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Competition Between Eurasian Collared-Doves and Mourning Doves

 

Philip Earhart

 

Undergraduate Student in Wildlife Biology,

 

Tennessee Technological University, Cookeville, TN 38501

 

 

Key Words: competition; behavioral dominance; behavioral interactions; food competition; exotic species introduction; native species displacement; Mourning Dove, Eurasian Collared-Dove; Zenaida macroura; Streptopelia decaoto.

 

Abstract:

Exotic species have plagued North America as long as humans have been traveling between continents. Some of these species have been intentionally introduced for food resources or for recreational purposes such as hunting. Eurasian Collared-Doves (Streptopelia decaoto) are a species that are a good example of this. They have been in the United States for several years now and have spread throughout the southeast. Since their first sightings, the Eurasian Collared-Doves unique ability to multiply exponentially have spread aided them in their rapid dispersal across parts of the country. In many of these regions, populations of the exotic Collared-Doves may have displaced the native Mourning Dove (Zenaida macroura) populations. Collared- Doves are physically larger than Mourning Doves which would seem to give them a distinct advantage over the smaller Mourning Doves permitting them to out-compete the native species for food resources.

 

 

Introduction:

The Mourning Dove is one of the most important game birds in the United States today (Hayslette 2001). Each year throughout the 1980s more than 2.4 million Mourning Dove hunters harvested 46 million birds (Romagosa and Labisky 2000). This popularity contributed millions of dollars to the economy and made these creatures a very important game species in many states, especially the southeast.

Both Mourning Doves and Collared-Doves are granivorous ground feeders and prefer to feed in open areas, especially harvested agricultural fields (Tomlinson et al. 1994; Romagosa 2002). Mourning Dove populations have seen declines over the past several years and studies are currently taking place in an attempt to isolate the reasons for the declines (Tomlinson et al. 1994). Due to this, the invasion of the Collared-Dove and the study of its effects are extremely important.

The Eurasian Collared-Dove has become increasingly more common in the United States over the past few years and has steadily increased the size of its range causing noticeable effects in the natural ecosystem (Stedman 1998). Collared-Doves have an amazing ability to reproduce and many times will give birth to a new clutch of eggs before the young of the year have even left the nest (Romagosa and Labisky 2000). The Collared-Dove is native to India and Sri Lanka and seems to thrive in areas of human inhabitance (Romagosa and McEaney 1998). Collared-Doves show a tendency to be much more aggressive than other native species including Mourning Doves and song birds and have actually been seen chasing other birds away from feeding stations (Romagosa and McEaney 1998).

The population of Collared-Doves currently located in the United States originated from no more than 50 birds that escaped from a pet breeder in the Bahamas in 1974 (Hengeveld 1993). The species arrived in Florida sometime in the early 1980s but the date is uncertain due to the similarity to the Ringed Turtle-Dove (Romagosa and Labisky 2000).

There are many problems associated with the introduction of these invasive, exotic species. At the top of the list is the potential these birds have for completely destroying the native Mourning-Dove populations as well as the potential of disease introduction (Romagosa and Labisky 2000). Competition between the two species is likely to exist and evolve if they are actively seeking the same resources. This competition is likely to be increased when resources are in low supplies (Reed 2001).

A leading expert on the Eurasian Collared-Dove, Christina Romagosa 1999, identified the need for research in the dietary niche overlap and competitive interactions with native doves in North America. This helps to exemplify the need for this study.

During this study we will attempt to determine whether or not competition between the Eurasian Collared-Dove and the Mourning Dove exists and if so, to what degree. We will try to determine the potential effects of the introduction of the Collared-Dove to the southeast and whether or not they could potentially displace the native Mourning Dove. I believe that there will be a level of competition between these two closely related species and that the larger, exotic Eurasian Collared-Doves will be able to physically out-compete the smaller, native Mourning Dove for limited food resources.

 

Materials and Methods:

We will be using birds that were trapped from the Manchester, TN area. These birds have been housed at a holding facility on the Tennessee Technological University Campus since the capture date. The birds are contained in individual pens and given food and water ad libitum. There are two individuals of the same species in each of the pens since it has been established that in studies the birds do better in pairs than they do alone (Hayslette and Mirarchi 2002).

During the study, selected pairs of Mourning doves and Eurasian Collared-Doves will be placed in the aviary where they will be allowed to compete for food. The birds selected will be out of the stock that was previously trapped and currently housed in the holding pens. The birds will first be fasted for 12 hours prior to the study, but still allowed access to fresh water ad libitum.

Seed mixtures of the 6 previously stated seed types will be placed on a wooden 0.45 m x 0.45 m x 5 cm tray which will be placed in the aviary containing the two study animals. Observers will be hidden from the birds view and will tabulate data of interactions between the birds for 30 minutes after the food is placed in the aviary. The birds will be able to freely interact with no disturbances for the entire 30 minute period. These techniques were adapted from the previous research of granivorous rodents in the Tucson desert (Brown 1988).

Reed 2001, classified the competition between two different species of mountain goat as Slight: walking away from stimulus, Moderate: trotting away from stimulus, or Intense: running away from stimulus. I am adapting this procedure and classifying interactions between the two species of birds as either indirect or direct interactions. Indirect interactions are classified as either chasing or gazing between the birds. Direct interactions are classifies when one of the two species actually physically touches the other. These will be tabulated on the data sheets by researchers.

 

Results:

The results of the study are explained in the following table 1 and chart 1. The birds displayed a significant number of interactions that could be tabulated by the researchers. Both the Eurasian Collared-Doves and the Mourning Doves displayed signs of competition and aggression. Table 1 represents the data collected during the trials.

 

Table 1:

Interactions Between Eurasian Collared-Doves and Mourning Doves

 

 

 

 

 

 

 

Trial #

MD Direct

MD Indirect

MD Total

ECD Direct

ECD Indirect

ECD Total

1

11

5

16

16

5

21

2

5

8

13

12

7

19

3

7

8

15

4

3

7

4

6

4

10

3

4

7

5

6

4

10

4

4

8

6

6

5

11

2

5

7

Total

41

34

75

41

28

69

 

The abbreviations MD represent Mourning Doves and ECD represent Eurasian Collared-Dove. As table 1 shows, the Mourning Dove and the Collared-Dove directly interacted 41 times each, indirectly 34 and 28 times respectively, and total numbers of interactions were 75 and 69 respectively.

The interactions between the two species were also broken down and visually explained in the following chart 1.

 

 

 

 

 

 

 

 

 

Chart 1: (Please refer to paper folder if chart does not appear)

 

The abbreviations for Chart 1 are the same as those found in Table 1. The columns representing total are sums of all of the interactions in each of the 6 trials.

 

Discussion:

The two species of birds definitely displayed a level of competition amongst themselves. This competition, however seemed to be on an individual-to-individual basis rather than a species-to-species basis as hypothesized. Mourning doves and Collared-Doves showed nearly equal numbers of interactions throughout the entirety of the study.

Contrary to the results found by Reed 2001, there was no distinct difference in the number of interactions in either of the species. Reed 2001 found that mountain goats, rather than bighorn sheep initiated most contacts, whereas neither the Mourning Dove nor the Eurasian Collared-Dove initiated contact many more times than the other. For this reason neither one of the species can be identified as the primary aggressor. They seem to compete on an individual basis, rather than on a species-wide basis.

The study did however mimic the behaviors associated with studies conducted by Hayslette and Mirarchi 2002 in respect to the ways the doves actively foraged for the food resources at hand. Both species of doves exhibited many of the same behaviors when it came to feeding. Collared-Doves did however seem to prefer larger food sources such as corn instead of the smaller seeds the Mourning Doves seemed to prefer such as milo (Hayslette and Mirarchi 2001). Whether or not this was a factor remains unknown, but would be a good aspect for future studies.

One aspect that was not explored by this study was the aggressiveness of the Eurasian Collared-Dove around the nest. Collared-Doves have been seen actively attacking other birds in the vicinity of their nest (Romagosa 2002). This is one area that would possibly clarify whether or not the Collared-Dove is capable of out-competing the Mourning Dove in areas other than that of food supply. Reproduction is equally as important as food supply in regards to the total fitness of the species and the continuation of life. This is another area in this debate that is open to future studies. This fact is also reaffirmed by the studies of competition of Red-Cockaded Woodpecker (RCW) cavities conducted by Loeb and Hooper 1997 who found that the utilization of RCW nest sites by other species was a determinate factor in the success of the brood.

Earlier researchers appreciated the need for study into the behaviors of the Collared-Dove and the possible effects they could have on the ecosystem. Hengeveld 1993 stated, That the invasions of the Collared-Dove into North America give a unique opportunity to study several aspects common to all invasions. This early appreciation of the importance of this study exemplifies the need for further research.

 

Conclusion:

Although there were significant levels of competition between these two species of birds, the evidence did not conclusively state that the Eurasian Collared-Dove is actively displacing the Mourning Dove. My hypothesis that the larger Collared-Dove would displace the smaller Mourning Dove has been disproved by the data that I obtained during this study. I attribute this to the aggressiveness of the Mourning Doves used in the study and to the mildness of the Collared-Doves potentially due to the season of the year and its distance from the mating season. Further research will be needed to determine what effects the invasion of the Collared-Doves will have on the declining native Mourning Dove populations.

 

Acknowledgements:

I would like to thank Trisha Poling for all of her help and assistance on the project as well as the Tennessee Wildlife Resources Agency for their assistance in funding.

 

 

 

 

 

Literature Cited:

Brown, J.S. 1988. Patch Use as an Indicator of Habitat Preference, Predation Risk, and Competition. Behavioral Ecology and Sociology. 22: 37-47.

Hayslette, S.E. and R.E. Mirarchi. 2001. Patterns of Food Preferences in Mourning Doves. Journal of Wildlife Management. 65: 816-827.

Hayslette, S.E. and R.E. Mirarchi. 2002. Foraging-Patch Use and Within-Patch Diet Selectivity in Mourning Doves, Zenaida macroura. Journal of Wildlife Management. 83 (9): 2637-2641.

Hengeveld, R. 1993. What to do about the North American Invasion by the Collared Dove. Journal of Field Ornithology. 64 (4): 477-489.

Loeb, S.C. and Hooper, R.G. 1997. An Experimental Test of Interspecific Competition for Red-Cockaded Woodpecker Cavities. Journal of Wildlife Management. 61 (4): 1268-1280.

Reed, D.F. 2001. A Conceptual Interference Competition Model for Introduced Mountain Goats. Journal of Wildlife Management. 65 (1): 125-128.

Romagosa, C.M. 2002. Eurasian Collared-Dove. The Birds of North America. 629: 1-20.

Romagosa, C.M. and Labisky, R.F. 2000. Establishment and Dispersal of the Eurasian Collared-Dove in Florida. Journal of Field Ornithology. 71 (1): 159-166.

Romagosa, C.M. and McEneaney, T. 1999. Eurasian Collared-Dove in North America and the Caribbean. North American Birds. 53 (4): 348-353.

Stedman, S.J. 1998. Changing Seasons: The Nesting Season. North American Birds. 52 (4): 424-426.

Tomlinson, R.E. et al. 1994. Mourning Dove. Migratory Shore and Upland Game Bird Management in North America. 47 (3): 5-26.

 

 

Appendix:

 

Competition

Paired Bird # 1,2,3,4,5,&6

 

Eurasian Collared-Dove Mourning Dove

Band Number 1,2,3,4,5,&6 Band Number 10,11,12,13,14,&15

Mass average 185 g Mass average 141 g

Mass Difference average 44 g

 

Single Patch Trial

 

Date ________ Time Start ________ Temp Start ______ Weather Start _________

Time End _________ Temp End ______ Weather End __________

 

Interactions Between Species

Number of Interactions

ECD directly displaces MD (touch)

41

ECD indirectly displaces MD (chase)

16

ECD indirectly displaces MD (look)

12

MD directly displaces ECD (touch)

41

MD indirectly displaces ECD (chase)

20

MD indirectly displaces ECD (look)

14

Total Interactions

144

 

 

 

Comments: This is a representation of all of the data sheets combined for all 6 of the studies. It contains all of the pertinent information. It is however lacking of the information such as the weather for the day of study and other non-influential factors.