Faculty of Science
THE EFFECTS OF HATCH-ORDER AND GENDER ON THE BEHAVIOUR OF
BURROWING OWLS (Athene cunicularia)
2020 | JOHN CAMERON GRAY

B.Sc. Honours thesis – Biology

THE EFFECTS OF HATCH-ORDER AND GENDER ON THE BEHAVIOUR OF
BURROWING OWLS (Athene cunicularia)

by

JOHN CAMERON GRAY

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF
BACHELOR OF SCIENCE (HONS.)
in the
DEPARTMENT OF BIOLOGICAL SCIENCES
(Animal Biology)

This thesis has been accepted as conforming to the required standards by:
Dr. Nancy Flood (Ph.D.), Thesis Supervisor, Department of Biological Sciences
Dr. Matt Reudink (Ph.D.), Co-supervisor, Department of Biological Sciences
Dr. Tom Dickinson (Ph.D.), External examiner, Department of Biological Sciences

Dated this 16th day of June, 2019, in Kamloops British Columbia, Canada

© John Cameron Gray, 2019

ABSTRACT
Burrowing Owls (Athene cunicularia) have an asynchronous hatch: females begin incubating well
before the last eggs are laid, which results in age, size and developmental differences among the
members of a clutch. Mating monogamously, for rarely longer then a season, Burrowing Owls
have different sex-based roles within a mating pair. Males are typically more territorial than
females, and might thus be expected to be generally more aggressive. Males defend their burrows,
mates and offspring from predators or competing males while females spend more time incubating
and caring for their offspring. I examine the effects of an asynchronous hatch and gender on the
behaviour of juvenile Burrowing Owls. Intraspecific interactions between individual owls were
observed within an enclosure, in which captive-bred owls are held before release and the relative
aggressiveness or submissiveness of each bird was determined during each interaction. The results
indicate that although there appears to be an association between the gender and asynchronous
hatch on the behaviour of Burrowing Owls there does not appear to be any association between
the clutch size and hatch weight on their behaviour.
Thesis Supervisor: Dr. Nancy Flood.

ii

ACKNOWLEDGEMENTS
I would like to thank my supervisors Dr. Nancy Flood and Dr. Matt Reudink along with
my advisor Adrienne Clay for the contributions, insights, advice and knowledge that they have
provided. It has allowed me to further advance my interests in research and conservation, which I
would not have had access to in an ordinary classroom setting.

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TABLE OF CONTENTS
ABSTRACT.................................................................................................................................... II
ACKNOWLEDGEMENTS .......................................................................................................... III
INTRODUCTION .......................................................................................................................... 1
METHODS ..................................................................................................................................... 3
FIELD SITE ................................................................................................................................ 3
MONITORING INTRASPECIFIC BEHAVIOUR .................................................................... 5
DOMINANCE STATUS ............................................................................................................ 5
RESULTS ....................................................................................................................................... 8
DISCUSSION ............................................................................................................................... 13
LITERATURE CITED ................................................................................................................. 16

LIST OF FIGURES
Figure 1. Experimental Burrowing Owl enclosure at the BC Wildlife Park………………………..4
Figure 2. Enclosed burrow locations within the aviary at the BC Wildlife Park…………………....4
Figure 3. Juvenile sex based flight pens at the BC Wildlife Park…………………………………..4
Figure 4. Interval plot of the behaviour rating of juvenile males and females. The dots indicate the
mean and the interval bars show standard deviation……………………………………………….9
Figure 5. Interval plot of the mean behaviour rating of chicks based on whether they hatched in
the first or second half of their clutches…………………………………………………………..11
Figure 6. Interval plot of the total behaviour rating of chicks based on the number of eggs in a
clutch……………………………………………………………………………………………..12

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LIST OF TABLES
Table 1. Descriptive statistics of the Paired T-test showing the differences in the behaviour ratings
of chicks before and after they were separated from the mature owls………….………….……….8
Table 2. Descriptive statistics of the 2-Sample T-test showing the differences in the behaviour
rating of male and female chicks after they were separated from the mature owls……………..…..9
Table 3. Differences in the behaviour rating of the first and last 2 chicks to hatch within a clutch..10
Table 4. Descriptive statistics of the differences in the behaviour rating of chicks depending on if
they hatched in the first or second half of a clutch………………………………………………...10
Table 5. Association between hatch weight and behaviour……………………………………….12
Table 6. Descriptive statistics of the differences in the hatch weight of chicks depending on if they
were the first or last 2 chicks to hatch in a clutch………………………………………………….13
Table 7. Descriptive statistics of the differences in the hatch weight of chicks depending on if they
hatched in the first or second half of a clutch……………………………………………………..13

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INTRODUCTION
The Burrowing Owl (Athene cunicularia) is a small, ground-dwelling owl that ranges throughout
the western part of the Americas, from south-central British Columbia and southern Alberta,
Saskatchewan and Manitoba, through the midwestern United States and into Central and South
America (Campbell et al. 1990; Wilkerson and Siegel 2011). They inhabit arid regions, such as
grasslands, deserts and prairies, where they build their nests in abandoned burrows dug by
mammals such as badgers (Taxidea taxus), ground squirrels (Urocitellus richardsonii), blacktailed prairie dogs (Cynomys ludovicianus), Mexican prairie dogs (Cynomys mexicanus), etc.
(Ayma et al. 2016; Poulin et al. 2011; Ray et al. 2016). Because they rely on other species—some
of which are endangered—to dig burrows that the owls can use for nesting, burrow availability is
often the greatest factor limiting Burrowing Owl populations (Klute et al. 2003).
Due to various factors, many of which can be associated with human activity, Burrowing Owls are
not as abundant as they once were (Conway and Macias-Duarte 2015; Poulin et al. 2011;
Wellicome 1997). Populations have been declining drastically due to increased mortality, range
contraction, and increased predation associated with habitat fragmentation, degradation,
contamination and loss, etc. (Poulin et al. 2005; Wellicome et al. 2014; Wilkerson and Siegel
2011). In Canada alone, their range has contracted by 65% and their numbers have declined 614% per year since the 1990’s, resulting in a loss of more than 90% of the Canadian population
(Conway J. 2018; Wellicome et al. 2014). Conservation efforts have been implemented throughout
their international range to minimize owl mortality and habitat alteration (Environment Canada
2012).
As largely short distance migrants, Burrowing Owls are protected under the Migratory Bird Treaty
Act (MBTA 1918) which is binding in Canada, the United States and Mexico. However, further
protection of the birds varies among the three countries. (Lincer et al. 2018; Poulin et al. 2011). In
Canada, they are listed as an Endangered Species according to the Species at Risk Act (S.C. 2002,
c. 29). Different conservation techniques, such as captive breeding projects, building of artificial
burrows and creation of conservation reserves have been implemented to limit and reverse the
decline in Burrowing Owl populations by re-establishing self-perpetuating populations or
reinforcing existing populations (Environment Canada 2012; Wellicome 1997). By better

1

understanding the behaviour, physiology, feeding habits, migration patterns and distributions of
these birds, conservation efforts can be established in a way that minimizes detrimental outcomes
(Johnson et al. 2010).
In many animals, the offspring of a single reproductive event are hatched or are born over a short
period of time. In others, however, including Burrowing Owls, this is not always the case (Poulin
et al. 2011; Wellicome 2005). Burrowing Owl young typically hatch asynchronously, over an
extended period of time, as a result of the fact that females begin incubating before the entire clutch
is laid (Conway et al. 2011; Podlas and Richner 2013; Wellicome 2005). Asynchronous hatching
results in developmental differences between the first and last hatched chicks of a clutch (Podlas
and Richner 2013; Wellicome 2005). This often has a detrimental effect on later hatched chicks,
as they are generally smaller and have reduced chances of survival (Conway et al. 2011; Nilsson
and Svensson 1996; Podlas and Richner 2013). The larger the clutch, the greater the degree of
hatching asynchrony (Conway et al. 2011).
Female Burrowing Owls lay clutches of 6 to 12 eggs over a period of 8 to 17 days (Poulin et al.
2011; Wellicome 2005). Incubation usually begins once about half of the clutch is laid, but varies
depending on the clutch size and distribution (Poulin et al. 2011; Wellicome 2005). Incubation
lasts for 17 to 32 days and the eggs hatch within 1 to 7 days of each other, over an average time
period of 3.8 days (Conway et al. 2011; Wellicome 2005). The resulting developmental differences
between the earlier and later hatched chicks of a clutch may result in behavioural variations in
addition to the obvious size differences (Beissinger and Waltman 1991; Podlas and Richner 2013).
Chicks that hatch earlier, which are presumably larger, may be more aggressive as their greater
size offers an advantage when competing against their smaller clutch mates for access to food
(Stier et al. 2015). Conversely, chicks that hatch later, and that are thus smaller, may be less
aggressive when competing against the larger members of the clutch for food (Kim et al. 2010).
These smaller chicks may behave less aggressively than their larger clutch mates as a result of
them being unable to confront these larger opponents.
Burrowing Owls mate monogamously (Conway and Macias-Duarte 2015). However, pair bonds
of owls are not permanent and last rarely longer than a season (Poulin et al. 2011). Female
Burrowing Owls spend much of the time within or near their burrows where they care for the
young (Poulin et al. 2011). In contrast, males spend much of the time outside of the burrow,

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guarding their mates and young from predators and competing males (Herse 2016; Poulin et al.
2011). As such, male Burrowing Owls may tend to be more aggressive than females. Conversely,
female Burrowing Owls may tend to be less aggressive than males as they do not have compete
for access to mates.
This study will examine whether asynchronous hatch and/or sex have any effect on the behaviours
of Burrowing Owls in a captive setting.
METHODS
Field site
At the BC Wildlife Park, in Kamloops BC, Burrowing Owls are bred and the young are raised in
an aviary before being released into the wild (at one year of age) to establish or reinforce
populations of owls throughout British Columbia, Canada and Washington, USA. Within the
aviary, there is a large flight pen encircling a central research centre that contains the burrows
where mating pairs establish their nests (Figure 1). The flight pen is 40 m long, 25 m wide and 3
m tall (Figure 1). Each mated pair nests in its own burrow, contained within a small pen measuring
4 m long, 2 m wide and 3 m tall (Figure 2). These small pens, located inside the larger circular
flight pen, allow the burrows and associated Burrowing Owl pairs to be isolated from each other
while the birds are laying eggs and raising their young. Once the chicks are six weeks of age, the
pens that separate each burrow within the flight pen are opened to allow for interactions among
both juvenile and mature individuals between and within the different clutches. Adjacent to the
circular flight pen there are two separate flight pens. At six months of age, the juvenile owls are
placed into these two flight pens, based on their sex, to prevent premature pair formation (Figure
3). The mature owls remain in the initial circular flight pen (Figure 1.).
In some burrows (4 in the year of my study), a camera is used to determine when the eggs within
a clutch are laid and hatch. After laying, eggs are marked sequentially, using a Sharpie marker, to
provide a record of laying and hatch order. After hatching, a series of coloured plastic bands are
added to one or both legs of each chick to allow for individual identification. At six weeks of age,
blood samples are taken and the plastic leg bands are replaced with metal ones, each of which has
a unique combination of a letter and a two-digit number, on each of the chicks. These letter-number
combinations are large enough to be seen from the opposite end of the flight pen when using

3

binoculars. The blood samples are used to determine the sex of each of the chicks using DNA
analysis.

Figure 2. Enclosed burrow locations within
the aviary at the BC Wildlife Park.

40m

Figure 1. Experimental Burrowing Owl
enclosure at the BC Wildlife Park.

2m

4m

5m

5m
30m
Figure 3. Juvenile sex based flight pens at the BC Wildlife.

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Monitoring intraspecific behaviour
I observed the Burrowing Owls during randomly determined time intervals, which occurred at
different times of the day, on different days of the week and both before and after they were fed
between August 2018 and November 2018. I recorded all intraspecific behaviours of all of the
birds that I could identify based on their unique leg bands. I sat in corners of the pen where I could
observe at least one half of the enclosure at one time. I spent 30 minutes in one corner that
maximized my visibility of the flight pen. After 30 minutes, I would observe from the opposite
corner of the flight pen for an additional 30 minutes. Once the juveniles were separated into the
sex-based pens (at 6 months of age) I would then spend a total of 30 minutes in each of the two
sex segregated enclosures. The sex segregation enclosures were small enough that I could sit at
one end of the pen and identify each of the owls within the pen.
While observing the owls, I took notes on any interactions between individuals, identifying the
birds that took part and describing the interaction (which bird initiated it, how the individuals
involved reacted, how long the interaction lasted, the cause of the interaction if known, and the
time during the observation period that the interaction took place).
Dominance status
Dominance status was assigned once observations were complete. Documented behaviours were
analyzed to determine pairwise dominance interactions between birds. Dominance within an
interaction was inferred when one of the individuals supplanted or chased the other, or when one
individual within an interaction resisted a supplanting attack by another individual in such a way
that the resister was clearly dominant. Submissiveness was inferred when one of the individuals
within an interaction did not resist an attack or when chased, tried to escape.
Within pairwise dominance interactions, individuals that were dominant were given a dominance
score of 1. In comparison, individuals that were submissive; were given a dominance score of 0.
For example, if bird A chased bird B and in response bird B flew away, bird A would receive a
dominance score of 1 while bird B would receive a dominance score of 0. Interactions that included
a group of individuals were considered as separate pairwise interactions for all the individuals
involved. For example, if bird A chased a group of birds including birds B, C and D, a dominance
score would be assigned for each of the pairwise interactions. That is, bird A would acquire a

5

dominance score of 3—1 for each 3 of the birds it dominated while birds B, C and D would each
receive a dominance score of 0.
The dominance status of an individual over an observation period was determined by accumulating
all the dominance scores of an individual and dividing it by the number of pairwise interactions it
was involved in over that observation period. Therefore, during an observation period, the closer
the dominance status of an individual was to 1, the more aggressive that individual was during that
period. Conversely, the closer an individual’s dominance status was to 0 the more submissive that
individual was. A dominance status of 0 could be achieved if an individual was not observed
interacting with other individuals during that observation period or if it only behaved submissively
during all the observed interactions.
Each 30 minute observation period was subdivided into two, 15-minute segments. Since the
dominance status of an individual was the number of dominance interactions divided by the
number of interactions, an individual could acquire a maximum dominance status of 1 over a 15minute observation period. Therefore, an individual could acquire a dominance status score of 2
for each complete, 30 minute observation period. This would therefore accumulate to give a total
dominance status that is more representative of the bird’s dominant or aggressive nature
throughout the observation period.
A “behaviour rating” represents the total dominance status of an individual over all observation
periods and was used to compare the dominance of different individuals. A behaviour rating is the
sum of all the dominance status scores acquired from each of the observation periods. The higher
the behaviour rating, the more frequently that individual was observed behaving aggressively.
First, I wanted to know if there were differences in the behaviour of juvenile owls before and after
their separation from the mature owls into sex-based pens. The differences in the behaviour ratings
of the juvenile owls, before and after their separation, was tested for normality using a Ryan-Joiner
Test and the data was found to be normally distributed (RJ = 0.996; p = >0.100). As the data was
normally distributed and was not independent, I used a Paired T-Test to determine if there were
differences in the behaviour of juvenile owls before and after their separation from the mature owls
into sex-based pens.

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I also compared the difference in behaviour of juvenile male and female owls after separation from
the mature owls. The behaviour ratings of juvenile males and females was tested for normality
using a Ryan Joiner Test (Females: RJ = 0.970; p = >0.100; Males: RJ = 0.972; p = >0.100) while
the equality of variances was tested using an F-Test, assuming a normal distribution (p = 0.054).
Since the data was found to follow a normal distribution and had equal variances, a 2-Sample TTest with pooled variances was used.
I then compared the behaviour ratings of the first two and last two chicks to hatch in all clutches.
Clutches where hatch order was not known were not included. I determined the mean behaviour
ratings of the first two chicks to hatch and the last two chicks to hatch in each clutch. A Ryan
Joiner Test was used to test for normality of the differences of behaviour between the first and last
two chicks to hatch within all the clutches. Since the differences in the behaviour were found to
be normally distributed (RJ = 0.987; p = >0.100), a Paired T-Test was used for this comparison.
A Paired T-Test was used to compare the behaviours of individuals that hatched in the first of a
clutch to that of individuals hatching in the second half. Again, clutches where hatch order was
not known were not included in this comparison. I determined the mean behaviour ratings for
individuals in the first half of the clutch and similarly, the mean behaviour ratings for individuals
hatching in the second half of all the clutches. I then tested the difference between these scores for
normality using a Ryan-Joiner Test (RJ = 0.945 p = >0.100).
I examined whether the behaviour of birds, after they were separated from the mature owls, was
related to their hatch weight. The hatch weight of each chick was considered to the nearest gram,
and birds were grouped into categories of 6, 8, 10, 12 and 14 grams. The mean behaviour ratings
of the birds in each weight group were compared. There are some issues with pseudoreplication in
these data, since often there was more than one bird in each weight group from a single clutch.
However, they were treated as independent in order to have large enough samples for comparison.
The normality of the data was tested using a Ryan-Joiner Test (Chicks weighing 6 grams: RJ =
0.988; p = >0.100, chicks weighing 8 grams: RJ = 0.968; p = >0.100, chicks weighing 10 grams:
RJ = 0.968; p = >0.100, chicks weighing 12 grams: RJ = 1.000; p = >0.100 and chicks weighing
14 grams: RJ = 0.903; p = >0.100), which showed that the data in all groups was normal. I then
examined whether the variances were homogenous using a Bartlett’s test. (p = 0.840). Due to the

7

fact the data followed a normal distribution and had equal variances, a one-way ANOVA was used
to compare the dominance scores of birds in different weight classes.
Finally, I examined whether that was any correlation between hatch order and hatch weight. A
Paired T-Test was used to determine whether there were any differences in mean hatch weights of
the first two versus the last two chicks to hatch in all clutches and then of chicks hatched in the
first vs. the second half of their clutches.
RESULTS
There was no difference in the behaviour of juvenile individuals before and after they were
separated from the mature owls into sex-based pens (T = -1.27; p = 0.211), (Table 1).
Table 1. Descriptive statistics of the Paired T-Test showing the differences in the behaviour
ratings of chicks before and after they were separated from the mature owls.
Sample

N

Mean

StDev

SE Mean

Behaviour rating of
juveniles before separation

35

0.343

0.553

0.093

Behaviour rating of
juveniles after separation

35

0.573

0.858

0.145

There was a significant difference in the behaviour of juvenile males compared to juvenile females
after they were separated into the sex-based enclosures (T = -3.10; p = 0.004), (Table 2). These
results indicate that males tend to behave more aggressively than females of the same age, while
exposed to individuals of the same age and sex (Figure 4). Thus, male Burrowing Owls tend to
have a greater frequency of aggressive or dominant behaviours compared to females of the same
age.

8

Table 2. Descriptive statistics of the 2-Sample T-test showing the differences in the behaviour
rating of male and female chicks after they were separated from the mature owls.
N

Mean

StDev

SE Mean

Behaviour rating of
juvenile females

23

0.283

0.618

0.13

Behaviour rating of
juvenile males

12

1.128

0.998

0.29

Behaviour Rating

Sample

Figure 4 . Interval plot of the behaviour rating of juvenile males and females. The dots indicate
the mean and the interval bars show standard deviation.
There appeared to be no statistical difference in the behaviours of the first and last two chicks to
hatch within a clutch (T = 0.18; p = 0.872), (Table 3).

9

Table 3. Differences in the behaviour rating of the first and last 2 chicks to hatch within a clutch.
Mean Behaviour Rating

N

Mean

StDev

SE Mean

First 2 chicks to hatch
within all clutches

3

1.000

0.433

0.250

Last 2 chicks to hatch
within all clutches

3

0.933

0.404

0.233

Since the asynchronous hatch seen in Burrowing Owls could result in behavioural differences
among chicks within a clutch, I compared the behaviour ratings of chicks that hatched in the first
half of each clutch to those in the second half of each clutch. It appears as though individuals that
hatched in the first half of a clutch were more dominant than those that hatched in the second half
of a clutch (T-Value = 5.68, p = 0.005), (Table 4, and Figure 5).
Table 4. Descriptive statistics of the differences in the behaviour rating of chicks depending on if
they hatched in the first or second half of a clutch.
Mean Behaviour Rating

N

Mean

StDev

SE Mean

Chicks of 1st half of all
clutches to hatch

5

0.922

0.347

0.155

Chicks of 2nd half of all
clutches to hatch

5

0.350

0.418

0.187

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Mean Behaviour Rating

Figure 5. Interval plot of the mean behaviour rating of chicks based on whether they hatched in
the first or second half of their clutches.
There were not enough samples to analyze the association between clutch size and behaviour.
Therefore, I have simply examined the relationship graphically (Figure 6). As can be seen by
Figure 6, the data does not appear to be suggest that clutch size influences the behaviour of
Burrowing Owls.

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Behaviour Rating

Figure 6. Interval plot of the total behaviour rating of chicks based on the number of eggs in a
clutch.

The association between hatch weight and behaviour was tested using and a one-way ANOVA. It
appears as though there is no significant association between the hatch weight of an individual and
their behaviour, (F-Value = 0.41, p = 0.800), (Table 5).
Table 5. Association between hatch weight and behaviour.
Hatch Weight

N

Mean

StDev

6 grams

4

0.911

0.679

8 grams

10

0.600

0.810

10 grams

8

0.344

0.972

12 grams

2

0.925

0.955

14 grams

3

0.907

1.384

There was no significant difference between the average hatch weight of the first two chicks and
the last to chicks to hatch in a clutch (T = 0.945, p = 0.444), (Table 6). Although the first birds to
hatch were slightly heavier, the sample size was small.

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Table 6. Descriptive statistics of the differences in the hatch weight of chicks depending on if they
were the first or last 2 chicks to hatch in a clutch.
Mean Hatch weight

N

Mean

StDev

First 2 chicks to hatch
within all clutches

3

9.667

14.333

Last 2 chicks to hatch
within all clutches

3

8.000

1

There was also no significant difference in the average hatch weight of the chicks in the first half
of a clutch compared to the average hatch weight of chicks that hatched in second half of the same
clutch (T = 0.915, p = 0.428), (Table 7). Again, however, the sample size is small, and the average
weight of chicks that hatched in the first half of a clutch was slightly greater than the average
weight of those that hatched in the second half of the same clutch.

Table 7. Descriptive statistics of the differences in the hatch weight of chicks depending on if they
hatched in the first or second half of a clutch.
Mean Hatch weight

N

Mean

StDev

Chicks in 1st half of all
clutches to hatch

4

9.3

6.76

Chicks in f 2nd half of all
clutches to hatch

4

8.375

1.229

DISCUSSION
Within a mated pair, Burrowing Owls have different sex-based roles (Conway. 2018). Male
Burrowing Owls are more territorial and seem to have an innate tendency to protect their mate,
their chicks and their burrow from predators and competing males (Poulin et al. 2011). Conversely,
females are involved primarily in brooding and so spend much of the time within their burrows
(Kim et al. 2010). I thus hypothesized that juvenile males would behave more aggressively than
females and the data confirms this.
Unlike many bird species, Burrowing Owls chicks hatch asynchronously (Lincer et al. 2018). That
is, eggs that are laid and incubated earlier, also hatch earlier, which puts them at a developmental

13

advantage compared to their later laid and incubated clutch mates (Conway et al. 2011; Wellicome
2005). I hypothesized that the developmental differences that result from an asynchronous hatch
would result in behavioural differences between the members of a clutch. Chicks that hatch earlier
and that are presumably larger will be more aggressive than their later hatched and thus smaller
clutch mates. It appears as though the asynchronous hatch as seen in Burrowing Owls is associated
with differences in behaviour. The data indicates that chicks that hatched in the first half of their
clutches tend to be more aggressive or dominant than those chicks that hatched in the second half
of their clutch.
A greater degree of hatching asynchrony, the span of time between the first and last hatched
members of a clutch, could be associated with greater variations in intraspecific behaviours
(Conway et al. 2011). Increasing hatching asynchrony would result in greater age and size
differences (Kim et al. 2010; Conway et al. 2011). It is possible that the increased hatching
asynchrony could result in more pronounced behavioural adaptations within the members of a
clutch (Wellicome 2005).
Additionally, it is possible that the environment in which the owls are raised could influence their
behaviours (Gilby et al. 2013). Clutches that hatch in the wild are faced with greater food
limitations than those raised in captivity, which have a constant supply of nutrient-rich food, such
as was the case in this study. Food limitations during breeding, egg formation, egg laying and
brooding could result in an even stronger association between, behaviour and hatching asynchrony.
Asynchronous hatching in altricial birds, such as Burrowing Owls, is thought to be an adaptive
response to unpredictable food availability as it facilitates the differential growth and survival of
chicks (Skagen 2019). When food is limited in asynchronous clutches, the largest chicks grow
faster than the smallest chicks, as the later hatching and thus smaller chicks are fed less than their
older and larger clutch mates (Skagen 2019). Therefore, the increasing separation in size as a result
of food limited situations, as would occur in wild population, could result in more polarizing
behaviour.
Chicks born in a larger clutch would have to compete against more individuals for access to
necessary resources required for development than those from smaller clutches (Wellicome 1997,
Dijkstra et al. 1990). Additionally, individuals of a greater hatching weight would have a size
advantage over their clutch mates and so would be able to access more food resources by

14

dominating their smaller clutch mates by behaving more aggressively (Podlas and Richner 2013).
Chicks of lower hatching weight would have to behave more aggressively to compete against their
larger clutch mates for access to food. Accordingly, I hypothesized that behaviour would be
associated with both clutch size and hatch weight. However, it appeared as though the behaviour
of the owls was independent of both clutch size and hatch weight. Again, this may be due to the
fact that food was not limited in this captive environment.
Interestingly, the results suggest that hatch order does not appear to be associated with hatch
weight; that is, chicks that hatch earlier in a clutch are not significantly larger than those that hatch
later. Therefore, the increasing dominance or aggression seen in chicks that hatched among the
first 2 or within the first half of their clutch was not simply, or definitively a result of their hatch
weight. The increasing aggression seen in these earlier hatching chicks cannot be associated only
with hatch weight and may therefore be associated with other phenomenon, such as simply age
(time out the egg).
Overall, the results of this study suggest that there is no effect of clutch size or hatching weight on
the behaviour of Burrowing Owls in captivity. However, there appeared to be a significant
association between the behaviour of individuals and their gender, and early hatched chicks were
more dominant than those that hatched later. The greatest limitation faced by the study was the
fact that the birds were all captive raised. Therefore, an important continuation of this work would
be to examine the effects of captivity on asynchronous hatch, clutch size and hatching weight; that
is, how these factors vary between captive and wild young. As well as how these factors affect the
behaviour of the owls in a wild environment.

15

LITERATURE CITED
Ayma R, Kerstupp O, Duarte M, Velasco G, Rojas G. 2016. Population density of the western
burrowing owl (Athene cunicularia hypugea) in Mexican prairie dog (Cynomys mexicanus)
colonies in northeastern Mexico. BMC Ecology, 16; 38. doi: 10.1186/s12898-016-0091-y
Beissinger S and Waltman J. 1991. Extraordinary Clutch Size and Hatching Asynchrony of a
Neotropical Parrot. The AUK, 108; 863-871.
Campbell W, Dawe N, McTaggart-Cowan I, Cooper J, Kaiser G, McNall M. 1990. The Birds of
British Columbia, Diurnal Birds of Prey through Woodpeckers. Victoria (BC): The Royal British
Columbia Museum, 2; 368-371.
Conway C. 2018. Spatial and Temporal Patterns in Population Trends and Burrow Usage of
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