckling, pup checks, alert examination of the surroundings and fighting with other seals (Kovacs, 1987).

            It can be postulated that the extent or frequencies of such behaviours can change in light of varying conditions related to either the pup or the environment. For instance, maternal behaviours such as pup checks and alertness can be influenced by pup age. In effect, mothers may engage less in protective behaviours as pups grow and become less vulnerable. This would allow mothers to either conserve energy or engage in other behaviours. Proximity to anthropogenic disturbances could also influence the behaviours of mother-pup seal behaviours.

            Past behavioural studies on the grey seal, Halichoerus grypus, have provided insights relevant to such postulations. A study done by Coulson and Hickling (1964) found that mortality risks gradually decreased with increasing pup age. Hence mother seals could possibly reduce their protective behaviours and devote their time to other activities. Another study (Bishop et al., 2015) found that male activity budgets did not vary significantly in the presence of anthropogenic disturbances. However, whether this also applies to mother seals remains to be seen.

            To further assess the influence of changing conditions on maternal behaviour, this study evaluated multiple related hypotheses. The first hypothesis posited that mothers with younger pups would be more attentive, so that they engage more in the protective behaviours of pup checks and alertness. The second hypothesis assumed that mothers closer to sources of anthropogenic disturbances would similarly be more attentive through the above behaviours as well. Evaluation of these hypotheses involved obtaining observational data for the activity budget and number of pup checks as seen in mother-pup pairs within a population of H. grypus.


Methods

            Observational studies were carried out on 8th December 2015 from approximately 12:00 to 1:00 pm for 48 mother-pup pairs of H. grypus. The studied population was a seal colony located at the Donna Nook National Nature Reserve in Lincolnshire, the United Kingdom. The terrain mainly consisted of salt marsh and sand flats.

            The observed pairs were selected and split into groups on the basis of their proximity from the path fence by which observers carried out the study. Pairs in the “Near” group were within 10 meters from the fence, while pairs in the “Far” group were at least 20 meters from the same fence. The pup age for each pair was also noted. For this study, pup ages were sorted into two categories: “Young” (corresponding to phase 1 and 2 of typical age classes) and “Old” (corresponding to phases 3 – 5).

            Behavioural observations were made in 30-minute periods for each pair, during which instantaneous scans for recording a pre-defined set of exhibited behaviour were done in 30-second intervals. The total number of pup checks done by the mother was also recorded for individual pairs according to an all-occurrence protocol.

            To evaluate the study’s hypotheses, four sets of figures were subjected to statistical analysis. The first two data sets were sorted out by separately associating each pair’s number of pup checks and the percentage of time spent in an alert state (henceforth referred to as “alertness”) with their corresponding age category values, respectively. The other two data sets were similarly obtained by replacing age category with proximity as the associating variable. The Shapiro-Wilk test was first used to evaluate the normality of the data distribution for each data set, followed by the application of the Mann-Whitney U-test with a significance level set at 0.05. All statistical tests were done using the IBM SPSS Statistics V22.0 software.


Results

            Table 1 shows the activity budget in the form of selected statistical figures, as derived from the observed mother seal behaviours. As can be seen, the most frequent behaviour is Rest, with a mean 71.61% of total time spent in this state by mother seals.

            Figure 1 shows the mean values of total pup checks for mother-pup pairs with the different associated age categories or proximity. Mean total pup checks were higher for pairs with pups that were either younger or closer to the fence. Analysis with the Mann-Whitney U-test showed that the mean ranks for the number of pup checks did differ significantly between mother-pup pairs with varying proximities (U=189.5, p=0.042). In contrast, there was no significant difference for pairs with varying pup age categories (U=214, p=0.13).

Table 1. Activity Budget Exhibited by Observed Seal Mothers

 

R

A

L

M

MP

N

AGM

AGF

AGP

ATCOP

COP

X

Mean

71.61

9.13

1.10

3.34

3.51

9.66

0.13

0.07

0.10

0.17

0.03

1.14

Standard Deviation

24.18

9.24

1.87

3.24

7.57

19.40

0.45

0.48

0.49

1.18

0.23

3.46

Standard Error

3.49

1.33

0.27

0.47

1.09

2.80

0.06

0.07

0.07

0.17

0.03

0.50

 

Figures are derived from percentages of time spent by observed mother seals engaged in in the associated behaviour.

Behaviour Key:
R= Rest; A = Alert; L = Locomotion; M = Other movement; MP = Mum-pup contact;
N = Presenting/Nursing; AGM = Aggression with Male; AGF = Aggression with Female;
AGP = Aggression with Pup; ATCOP = Attempted Copulation; COP = Copulation; OOS = Out of Sight;
X = Other behaviour


Figure 1. Box plots for Mean Total Pup Checks for all individual Mother-Pup pairs in differing: A. Age Categories and; B. Proximity. Standard Errors are given by the error bars.

            Figure 2 similarly gives the mean values of alertness for mother seals in with the associated age categories or proximity. In general, mothers who were in pairs with either younger or nearer pups were had higher alertness. However, Mann-Whitney U-test results showed that mean ranks for alertness were significantly different between pairs with differing age categories (U=186, p=0.035), while the opposite was true for proximity (U=259, p=0.55).

Figure 2. Box plots for Mean Percentage of Time Being Alert (“Alertness”) for Mother-Pup pairs in differing: A. Age Categories and; B. Proximity. Standard Errors are given by the error bars.


Discussion

            The study found that there was a significantly higher level of exhibited pup checking behaviour in H. grypus mother-pup pairs that were closer to sources of anthropogenic disturbances. Yet there was no significant difference in pup checking between pairs with differing pup age categories. It was also found that pairs with younger pups had higher alertness as opposed to older pups, while no significant difference was found between pairs with different proximity to anthropogenic disturbances.

            Solely interpreting the significant relationships found by the study, the hypotheses set out by this study are only partly supported. Specifically, attentiveness was only higher under defined conditions of young pup age or proximity to human activity for a specific attentive behaviour. Indeed, it appears that pup check and alertness were specific behavioural responses to the different conditions. Thus increased pup checks were a result of a greater proximity to anthropogenic disturbance, while, higher alertness may be a targeted behavioural strategy during times when pups were young.

            It can be speculated that mother seals exhibit different specific behaviours to attend to their pups because they are more effective under the different relevant conditions. For example, younger pups may be more vulnerable to predation or conspecific attacks. Hence spotting any trespassers of the area occupied by the mother and pup through maternal alertness could be an effective means to protect the young pup. Conversely, anthropogenic disturbances may not be clearly identified by mothers as a potential threat, thus mothers may opt to simply check on their pups’ wellbeing directly.

            It can be assumed that mother seals would seek to maximise the effectiveness of attentive behaviours so that they do not need to engage in additional attentive responses. The costs of nursing pups can be quite high for mothers and can affect the success of future pupping (Pomeroy, 1999). Thus it can also be expected that seal mothers will be inclined to minimise energy expenditure, including those from attentive behaviour. Indeed, the collected data shows that seal mothers mostly were mostly resting during the observed period.

            It should be noted that the hypotheses separately treated the influence of pup age and proximity on mother attentiveness. Yet it is quite possible that these factors may be interacting in the observed populations. Thus further statistical test such as ANOVA can be used on the data to evaluate whether the two conditions compliment or cancel out one another.

            Also, the study did not account for the effect of population densities on attentiveness. Different densities will affect the probability of the pup encountering conspecifics, which can be a danger to the pups. Indeed, for one mother-pup pair a mother was consistently alert for an extended period due to the proximity of two trespassing males. Thus population densities may be a confounding factor in this study.

            Limitations for the study include the fact that Donna Nook reserve was open to public, and as such can present a highly variable environment for the seals with regards to anthropogenic disturbances. Thus the exhibited behaviour can be affected by this variation.


References

 

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